评价煤层吸附气解吸能力的生产数据系统分析新方法

发布时间：2018-04-11 09:54

本文选题：煤层气 + 吸附气解吸　；参考：《煤炭学报》2017年12期

【摘要】：主要考虑了煤层气开发过程中吸附气非稳态解吸的关键因素作用,建立了考虑吸附气非稳态解吸的煤层气直井的线性渗流模型,并通过全隐式有限差分方法求得了内边界定流量、外边界封闭渗流模型的数值解。通过数值结果分析主要表明了非稳态解吸系数会使得无因次瞬时井底压力与压力导数的双对数特征曲线在封闭边界控制的拟稳态流动段均出现下落趋势,两曲线间距离变宽,不再急剧上翘收敛为一条直线;这是由于吸附气解吸能及时补充到气藏,减缓了地层压力的降落;而井筒储集系数不影响由封闭边界控制、受吸附气解吸作用影响的拟稳态流动段;表皮因子影响拟稳态流动段无因次井底压力的变化,但不影响拟稳态流动段无因次井底压力导数的变化。该线性渗流模型仍满足Duhamel原理,生产数据分析时可利用反褶积技术手段,首先将按照拟压力定义线性化的变流量生产数据转化为单位流量下瞬时井底拟压力数据,然后基于所建渗流模型的数值解以及主要参数的敏感性影响分析结果,通过瞬时井底压力特征曲线拟合方法对反褶积处理后的归一化生产数据进行分析,可解释出表征煤层吸附气解吸能力的非稳态解吸系数、煤层渗透率、表皮因子、外边界半径等重要参数。由此建立了煤层气直井生产数据的特征曲线系统分析方法。最后,通过一口煤层气直井的实际生产数据分析验证了所提出的煤层气直井生产数据特征曲线分析方法的有效性和实用性;并采用解释参数数据进行模型计算,分析了吸附气解吸作用对煤层气井流量贡献的瞬时变化规律;还通过公式推导表明了当煤层中渗流到达稳态时,整个煤层吸附气解吸速度将等于煤层气井生产的流量。
[Abstract]:In this paper, the key factors of unsteady desorption of adsorbed gas during the development of coalbed methane are considered, and the linear seepage model of straight well with unsteady desorption of adsorbed gas is established.The numerical solution of the internal boundary defined flow model and the outer boundary closed seepage model is obtained by using the fully implicit finite difference method.The numerical results show that the unsteady desorption coefficient can make the logarithmic characteristic curves of dimensionless instantaneous bottom pressure and pressure derivatives fall in the quasi-steady flow section controlled by closed boundary, and the distance between the two curves becomes wider.This is because the adsorption gas desorption energy is replenished to the gas reservoir in time, which slows down the fall of formation pressure, and the wellbore reservoir coefficient does not affect the control by the closed boundary.The pseudo-steady-state flow section affected by adsorption gas desorption, the epidermal factor affects the change of dimensionless bottomhole pressure in the pseudo-steady flow section, but does not affect the variation of dimensionless bottom-hole pressure derivative in the pseudo-steady-state flow section.The linear seepage model still satisfies the Duhamel principle, and the deconvolution technique can be used to analyze the production data. Firstly, the variable flow production data linearized according to the quasi-pressure definition is transformed into instantaneous bottom-hole pressure data under unit flow.Then, based on the numerical solution of the established seepage model and the results of sensitivity analysis of the main parameters, the normalized production data after deconvolution is analyzed by the fitting method of instantaneous bottomhole pressure characteristic curve.The unsteady desorption coefficient, coal seam permeability, skin factor, outer boundary radius and so on can be explained.Based on this, a systematic analysis method of characteristic curve for production data of coal bed methane (CBM) vertical well is established.Finally, the validity and practicability of the proposed method are verified by analyzing the actual production data of a coal bed methane vertical well, and the model calculation is carried out by using the interpretation parameter data.The instantaneous variation law of adsorption gas desorption to the flow rate of coalbed methane well is analyzed, and the formula derivation shows that the desorption rate of the whole coal bed adsorbed gas will be equal to the flow rate of coal bed methane well when the seepage in coal bed reaches steady state.
【作者单位】：北京科技大学土木与资源工程学院;中国科学院力学研究所;
【基金】：国家自然科学基金资助项目(51404232) 中国博士后基金资助项目(2014M561074) 国家科技重大专项资助项目(2011ZX05046-03)
【分类号】：TD84

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