川东南盆缘复杂构造区深层页岩气富集特征

Enrichment characteristics of deep shale gas in tectonically complex regions of the southeastern Sichuan Basin

以川东南盆缘复杂构造区南川地区为研究对象,基于钻井、实验分析测试等资料,开展深层页岩气富集特征研究,重点讨论地层温度、地层压力等成藏环境变化对深层页岩气富集的影响作用。研究认为:①优势沉积相带是页岩气藏成烃的基础,研究区五峰组—龙马溪组一段形成于深水陆棚沉积环境,优质页岩发育,具备形成页岩气藏的良好物质条件。②有机碳含量控制纳米级有机质孔隙的发育程度,高压—超高压环境有利于孔隙的保持,对改善深层页岩物性发挥积极作用。③深层页岩气具有高温、高地应力的典型地质特征。温度较压力对页岩吸附能力的影响更为明显,深层页岩气赋存方式以游离气为主;高上覆地层压力导致页岩渗透率呈指数下降,页岩气运移能力显著减弱,逸散程度降低,有利于页岩气原位聚集。④温度、压力变化对气体扩散作用影响复杂,高温会增大气体的扩散系数,加剧气体的运移和逸散,而高压可以减缓或抑制气体的流动,有利于页岩气保存。⑤埋深与压力系数呈现一定的正相关性,埋深对向斜型页岩气藏压力系数的影响作用显著,表明深层向斜型页岩气保存条件趋好。埋深较大的残留向斜核部、凹中隆、有反向逆断层遮挡的斜坡区是复杂构造区页岩气勘探的有利目标。

In recent years, deep shale gas exploration breakthroughs have been achieved in the Wufeng-Longmaxi formations in the complex tectonic region of the Sichuan Basin and southeastern margin, showing good prospects for deep shale gas exploration and development. Based on the data from drilling wells and experimental analysis tests, the study of deep shale gas enrichment characteristics is carried out in the Nanchuan area of the complex tectonic region of the southeastern Sichuan Basin margin, focusing on the role of changes in the formation environment such as formation temperature and pressure on deep shale gas enrichment. The study concludes that:(1) The dominant sedimentary phase zone is the basis for hydrocarbon formation in shale gas reservoirs. The Wufeng Formation-the first member of Longmaxi Formation in the study area was formed in a deepwater shelf sedimentary environment with high-quality shale development, which has good material conditions for the formation of shale gas reservoirs.(2) Organic carbon content controls the degree of development of nanoscale organic matter pores, and the high-pressure-ultra-high-pressure environment is conducive to the maintenance of pores and it plays a positive role in improving the physical properties of deep shale.(3) Deep shale gas has the typical geological characteristics of high temperature, high ground stress, and exceptionally low permeability. The influence of temperature on the adsorption capacity of shale is more obvious than that of pressure, and the deep shale gas is mainly free gas. High pressure can slow down or inhibit the gas flow, which is beneficial to shale gas preservation.(4)The changes of temperature and pressure have complex effects on gas diffusion. High temperature will increase the diffusion coefficient of gas, aggravate the migration and escape of gas, while high pressure can slow down or inhibit the flow of gas, which is beneficial to the preservation of shale gas.(5) The burial depth and pressure coefficient show a certain positive correlation, and the burial depth has a more significant effect on the pressure coefficient of syncline shale gas, indicating that the preservation conditions of deep syncline shale gas reservoirs have a tendency to become better. The residual syncline core with larger depths, inner-sag uplift, and slopes with reverse faults can be favorable targets for shale gas exploration in complex tectonic zones.