紧邻碎软煤层的顶板岩层水平井开发煤层气技术

煤体结构破碎和渗透率低是碎软煤层"有气难出"的主要原因。为了提高该类储层的煤层气产量,以淮北矿区芦岭井田8号煤层为例,从水平井钻井、压裂和排采控制等3个方面加以综合考虑,基于紧邻碎软煤层的顶板岩层水平井开发煤层气的思路,在对顶板水平井穿层压裂裂缝扩展规律进行研究的基础上,对顶板水平井位置进行了优化,探索形成了紧邻碎软煤层的顶板岩层水平井开发煤层气技术,并进行了现场试验。研究结果表明:(1)顶板岩层水平井穿层压裂过程中形成的垂直裂缝能够从高应力值的顶板岩层向下延伸到低应力值的煤层中,且水平井的位置对穿层压裂效果会产生重要的影响,水平井距离煤层越近,穿层压裂裂缝延伸的效果越好;(2)水平井的位置应布置在距离煤层顶界1.5 m范围的顶板内,这样才能最大限度地满足顶板水平井的增产改造要求;(3)形成了"优质、快速、安全"钻井技术,深穿透定向射孔技术,"大排量、大规模、高前置液比、中砂比"活性水压裂技术等3项关键技术;(4)工程实践取得了较好的产气效果。结论认为,紧邻碎软煤层顶板岩层水平井开发煤层气技术可行,该研究成果为碎软煤层的煤层气开发提供了一条新的技术途径。

Application of CBM horizontal well development technology in the roof strata close to broken-soft coal seams

Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane (CBM) in broken-soft coal seams. In this paper, No.8 coal seam in the Luling Mine of the Huaibei Coal Field was taken as an example to study the way to improve CBM production of broken-soft coal reservoirs. First, drilling, fracturing and production of horizontal wells were considered comprehensively. Then, based on the idea of exploiting CBM through horizontal wells in roof strata close to the broken-soft coal seams, the propagation laws of fractures created by layer-penetrating fracturing of horizontal wells in roof strata were studied, and accordingly the location of horizontal well was optimized. Finally, the CBM horizontal well exploitation technology for the roof strata close to coal seams was developed and tested on site. And the following research results were obtained. First, the vertical fractures created during layer-penetrating fracturing of horizontal wells in roof strata can propagate from the roof strata with high stress values downward to the coal seam with low stress values. In addition, the location of horizontal well has an important influence on the effect of layer-penetrating fracturing. The closer the horizontal well is to the coal seam, the better the fracture propagation effect of layer-penetrating fracturing. Second, the horizontal well should be arranged in the roof strata 1.5 m away from the top of coal seam, so that fracturing stimulation requirements of horizontal wells in roof strata can be satisfied to the uttermost. Third, three key technologies are formed, including the "high-quality, fast and safe" drilling technology, the deep-penetration oriented perforating technology and the "large displacement, large scale, high pad ratio and moderate proppant concentration" active water fracturing technology. Fourth, the gas production with this technology in engineering practice is remarkable. In conclusion, the CBM development technology of horizontal wells in roof strata close to broken-soft coal seams is feasible. The research results prove a new technical method for the development of CBM in broken-soft coal seams.