煤层气井合理放气套压的确定及其应用

煤层气井提产阶段和稳产阶段需要确定合理放气套压,才能够获得稳定的气流补给。根据煤储层启动压力梯度、渗流理论和煤层气开发地质理论,构建了煤层气井憋压阶段套压变化的数学模型;利用沁水盆地大宁区块的煤层气勘探开发资料验证了该模型的准确性,并分析了放气套压差值对平均日产气量的影响规律。模型计算结果与现场数据吻合较好时,煤层气井的产气量较高;当计算出的放气套压与实际放气套压的差值小于等于0.15 MPa时,煤层气井稳产期的产气量能达到1 000 m3/d以上;大于0.15 MPa时,需要降低产气量来维持其稳定性。研究结果表明,日产气量随实际放气套压与计算值之间差值的增大呈幂函数减小,建立的煤层气井憋压阶段合理放气套压数学模型可为现场排采控制提供理论依据。 

The Determination of Casing Releasing Pressure of CBM Wells and Its Application

In the stage of stable production and production increase of coalbed methane wells, it is necessary to determine the reasonable casing releasing pressure to obtain stable air supply. Based on the threshold pressure of coal reservoir, seepage theory, CBM development geology theory etc., a mathematic model of releasing pressure for CBM wells was established. From CBM exploration and development data of Daning Block, Qinshui Basin, the accuracy of the mathematic model was verified. The relations between casing pressure drop and average daily gas production were analyzed. When predicted pressure from this model was in good agreement with that applied in field data, gas production of CBM Wells would be higher. When the pressure difference was within 0.15 MPa, the average daily gas production of CBM wells could be more than 1 000 m3/d in stable production stage. When the pressure difference was more than 0.15 MPa, daily gas production would be stabilized at lower gas production rate. The results showed that daily gas production is reduced in power function with casing pressure drop and the mathematical model of casing releasing pressure in coal bed methane well can provide theoretical basis for CBM wells production.