不同形态压降漏斗模型对煤层气井产能的影响

Effects of pressure drop funnels model of different shapes on CBM well productivity

为了研究压降漏斗形态对煤层气井产能的影响,探讨不同排采阶段煤储层压力变化规律,以期对煤储层解吸效果进行量化研究。针对径向流压力分布模型对数函数模型难以准确反映各阶段的压降漏斗形态这一问题,建立了对数、线性、抛物线和椭圆型函数压降漏斗模型,提出了煤储层“解吸系数”与“有效解吸系数”的概念,并分析不同函数模型对煤层气解吸半径、产能和采收率的影响。研究结果表明,在同等解吸半径条件下,椭圆函数模型的解吸气量、采收率最高(38.05%),对数函数模型的解吸气量、采收率最低(低于5%);相同压降漏斗半径条件下,对数、线性、抛物线、椭圆函数模型的解吸半径及有效解吸半径依次增大,其中椭圆函数模型的解吸系数、有效解吸系数最大,压降半径达到140 m时,其解吸半径达到135 m,有效解吸系数达到0.725,解吸半径范围内的煤储层中气体得到充分解吸。研究结果及认识对于掌握煤层气井排采过程中的储层压降规律,指导煤层气井排采具有重要意义。

In order to study the effect of pressure drop funnel shapes on CBM well productivity,the change law of pressure and the shape of pressure drop funnel in different drainage stages of CBM wells were discussed,the mathematical models of pressure drop funnel were established,the concept of“desorption coefficient”and“effective desorption coefficient”for coal reservoir were proposed to quantitative study desorption effect of the coal reservoir.Taking a CBM well in the west of Guizhou as an example,the research results show that the logarithmic function model of pressure distribution of radial flow is difficult to accurately reflect the shape of pressure drop funnel at all stages.Four different types of pressure drop funnel models of logarithmic function,linear function,parabola function and elliptic function were compared and analyzed under the same desorption radius,the gas desorption volume and recovery ratio of the elliptic function model was the highest,recovery ratio reached 38%.The gas desorption volume and recovery ratio of the logarithmic function model were the lowest,and the recovery rate was less than 5%.Under the same drop funnels radius,the desorption radius and effective desorption radius of logarithmic,linear,paraboloid and elliptic function models were expanded successively,the desorption coefficient and effective desorption coefficient of the elliptic function model were the largest,when the pressure drop radius reached 140 m,the desorption radius of coal reservoir reached 135 m,the effective desorption radius reached 0.725,and the coal reservoir within the desorption radius was fully desorbed.By studying the change rule of productivity,recovery ratio and effective desorption radius under different pressure drop funnel shapes and different desorption radius,it is beneficial to master the law of reservoir pressure reduction in the process of CBM well drainage and to provide guidance for the desorption control of CBM well.