川东南丁山与焦石坝地区五峰组—龙马溪组页岩气富集条件差异分析与思考

四川盆地东南缘（川东南）丁山构造五峰组—龙马溪组页岩气勘探已取得突破，但相比涪陵页岩气田焦石坝构造，其富集高产因素又体现出其自身的特殊性。以四川盆地丁山和焦石坝地区五峰组—龙马溪组为研究对象，综合利用钻井、测井、地震及分析化验等资料，明确了两地区主要富集条件的差异性，建立了2种目标类型页岩气成藏富集模式，研究发现：（1）丁山优质页岩层段TOC≥3%的页岩仅发育于五峰组—龙马溪组一段①—③层，厚15~19 m，明显比焦石坝薄（焦页1井近38 m）；（2）丁山构造保存条件明显受齐岳山断裂控制，平面上远离齐岳山断裂、埋深更大的斜坡带和深埋平缓带页岩气层压力系数、孔隙度和含气量明显增大，而焦石坝构造保存条件明显受周边控制构造的断裂影响，压力系数、孔隙度和含气量仅在断裂附近出现明显的降低；（3）丁山优质页岩层段在自身脆性方面与焦石坝无明显差异，但由于埋深变化较大，埋深处于3 500~4 500 m富集区的优质页岩层段的地应力、岩石破裂压力明显增大。研究认为沉积环境造成了两地区页岩原生品质具有一定的差异，其中丁山属于“较快速海退型”陆棚相沉积，而焦石坝属于“缓慢海退型”陆棚相沉积；而控制构造的断裂是造成页岩气逸散方式和程度不同的主要因素。根据以上特点，建立了丁山 “齐岳山断裂带主体控制、浅埋藏区垂向、横向联合逸散、深埋藏区富集”的盆缘“鼻状断背斜富集型”、焦石坝盆内“控边断裂垂向逸散为主、横向逸散微弱、主体稳定区富集”的“断背斜富集型”成藏富集模式。

Analysis and thinking of the difference of Wufeng-Longmaxi shale gas enrichment conditions between Dingshan and Jiaoshiba areas in southeastern Sichuan Basin

A breakthrough in Wufeng-Longmaxi shale gas exploration has been made in Dingshan tectonic area in the southeastern margin of Sichuan Basin, however, compared with the Jiaoshiba structure in Fuling shale gas field, its enrichment and high yield factors reflect its own particularity. Therefore, this paper takes Dingshan and Jiaoshiba Wufeng-Longmaxi formations in Sichuan Basin as the research object. Through the comprehensive use of drilling, logging, seismic and laboratory data, the differences of the main enrichment conditions in the two regions are identified, and two types of shale gas accumulation and enrichment models are established. The results show that: (1) For the Dingshan high-quality shale, the layer with TOC≥3% is only developed in the ①-③ layers of the first segment of Wufeng-Longmaxi formations, with a thickness of 15-19 m, which is significantly thinner than that of Jiaoshiba area (nearly 38 m of Well JY1); (2) The preservation conditions of the Dingshan structure are obviously controlled by the Qiyueshan fault, and the pressure coefficient, porosity and gas content of the shale gas layer increase significantly in the area far away from the Qiyueshan fault, deeper buried slope zone and in the deep buried gentle zone. However, the preservation condition of Jiaoshiba structure is obviously affected by the fault of the surrounding control structure, and the pressure coefficient, porosity and gas content are only significantly reduced near the fault; (3) There is no significant difference in brittleness between the high quality shale segment in Dingshan and that in Jiaoshiba. However, due to the large change of burial depth in Dingshan area, the in-situ stress and rock fracture pressure of the high quality shale segment with burial depth of 3 500-4 500 m increase obviously. The study shows that the sedimentary environment has caused some differences in the primary shale quality between the two regions. Dingshan area is “relatively rapid regressive” continental shelf facies, and Jiaoshiba area belongs to “slow regression type” continental shelf facies. The fault, which controls the structure characteristics, is the main factor that causes the different way and degree of shale gas escape. According to the above characteristics, the “nosed fault-anticline enrichment” accumulation model in basin margin of “Qiyueshan fault zone main body control, shallow burial zone vertical and horizontal joint escape, enrichment in deep buried areas” is established in the Dingshan area, and the accumulation model of “fault-anticline enrichment” in Jiaoshiba area of internal Sichuan basin is characterized by “vertical dispersion of the control edge fault is dominant, the transverse dispersion is weak and the main stable region is enriched”.