In order to effectively reduce the pressure drop loss of production fluid in the wellbore and make full use of the gas well energy for low-cost drainage and gas recovery, the jetting and helical combination drain tool was developed. Based on the design of the tool structure composition, the performance test system of tool was built, the wellbore hole simulator pressure drops with different structural parameters at different gas flow rates were tested, the single factor analysis and orthogonal test analysis of tool structure parameters were carried out, the optimal tool structure parameter combinations at different conditions were obtained. The results showed that the main structural parameters of the tool have an impact on the wellbore pressure drop. Moreover, different wells require different tools with different structural parameter combinations to achieve the minimum wellbore pressure drop loss. After the optimized tool was run in well A, the cumulative gas production increased by an average of 20.95% and the cumulative water production increased by an average of 21.59% over the same production period, the drainage stimulation effect of the tool was demonstrated. The successful application of this tool provided a new method and means for low cost drainage gas recovery in liquid loading gas wells.

Anisotropy is an inherent property of the formation. In highly deviated wells and horizontal wells, the anisotropy coefficient can be calculated by using the difference information of electromagnetic wave logging curves while drilling. In wells with small well deviation, although anisotropy has an impact on resistivity, there is no obvious difference. The traditional method of calculating formation anisotropy coefficient by using difference information is no longer applicable. In this paper, the high-resolution characteristics of micro-resistivity imaging logging and local measurement characteristics in different directions are used to divide the image gray scale, and the equivalent resistivity volume model is established to further calculate the equivalent horizontal resistivity and vertical resistivity, so as to obtain the anisotropy coefficient of the reservoir. Compared with the anisotropy coefficient calculated by the resistivity while drilling, it has good consistency, and the resolution of the anisotropy coefficient calculated by the micro-resistivity imaging is higher, which can well reflect the anisotropy characteristics of fractures, holes, and heterogeneous well sections, and provide a new method for evaluating the anisotropy of the formation.

At present, most of the polymer thickeners used in water-based fracturing fluid systems at home and abroad have poor salt resistance. Therefore, a salt-tolerant amphoteric polyacrylamide was synthesized by introducing anionic and cationic monomers into the acrylamide chain. The effects of different monomer total mass fraction, monomer mass ratio, initiator dosage and reaction pH value on the relative molecular weight of the thickener were studied, and the salt resistance of the thickener was investigated Temperature resistance, shear resistance, solubility and thickening performance. The results showed that when the total mass fraction of monomer was 25%,the mass ratio of monomer was AM/AMPS/DMC=65∶25∶10, the addition of complex initiator (NH)₂S₂O₇-NaHSO₃-2,2'- azodiisobutymidine dihydrochloride (V-50) was 0.2%, pH=6, and the initiation temperature was 20 ℃, the synthesized AMPAM had good salt resistance and thickening properties; The thickener with a dosage of 0.5% forms a gel in the sodium chloride solution with a salinity of 30000 mg/L and the crosslinking agent with a dosage of 0.5%. The viscosity of 140 mPa·s can still be reached after shearing for one hour at a temperature of 145 ℃ and a shear rate of 170 s⁻¹, which has good temperature resistance and shear resistance.

Long horizontal section horizontal well drilling is mostly used in Gulong shale oil development in Daqing Oilfield. However, during the drilling process of long horizontal section horizontal well, the broken cuttings in the annulus are easy to settle freely in the borehole drilling fluid to form cuttings bed. In order to prevent and avoid downhole safety accidents such as sand sinking and sticking caused by cuttings deposition, it is necessary to study the settlement law of cuttings particles and predict the final velocity of cuttings settlement. In this paper, the sedimentation behavior of particles in power-law fluid is recorded by visual device and high-speed camera system, and the experimental data of 196 groups of spherical particles and 224 groups of irregularly shaped cuttings are obtained. A mechanical model dependent on the force balance of settling particles is adopted, and the experimental results are analyzed in detail. The prediction model of drag coefficient of spherical particles in power-law fluid is established. On this basis, a two-dimensional shape description parameter is introduced to establish a model for predicting the drag coefficient of irregularly shaped cuttings in power-law fluids. According to the obtained cuttings drag coefficient prediction model, the sedimentation velocity is calculated by iterative method, and the average relative error is only 6.93%. The model can better predict the sedimentation velocity of shale cuttings in power-law fluids. It is concluded that the model obtained in this study can meet the needs of predicting cuttings settling velocity in drilling engineering.

In order to improve the accuracy of the calculation results of gas-liquid two-phase flow in the wellbore after gas invasion, the initial bubble size distribution characteristics at the bottom of the well were experimentally studied, and a prediction model for the average size of initial bubbles was established. Xanthan gum solution with different concentrations were used to simulate the drilling fluid and porous medium to simulate the formation, the size distribution characteristics of bubble groups at the bottom of the wellbore under different liquid phase rheology, average pore diameter of formation and different gas invasion rates were observed experimentally. The experimental results show that the larger the shear stress of the simulated drilling fluid and the larger the gas invasion velocity, the larger the size range of the initial bubbles generated. And the bubble size with the highest frequency and the maximum bubble size both increased. The formation pore diameter has no obvious effect on the initial bubble size. Through the dimensionless analysis of the experimental results, a prediction model for the average diameter of the invaded gas bubbles was established, which comprehensively considered the influence of factors such as drilling fluid viscosity, gas flow rate and surface tension, and the error between the experimental data and the model was within 10%. Considering the radial invasion characteristics of gas at the borehole wall and the influence of well deviation angle in the actual drilling process, a modified bottom hole bubble average diameter prediction model is proposed. The establishment of a prediction model for the initial bubble size at the bottom of the well provides theoretical support for the accurate calculation of the gas-liquid two-phase flow in the wellbore after gas invasion.

