煤层气井气水两相流入动态关系研究

Inflow performance relationship in two-phase CBM wells

为了准确预测煤层气井流入动态关系,基于流体稳定渗流的运动方程和连续性方程,建立了煤层中气水两相渗流的数学模型和气井流入动态预测模型.采用气水两相拟压力函数,研究了两相煤层气井产能方程.结果表明:该模型考虑了煤层渗透率、表皮效应和非达西效应的影响,预测结果具有较高精度,预测值与实测值间的整体误差控制在8%以内.井底流压充分反映产能的渗流压力特征,调整井底流压,可有效增大生产压差,利于煤层中气体解吸和水相渗流,提高产能,在井底流压由5.0 MPa降为2.1 MPa后,产能由0.1 kg/s提高到0.6 kg/s.随渗透率的增大和表皮系数的减小,流入动态曲线明显向右移动,渗透率由2×10-3μm2升为2×10-2μm2时,最大气水总流量由0.205 kg/s迅速增大到1.20 kg/s.开采中,煤层水的相对渗透率不断减小,而气的相对渗透率和泄流半径逐渐增大,导致动态曲线有向左移动的趋势,但其影响并不显著.

Based on the kinematic and continuing equations of the steady fluid flow, an approach was proposed to predict inflow performance relationship （IPR） for two-phase （gas and water） coalbed methane （CBM） wells. And the mathematical model of two-phase flow and IPR were developed. The function of pseudopressure was used to study the productivity equation for twophase CBM wells. The results show that the small errors of less than 8 % between the prediction and measured values are achieved due to the permeability, skin factor and non-Darcy flow. CBM productivity increases from 0.1 kg/s up to 0.6 kg/s when bottom hole pressures （BHPs） are from 5.0 MPa to 2.1 MPa. Adjusting BHP can effectively increase producing pres- sure drop, which is beneficial to gas desorption and water flow and enhance CBM production. The IPR curves move towards the right direction due to the increased permeability and de- creased skin factor. An enhanced permeability from 2 X 10 3 μm2 up to 2 X 10.2 μm2 leads to the enhanced production of gas and water from 0. 205 kg/s to 1.2 kg/s. During the pumpingproduction, the effective permeability of water decreases while the effective permeability of CBM and supply boundary increase, which makes the IPR curve move towards the left direc- tion.