煤层气井负压排采技术潜在增产因素分析

Analysis of Potential Increasing Production Factors for Negative Pressure Drainage Technology in Coalbed Methane Wells

排水降压采气是煤层气井开采的主要方式,而煤层气井开采过程中常出现自然产量低。为促进煤层气的解吸和渗流,现场多次采用了负压排采技术并取得了很好的增产效果,研究煤层负压排采技术的潜在增产因素可以完善其技术的理论基础,对今后更好地指导现场煤层气井开发生产以及推广至地质特征、生产特征相似的煤层气区块具有重要的增产意义。探讨了负压技术可能带来的潜在增产因素,并且对负压排采井的选择、使用负压设备的时机提供了排采建议。研究表明:由于煤层气常以吸附态赋存以及煤储层特点,负压排采技术在增大生产压差的同时,可能会起到提高裂缝导流能力、解除表皮污染、促进井间干扰以及增强甲烷滑脱和煤基质收缩等有利效果,同时也会起到加大应力敏感以及裂缝闭合的可能性。可见负压排采技术的正确使用,能最大限度降低废弃压力,提高煤层气的最终采收率。

Gas recovery by water drainage is the main method of CBM( coalbed methane) well production,while natural production is often low during CBM well production. In order to promote the desorption and seepage of coalbed methane,the negative pressure drainage technology has been adopted many times in the field and a good yield increase effect has been achieved. The theoretical basis of negative pressure drainage technology can be improved by studying the mechanism of increasing production,and it can provide CBM field which blocks have similar geological characteristics and similar production characteristics with better guidance in the future. The potential increasing production factors that may be brought about by negative pressure technology are discussed in this paper,and suggestions for the selection of negative pressure drainage wells and the timing of using negative pressure equipment are also provided. The research shows that: due to CBM adsorption and the characteristics of coal reservoirs,negative pressure drainage technology can increase the fracture conductivity,remove the skin damage and promote inter-well interference while increasing the production pressure difference. It also has the beneficial effects of enhancing the slippage effect of methane and the shrinkage of the coal matrix,and also has the disadvantage of increasing the stress sensitivity and the possibility of the fracture closure. It is concluded that the ultimate recovery of CBM will be enhanced by reducing abandonment pressure at the same time via using negative pressure drainage technology correctly.