四川盆地陆相页岩油气富集主控因素及类型

四川盆地陆相页岩气勘探虽然已在涪陵、元坝等地区下侏罗统大安寨段获得工业气流,但与海相下志留统龙马溪组页岩气相比,富集条件存在较大的差异,勘探潜力尚待探索。通过X衍射矿物组分、有机地化、氩离子抛光-扫描电镜、压汞-吸附联合测定、脉冲渗透率、纳米CT、含气性测试等方法技术,对控制陆相页岩气富集的岩性组合、成熟度和压力3个关键因素进行了研究。湖相碳酸盐湖坡风暴滩沉积的页岩与介屑灰岩不等厚互层,具有良好页岩气生烃(有机质丰度大于1.4%)、储集(孔隙度大于3%)、渗透(水平缝发育)和可压裂(脆性指数大于0.6)的配置条件,为最有利的岩性组合类型;成熟度控制着页岩储层有机质孔的发育和页岩油气的生成(以成熟度1.3%为界);超压(压力系数大于1.2)是陆相页岩油气富集高产的关键。据此将陆相页岩油气富集类型划分为超高压高成熟页岩与灰岩互层页岩气型和超压低成熟页岩与灰岩互层页岩油气型;优选涪陵北东岳庙段和元坝大安寨段为页岩气有利目标,涪陵北和阆中-平昌大安寨段、建南东岳庙段、元坝千佛崖组二段为页岩油气较有利目标。

Main controlling factors and types of continental shale oil and gas enrichment in Sichuan Basin

Continental shale gas has achieved commercial production in the Lower Jurassic Daanzhai Member in the Fuling and Yuanba areas in the Sichuan Basin; however, the accumulation conditions are different from the marine facies Lower Silurian Longmaxi shale gas, and the exploration potential remains to be explored. The X-ray diffraction analysis of mineral composition, geochemical analysis, argon ion polishing-scanning electron microscopy, mercury intrusion-adsorption combined measurement, pulse permeability, nano-CT and gas content were applied to study three key factors controlling the enrichment of lacustrine shale gas, including lithologic combination, maturity and pressure conditions. The shales deposited on a storm beach of the carbonate lake slope of the lake facies are interbedded with the coquina limestone of unequal thickness, which is the most favorable lithologic combination with favorable configuration conditions for shale gas generation (organic matter abundance greater than 1.4%), reservoir (porosity greater than 3%), permeability (horizontal fracture developed) and fracturing (brittleness index greater than 0.6). Maturity controls the development of organic pores and the formation of shale oil and gas (Ro=1.3% as the maturity boundary). Overpressure (pressure coefficient greater than 1.2) is the key to the enrichment and high yield of continental shale oil and gas. The accumulation of continental shale oil and gas can be divided into two types:ultra-high pressure, high maturity shale interbedded with limestone and ultra-high pressure, low maturity shale interbedded with limestone. The most favorable target for shale gas exploration in the lacustrine facies of the Sichuan Basin includes the Daanzhai Member in Yuanba and the Dongyuemiao section in Fuling. The Daanzhai Member in the northern Fuling and Langzhong-Pingchang, the Dongyuemiao Section in Jiannan, and the second section of Qianfoya Formation in Yuanba are secondary favorable target for shale oil and gas exploration.