In order to more rapidly calculate the definite integrals in the drilling design software, a fast calculation method of numerical integration was studied in this contribution. The north and east coordinate in the constant toolface model and the horizontal projection length in the spatial arc model are expressed by the definite integral equation. Based on the basic equation of the borehole trajectory model and the integral parameter conversion, seven trigonometric and one logarithmic calculations are reduced to three trigonometric and one logarithmic calculations for the quadratic function in the definite integral of the constant toolface method for the north and east coordinates. The trigonometric functions in the quadratic functions of the horizontal projection length definite integral of the space arc method are simplified , thus realizing a fast calculation. Using the variable step Simpson numerical integration formula to calculate these two definite integrals makes the calculation accuracy controllable to arbitrary accuracy. After numerical tests and comparisons, the new algorithm in this paper not only improves the calculation speed, but also has the same calculation accuracy as the public data. The algorithm in this paper is a further improvement and refinement of the well trajectory calculation and can be applied in the software development of drilling.

Western Sichuan is rich in oil and gas resources, but the geological conditions of ultra deep marine carbonate rocks are complex. Drilling engineering faces technical problems such as multi pressure system in vertical direction, frequent lost circulation, wellbore instability and collapse, poor drillability of some formations, high drilling risk and long drilling cycle. Through the technical breakthrough in recent years, the matching technologies for ultra deep and fast drilling in western Sichuan have been formed, mainly including ultra deep well casing structure optimization, key technologies for drilling speed increase, leakage prevention and plugging technology, pressure controlled drilling technology for high pressure and low permeability gas reservoirs, key technologies for ultra deep horizontal drilling, ultra deep and high steel casing windowing technology, pressure control balance method cementing technology, ultra deep short liner hanging cementing technology and other drilling and completion technologies, It has supported the exploration and development of ultra deep oil and gas resources in western Sichuan and created a number of drilling engineering records. However, at present, we are still faced with technical problems such as insufficient understanding of the geology of the risk area, great difficulty in controlling malignant lost circulation, unsatisfactory speed increase in some difficult to drill formations, and imperfect matching technology for safe drilling in the formation with lost circulation and collapse. We have put forward the direction of further technical breakthrough, so as to promote the rapid development of ultra deep well drilling technology in western Sichuan, and provide technical reserves and support for the follow-up 10,000 meter deep wells.

In petroleum exploration and development, it is necessary to obtain cores to analyze parameters such as physical properties, oil content, porosity and permeability of the formation. To solve the problem of difficulty in obtaining cores from deep exploration wells, a hydraulic rotary well sidewall coring tool with a maximum operating temperature of 205 °C and high reliability has been developed. The logging instrument consists of a ground system, a control acquisition short section and a mechanical hydraulic section, and adopts an integrated thermos bottle technology, passive thermal management technology and decoupling technology to effectively improve the temperature resistance and engineering safety of the instrument. These key technical functions were verified through simulation and ground tests. The actual operation results show that the logging instrument can operate normally in exploratory wells with high temperature and high pressure environment at 189 ℃, high relative density of drilling fluid and formation pressure difference, and the average core harvesting rate is over 90%, and it has the characteristics of high temperature resistance, anti-stick jam, high cored time efficiency and core harvesting rate, especially for complex well sections, such as expansion, reduction, well wall collapse, etc., with good formation adaptability and high safety and reliability performance. The cores can be harvested with high efficiency and high core harvesting rate.

As a complex industrial system, drilling engineering has always faced severe challenges of safety risks and cost-effectiveness. The industry has been seeking solutions in the direction of informatization and intelligence, and digital twin technology has shown great potential as an ideal paradigm for intelligent drilling. On the basis of analyzing the development status of digital twin technology in the petroleum industry, this paper clarified six supporting technologies involved in drilling digital twin. Combined with the business needs of drilling engineering, a drilling digital twin system is designed. The overall structure of the system, the function design and model design are described in detail. Through three R&D tests of wellsite data standard collection, mechanism calculation model coupling and 3D dynamic fusion display, the feasibility of the application of drilling digital twin technology is verified from a technical point of view. The construction of the drilling digital twin system should first lay the data foundation through the collection and aggregation of drilling engineering data, further study and build the "mechanism + data" dual computing core based on the business needs. Finally, realize the application of the drilling digital twin system by developing the twin model and business application modules as the carrier.

In the northern part of Dongsheng anticline, southeast Sichuan structural belt, Sichuan Basin, there are many karst layers in the shallow strata, and the fracture zone is thick. Especially in the drilling process of the strata above the 2nd member of Jialingjiang Formation, drilling fluid is lost and the fracture zone of the borehole wall is dropped seriously, resulting in frequent downhole failures and abandonment of many Wells.In order to improve the drilling efficiency of dongsheng anticline shale gas exploration and development Wells, the drilling time of karst shallow surface is improved and the drilling cycle is shortened by optimizing well structure, optimizing drill assembly by well sections, optimizing drilling fluid type by stage and using "combined" cementing to solidified broken zone wall. Finally, the safe and efficient drilling technology of shallow surface formation in the north of Dongsheng anticline is formed.The field application of this technology in 15 Wells in the northern block of Dongsheng Anticline has avoided drilling abandonment, reduced the probability of downhole complexity in shallow surface sections. The completion rate of shallow surface Wells has reached 100%, the ROP has increased by 25%, and the drilling cycle has decreased by more than 74.1%.The safe and efficient drilling technology of karst shallow surface stratum of shale gas well in southeast Sichuan could provide the technical support for the efficient development of the block.

