多层叠置煤层气系统合采方式及其优化

针对"多层叠置煤层气系统"这一特殊煤层气成藏模式,自主研发了多层叠置煤层气系统合采试验装置,并取得:(1)开展了储层气压分别为1.0,1.4,1.8和2.2 MPa条件下4层叠置煤层气系统常规合采试验,发现在合采过程中,气体由高气压煤层通过合采井筒流向低气压煤层,抑制了低气压煤层气体的产出,不利于煤层气的合采;(2)通过优化不同煤层产气时间开展了递进合采试验,有效避免不同煤层之间发生气体倒灌现象,使得最低储层气压煤层采收率和整体采收率分别提高了6.5%和1.3%;(3)递进合采能降低高储层气压煤层产能贡献率同时提高低储层气压煤层产能贡献率,使得产能分配更加合理;(4)叠置煤层整体差异系数呈先升后降的变化趋势,表明优化前后两种合采方式差异随着合采的进行处于动态变化之中,在合采中期达到最大,在合采后期略有下降。

Multiple layers superposed CBM system commingled drainage schedule and its optimization

The apparatus for the commingled drainage of multiple layers superposed coalbed methane(CBM) system has been developed specifically for the special CBM reservoir-forming characteristics of the “multiple layers superposed CBM system”.The following results were obtained:(1) Conventional commingled drainage test was carried out with four layers superposed coal seams and the reservoir pressures were 1.0 MPa,1.4 MPa,1.8 MPa and 2.2 MPa respectively.During the process of drainage,gas in high reservoir pressure coal seam flowed into the coal seams with low reservoir pressure,which suppressed the output of low reservoir pressure coal seam and was harmful to commingled drainage；(2) Progressive drainage test was carried out by optimizing gas production time in different coal seams and gas inversion between different coal seams was avoided effectively.The recovery ratio of lowest reservoir pressure coal seam and superposed coal seams were increased by 6.5% and 1.3%,respectively；(3) Progressive drainage can reduce the gas production contribution rate of high reservoir pressure coal seams and increase the gas production contribution rate of low reservoir pressure coal seams,which make gas production distribution more reasonable；(4) Superposed difference coefficient showed rising firstly and then decreasing,which indicated that the difference between conventional commingled drainage and progressive drainage was changing dynamically during drainage.It reached the maximum in the mid-term of drainage and decreased slightly in the late stage of drainage.