柴达木盆地三湖地区第四系七个泉组含水泥页岩气体吸附及流动能力分析

Analysis of gas adsorption and flowing capacity of cement mudshale gas from the Quaternary Qigequan Formation in Sanhu area,Qaidam Basin

柴达木盆地三湖地区第四系七个泉组泥页岩处于成岩早期阶段,含水饱和度高,极大地影响到天然气的吸附以及流动能力,进而影响泥页岩层段含气性以及气井产能。为此选用三湖台南地区和察尔汗地区第四系七个泉组泥页岩样品,开展扫描电镜与气体吸附—压汞联测,明确七个泉组泥页岩孔隙发育特征;开展不同含水饱和度条件下的等温吸附及覆压渗透率实验,以揭示含水饱和度对泥页岩的甲烷吸附作用与气体流动能力的影响。研究结果表明:七个泉组泥页岩黏土矿物含量较高,平均为33.0%;储集空间包括矿物粒间孔和粒内孔2类,孔径分布为单峰型,主峰孔径在50~150 nm之间,宏孔对孔体积的贡献最大,占比可达66.8%;七个泉组泥页岩随着含水饱和度的上升吸附气量逐渐降低,当含水饱和度超过临界值10%~20%,吸附气量下降幅度减缓。吸附气量与黏土矿物具有较好的正相关关系,其中伊利石对吸附气量的贡献最大;七个泉组泥页岩气体流动方式以滑脱流动为主。含水使得气体流动能力减弱,2 MPa条件下,当含水饱和度从10%升至50%,泥页岩渗透率平均降低52.93%。在同沉积背斜构造外围平缓区域,泥页岩气能够滞留成藏,泥页岩气井具有较好的含气丰度,开发潜力较强,为勘探有利区。

The shale of the Qigequan Formation of Quaternary in the Sanhu area, Qaidam Basin is in the early stage of diagenesis and has high water saturation, which greatly affects the adsorption and flow capacity of natural gas, and then affects the gas content of the shale interval and the productivity of gas wells. For this purpose, shale samples of the Quaternary Qiquan Formation in the Sanhu Tainan area and the Chaerhan area were selected to carry out scanning electron microscopy and gas adsorption-mercury intrusion combined measurement to clarify the pore development characteristics of the Qigequan Formation. Isothermal adsorption and overburden permeability experiments under water saturation conditions were performed to reveal the influence of water saturation on methane adsorption and gas flow capacity of shale. The research results show that the mud shale of Qigequan Formation has a relatively high content of clay minerals, with an average of 33.0%;the reservoir space includes two types of mineral intergranular pores and intragranular pores. The pore size distribution is unimodal, and the main peak pore size is 50-150 nm. The contribution of macropores to the pore volume is the largest, with an average proportion of up to 66.8%. Qigequan group mud shale gradually decreases with the increase of water saturation, when the water saturation exceeds the critical value of 10%-20%, the decline in the amount of adsorbed gas slowed down. The amount of adsorbed gas has a good positive correlation with clay minerals, among which illite has the largest contribution to the amount of adsorbed gas;the Qigequan Formation mud shale gas flow mode is mainly slip flow. Water content makes the gas flow capacity weaker. Under the condition of 2 MPa, when the water saturation increases from 10% to 50%, the shale permeability decreases by 52.93% on average. In the gentle area surrounding the syn-sedimentary anticline structure, shale gas can be retained and accumulate. The shale gas well has good gas abundance and strong development potential, making it a favorable area for exploration.