The existing kick and lost circulation detection methods using pit volume and flow out do not take the influence of pump on and off into consideration, they tend to misjudge the increase or decrease of flow out and pit volume caused by pump on and off as kick or lost circulation, leading to a high false alarm rate. In order to address this problem, the correlation relationship between drilling conditions and pit volume and flow out is established, and an intelligent kick and lost circulation monitoring method combining Bidirectional-Gated Recurrent Unit (Bi-GRU) and drilling conditions is proposed. The proposed model and other representative models for kick and lost circulation monitoring were tested using the data collected from 23 wells. The experiment results show that the identification accuracy of the proposed model achieves 94.25%, which is superior to those of the other models. Compared with the Bi-GRU model without incorporating the drilling conditions, the false positive rate of the proposed model drops from 12.52% to 1.12%. The proposed method reduces the false alarms caused by pump on and off during kick and lost circulation monitoring, which can provide technical support for safe drilling.

In order to monitor and evaluate the hole cleanliness of horizontal wells, a cutting return monitoring device is developed to accurately monitor the cuttings return. Based on the cuttings return data and the real-time data of engineering logging, the compensation method of missing cuttings during dumping period and the calculation method of actual cuttings return volume of the monitoring device were established under two operation modes. Based on the results of cuttings return rate and caving monitoring, the quantitative monitoring and evaluation technology of hole cleaning in horizontal well was developed. This technology has been applied in multiple shale gas horizontal wells in Luzhou block, southern Sichuan Province, realizing real-time and accurate monitoring of cuttings return volume and return rate in the monitoring well section, warning abnormal situation of hole cleaning for many times, and ensuring smooth drilling in the horizontal well section. The quantitative monitoring and evaluation technology of hole cleaning in horizontal well provides a new technical means for the monitoring of hole cleanliness in horizontal well and the prevention of pipe sticking and other complex downhole accidents of horizontal wells.

In order to solve the problems of incomplete factors and low accuracy of the existing calculation model of layered water injection allocation, a set of coupling model of wellbore pipe flow, nozzle orifice flow and formation seepage is established to calculate and predict layered water injection volume, and a set of inversion calculation method of layered water distributor nozzle allocation is established considering the constraints of wellhead pressure and ground pressure, The forward and inverse calculation results of the model under different conditions are analyzed and discussed. The results show that the model can accurately calculate the injection volume and pressure of each water injection layer at different times. The diameter of the single layer water distributor nozzle is positively correlated with the injection volume of this layer, and inversely correlated with the injection volume of other layers. The research shows that the model can give the optimal nozzle allocation scheme under the condition of meeting the pressure constraint conditions, provide a more accurate injection rate calculation and nozzle allocation method of water distributor for layered water injection technology, and guide the on-site layered water injection allocation.

To understand the pattern of hydraulic fracture propagation in deep fracture-cavity carbonate reservoir, a mathematical model of hydraulic fracture propagation is established based on elastic mechanics, fracture mechanics and fluid-solid coupling theory. Numerical simulation is used to analyze the interaction pattern hydraulic fracture and fracture-cavity sweet spot, and the technique applicability of cave communication by fractures is also discussed thoroughly. The numerical simulation results show that the local induced stress field around the fracture-caved sweet spot will be affected when the natural fractures develop around the cave, which making it easier for hydraulic fractures to connect with the fracture-cavity sweet spot. The pumping injection parameters with high injection rate and low viscosity or high viscosity and middle/low injection rate can only connect to cave which has a low-angle with the initial hydraulic fracture propagation direction, while for the cave with high-angle, forced steering technology should be considered for connect. The results show that, based on the distribution relationship between wellbore and fracture-cavity sweet spot, three fracture-cavity connection modes including direct connection, directional connection and seam connection can be achieved using the technique of cave connection by natural fracture, which significantly improves the production range of reserves.

In order to solve the difficult problem of horizontal well logging and drilling string running, a telescopic downhole robot is developed. The control system of the telescopic downhole robot technology is the key technology that affects the reliability and stability of the telescopic downhole robot. According to the working principle of the telescopic downhole robot, a new electro-hydraulic control system of the telescopic downhole robot is proposed, and a numerical simulation model based on electro-hydraulic coupling control is established by comprehensively considering the electric, hydraulic systems and actuators; By analyzing the influence of displacement, load and shaft wall size of the robot system on the robot kinematics, the motion law of the robot under different working parameters is revealed; An experimental scheme of the electro-hydraulic control system is designed, and the influence of the displacement of the system on the motion cycle of the robot is studied. The experimental results show that the simulation curve of robot motion cycle under different system displacement is basically consistent with the experimental curve. The research results can provide reference and theoretical basis for the design and research of hydraulic telescopic downhole robot.

As a new tool of surface wellhead construction in deepwater oil-gas field, the wellhead suction anchor has the risk of wellhead collapse or the formation is too hard to run in place. On the basis of analyzing the running principle of the conductor anchor node, the bearing capacity model considering the installation effect is established. Considering the most dangerous working conditions of second spud cementing, the maximum wellhead load calculation formula is derived during drilling. And a conductor anchor node lowering depth model is established with the safety factor of the pile foundation. Using the calculation model of the running depth, it is calculated that the minimum mud depth of the conductor anchor node of Well X in the South China Sea is 10.56 m. Based on the environmental parameters of the South China Sea X well, the finite element model is established by ABAQUS software. And the vertical bearing capacity of the conductor anchor node is calculated to be 8 593.22 kN. At same depth, by the theory the vertical bearing capacity is 8 063.59 kN. Comparing two solutions, the error of calculation is 6.16%. The results show that the conductor anchor node running depth model based on the ultimate bearing capacity can accurately predict the minimum running depth, and effectively improve the safety of the subsea wellhead in the South China Sea during the installation and drilling stages.

