四川盆地川西坳陷东坡地区下侏罗统大安寨段储层裂缝分布预测

Prediction of fracture distribution in the Lower Jurassic Da’anzhai Member on the eastern slope of the Western Sichuan Depression,Sichuan Basin

四川盆地川西坳陷东坡地区下侏罗统大安寨段是致密油气的主要开发目的层,裂缝是大安寨段储层能否获得高产的关键因素。由于大安寨段地层岩性复杂,传统裂缝预测评价方法适用范围窄、预测结果精度低。基于岩心裂缝调查及薄片鉴定资料,运用地质统计学及数值模拟方法,明确了不同岩性储层的岩石学特征,揭示了大安寨段裂缝发育特征;结合岩石破裂基础和破裂外力二大因素,在区分岩性及亚段的条件下,提出并构建了3项裂缝评价因子,对各亚段裂缝平面分布进行预测评价。研究表明:(1)大安寨段储层为(介壳)灰岩、砂岩及泥页岩相互叠置的复杂岩性;(2)主要发育全充填裂缝,(介壳)灰岩主要发育构造裂缝,砂岩和泥页岩主要发育层间缝,缝面存在溶蚀现象,对油气流动具有积极意义;(3)提出并构建了岩性厚度评价因子、构造变形强度因子和断裂破裂强度因子3项裂缝评价因子,并建立裂缝综合预测评价定量模型,对各亚段裂缝平面分布进行综合预测评价,预测的裂缝密度与单井识别的裂缝发育指数吻合性较好,预测结果可靠。该裂缝平面分布预测评价方法对于同类型油气藏的评价具有借鉴意义。

The Da’anzhai Member of the Lower Jurassic on the eastern slope of the Western Sichuan Depression in the Sichuan Basin is a main target for the development of tight oil and gas.Fractures are essential for achieving high production in the Da’anzhai Member reservoirs.Due to their complex lithology,traditional methods for frac⁃ture prediction and evaluation have limited applicability and low prediction accuracy.Based on core fracture investigations and thin⁃section identification data,combined with geological statistics and numerical simulations,the lithological characteristics of various reservoirs were clarified,and the fracture development characteristics in the Da’anzhai Member were revealed.Considering both the fracture foundation and external fracturing forces,three fracture evaluation factors were proposed and constructed to predict and evaluate the planar distribution of fractures in each sub⁃member by distinguishing lithology and sub⁃members.The results showed that:(1)The Da’anzhai Member reservoirs had complex lithologies with interbedded(shell)limestone,sandstone,and shale.(2)Fully filled fractures were mainly developed,and(shell)limestone exhibited mainly structural fractures,while sandstone and shale mainly showed interlayer fractures with dissolution features on the fracture surfaces,which was beneficial for enhancing oil and gas flow.(3)Three fracture evaluation factors were proposed and constructed,which included lithologic thickness,tectonic deformation intensity,and fracture rupture intensity.A quantitative model for comprehensive prediction and evaluation of fractures was established to predict and evaluate the planar distribution of fractures in each sub⁃member comprehensively.The predicted fracture density aligned well with the fracture development index identified in individual wells,indicating the reliability of the prediction results.This method for fracture planar distribution prediction and evaluation offers a reference for similar oil and gas reservoirs.