四川盆地西南缘深层龙马溪组页岩储层地质特征——以昭通页岩气示范区雷波地区为例

Geological characteristics of ultra-deep Longmaxi Formation shale reservoirs in the southwest margin of Sichuan Basin:Case study of Leibo block in Zhaotong National Shale Gas Demonstration area

为探讨四川盆地上扬子西南缘昭通页岩气示范区深层龙马溪组页岩储层地质特征,以雷波地区为例,在野外地质勘查和室内实验数据的基础上,通过区域地质资料,对研究区龙马溪组页岩的岩石学特征、沉积相展布、有机地球化学参数及储集空间类型和特征展开了系统研究。结果表明:研究区矿物组分以石英和黏土矿物为主,平均值分别为36.3%和34.85%,并含少量碳酸盐矿物、长石和黄铁矿;TOC含量为0.12%~5.94%,平均为2.12%;在中都镇—南岸镇附近和雷波县城以东2个地区分别形成了TOC高值区和沉积中心,其中,沉积相以深水陆棚为主,并向西演变为浅水陆棚。TI值为36.5~82.5,以Ⅱ1型干酪根为主;R_(O)值为2.34%~2.72%,平均为2.48%,为高演化阶段;平均孔隙度为8.99%,平均孔径为5.682 nm,孔隙类型以有机质孔、矿物溶蚀孔和微裂缝为主,孔隙形态以纳米级的开放四边平行板状孔和密集堆积球形颗粒间孔为主,含少量开放圆筒孔和裂缝结构,且页岩孔隙度与渗透率呈现正向相关性。与国内外主要页岩气产地对比,四川盆地西南缘龙马溪组页岩下段表现出高TOC含量、高成熟度、高脆性矿物含量、有机质孔发育的特点,按照其生烃能力和可开采性将其划分为烃源岩段和以储层为主的层段;龙马溪组上段表现出TOC含量低、黏土矿物含量高和微裂缝发育的特点,属非烃源岩和以盖层为主的层段。

In order to discuss the geological characteristics of deep Longmaxi Formation shale reservoir in Zhaotong Shale Gas Demonstration area in the southwest margin of the Upper Yangtze River,taking Leibo area as an example,on the basis of field geological survey and indoor experimental data,and through regional geological data,a systematic study was carried out on the petrological characteristics,sedimentary facies distribution,organic geochemical parameters,and reservoir space types and characteristics of Longmaxi Formation shale in the study area.The mineral components in the study area are mainly quartz and clay minerals,with an average of 36.3%and 34.85%respectively,and contain a small amount of carbonate minerals,feldspar and pyrite;TOC content is 0.12%-5.94%,with an average of 2.12%;The two areas near Zhongdu town-Nan'an town and the east of Leibo county are high TOC value areas and sedimentary centers in the study area.The sedimentary facies are mainly deep-water continental shelf,which evolved to the West into shallow water continental shelf.TI value is 36.5-82.5,mainly type Ⅱ_(1) kerogen;R_(O) is 2.34%-2.72%,with an average of 2.48%,which is at over mature stage;The average porosity is 8.99%and the average pore diameter is 5.682 nm.The pore types are mainly organic matter pores,mineral dissolution pores and micro fractures.The pore morphology is mainly nano-sized open quadrilateral parallel plate pores and densely stacked spherical intergranular pores,with a small amount of open cylindrical pores and fracture structures.The porosity of shale shows a positive correlation with permeability.Compared with the major shale gas producing areas at home and abroad,the lower shale of Longmaxi Formation in the southwest margin of Sichuan Basin shows the characteristics of high TOC content,high organic matter abundance,high maturity,high content of brittle minerals and development of organic matter pores.According to its hydrocarbon generation capacity and exploitability,it is divided into source rock section and reservoir dominated section.The upper member of Longmaxi Formation is characterized by low TOC content,high clay mineral content and developed microcracks.It is a non-source rock and a cap dominated interval.