Research on the Optimal Proportions of the New and Old Fractures in Refracturing of Horizontal Wells in Ultra-Low Permeability Reservoirs
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摘要:
超低渗透油藏初次压裂投产后，由于地层能量亏空严重、裂缝失效等原因，油井产量递减迅速，无法满足生产需求，需要进行重复压裂，重复压裂设计的关键是确定合理的布缝位置和重复压裂的新缝数量。基于长庆油田元284井区储层地质特征，结合初次压裂生产情况，建立了水平井重复压裂裂缝延伸数值模拟模型；对比了不同新老缝配比条件下重复压裂储层改造体积与最终开采效果，明确了重复压裂前注水补能提高重复压裂改造效果的机理；通过分析经济收益，获得了合理的新老缝配比关系。模拟结果表明：重复压裂新缝为2条、缝间距为20 m时，更有利于形成复杂缝网，提高采收率；随着2条老缝间重复压裂新缝数量增加，更有利于裂缝间相互沟通形成复杂缝网，提高储层改造效果；老缝间重复压裂的新缝数量较多时，由于裂缝之间的相互干扰，会导致开发生产前期产量增幅递减，但随着不断生产，由于储层改造更为充分，对后期稳产较为有利。研究结果为超低渗透油藏水平井重复压裂方案设计提供了理论依据。
Abstract:After the initial hydraulic fracturing of the ultra-low permeability oil reservoir, there is a rapid decline in oil production due to the depletion of formation energy and fracture failure. This decline fails to meet the production demands, and the refracturing is needed. In the design of refracturing, the key lies in determining the optimal positioning and number of new fractures. In this study, a numerical simulation model for fracture extension during refracturing of horizontal wells was established, based on the geological characteristics of the Changqing yuan 284 well block oil reservoir and the production data from the initial hydraulic fracturing. A comparative analysis of the reservoir stimulation volume and ultimate developing effect was conducted with varying proportions of new and old fractures. The study found that energy replenishment by water injection before refracturing as a mechanism could effectively improve the reservoir stimulation effect of refracturing. Furthermore, an economic benefit analysis was performed to determine an reasonable proportion of new and old fractures. Simulation results indicated that a favorable condition for the formation of a complex fracture network and increased oil recovery was observed when there were two new fractures by refracturing, with a spacing of 20 m between fractures. As the number of new fractures between two old fractures increased, the formation of a complex fracture network and reservoir stimulation effect were further enhanced. However, a large number of new fractures between old fractures led to mutual interference, resulting in a decrease in the range of production increase during the early stage of development. Nonetheless, as development and production continued, there will be a more thorough reservoir stimulation effect, which is beneficial for stable production in the later period. These research findings offer a theoretical foundation for designing refrcuturing schemes for horizontal wells in ultra-low permeability oil reservoirs.
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图 2 压裂过程中水力裂缝与天然裂缝交互图
Figure 2. Interaction between hydraulic fractures and natural fractures during fracturing
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图 3 压裂过程中水力裂缝与天然裂缝交互图
Figure 3. Interaction between hydraulic fractures and natural fractures during fracturing
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图 4 注水补能前后孔隙压力分布
Figure 4. Pore pressure distribution before and after waterinjection for energy replenishment
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图 5 注水补能前后应力阴影分布
Figure 5. Stress shading distribution before and after water injection for energy replenishment
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图 6 注水补能前后两向应力差分布
Figure 6. Two-way stress difference distribution before and after water injection for energy replenishment
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图 9 不同新老缝配比下的油井生产动态曲线
Figure 9. Oil well production dynamic curve with different proportions of new and old fractures
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图 10 不同新老缝配比下的经济收益对比
Figure 10. Economic benefits change with different proportions of new and old fractures
表 1 不同新老缝配比下重复压裂裂缝延伸模拟参数
Table 1 Fracture extension simulation parameters with different proportions of new and old fractures
方案 裂缝导流能力/
（mD·m）单段裂缝
半长/m缝网复杂
程度新老缝配比1∶2 259.3 187.9 0.26 新老缝配比2∶2 216.8 156.6 0.28 新老缝配比3∶2 202.8 126.7 0.35 
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表 2 不同新老缝配比下的储层改造体积
Table 2 Reservoir stimulation volume with different proportions of new and old fractures
方案 平均裂缝改造体积/
108m3总改造体积/
108m3新老缝配比1∶2 0.237 0.488 新老缝配比2∶2 0.139 0.529 新老缝配比3∶2 0.118 0.606
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