松河井田地温特征及煤层气井适配性压裂工艺

Geothermal characteristics and suitable CBM well fracturing technology in Songhe Mine Field

基于煤层气勘查开发示范工程,分析了黔西松河井田地温特征及其对煤层气开发的影响,探讨了龙潭煤系上煤组压裂工艺优选及下煤组压裂工艺优化方案。研究表明：受泥岩、煤层热导率低及煤系隔水性好、富水性弱的共同影响,龙潭煤系纵向地温梯度达3.57~4.65℃/hm,表现出明显的正地温梯度。基于不同温度下煤的等温吸附试验,45℃条件下下煤组各煤层煤层气可采系数与30℃相比提高了4.55%~11.67%;受此影响,下煤组压裂深度为620~900 m时,煤层气采收率较高。采用CO2泡沫压裂工艺适合井田下煤组超压、低渗、敏感性及滤失性强的储层特点,煤层埋深超过750 m即满足CO2泡沫压裂对储层温度的要求。同时,利用低温活性水压裂液注入可大幅降低上煤组储层温度,实现煤层气开发过程中的升温解吸、渗流。

Based on the demonstration project of coalbed methane（ CBM） exploration and development,this paper analyzed the geothermal characteristics and its effect on CBM development,and discussed the coal group fracturing optimization scheme of Longtan Formation in Songhe Mine Field,West Guizhou. The research has shown that vertical geothermal gradient was 3.57 ~ 4.65 ℃ / hm in Longtan Formation by the combined effect of low thermal conductivity of mudstone and coal seam,hydrogeological conditions of well water-resisting property and low water-richness,therefore,the geothermal gradient showed positive abnormal significantly in the Longtan Formation. According to the experimental results of isothermal adsorption under different temperatures,CBM recoverable coefficient increased by 4. 55% ~11.67% in lower coal group under the temperature condition of 45 ℃ compared with 30 ℃. Affected by this,CBM recovery ratio would be higher when the burial depth of lower coal group was 620 ~ 900 m. CO2 foam fracturing technology was suitable for the reservoir characteristics of high reservoir pressure,lower original,strong sensitivity and filtration permeability in lower coal group,and reservoir temperature could meet the CO2 foam fracturing requirement of higher than 40 ℃,while the burial depth of lower coal group was more than 750 m.Low temperature active hydraulic fracturing fluid injection could significantly reduce the reservoir temperature of the upper coal group,and forms CBM desorption,exploitation with coal reservoir temperature rising in the process of CBM development.