In order to enhanced shale gas recovery, Fuling shale gasfield has explored the three -dimensional development technology that increased the network density of the lower small layer, evaluated the middle layers and the developed the upper layers for the first time in China. However, many challenges presented, such as the variable formation pressure system is seriously disturbed by fracturing; the difficulty of avoiding collision and bypassing obstacles and trajectory control has increased sharply; the horizontal extension leads steering and speeding up drilling extremely hard. Based on the research, the fast drilling technology of stereoscopic development has been formed. The core technologies include well group drilling engineering design technology, drilling speed-up technology, trajectory control technology based on pre-drilling, low-cost and high-performance drilling fluid, long-term sealing cementing technology. The technology has been promoted and applied in 185 wells. Compared with previous wells, the ROP has increased by 25.53%, drilling time has been reduced by 30.8%, and cost has been reduced by 35.07%. The recovery rate of the stereoscopic development zone in the Jiaoshiba block has reached 39.2%, which is equivalent to the indicators in North America.

Wellbore instability is a state instability driven by energy. Based on the principle of energy dissipation, the triaxial compression experiments were used to study the mechanism of wellbore instability in sandstone formation during gas drilling. The conclusions are as follows: the energy evolution of sandstone can be divided into a first stage of stable accumulation of elastic energy, a second of slow accumulation of dissipated energy and a third stage of elastic energy release with a rapid accumulation of dissipated energy; as the confining pressure decreases, the dissipated energy index required to destroy the sandstone decreases, yet the elastic energy storage limit decreases linearly. When the loading rate increases, the dissipation energy required to destroy the sandstone decreases first and then increases, which means a critical loading rate exists. The conversion rate of dissipated energy in sandstone is positively correlated with confining pressure and loading rate. The higher conversion rate of dissipated energy in sandstone causes weakening of cohesive force and strengthening of friction. Too fast gas drilling rate will increase the instability area of wellbore, which is more serious in the case of high formation pressure. Therefore, reducing the drilling rate appropriately and giving the formation sufficient time to depressurize is beneficial to wellbore stability during gas drilling. The research results are of great significance for optimizing the gas drilling rate.

In view of the complex drilling of diabase in the Shunbei oil and gas field, the influence of structural characteristics, physical and chemical properties, rock mechanics characteristics, and drilling tool vibration on the stability of the wellbore was studied through X-ray diffraction, scanning electron microscopy, high-pressure mercury injection, linear expansion, rolling recovery and mechanical properties. It is clear that the weak surface effect of micro-fractures can easily induce the collapse and instability of the diabase rock mass, the torsional vibration and lateral vibration of the drilling tool will have a greater impact on the instability of the diabase shaft wall. Therefore, the density, plugging performance and rock carrying performance of the drilling fluid were optimized, and the diabase sidewall stable drilling fluid technology was formed, and the supporting drilling technology was studied. The technical countermeasure was applied in three level casing of Shunbei X well, successfully drilling through the 22m thick diabase formation, the performance of drilling fluid is good, there is no obvious complexity, and tripping is normal. Logging results show that the average diameter expansion rate of the diabase section is only 6.0%. The stability drilling fluid technology can effectively ensure the safe and smooth drilling of diabase well section and borehole rules, and has a good effect on solving the complex diabase borehole instability.

Using CO₂ to improve the recovery efficiency of offshore oil and gas fields can not only increase the utilization rate of oil and gas resources, but also contribute to regional CO₂ capture and storage. The long-term safety of offshore oil and gas Wells is a key factor for CCUS, but the theory and technology need to be improved. By analyzing and summarizing key technologies of CCUS (Carbon Capture, Utilization and Storage) wellbore integrity in domestic and foreign offshore oil and gas fields, the technical challenges that restrict CCUS wellbore integrity in shallow offshore oil fields are analyzed. This paper studied the cementing technology of carbon sequestration Wells, the research and prevention of carbon sequestration casing corrosion, carbon sequestration water-rock reaction wellbore plugging, wellbore pressure monitoring and diagnosis, etc. The development prospect of CCUS in shallow sea oil and gas fields was prospected from the aspects of national "dual carbon" target, EOR/EGR technology requirements and domestic and foreign new technology experience. Although China has initially been equipped with the capability to carry out offshore CCUS, there are still technical problems that need to be continuously solved. Technical problems should be strengthened in the aspects of high-toughness CO₂ corrosion prevention cement slurry system, low-cost anticorrosive material selection, wellbore efficient descaling and plugging process, CO₂ leakage monitoring technology, and three-dimensional stress field research of underground traps.

In order to follow the trend of technological syncretisation and promote the rapid and efficient development of petroleum engineering technologies, measures for cross-border syncretisation innovation of petroleum engineering technologies in the past ten years were studied. It was believed that the cross-border syncretisation innovation of petroleum engineering technologies mainly includes cross-border scientific research alliance and technological cooperation, venture capital, technological syncretisation innovation, technological merger and acquisition, etc. The operating environment of oilfield service enterprises is increasingly transparent, and the operation mode is more flexible. The operation mode and procedure are constantly optimized, and the construction performance index is constantly improved. Furthermore, the scope of application is constantly expanded, and the connotation of oilfield service is increasingly enriched. According to the influence of cross-border syncretisation innovation on petroleum engineering technologies, four development suggestions on cross-border syncretized innovation of petroleum engineering technologies were put forward, including improving the ability to scan external technologies, strengthening the external connection ability, creating a symbiotic innovation ecology, and focusing on the cultivation and aggregation of talents with T-shaped knowledge structures. The results and suggestions are of great significance to accelerate the development of cross-border syncretisation of petroleum engineering technologies.

