单相水流动煤层气井流入动态分析

INFLOW PERFORMANCE ANALYSIS OF SINGLE-PHASE WATER FLOW IN COALBED METHANE WELLS

单相水流动煤层气井流入动态是确定煤层气井合理工作制度的依据和分析煤层气井动态的基础。基于煤层流体的渗流规律,建立满足达西渗流和非达西渗流煤层气井的流入动态预测模型,通过鄂尔多斯盆地现场实例验证,得到单相水流动煤层气井的流入动态。结果表明:预测模型考虑煤层参数、流体物性和非达西表皮效应,结果具有较高精度,整体误差可控制在12%以内。煤层流体渗流速度不大时,宜采用煤层供给边缘压力不变时的达西渗流模型分析流入动态,而在雷诺数大于0.3和产水量超过30 m3/d时,需采用非达西渗流模型。排采前期加大生产压差,可有效控制排液量大小,防止煤粉运移而破坏储层,利于煤层水的渗流,压力差由0.44 MPa上升为3.68 MPa后,产能由10 m3/d提高到40 m3/d。增大煤层渗透率会提高储层的综合导流能力,显著增大煤层气井产能,渗透率由0.9×10-3μm2变为6.15×10-3μm2时,产水量由3.5 m3/d增大到15.9 m3/d;减小表皮系数使流入动态曲线明显向右移动,同一井组的表皮系数为-3.10和-4.85时,产水量分别为34.8和45.6 m3/d。

Inflow performance relationship（IPR） in single-phase（water） coalbed methane wells provides the basis for the reasonable operating practice and dynamic analysis. The mathematical models of IPRs for Darcy and non-Darcy flow in coalbed methane（CBM） wells are developed based on the fluid mechanism in porous medium. The IPR curves are obtained with the field examples in Ordos Basin. The results show that the small errors of less than 12% between the prediction and measured values are achieved due to the reservoir parameters, fluid physical property and non-Darcy skin factor. The IPR should be analyzed by the Darcy model with constant supply boundary pressures for the low flow velocity. However, the non-Darcy model should be involved while the Reynolds number is over 0.3 and water production is more than 30 m3/d. During the initial pumping production, the water flow rate and coal particle migration can be controlled due to the increase of pressure drop, which is beneficial to water flow. And an increased pressure drop from 0.44 MPa up to 3.68 MPa leads to the enhanced water production from 10 m3/d to 40 m3/d. The increase in the integrated flow conductivity of coalbed and deliverability occurs with the increment of permeability. And the increase of permeability from 0.9×10-3 μm2 up to 6.15×10-3 μm2 leads to an increment in water production from 3.5 m3/d to 15.9 m3/d. The decrease of skin factor makes the IPR curves move towards the right direction. And the reduction in skin factor from -3.10 to -4.85 yields the increase of water production from 34.8 m3/d up to 45.6 m3/d.