强改造区龙马溪组页岩气保存条件指数评价

Index Evaluation of Shale Gas Rreservation Conditions of Longmaxi Formation in Strong Reconstruction Zone

研究区内龙马溪组页岩有机质类型以Ⅰ型和Ⅱ型干酪根为主,富有机质页岩厚度一般大于30m,总有机碳质量分数普遍大于2%,有机质总体仍处于过成熟阶段,岩石脆性矿物含量相对高、黏土矿物含量相对低,具低孔、渗特性,为页岩气成藏提供良好的物质基础;自中生代以来,研究区经历了5期构造运动,为强隆升、强剥蚀、强变形的强改造区;野外采集了海拔、地层出露特征、地层剥蚀情况、褶皱形态、节理及断裂特征、泉水及热液矿床的分布等资料,以海拔、剥蚀、倾角、变形、破裂5个指数定性半定量评价页岩气保存条件。结果表明:研究区西北部海拔较低,剥蚀量相对小,地层倾角相对较缓,变形强度、破裂强度相对小,页岩气保存条件好;东南部海拔虽低,但剥蚀量相对大,多为高角度地层,变形强度、破裂强度相对大,页岩气保存条件差。

The organic matter type of Longmaxi Formation shale in the studied area was dominated by Type I and II kerogen,the thickness of the rich organic shale was generally greater than 30 meters,w(TOC)was generally higher than2%,organic matter was still at the mature stage,the fragile mineral content was higher than the clay mineral content in the rock,the porosity and permeability of the shale were lower,these provide good material base for shale gas accumulation;Since Mesozoic,the study area has experienced five periods of tectonic movement.The area is a strong transformation zone with the characteristics of strong uplift,strong denudation and strong deformation.The data of altitude,strata characteristics,strata denudation,fold morphology and the features of the joint and fracture and the distribution of spring and hydrothermal mineral were collected.The shale gas storage conditions were qualitatively evaluated and semi-quantitatively by using altitude,denudation,dip,deformation and fracturing.The result indicates that in the northwest of the study area,the altitude is relatively lower,the denudation is relatively small,dip is relatively slow,the intensity of deformation and fracture is relatively weak,it is good for shale gas preservation.In the southeast of the study area,the altitude is relatively lower,the denudation is relatively big,the dip is relatively steep,the intension of deformation and rupture is relatively strong,it is not good for shale gas preservation.