柴达木盆地东坪地区基岩储层裂缝特征及影响因素

Fracture Characteristics and Influencing Factors of Bedrock Reservoir in Dongping Area,Qaidam Basin

在基岩风化壳储层中裂缝发育的影响因素是近年来基岩储层裂缝分布规律研究的热点问题之一。本文通过研究区岩心观察、薄片鉴定及常规物性等分析化验资料,分析了柴达木盆地东坪地区基岩风化壳储层的岩石相特征、储集空间类型及基本特征,在此基础上探讨了基岩风化壳储集空间的影响因素。东坪基岩储层的岩石类型可分为侵入岩浆岩类和变质岩类两大类,储集空间类型为构造缝、溶蚀缝和溶蚀孔洞三种,属于裂缝-孔隙型基岩风化壳储层。结果表明:构造成因裂缝主要受控于构造活动强度、断层规模和性质、裂缝与断层之间的距离、裂缝与风化壳顶面的距离以及储层岩性等因素,构造强烈部位比非构造强烈部位的裂缝有效性好。溶蚀成因的裂缝、孔洞多发育在基岩风化壳的上段,古地貌高部位或斜坡带的位置,主要受到的建设性成岩作用有溶蚀、破碎、蚀变和风化作用,破坏性成岩作用如充填作用。

The influencing factors of fracture development in bedrock weathering crust reservoirs are one of the hot issues in the study of fracture distribution in bedrock reservoir in recent years.Based on the data of core observation,thin section identification and routine physical property analysis in the study area,the petrographic characteristics,reservoir space types and basic characteristics of the bedrock weathering crust reservoirs in Dongping area of Qaidam basin were analyzed,and the influencing factors of the reservoir space in the bedrock weathering crust were discussed.The rocks of Dongping bedrock reservoirs can be divided into intrusive magmatic rocks and metamorphic rocks two types.The reservoir space types are tectonic fractures,dissolution fractures and dissolution holes,which belong to fractured-porous bedrock weathering crust reservoir.The results show that the tectonic fractures are mainly controlled by the intensity of tectonic activity,the scale and characteristics of faults,the distance between fractures and faults,the distance between fractures and the top surface of weathering crust,and the lithology of reservoirs,etc.The effectiveness of fractures in the strong tectonic part is better than that in the non-strong tectonic part.The fractures and holes caused by dissolution mostly develop at the upper part of bedrock weathering crust,high part of palaeogeomorphology or slope zone,which are mainly affected by dissolution,fragmentation,alteration and weathering and other constructive diagenesis,and destructive diagenesis like filling.