地面井煤层气含量精准测试密闭取心技术及设备

Technology and equipment of sealed coring for accurate determination of coalbed gas content in ground well

煤层气含量是表征煤储层特征的重要参数,是煤层气资源勘探开发和煤矿瓦斯防治的重要依据。针对地面井常规取心方法获取的煤层气含量比煤储层实际气量明显偏低(碎软煤层尤其突出)的现实问题,提出了适合于碎软煤储层特征的煤层气含量精准测试密闭取心方法。根据煤储层特征(与油气储层相比,埋藏较浅、压力较小、温度较低、煤体强度低)和煤层气含量精准测试要求,设计并试制了适用于地面井煤层气含量测定的“三筒单动、球阀关闭、取心筒与解吸罐一体化”的密闭取心器和“前端小径钻心、后端大径钻井”的碎软煤层双径PDC密闭取心钻头。密闭取心器外筒直径120 mm,采取煤(岩)芯直径可达38 mm,密闭保压能力达10 MPa以上,适用于煤层埋深1000 m的地面井密闭取心;双径PDC密闭取心钻头减少了取心钻进过程中钻井液对煤芯的冲洗旋流作用,提高碎软煤层的煤芯采取率。利用密闭取心设备在我国的淮南潘三煤矿和淮北芦岭煤矿碎软煤层中开展了2口地面井煤层气含量测定密闭取心工程应用对比试验,共采得密闭取心煤样5组,常规取心煤样3组;8组煤层气含量测试结果表明,由密闭取心法获得的煤层气含量比常规取心法获得的煤层气含量高20.23%~40.34%,均值27.22%;研究结果表明采用密闭取心技术能够提高煤层气含量测试精度。地面井密闭取心设备研制成功及推广应用将为碎软煤层煤层气资源勘探开发、煤矿瓦斯灾害预测及治理提供更为准确的煤层气含量参数。

Coalbed gas content is an important parameter of the characteristics of coal reservoirs and an important basis for the exploration and development of CBM resources,gas prevention and control in coal mines.In view of the fact that the coalbed gas content obtained by conventional coring method in surface wells is obviously lower than the actual content in coal reservoirs(especially in broken and soft coal seams),a sealed coring method for an accurate determination of coalbed gas content is proposed,which is suitable for the characteristics of broken and soft coal reservoirs.According to the characteristics of coal reservoirs(compared with oil-gas reservoirs,shallower burial,lower pressure,lower temperature and lower strength of coal body)and the requirement of an accurate determination of coalbed gas content,the sealed coring device,in which the outer barrel rotates and two inner barrels holds still,the ball valve is closed,the core barrel and the desorption tank are integrated,and the dual-diameter PDC core drilling bit has small-diameter at front and big-diameter at rear,have been are designed and trial-produced for broken and soft coal seams,which is suitable for the determination of coalbed gas content in surface wells.The diameter of the outer cylinder of the sealed coring device is 120 mm,the diameter of coal(rock)core can be up to 38 mm,the pressure-holding capacity is up to 10 MPa,and it is suitable for the sealed coring of surface wells for coal seams with a burial depth of 1000 m.The dual-diameter PDC sealed coring bit reduces the flushing effect of drilling fluid on the coal core during coring drilling,and improves the recovery of coal core in broken and soft coal seams.The sealed coring equipment was used to carry out the comparative test of coalbed gas content determination for two surface wells in the broken and soft coal seams in Pansan coalmine of Huainan and Luling coalmine of Huaibei,which has got five sets of sealed coring coal samples and three sets of conventional coring coal samples.The test results of eight sets of coalbed gas content show that the coalbed gas content obtained by the sealed coring method is 20.23%to 40.34%higher than that obtained by the conventional coring method,and the mean value is 27.22%,which shows that the sealed coring technology can improve the testing accuracy of coalbed gas content.The successful development and application of the sealed coring equipment in surace well will provide more accurate parameters of coalbed gas content for CBM resource exploration and development,gas disaster prediction and precision control in coalmines.