The temporary plugging and diversion fracturing technology is the key method for efficient development of shale gas reservoirs in the Sichuan Basin. However, current operations mainly rely on field experiences. To further optimize the efficiency of this technology, this paper summarizes shale reservoir characteristics in the Sichuan Basin, reviews the background and development history of this technology, and summarizes the key advances of this technology in terms of temporary plugging materials and mechanisms, fracture diverting mechanisms, temporary plugging technology, and field applications. The paper points out the challenges for field operations and the corresponding suggestions. Micro seismic and field production data indicate that the near-wellbore and far-field temporary plugging and diversion fracturing technologies generate obvious improvements in shale reservoir stimulation efficiency in the Sichuan Basin. The performance of the frequently used temporary plugging ball and particle temporary plugging agents generally satisfies the needs of temporary plugging and diversion fracturing in shallow and some of the deep shale reservoirs. However, the optimal selection of the type of temporary plugging materials and optimization of field operation parameters are still lack of theoretical support, and there are still challenges caused by the complex reservoir conditions of deep shale reservoirs. The next step is to figure out the evaluation criterion of temporary plugging materials, investigate the temporary plugging mechanisms for different materials, develop new temporary plugging materials, and provide theoretical guidance for operation parameter optimization and stimulation efficiency enhancement.

Well site NMR technology have developed rapidly in the 21^st century and has played an important role in oil and gas drilling and exploitation. In this paper, we introduce the connotation, system and application of NMR technology in well site. Well site NMR refers to the measurement, analysis and application of NMR in the complex and harsh environment of oil and gas drilling sites, including wireline NMR logging, NMR logging while drilling, NMR downhole fluid analysis, well site multiphase flow NMR metrological analysis, well site full-size NMR scanning analysis and NMR mud logging, involving theoretical foundation, measuring instruments, data acquisition and processing, interpretation and application and other aspects. China's well site NMR technology germinated in the eighties of the last century, with the continuous maturity of international NMR logging technology, China's sciences and engineers opened the development road of "import-digestion-absorption-integrated innovation-original innovation", forming NMR measurement and analysis technology suitable for terrestrial oil and gas and several novelty and forward-looking technical reserves. The development process and key breakthroughs of NMR theory, methods and instrument technology at well sites in China were reviewed. The application prospects and technical challenges of well site NMR technology in the exploration and development of complex oil and gas, shale oil and gas are prospected, to promote the NMR applications to oil and gas exploration and development in ultra-deep complex reservoirs.

Deepsea is the main battlefield of the international oil and gas exploration and development and the commanding point of technology competition. The deep-sea oil and gas resources in the South China Sea are abundant, but it faces harsher marine environment, more complex shallow geological disasters, more challenging deep geological conditions, and more stringent deep water oil and gas exploitation conditions. The disaster mechanism is complex, and the operation risk is extremely high. Therefore, it is the key to ensure the safe and efficient exploitation of deep-sea oil and gas that exploring the risk assessment and safety control technology system for deep sea oil and gas exploitation in the South China Sea. Through technical research and engineering practice, the basic theory and key technology system of risk assessment for deep sea oil and gas exploitation with the characteristics of the South China Sea has been formed which is aiming at the four major risk challenges of environment, shallow layer, deep layer, and exploitation faced by deep sea oil and gas exploitation. The system includes deep sea marine environment risk assessment and control, deep water shallow geological disaster prediction and control, deep sea drilling well control and emergency rescue, deep water oil and gas production facilities safety detection and monitoring and other key technologies. It is pointed out some major problems in the field waiting for exploration of ultra-deep water, deep water and deep layer and deep sea which is urgent to solve, such as high risk of complex well operation, dependence on imports of key core equipment and engineering software, extremely high requirements for deep water safety and environment protection, digital intelligent transformation and etc., also proposed to continue to pursue intrinsic safety, promote domestic substitution, improve efficient risk prevention and control and emergency response capabilities, intelligent security and other development suggestions. All of the above is for further promote the development and progress of risk assessment and safety control technology for deep water oil and gas exploitation and realize safe, efficient, independent and controllable exploitation of deep-water oil and gas in the South China Sea.

Influenced by the wellbore wall surface roughness, drilling mud residue, and temperature-pressure disturbance, the cement-formation interface is the weakest part in the annulus sealing system. The corresponding tensile fracture of the interface is prone to occur and could induce annulus sealing failure. But the existed method could only evaluate the bonding shear strength of the interface, which could not provide reference on the interface bonding tensile property. Therefore, a new laboratory evaluating method of the bonding tensile strength of cement-formation interface is established, considering main factors such as lithology, surface roughness, drilling mud deposition, flushing fluid washing, cement slurry system, and so on. The bonding tensile strength of the second interface is evaluated from the aspects of flushing efficiency, cementation meso-structure, tensile strength, and fracture morphology. Results show that the proposed method is scientific and reasonable, simple and applicable, with small data dispersion and good discrimination, and has a high value of promotion. It further improves the evaluation system of the cementation second interface.

