Research and Field Test on Energy Storage Fracturing Mechanism of Horizontal Wells in Ultra-Low Permeability Reservoirs
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摘要:
针对超低渗透油藏部分水平井生产一段时间后，出现单井产能降低的问题，开展了超低渗透油藏水平井储能压裂机理研究与现场试验。根据岩石破坏机理，进行了室内储能压裂模拟试验，利用声发射信号检测储能压裂对试件内部的破坏情况，并采用有限元法计算近井地带地应力变化情况。试验及数值模拟结果表明：在高孔隙压力作用下，天然裂缝面错动痕迹明显，憋压过程中试件内部产生了大量微破裂；压裂后焖井过程中，一段时间内地应力场受到影响。研究表明，压裂前注入适量的驱油压裂液，压裂后焖井进行渗吸扩散，可以有效补充地层能量，同时结合优化后的体积压裂重复改造技术，能够进一步增大压裂改造体积和裂缝复杂程度。该技术对能量亏空、裂缝闭合导致的低产水平井提高产量具有较好的适应性，可为同类超低渗透油藏重复压裂提供技术参考。
Abstract:After the production of some horizontal wells in ultra-low permeability reservoirs for a period of time, the production capacity from those wells start to decrease. A research and test on energy storage fracturing mechanism of horizontal wells in ultra-low permeability reservoir have been carried out. According to the failure mechanism of the rock, the laboratory simulated energy storage fracturing experiment was performed, in which the failure of the rock sample within the specimen was detected by acoustic emission. In addition, the stresses change near a wellbore was calculated through finite element method. Experimental and numerical simulation results showed that natural fracture surface has obvious dislocation traces, and a large number of microfractures are produced in the specimen during building up of high pore pressure. During well soaking process after fracturing, in-situ stress field is disturbed for a period of time. The research results showed that the injection of appropriate amount of oil displacement fracturing fluid before fracturing treatment and the imbibition and diffusion by well soaking after fracturing could effectively provide supplement energy in the formation. At the same time, the treated volume and complexity of fractures could be further increased when combined with the optimized volume refracturing. This technology has a good effect in increasing the production of low production horizontal wells due to energy deficit and fracture closure, and it has some reference value for the same ultra-low permeability reservoirs.
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图 1 储能压裂过程中的声发射事件分布
Figure 1. Distribution of acoustic emission events during energy storage fracturing
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图 2 焖井前最大主应力分布
Figure 2. Distribution of the maximum principal stress before well soaking
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图 4 焖井前最小主应力分布
Figure 4. Distribution of the minimum principle stress before well soaking
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图 3 焖井后最大主应力分布
Figure 3. Distribution of the maximum principle stress after well soaking
表 1 储能压裂前后各参数的变化情况
Table 1 Changes of parameters before and after energy storage fracturing
条件 渗透率/mD 孔隙度，% 单井产量/（t∙d–1） 采收率，% 压裂前 0.30 11.50 1.18 6.77 压裂后 27.80 19.50 4.60 17.00 
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