碳酸盐岩储层裂缝特征及主控因素

伊拉克A油田Asmari组为连陆局限-半局限台地沉积,发育白云岩、灰岩、砂岩和泥岩多种岩性,由于受扎格罗斯造山运动影响,断层及裂缝发育,导致储层结构复杂、非均质性强。基于岩心、薄片、成像测井和地震等资料对A油田Asmari组碳酸盐岩储层裂缝开展综合研究发现,A油田发育构造缝和成岩缝两种类型裂缝,主要以构造缝占主导。其中,以白云岩为主的A段裂缝发育程度高,裂缝密度大,但裂缝尺度小;以灰岩为主的B段裂缝发育程度低,裂缝密度小,发育中-大尺度裂缝。综合应力场模拟和地震叠前方位角各向异性研究A油田裂缝平面分布发现,裂缝主要分布在应力相对集中的断层附近和背斜轴部。结合构造及储层特征研究裂缝发育控制因素表明,扎格罗斯造山运动是研究区裂缝形成的主控因素,其控制了裂缝平面分布,距离断层越近,裂缝密度越大;而储层的岩性、物性及厚度主要控制了裂缝纵向发育规律。

Fracture characteristics and controlling factors of carbonate reservoir

Asmari formation in A oilfield of Iraq is continental limited-semi-limited platform sediment,which develops multiple lithologies with dolomite,limestone,sandstone and mudstone.Due to the influence of Zagros orogeny,faults and fractures developed,resulting in complex reservoir structure and strong heterogeneity.Based on cores,thin section,imaging logging and seismic data,the fracture development characteristics of carbonate reservoir of Asmari formation in A oilfield are comprehensively studied.It is found that there are two types of fractures,structural fracture and diagenetic fracture,in the study area,mainly dominated by structural fracture.The reservoir of member A with dolomite has high fracture development degree,high fracture density,but small fracture scale.The reservoir of member B with limestone has low fracture density and medium-large scale fractures.Post-stack seismic stress field and pre-stack azimuth anisotropy analysis are used to predict the fracture planar distribution in the study area.Fractures are mainly developed in regions with strong stress near faults and the structural axis.Zagros movement is the main controlling factor of fracture generation in the study area,which controls the fracture planar distribution.The closer to the fault,the greater the fracture density.The lithology,physical properties and thickness of reservoir mainly control the vertical distribution of fractures.