Surface logging is not only an oil and gas exploration technology, but also a petroleum engineering technology, its importance is self-evident, but the progress is relatively slow. What direction and how to develop surface logging is troubling the science and technology management and technology research and development layer personnel. Therefore, according to the surface logging technology developed by Sinopec during the "13^th Five-Year Plan" period, the development of drilling fluid on-line surface logging instrument is analyzed from two aspects of oil content and performance. The progress of rock sample surface logging instruments is analyzed from four aspects: elemental on-line detection, three-dimensional nuclear magnetic resonance, laser confocal and cuttings acoustic wave. The progress of surface logging evaluation methods is analyzed from four aspects: identification and evaluation of oil content of drilling fluid mixed source, identification and evaluation of oil and water information of shale in different occurrence states, calculation and application of formation multiple parameters based on elements, and carbon isotope of gas in different occurrence states. On this basis, the paper further analyzes the requirements of "deep, high, many, non, low, thin, micro, new" and other complex geological or engineering conditions on the four aspects of timeliness, accuracy, comprehensiveness and economy of surface logging, and proposes to deepen the basic research of surface logging from the aspects of spectrum decoupling, data recovery, multiple fusion, general model and so on. It is proposed to deepen the basic research of surface logging from the aspects of spectrum decoupling, data recovery, multiple fusion and general model, break through the existing collection mode from the aspects of standardization, automation, online, integration and intelligence, and innovate interpretation and evaluation methods from the aspects of single technology exploration, multi-technology integration, artificial intelligence introduction and emerging field support. The proposal of these directions has important guiding significance for promoting the progress of surface logging technology and promoting the high quality development of surface logging industry.

with the deepening of exploration and development in Shunbei Oil & Gas Field, the well depth in the western region has reached 8000−8800 m. The problems of long drilling cycle and high cost caused by slow drilling speed and short bit life in Paleozoic strata have become more prominent, which restricts the efficient and economic exploration and development of Shunbei Oil & Gas Field. This paper analyses the influence the efficiency of the upper Paleozoic strata rock hard to drill the formation characteristics and speed up the difficulty, reviewed in view of the Permian and carboniferous and Santa wood generation and distribution as well as the group drilling speed technology, the speed of the technical principle and technical characteristics, field application results show that the technology along the north by accelerated the upper Paleozoic strata effect is remarkable. Further, the existing problems of the acceleration technology are discussed. The large difference of the acceleration effects of various technologies, the lack of theoretical basis and the unclear acceleration space are still the technical bottlenecks restricting the development of the drilling acceleration technology in Shunbei Oil & Gas Field. Therefore, the technical development suggestions of the Paleozoic formation acceleration are given. which provides a new idea for further improving the rock breaking efficiency of Shunbei Paleozoic formation.

"Deepwater No.1" is the first self-operated deepwater gas field in China. The gas reservoirs are scattered and the sea conditions are complex. The second phase of the project is faced with HTHP geological environment. The development, drilling and completion of the gas field are faced with technical and cost challenges. In order to solve the above problems, the key technologies of drilling and completion design, such as multi-dimensional underwater wellhead optimization, multi-factor exploration and development well evaluation, safe drilling cycle prediction of deepwater extended reach wells, and intelligent completion of deepwater gas wells, have been studied and created; A series of domestic tools and equipment, such as deep-water underwater wellhead, deep-water underwater Christmas tree, deep-water early overflow monitoring device, and multi-channel bypass screen, have been developed and successfully put into use; It has developed efficient operation technologies such as large-scale surface batch drilling and inter-well displacement of deepwater development wells, safety guarantee of deepwater drilling platform-riser operation in extreme sea conditions, efficient drilling speed increase in non-target intervals, and integration of upper and lower completion of deepwater development wells. The engineering practice shows that the above technologies effectively support the safe and efficient drilling and completion operation of the first self-operated ultra-deep water gas field "Deepwater No.1" in China, and look forward to the future direction of China's deepwater drilling and completion technology, which has certain guiding significance for the future development of deepwater oil and gas fields in the South China Sea.

In the process of drilling for oil, gas and hydrate in deep water, the establishment of wellhead is the key to the safety and aging of the whole drilling operation. As a new well construction model, suction pile well construction has become a research hotspot in the field of ocean engineering in the world. It is of great significance to study the suction pile well construction model to improve the technological innovation and efficiency of deep sea well construction. Therefore, through a large number of literature research and field investigation, centering on the suction pile well construction technology, suction pile design and shaft design, the process method and technical characteristics of suction pile well construction mode are systematically sorted out. Suction pile installation depends on the negative pressure effect, the soil disturbance is small, the bearing capacity is large, the mud depth is much lower than the traditional well construction model; The suction pile can be extended to accommodate multiple shafts, and combined with the wellbore predeflection design, the problem of soft formation deviation can be overcome. According to the shallow soil characteristics and drilling targets in South China Sea, The research shows that the suction pile well construction model can be well adapted to the well construction engineering of deep sea oil, gas and hydrate exploration and development, and provides a new way for the well construction of deep sea resources exploration and development.

