基于热—流—固—化耦合的深层致密砂岩储层压裂裂缝扩展规律

Propagation patterns of hydraulic fractures in deep tight sandstone reservoirs based on thermo-fluid-solid-chemical coupling

  • 摘要: 塔里木盆地库车坳陷北部斜坡带深层致密砂岩气是中国天然气增储上产的重要领域,储层水力压裂技术是油气增产的关键手段。然而,深部地质条件复杂,导致压裂裂缝扩展样式及影响因素尚不清晰,需量化分析以揭示多场耦合作用下压裂裂缝的扩展规律。针对库车坳陷北部斜坡带深层气藏高温、高压地质环境,考虑“应力、裂缝弱面”等地质力学因素,建立热—流—固—化耦合模型,借助有限元数值模拟,阐明水力压裂裂缝扩展规律。研究表明:(1)水力压裂裂缝的动态扩展过程受热—流—固—化耦合作用影响显著,决定着压裂裂缝扩展样式;(2)水平应力差低值区易形成复杂缝网,水平应力梯度差异诱导压裂裂缝非对称扩展;(3)压裂裂缝扩展过程中优先激活天然裂缝,且天然裂缝产状影响压裂裂缝扩展方向,当天然裂缝与压裂裂缝夹角较大时压裂裂缝扩展偏向于停止和穿过,而当天然裂缝与压裂裂缝夹角较小时压裂裂缝偏向于激活或激活+穿过;(4)射孔倾角与裂缝偏转角呈正相关,注入速率对裂缝面积的影响存在最优上限,流体与地层温度差越大,越易产生张裂缝,起裂压力越小。

     

    Abstract: The deep tight sandstone gas reservoirs in the northern slope belt of the Kuqa Depression, Tarim Basin, are key area for natural gas reserve expansion and production enhancement in China, and hydraulic fracturing technology for these reservoirs is a critical means for hydrocarbon production enhancement. However, the complex geological conditions in deep layers lead to unclear propagation patterns and influencing factors of hydraulic fractures, requiring quantitative analysis to reveal the propagation patterns of hydraulic fractures under the action of multi-field coupling. Focusing on the high-temperature and high-pressure geological environment of deep gas reservoirs in the northern slope belt of the Kuqa Depression, a thermo-fluid-solid-chemical coupling model was established considering geomechanical factors such as "stress and fracture weak planes". Using finite element numerical simulation, the propagation patterns of hydraulic fractures were elucidated. The results showed that: (1) The dynamic propagation process of hydraulic fractures was significantly influenced by thermo-fluid-solid-chemical coupling, which determined the propagation patterns of hydraulic fractures. (2) Complex fracture networks tended to form in zones with low horizontal stress differences, and differences in horizontal stress gradient induced asymmetric propagation of hydraulic fractures. (3) During the propagation of hydraulic fractures, natural fractures were preferentially activated, and the occurrence of natural fractures affected the propagation direction of hydraulic fractures. When the angle between natural fracture and hydraulic fracture was large, the propagation of hydraulic fractures tended to stop and pass through natural fractures. When the angle was small, hydraulic fractures tended to activate natural fractures or both activate and pass through them. (4)The perforation inclination angle was positively correlated with the fracture deflection angle. The effect of injection rate on fracture area had an optimal upper limit. A greater temperature difference between fracturing fluid and formation more easily generated tensile fractures and resulted in a lower fracture initiation pressure.

     

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