深层页岩含气量评价及其差异变化——以四川盆地威荣、永川页岩气田为例

近年来我国页岩气勘探开发逐渐走向深层，但对高温高压条件下页岩吸附特征、游离气的赋存特征还不清楚，制约了深层页岩气大规模开发。以四川盆地威荣、永川地区深层页岩为研究对象，对不同有机碳含量和孔隙度的样品开展了高温高压(135 ℃、80 MPa)等温吸附实验和孔隙度实验，计算了页岩吸附气量、游离气量和总含气量的理论值，并与实际值进行对比。研究表明:①页岩吸附气含量随着压力增大逐渐增加，当压力大于40 MPa后，吸附气量增加趋于平缓，最大可达4.46 cm3/g。②页岩理论含气量随着地层压力的增加而增加，当地层压力达到80 MPa时总含气量达到最大，此时理论最大值为11.3 cm3/g；计算的游离气含量为6.8 cm3/g，吸附气含量为4.5 cm3/g，分别约占总含气量的60%和40%；游离气/吸附气比例随深度增加逐渐增加。③基于现场解吸实验，实测威页11-1井总含气量最大值为5.95 cm3/g，最小值为3.29 cm3/g，平均为4.52 cm3/g，对比理论含气量10.3 cm3/g，表明有近50%的气体在抬升过程中散失，同时一定程度上也说明了深层页岩气保存条件的复杂性，建议加强对保存条件的研究。 

Shale gas content evaluation for deep strata and its variation: a case study of Weirong,Yongchuan gas fields in Sichuan Basin

The exploration and development of shale gas in China are recently focusing on the deep layers. However, the occurring characteristics of shale gas under high temperature and high pressure are not clear, which imposes great restrictions to deep shale gas development on a massive scale. Taking the deep shale in Weirong and Yongchuan regions of Sichuan Basin as research objects, for core samples with different organic carbon content and porosity, the isothermal adsorption experiments and porosity testing at high temperature and high pressure (135 ℃,80 MPa) were carried out, and the theoretical values of shale adsorption gas, free gas and total gas content and compared with actual values. Results show that: (1) The content of adsorbed gas in deep shale increases gradually with pressure growing up. When the pressure surpasses 40 MPa, the increment flattens out, making 4.46 cm3/g the maximum of adsorbed gas content. (2) The theoretical gas content of shale increases with the growing formation pressure. The total gas content reaches its maximum 11.3 cm3/g under 80 MPa, which is made up with calculated free gas with an average of 6.8 cm3/g and adsorbed gas with an average of 4.5 cm3/g, accounting for about 60% and 40% of the total gas content, JP]respectively. The ratio of free gas versus adsorbed gas gets larger with a greater buried depth. (3) Based on field desorption experiment, the actual measurement maximum gas content of well Weiye 11-1 is 5.95cm3/g, the minimum value is 3.29cm3/g, and the average content is 4.52 cm3/g. Compared with the theoretical value of 10.3 cm3/g, the result indicates that nearly 50% of gas leaked in the process of formation uplift, displaying the complexity of the deep shale gas preservation conditions. It is recommended to strengthen research on preservation conditions.