In China, deep and ultra-deep oil and gas well cementing faces challenges such as high temperature (>150℃), high pressure (>105 MPa), complex fluid medium (H₂S and other acidic gases), complex working conditions (massive hydraulic fracturing, etc.). The sealing integrity of cement sheath cannot be guaranteed. Conventional cementing technology and equipment cannot meet the needs. Therefore, it is urgent to develop new wellbore integrity cementing theory and technology. In recent years, Sinopec has improved the integrity theory system of the cementing cement sheath, established sealing failure control methods of the cement sheath under complex working conditions, developed the high-performance cement slurry of "anti-channeling, anti-corrosion, anti-leakage, and anti-damage", and developed cementing liner hangers, stage cement injectors, and supporting accessories suitable for deep complex working conditions, established new methods for optimal cementing design, forming a new cementing technology for deep complex oil and gas reservoirs. In the future, it is suggested to further improve the technical system of characteristic cement slurries, develop green and intelligent environment-friendly materials, improve the informatization and intelligence of cementing technology, continuously promote basic theoretical research, and improve the cementing quality of deep and ultra-deep complex oil and gas wells.

In recent years, through continuous research and field practice, domestic drilling fluid technology has made new progress. In order to systematically understand the research and application of drilling fluid technology in China and promote the improvement of drilling fluid system and performance, The research and application of water-based drilling fluid system(strong inhibiting polyalcohol drilling fluid, amine inhibiting drilling fluid, organic salt drilling fluid and alkyl glycoside drilling fluid and ultra-high temperature drilling fluid, micro-bubble drilling fluid, strong plugging drilling fluid, environmental protection drilling fluid and soil-free/solid water-based drilling fluid, etc,), oil-based drilling fluid system(Including all-oil-based drilling fluid, water-in-oil emulsion drilling fluid and soilless oil-based drilling fluid) and synthetic-based drilling fluid system(Including hydrocarbon synthetic-based drilling fluid and biomass synthetic-based drilling fluid) are summarized, the problems in the research and field application of drilling fluid are pointed out, the causes of the problems are analyzed, It also puts forward suggestions for future development based on field needs and drilling fluid research, application and specifications. The summary has certain reference and use for referenc value for the development and application of domestic drilling fluid system.

For the maximization of the efficacy of the polycrystalline diamond compact (PDC) bit in drilling engineering, comprehensive research, including theoretical analysis, laboratory test, case study, and on-site trials, was conducted to investigate how a high weight-on-bit (WOB), a high rotary speed, and other optimized drilling parameters work on the rate of penetration (ROP) and the wear of a PDC bit. Furthermore, the wear mechanism of PDC bit and the primary cause of the premature failure of the bit were analyzed. The results indicated that : 1) The ROP of PDC bit was directly and primarily affected by the WOB. When the bit was in an efficient rock-breaking state, the WOB was invariably in a linear relationship with the ROP whether the formation encountered was a conventional one or a hard rock formation. Adding a high WOB over 200 kN into the normal pressurization range of the PDC bit was recommended if the formation encountered was a homogeneous hard rock formation. 2) ROP improvement could be achieved by enhancing the rotary speed. Although the wear of the PDC bit could be aggravated by a high rotary speed, the requirement on a PDC bit to penetrate most formations for a long time at a high rotary speed (400–500 r/min) could be readily met by the quality of the currently available cutting teeth. 3) The ROP of the bit was also affected by tooth density, but not in a direct manner. As long as a dynamic balance among “capabilities to bite into the formation, cut the rock, and discharge the cuttings in time” was reached, the optimized fast drilling could be achieved even by a PDC bit with a high tooth density. 4) The wear of the PDC bit was less severe under the higher rock-breaking efficiency of the bit. For example, an enhanced WOB could improve the ROP and reduce the bit wear. Dynamic impact and inefficient rock-breaking were considered the primary causes of the premature failure of the PDC cutting teeth and bit. The key for the PDC bit to achieve efficient penetration was to improve rock-breaking efficiency and restrain bit vibration. The above results could be used as a reference for the proper utilization of PDC bits and the innovation of ROP improvement technologies.

In order to realize the efficient development of horizontal wells with the ultra-long horizontal section of shale gas, Sinopec has conducted research on shale gas geological selection evaluation, equipment supporting, friction and drag reduction, low-cost and efficient guidance, layered optimization of drilling parameters, long-life and high-efficiency rock breaking tools and high-efficiency cementing technologies. In addition, Sinopec has successfully drilled 15 horizontal Wells with more than 2700m horizontal section and 5 horizontal Wells with more than 3000m horizontal section. The drilling technology system for ultra-long horizontal section shale gas Wells with 4000m horizontal section has been initially formed, which strongly supported the efficient development of shale gas in Dongsheng Block and Jiaoshi Block. However, compared with abroad, there is still a big gap in drilling technology of ultra-long horizontal section shale gas Wells of Sinopec. It is necessary to focus on key tools and technologies such as geological selection and evaluation technology, key speed enhancing tools, high-efficiency drilling fluid system, friction and drag reduction technology, casing running and long-term sealing, etc., to provide technical support for safe and efficient ultra-long horizontal wells drilling.

The exploration and development of oil and gas resources from deep and ultra-deep reservoir in China is drawing great attention. However, the complicated wellbore instability in deep hard brittle shale seriously restricts the development of deep and ultra-deep oil and gas reservoir. In essence, the wellbore instability in deep hard brittle shale under the chemo-mechanical coupling interaction is a complicated problem involving the multiscale evolution process of microcracks (micro-scale, meso-scale and macro-scale). In this paper, the basic principle of wellbore instability in hard brittle shale under the chemo-mechanical coupling interaction is briefly introduced. In addition, the previous studies on microscopic interaction mechanism between shale and drilling fluid, quantitative description of mesostructured damage, description of macroscopic mechanical deterioration of shale after hydration and quantitative analysis of wellbore stability, are reviewed and points out a new idea to study wellbore stability in hard brittle shale through considering the evolution process of microcracks under the mechanical and chemical coupling interactions.

