超深层致密砂岩构造裂缝发育特征及控制因素——以塔里木盆地库车坳陷博孜—大北地区下白垩统储集层为例

Characteristics and controlling factors of tectonic fractures of ultra-deep tight sandstone:Case study of the Lower Cretaceous reservoir in Bozi-Dabei area,Kuqa Depression,Tarim Basin

塔里木盆地库车坳陷博孜—大北地区下白垩统巴什基奇克组和巴西改组砂岩优质储层发育,已于埋深8200 m内获高产工业气流,目的层经历多期构造运动,多成因裂缝发育为储集层提供有效的储集和渗流空间。综合利用钻井岩心、野外剖面调查、成像测井及实验测试分析,对博孜—大北地区下白垩统致密砂岩储层裂缝进行表征刻画,明确了多成因、多期次裂缝发育特征和控制因素,提出了应力控制下的有效裂缝发育模式。结果表明:博孜—大北地区处于强挤压应力环境,变形相对平缓,以区域构造裂缝和断层共派生裂缝为主,局部构造变形相关裂缝发育程度较弱;基于薄片、岩心、裂缝切割关系、流体期次判定技术、阴极发光测试及热埋藏史等多属性资料综合判定技术,确定储集层裂缝经历了3期主要的构造运动。区域构造裂缝发育主要受到地层岩性、地层厚度控制;断层共派生裂缝则主要受距断裂距离以及断裂上下盘位置的影响。博孜—大北地区后期水平最大主应力方向转变会使早期裂缝在不同条件下开启或闭合,进而影响裂缝的开启程度和有效性:当水平最大主应力发生偏转并与早期裂缝以更小角度相交甚至叠合时,偏转方向相关组系裂缝有效性更好,整体协调性发育,其高产储集层的裂缝系统分布特征是多期活动的优势配置结果。

High-quality reservoirs developed in the Bashijiqike Formation and Baxigai Formation sandstones of the Lower Cretaceous in the Bozi-Dabei area,Kuqa Depression of Tarim Basin,in which highly yielding industrial gas flow is obtained within a burial depth of 8200 m.The target formation has experienced multiple phases of tectonic movements,and the development of multi-genetic fractures provides the reservoir with efficient storage and seepage space.Based on the results of drilling core,field profile survey,imaging logging,and experimental analysis,the authors portray the fractures in the Lower Cretaceous dense sandstone reservoir of the Bozi-Dabei area,clarify the characteristics and controlling factors of multi-genesis and multi-period fractures,and propose an effective fracture development model under geo-stress control.The Bozi-Dabei area is subjected to a high extrusion stress environment with relatively gentle deformation,mainly developed regional tectonic fractures and fault related fractures,where deformation-related factures are less developed.The results of a combination of multi-attribute data determination techniques,including fracture filling,inter-cutting relationship,fracture filling isotope,inclusions and cathode luminescence tests,indicate that the reservoir fractures have experienced three major periods of tectonic movement.Regional tectonic fracture development is mainly controlled by stratigraphic lithology and stratigraphic thickness;Fault co-derived fractures are influenced by the distance from the fault and the location of the upper and lower plates of the fault.The shift in the direction of the late horizontal maximum principal stress will cause the early fractures to open or close under different conditions in the Bozi-Dabei area,which in turn affects the degree of fracture opening and effectiveness.When the horizontal maximum principal stress is deflected to intersect with the early fractures at a smaller angle or even superimpose,the fracture effectiveness of the related group system in the deflection direction is better,and the overall coordination is developed.The distribution characteristics of the fracture system in the highly productive reservoir are the result of a dominant configuration of multi-phase activities.