煤系气合采产出数值模拟研究

Numerical simulation of coal measure gases co-production

实现煤系煤层气、致密气和页岩气("三气")同井筒合采,是提高单井产能和地下资源可动用率的有效手段,但是合采条件下的气、水产出过程,特别是不同层位的气水贡献率、产气压力和含气饱和度变化均不清晰。建立煤层气和致密气协同产出的数值模型,结合现场试验井地质参数和气水产出曲线,查明了煤层气和致密气产出过程,分析了其影响因素。结果表明:合采模型可与单采模型对比验证,具有很好的适用性;可实现气井产能劈分,明确不同层位的气、水产出贡献;排采过程中压降速度降低,产气高峰推迟,但后期产气量变化不大;煤层与砂岩之间压力系统越相近,合采效果越好;改善压裂效果可短期提高产气能力,但对总产气量影响不大;煤层的基质收缩和应力敏感会影响产气效果,但深部地质条件下的变化特征有待进一步探讨。相关结果可对煤系气协同开发方案的制定和完善提供指导,并进一步推动煤系"三气"的同井筒合采。

The co-production of coalbed methane,tight gas and shale gas（ ＂Three gases＂） from one well bore is an effective method to improve the productivity of single well and utilization rate of underground resources.However,the gas and water production process under geological conditions,especially the contribution rate from different layers,gas production pressure and gas saturation variation are not clear. In this paper,a numerical model of coalbed methane and tight sand gas co-production was established for the first time.Combined with the geological parameters and gas-water output curve of the test well,the factors controlling the gas production were identified.The results show that that the applicability of the co-production model can be compared with single production models,which shows a good suitability;the model can achieve the purpose of production rate classification and the contribution of different layers can be classified; the pressure drop rate decreases,the later of the gas production peak come,however,the production rates in late stages show no much difference; the similar of the sandstone and coal pressure systems,the better of the co-production effect; improving the hydro fracturing results can improve the gas production rate in short term,but show little influence on the accumulated gas production; the effect of shrinkage and stress sensitivity of the coals can significantly improve the gas production effect,however,the physical properties of the coal seam under deep geological conditions need to be further explored.The related results would provide a guidance for the formulation and improvement of drainage systemsof coal measure gases and promote ＂three gases＂co-production from one wellbore a step further.