In response to global climate change, major countries and regions in the world have set emission reduction targets for carbon neutral. As traditional fossil energy, low-carbon transformation of oil and gas is the only way for sustainable development. it has become consensus to reduce carbon emissions through technology innovation and management. In this context, the development of green and low-carbon oil and gas development engineering technology also presents a new development trend, which is worthy of our learning and reference. This paper expounds the low-carbon development industry background of oil and gas development engineering technology, analyzes on the development trend of green and low-carbon oil and gas development engineering technology. In combination with the situation and challenges of oil and gas development in China under the background of carbon neutralization, puts forward some of the best future development direction of engineering technology, including low-carbon technology including high efficiency engineering technology, digital and intelligent technology, carbon capture, utilization and storage technology, energy conservation and tail waste utilization technology, new energy co-location technology. Focusing on the key technologies involved in the development direction of these technologies, it is of great significance for achieving the goal of net zero emissions and improving the overall economic benefits to carry out R&D and application to China as soon as possible.

Intelligent drilling and completion technology is the integration of drilling and completion engineering with artificial intelligence, big data, cloud computing and other advanced technologies. It can realize fine characterization, optimal decision-making and closed-loop control of oil and gas drilling and completion, and is expected to significantly improve drilling and completion efficiency, reservoir drilling rate and oil and gas recovery efficiency. It is a research frontier and hot spot in the oil and gas field. In this paper, the application scenario system of AI in oil and gas drilling and completion is constructed from the engineering practice, and the development level of intelligent drilling and completion technology is divided according to the integration depth of drilling and completion engineering and AI. This paper expounds the research status of intelligent drilling and completion at home and abroad, puts forward the medium and long term development plan combined with the development trend of AI and drilling and completion engineering, and summarizes the problems and key directions of intelligent drilling and completion technology. The paper can provide reference for speeding up the basic theoretical research and application of intelligent drilling and completion technology in China.

In recent years, in response to the problems of high formation hardness, high temperature and low productivity in the exploration and development of deep and extra-deep, unconventional and low-permeability oil and gas, Sinopec has developed a batch of key core technologies and equipment such as 9000 m extra-deep well safe and efficient drilling technology, shale oil engineering technology and middle-deep shale gas engineering technology. Five 9000m ultra-deep Wells, 17 special exploration Wells for shale oil and 2 shale gas Wells with displacement exceeding 4000m have been efficiently drilled, which strongly supports the smooth implementation of deep-earth engineering and guarantees the exploration and development of various oil and gas resources.However, with the deepening of exploration and development, petroleum engineering technology is confronted with a series of new challenges such as more complex geological conditions. However, with the deepening of exploration and development, petroleum engineering technology is confronted with a series of new challenges such as more complex geological conditions. It is suggested that Sinopec speed up the formation of independent innovation capability in the aspects of safe drilling, high temperature and high pressure logging, refracturing and other technologies, pay attention to the application of new materials, green and low-carbon technologies, and build a more mature petroleum engineering technology system with a higher level of specialization to provide support for the realization of the new target of increasing storage and production.

The goal of unconventional reservoir volume fracturing technology is to maximize the ESRV (effective stimulated reservoir volume) and single well control EUR(estimated ultimate recovery), and has experienced the development process of the first generation and the second one. Its technical logo is mainly reflected in the technical boundary difference and iterative upgrade of "close cutting-higher proppant intensity-temporary plugging to divert fractures -vertical fracture penetration". However, due to the restriction of various subjective and objective factors, the effect of volume fracturing is greatly reduced. In conclusion, the concept, connotation and realization method of the new generation of volume fracturing technology are proposed. Which mainly includes: the concept of five factor of three-dimensional fracture network index and model, "Fracturing- imbibition - energy enhancement-oil displacement" integration to improve oil recovery mechanism, "moderate close cutting- higher proppant intensity in multi-scale fractures -efficient double temporary plugging to divert fractures-vertical fracture penetration along the whole fracture length" of fracturing mode and parameters boundary, development of integrated multi-functional fracturing fluid with different viscosity and economic analysis of quartz sand replacing the ceramic proppant, dynamic integration of geological-engineering concept, model and fracturing real-time parameter adjusting technology, and the closed loop system establishment of "fracturing design-implementation-post evaluation" with the characteristics of iterative upgrading, etc. furthermore, the above research results have been applied and preliminarily verified in the field fracturing practice, and have achieved effective breakthroughs in some key Wells. Therefore, it is of important reference and guiding significance for the efficient exploration and development of various types of unconventional reservoirs and conventional ones in the future all over the world.

In view of the application of the dragging string technique for water prospecting in the long horizontal section of Changqing oilfield, it is difficult to control the setting tonnage of the mechanical packer, and the damage of the repeatedly setting rubber cylinder results in the reduction of the stability of the Packer, an electric controlled packer for horizontal wells is developed, which can set and unseal in time or in real time and can realize arbitrary interval packings. In the design of the Packer, the repeated setting times of the horizontal well section and the pressure bearing performance of the seal are fully considered, in particular, the power output part of the drive mechanism adopts the direct current Motor + planetary reducer, and the motion conversion part adopts the lead screw and nut mechanism to ensure that in the allowable casing space, the output torque is maximized and the packer rubber cylinder is compressed and set. The performance of temperature and voltage resistance, output torque and setting thrust of the electronic controlled Packer were evaluated by indoor test, and the related indexes could meet the design requirements. Field tests have been conducted in three wells in Truong Khanh oilfield. The results show that the new packer can minimize the impact of engineering conditions and improve the success rate and test quality, it makes the test technology of dragging pipe string more convenient and lower cost.