川东北元坝地区长兴组礁滩相储层裂缝特征及主控因素

Development characteristics and main controlling factors of natural fractures in reef-flat facies reservoirs of Changxing Formation in Yuanba area,northeastern Sichuan Basin

四川盆地东北部元坝地区是我国天然气勘探开发的重要区域。该区长兴组礁滩相储层天然裂缝普遍发育、控制因素复杂,是影响储层物性和气藏开采效果的关键因素。综合利用岩心、薄片、成像测井等资料,对该区长兴组储层天然裂缝的成因类型和发育特征进行了系统研究,在此基础上阐明了裂缝发育的主要控制因素。研究结果表明:①元坝地区长兴组礁滩相储层主要发育构造裂缝和成岩裂缝,根据力学性质构造裂缝可进一步划分为剪切裂缝和张性裂缝;成岩裂缝主要包括溶蚀裂缝、构造一溶蚀裂缝及压溶裂缝3类;②构造剪切裂缝为主要天然裂缝类型,裂缝走向以NW SE向为主,主要为高角度裂缝和斜交裂缝,绝大多数裂缝高度小于30cm.裂缝总体有效性较好;③天然裂缝的发育主要受构造与应力、岩性、层厚和沉积微相等因素综合控制,受构造与应力影响,裂缝走向具有明显优势方位;白云岩类较灰岩类裂缝更为发育;高角度裂缝和斜交裂缝规模和发育程度受层厚控制明显;不同沉积微相中构造裂缝发育程度存在较大差异。

The Yuanba area in northeastern Sichuan Basin is an important area for gas exploration and devel opment.Natural fracture with complex controlling factors is widely developed in the reeflat facies reser voirs of Changxing Formation in Yuanba area,which is one of the key factors affecting reservoir physical property and recovery effectiveness of gas reservoirs.The genetic types and development characteristics of fractures in Changxing Formation in Yuanba area were studied systemically by comprehensive utilization of cores,thin sections and image logging.And the main factors controlling the development of fractures were analyzed.The results show that(1)fractures developed in Changxing Formation in Yuanba area including tectonic fractures and diagenetic fractures,among which tectonic fractures include shear fractures and ten sion fractures,and diagenetic fractures include dissolution fractures,structural-dissolution fractures and stylolite.(2)Shear fracture is the main type of natural fracture in the study area.These fractures are in NW-SE strike with high angle and oblique angle in most cases.The highest of most factures are less than 30cm and the overall effectiveness of them are well.(3)The development characteristics of natural fractures are mainly controlled by structure,stress,lithology,layer thickness and sedimentary microfacies.The orienta tion of each type of fracture is dominantly controlled by local structure and stress.Fractures are more de veloped in dolomite than in limestone.The development degree and scale of high angle fractures and oblique fractures are closely related to rock thickness.The development characteristics of fractures in different sedi mentary microfacies are distinctly different.