前置酸压裂提高煤层气单井产量机理与适用性研究

针对目前我国煤层气地面开发单井产量低、开发效益差的现状,为探索研究适用于煤层气井的经济高效增产改造技术,借鉴常规油气藏前置酸压裂技术的成功经验,采集焦坪矿区4-2煤层煤样,进行前置酸改善压裂效果评价实验,结合宏观观察、X射线衍射分析及扫描电镜–能谱手段对比分析实验前后矿物质成分与含量变化,研究前置酸压裂技术煤层增产机理...

Mechanism and applicability of increasing coalbed methane well production by pre-positioned acid fracturing

At present, the production shortfall and benefits decline of the coalbed methane reservoirs in China are the leading problems. In order to explore and study the economic and efficient stimulation technology suitable for the coalbed methane wells, this paper studies mechanism and applicable conditions on increasing coalbed methane well production by the pre-positioned acid fracturing technology, by drawing on the successful experiences of conventional oil and gas reservoir with this technology. The coal samples of No.4-2 coal seam in Jiaoping Mining Area were collected to evaluate the effect of improving fracturing with acid preposition. The changes of mineral composition and content before and after the experiment were analyzed by macroscopic observation, X-ray diffraction and scanning electron microscope energy dispersive spectrometry. The results indicate that the pre-positioned acid achieved remarkable effect in improving the connectivity between pores and fractures of coal reservoir and reducing the damage of fracturing fluid to coal seam. The main stimulation mechanisms is acid dissolving plugging and interstitial materials, and the auxiliary stimulation mechanisms include forming irregular acid dissolution surface and promoting CH₄ desorption by CO₂ generated from acid salt reaction. Pre-acid fracturing technology is suitable for increasing production and reforming of coal seams with high mineral content and poor permeability, and near the well zone plug removal. The coal seams with rich acid-soluble fillings such as calcite, dolomite, siderite and hematite are the first choice. While for coal seams containing high clay minerals or for the purpose of eliminating pollution near well, the negative effect caused by secondary sedimentation should be mainly considered. It is suggested to adopt secondary sediment prevention measures, combined with anti-filtration technology, low density proppant, low damage/high viscosity fracturing fluid and other countermeasures to solve the problems of secondary damage after pre-acid acidification and large filtration loss of fracturing fluid in coal seam.