大邑构造须家河组气藏裂缝发育特征及主控因素

Characteristics and main controlling factors of fractures in gas reservoir of Xujiahe Formation,Dayi Structure

大邑构造须家河组气藏为裂缝性气藏,裂缝发育程度是天然气富集高产的关键因素。通过对14口钻井岩心、测井资料分析统计,结合构造、沉积相分析及古构造应力场模拟认为,大邑构造须家河组气藏发育构造缝、层理缝及异常高压泄压缝3种成因类型裂缝。构造缝和层理缝有效性相对较好,但其总体具数量少、延伸短、宽度窄、充填程度相对较高、非均质性较强的发育特征。地层所受应力小、变形弱是构造缝发育程度相对较差的根本原因。喜马拉雅期派生羽状断裂控制了构造缝的形成和展布;发育于三角洲平原、前缘分流河道的平行层理、斜层理是层理缝形成的主要层理构造。裂缝成因类型、充填特征、后期溶蚀作用及现今地应力场共同控制了裂缝的有效性。

The gas reservoir of the Xujiahe Formation in the Dayi Structure is a fractured reservoir. The generation degree of fracture is the key factor for natural gas enrichment and high productivity. According to the core and logging data from 14 wells, combined with structural and sedimentary facies analyses as well as ancient tectonic stress field simulation, it has been concluded that 3 genetic types of fractures exist in the study area, including structural fracture, stratification fracture and abnormal pressure blowdown fracture. Structural and stratification fractures are relatively more effective; however, they are usually in smaller amount, and extend for short distance and narrow width. They are filled for higher degree and have stronger heterogeneity. Small formation stress and weak deformation are the primary causes for the poor development of structural fractures. Induced feather fractures during the Himalayan period control the formation and distribution of structural fractures. Parallel beddings and inclined beddings which develop in the distributary channels of delta plains and delta fronts are the main bedding types for stratification fracture formation. The genetic types of fractures, filling characteristics, later denudation and current ground stress field control the effectiveness of fractures.