昭通示范区黄金坝气田五峰—龙马溪组页岩气储层地质特征

昭通国家级页岩气示范区黄金坝气田是继礁石坝和长宁—威远之后中国又一个在页岩气勘探、开发领域实现重大突破的地区,为了系统地展示黄金坝气田页岩气资源富集的储层条件,为未来的勘探工作提供参考,以五峰—龙马溪组页岩气储层为研究对象,从区域地质条件、储层岩石学、物性和地球化学4个方面对该页岩气储层进行了综合研究。结果表明稳定的区域构造和良好的顶底板条件是黄金坝地区页岩气资源富集的关键,良好的保存条件使储层维持了较高的压力(压力系数1);较高的孔隙度(平均4%)和TOC含量(目的层2%)提供了良好的储集空间,使储层具有较高的含气量(1.35~3.48 cm3/g,平均2.50 cm3/g);天然气地球化学数据表明,区内天然气主要成分为CH4(97%),其次还含有少量的C2H6、C3H8和CO2;天然气同位素数据表明烃类C同位素组成发生了倒转,表明储层具有良好的封闭性。但储层孔隙系统较为复杂,且非均质性极强,从而导致渗透率较低,在储层改造施工过程中应予以充分考虑。总体上,黄金坝气田具有较好的开发前景,生产测试表明,区内直井压裂产量为0.5×104~3.5×104m3/d/井,水平井压裂产量可达12×104~40×104m3/d/井。

Geological characteristics of Wufeng-Longmaxi shale-gas reservoir in the Huangjinba gas field, Zhaotong National Shale Gas Demonstration Area

Following Jiaoshiba and Changning-Weiyuan areas, Huangjinba shale gas field in Zhaotong National Shale Gas Demonstration Area is the place where the shale gas exploration and development have received a good achievement. To systemically demonstrate the reservoir conditions for shale gas accumulation in the Huangjinba shale gas field and provide a reference for future exploration, the authors studied the Wufeng-Longmaxi shale gas reservoir in detail in such aspects as regional geological setting, reservoir petrology, physical properties and geochemistry. The results indicate that the stable regional tectonics and well-developed roof and floor formations are crucial factors for shale gas enrichment in this region. These good preserving conditions help the reservoir maintain a high pressure (pressure coefficient >1). High porosity (mean=4%) and TOC content (target bed >2%) of the reservoir provide good spaces for hydrocarbons, and cause the reservoir rocks to have high gas values (1.35-3.48 cm³/g, >2.50 cm³/g on average). The geochemical data of natural gas show that the predominant composition is CH₄(>97%), with minor compositions including C₂H₆, C₃H₈ and CO₂. The isotopic data of natural gas show that the C isotopic constituents of hydrocarbons have been preserved, indicating that the reservoir is closed or semiclosed. Nevertheless, the pore system of the reservoir is very complicated and heterogeneous, which leads to the low permeability of the reservoir, and such a condition should be carefully treated during stimulation processes. In general, the shale gas development potential of the Huangjingba gas field is good, and the production test shows that the gas production quantity of fractured vertical well is 0.5×10⁴-3.5×10⁴ m³/day/well, and the quantity for fractured horizontal well is 12×10⁴-40×10⁴ m³/day/well.