摘要:
为研究煤层气开发过程中有效应力增加对煤储层孔渗各向异性的影响,采用不同方向的煤岩样品对沁水盆地南部煤层气储层各向异性进行了评价。结果表明,煤层气储层孔隙度和孔隙结构具有明显各向异性特征:面割理方向核磁共振曲线为双峰型,以大孔、割理为主;端割理方向为宽底单峰型,以中孔为主;垂直煤层理方向为单峰型,中、小孔发育。有效应力加载至10 MPa后,3个方向核磁共振信号强度均降低,表明煤样部分孔隙被压缩、割理闭合。煤层气储层渗透率具有明显各向异性特征:面割理方向渗透率达到垂直层理方向的9倍以上;随有效应力增加,储层各向异性程度降低,但面割理方向与垂直层理方向渗透率异质程度最强。煤层气储层应力敏感性具有明显各向异性特征:面割理方向应力敏感性最强,应力敏感性系数和渗透率损害率均最大;垂直煤层理方向应力敏感性最弱,应力敏感性系数和渗透率损害率均最低。有效应力卸载后,不同方向煤岩渗透率恢复率不同,面割理方向最高,达到55.3%,垂直煤层面方向恢复率最低,为40.2%。
Abstract:
In order to study the effect of the increase of effective stress on the anisotropy of permeability and porosity of CBM formation during the development process of CBM reservoir, coal samples from different directions are adopted and the anisotropy of the CBM reservoir in southern Qinshui Basin is evaluated and the influence of the increase of effective stress on the anisotropy of porosity, permeability and stress sensitivity for CBM reservoir is studied on focus. The results show that the porosity and pore structure of CBM reservoir have obvious anisotropy. The T2 spectrum from NMR in the direction of face cleat is bimodal, mainly developing macropores and cleats, while the T2 spectrum in butt cleat direction is single peak with wide bottom, mainly developing mesopores, with the single peak in vertical coal bedding direction and developing micropores. The NMR signal strength in all three directions decreased, after the effective stress was loaded to 10 MPa, indicating that some pores of these coal samples were compressed and some cleats was closed. The permeability of CBM reservoir has obvious anisotropic characteristics and the permeability in the direction of face cleat is more than 9 times that in the direction of vertical coal bedding. With the increase of effective stress, the degree of anisotropy of reservoir decreases, but the heterogeneity degree of permeability between the face -cleat direction and the vertical-coal-bedding direction is the strongest. The stress sensitivity of CBM reservoir has obvious anisotropic characteristics: the stress sensitivity in the direction of face cleat is the strongest, and the values of the stress sensitivity coefficient and permeability damage rate are the largest. While the stress sensitivity in vertical-coal-bedding direction is the weakest, with the lowest values of the stress sensitivity coefficient and permeability damage rate. After the effective stress unloading, the permeability recovery rate in different directions is different, and the face cleat direction is the highest, up to 55.3%, and the recovery rate of the vertical-coal-bedding direction is the lowest, only reaching to 40.2%.
百度学术
下载:
