鄂尔多斯盆地西部古峰庄地区三叠系延长组裂缝特征及其对低渗透油藏的控制作用

Fracture characteristics of Triassic Yanchang Formation in the Gufengzhuang Area,Western Ordos Basin and its control on low permeability reservoirs

[研究目的]鄂尔多斯盆地西部古峰庄地区三叠系延长组属于低渗透储层,天然裂缝较为发育,以往对裂缝特征研究较少,开展天然裂缝特征和形成时期研究对低渗透油藏勘探开发具有重要作用。[研究方法]文章通过野外露头、钻井岩心、成像测井、扫描电镜裂缝识别和流体包裹体、断裂活动、构造应力分析等方法展开了古峰庄地区延长组天然裂缝特征和控藏作用研究。[研究结果]延长组各段天然裂缝均发育,以长7段最为发育,其次为长8、长6段;裂缝以高角度裂缝和垂直裂缝为主,走向以NEE向为主,NE向次之,少量NW和NWW向;裂缝面可见方解石充填和明显过油痕迹。天然裂缝发育程度与岩层厚度、断裂活动密切相关。裂缝形成时期具有多期性,主要为燕山期和喜马拉雅期。[结论]延长组天然裂缝的发育改善了研究区低渗透储层的孔渗能力和储集空间,为低渗透油藏运移、储集和富集提供了良好条件,其发育程度与形成时期影响着低渗透油藏的成藏和产能。

[Objective]The Triassic Yanchang Formation in the Gufengzhuang area of the western Ordos Basin develops low-permeability reservoir with abundant natural fractures,and few investigations have focused on the features of the fractures that are of great significance for the exploration and development of low-permeability reservoirs.[Methods]In this paper,by means of fracture identification from the outcrops,cores,imaging logging,scanning electron microscope and fluid inclusion,fault activity and tectonic stress analysis,the fracture characteristics and influence on low permeability reservoirs are studied.[Results]The results show that natural fractures are all developed in each Member of the Yanchang Formation,with Chang 7 being the most developed Member,followed by Chang 8 and Chang 6 Members.The fracture mainly orients in the NEE direction,secondly in the NE direction,and lastly in the NW and NWW directions.Calcite filling and obvious oil migration marks can be seen on the surfaces of the cracks.The development degree of natural fractures is closely related to the thickness of rock layers and intensity of fault activity.Comprehensive analysis of the fluid inclusions in fractures,faults and tectonic activities shows that the formation period of fractures is multi-stage,mainly in the Yanshanian and Himalayan periods.[Conclusions]The development of natural fractures has improved the porosity and permeability and reservoir space of low-permeability reservoirs in the study area,and provided favorable conditions for oil migration,accumulation and enrichment in low-permeability reservoirs.The development degree and formation period of natural fractures affect the reservoir forming and productivity of low-permeability reservoirs.