四川盆地二叠系龙潭组深层煤岩气地质特征与勘探潜力

Geological characteristics and exploration potential of deep coalbed methane in the Permian Longtan Formation， Sichuan Basin： A case study of well NT1H

文龙 明盈 孙豪飞 张本健 陈骁 陈世达 李松 李海琪

Long WEN Ying MING Haofei SUN Benjian ZHANG Xiao CHEN Shida CHEN Song LI Haiqi LI

为探索四川盆地二叠系龙潭组深层煤岩气勘探潜力，利用风险探井NT1H井煤层取心样品，进行龙潭组煤岩煤质、储层物性、吸附性和含气性实验测试，研究了龙潭组深层煤岩气地质特征与勘探潜力。研究结果表明：①龙潭组深煤层煤体结构完整、割理发育，镜质体反射率（）为2.70 % ~ 3.13 %，镜质组、惰质组和无机组分平均含量分别为60.6 %，23.4 %和16.0 %，矿物组分以黏土矿物为主。②煤层总孔隙度较高，孔隙度为4.83 % ~ 10.13 %，有效孔隙度为2.82 % ~ 9.66 %，平均值为6.53 %。孔隙结构非均质性强，孔隙以粒径小于2 nm的微孔为主，其次为粒径大于10 μm 的宏孔或裂隙，粒径2 ~ 50 nm介孔相对不发育。③120 ℃温度条件下煤岩兰氏体积普遍大于25 m/t，兰氏压力平均值为3.24 MPa。④保压取心煤层含气量26.52 ~ 31.24 m/t，含气饱和度123 % ~ 146 %，游离气含量约5 ~ 10 m/t，原位含水饱和度相对较低，为18.2 % ~ 48.6 %。总含气量随埋深加大而增高。综合研究认为深层煤储层含气条件优越。四川盆地龙潭组深层超饱和煤岩气藏具有较大的勘探潜力，建议通过以小间距煤层组为整装对象进行体积压裂立体改造开发煤岩气。

To investigate the exploration potential of deep coalbed methane （CBM） in the Longtan Formation， Sichuan Basin， we conduct coring of coal seams in risk exploratory well NT1H. Through experiments and tests on the coal quality and the physical properties， adsorption， and gas-bearing properties of coal reservoirs in the Longtan Formation， we examine the geological characteristics and exploration potential of deep CBM in the formation. The results indicate that the deep coal seams in the Longtan Formation exhibit coals with intact structure and well-developed cleats， vitrinite reflectance （） ranging from 2.70 % to 3.13 %， average vitrinite， inertinite， and inorganic component contents of 60.6 %， 23.4 %， and 16.0 %， respectively， and minerals dominated by clay. These coal seams feature high total porosity， with a porosity varying from 4.83 % to 10.13 % and effective porosity from 2.82 % to 9.66 % （average： 6.53 %）. Their pores， with strong structural heterogeneity， are dominated by micropores with sizes less than 2 nm， followed by macropores or fractures with sizes greater than 10 μm， while pores with sizes ranging from 2 to 50 nm are relatively underdeveloped. The coals in the Longtan Formation display Langmuir volume generally exceeding 25 m/t and average Langmuir pressure of 3.24 MPa at 120 ℃. Pressure coring reveals that the coal seams manifest gas content varying from 26.52 to 31.24 m/t， gas saturation from 123 % to 146 %， free gas content from approximately 5 to 10 m/t， and low in-situ water saturation from 18.2 % to 48.6 %. Their total gas content increases with burial depth. In all， the comprehensive investigation suggests that the deep coal reservoirs in the Longtan Formation exhibit conditions favorable for gas-bearing properties. Therefore， the deep reservoirs with supersaturated CBM in the Upper Permian Longtan Formation in the Sichuan Basin have great exploration potential. For these reservoirs， it is recommended to target closely spaced coal seams for integrated volume fracturing and three-dimentional reconstruction for CBM recovery.

10.11743/ogg20240614