Influencing factors of the dynamic permeability of CBM reservoir and CBM well drainage control measures
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摘要: 排采管控方法对煤层气储层动态渗透率具有显著影响。基于煤层气井不同排采阶段渗透率的主控因素，以提高和改善渗透率为目标，提出了针对性的排采对策。井底流压大于原始储层压力时，降压速度为0.03~0.05 MPa/d，可降低压裂液和速敏伤害；井底流压在原始地层压力和解吸压力之间时，以小于0.03 MPa/d的速度降压，避免加剧储层"渗透率漏斗"；在解吸压力以上0.2~0.3 MPa时开始以0.01 MPa/d速度降压，在解吸压力附近稳压排水30 d，解吸后套压控制在0.2~0.3 MPa左右，避免两相流造成的水相渗透率下降；提产段通过变速提产强化基质收缩作用改善储层渗透率；稳产段主要通过单位压降增产量来确定合理的稳产产量，实现煤层气井长期高产稳产。现场试验表明，该方法取得了较好的应用效果。Abstract: The drainage and production control method has significant impact on the permeability of coalbed methane reservoir. Based on the main control factors of the permeability at different stages of drainage and production of coalbed methane wells, this paper puts forward targeted drainage and production countermeasures with the goal of improving the permeability. When the bottom-hole flow pressure was greater than the original reservoir pressure, the step-down velocity was between 0.08 and 0.1 MPa/d to reduce fracturing fluid and velocity-sensitive damage. When the bottom hole flow pressure was between reservoir pressure and desorption pressure, the pressure could be reduced at a rate less than 0.03 MPa/d to avoid aggravating the "permeability funnel" of the reservoir. When the desorption pressure was 0.2-0.3 MPa, the pressure decreased at the rate of 0.01 MPa/d. When the pressure was stabilized for 30 days near the desorption pressure, the casing pressure was controlled at about 0.2-0.3 MPa after desorption, so as to avoid the decrease of water-phase permeability caused by two-phase flow. The permeability of reservoir was improved by increasing matrix shrinkage with variable speed. In the stable production period, the reasonable stable production could be determined by increasing production per unit pressure drop to achieve long-term high and stable production of CBM wells. The field test shows that the method is effective.
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