黔北煤田长岗向斜煤储层特征与压裂可改造性研究

Study on coal reservoir features and fracturing reconstruction in Changgang Syncline of Qianbei Coalfield

为指导黔北煤田长岗向斜煤层气的勘探开发和选区,基于钻探、试井资料及煤样测试数据,分析研究了黔北煤田长岗向斜煤储层特征,结合煤层气井试采效果,从煤体结构和煤层及其围岩特征研究了煤储层压裂可改造性。研究结果表明:长岗向斜煤层多而薄,主要为低灰~中灰、高硫分的贫煤~无烟煤,煤层埋深适中;煤的比表面积大,吸附性强,含气量高,资源储量较好。而煤层气解吸难度大,孔隙度低,孔裂隙系统不发育,为低孔、低渗、欠压储层,给开发造成一定困难;向斜北部受断层破坏,煤体结构破碎,以碎粒煤和粉煤为主,不利于压裂;向斜南部煤体结构较完整,各煤层岩石力学性质强,顶底板以较薄的泥岩为主,与煤岩力学性质差异较明显。仅采煤层气,优先压裂3号和7号煤层;若实施煤系气共采,则多数煤层都是合适的压裂选层。

In order to guide the exploration,development and block selection of coalbed methane in Changgang Syncline of Qianbei Coalfield,based on the exploration,test well information and coal sample test data,the paper had an analysis and study on the coal reservoir features in Changgang Syncline of Qianbei Coalfield. In combination with the trial drainage effect of coalbed methane wells,from the coal structure and the seam as well as the surrounding rock features,a study was conducted on the fracturing reconstruction of the coal reservoir. The study results showed that Changgang Syncline seam was many and thin,mainly the lean coal-anthracite coal with a low ash content-medium ash content,high sulfur content and the seam depth was moderate. The coal specific surface area was large,the adsorption was strong and the gas content was high and the resource base was good. Also the coalbed methane desorption difficulty was high,the porosity was low and the borehole crack system was not developed. The seam was a low porosity,low permeability and over pressure reservoir and would cause a certain difficulty to coal seam development. In the north area of the syncline,due to the failure by faults,the coal structure was broken and mainly the broken partical coal and fine coal were not be favorably fractured. In the south syncline,the coal structure was relatively completed,the mechanics property of rock in each seam was strong,the roof and floor were mainly thin mudstone and were obviously different to coal and rock mechanics property.Only coalbed methane would be mined,the fracturing of No. 3 seam and No. 7 seam would be optimally selected. If the co-mining of the coal measure gas,thus most seams could be the fractured seams suitably.