贵州深部煤层气地质特征及其资源潜力

Geological characteristics and resource potential of deep coalbed methane in Guizhou

加快深部(1000 m以深)煤层气资源勘探开发是煤层气走向规模化开发的重要途径,是近年来煤层气产业的重要发展方向。贵州省煤层气资源丰富,深部煤层气资源占比大,然而目前尚未开展深部煤层气资源的地质研究和勘探开发。立足于贵州煤层气地质背景,基于大量的煤层气试井资料和测试化验资料,分析了深部煤层气地质特征及其资源潜力。研究结果显示:贵州深部煤层气资源主要分布于六盘水、黔北和织纳煤田的众多向斜单元。沉积分异和构造分区导致深部煤储层地质条件具有区域差异性,六盘水煤田以“超压明显、低温、较高应力”为特征,织纳煤田以“超压、较高温度、较低应力”为特征,黔北煤田以“超压、高温、高应力”为特征。深部煤储层渗透率偏低,1000 m以深渗透率将普遍低于0.1×10^(-15)m^(2)。煤储层含气量较高,在1000 m以浅,以六盘水煤田为代表的中阶煤储层平均含气量为10.03 m^(3)/t,以织纳、黔北煤田为代表的高阶煤储层平均含气量为14.51 m^(3)/t,400 m以深超饱和现象较为明显。优选游离气、吸附气预测模型,考虑煤阶随深度的变化,预测深部整体含气量将进一步增加,超饱和现象更为明显,游离气占比增大,在2000 m左右,游离气占比普遍达到10%~25%,且中阶煤游离气占比要高于高阶煤。在此基础上,计算了包含2000 m以深的贵州省重点向斜的煤层气地质资源量,贵州省煤层气地质资源量为3.85万亿m^(3),其中1000 m以深煤层气地质资源量达到了1.90万亿m^(3),六盘水和黔北煤田深部煤层气资源占比大。综合考虑资源规模和资源丰度,提出了开发次序建议,盘关—土城—照子河—旧普安向斜和格目底向斜为首选开发单元,以上向斜均属于高丰度大型气田。

Accelerating the exploration and development of deep(>1000 m)coalbed methane(CBM)resources is an important way for the large-scale development of CBM and an important development direction in recent years.Guizhou Province is rich in CBM resources,with a large proportion of deep CBM resources.However,up to now,the geological research and exploration of deep CBM resources have not been carried out.Based on the geological background of CBM in Guizhou,this paper analyzes the geological characteristics and resource potential of deep CBM in Guizhou Province using a large number of CBM well test data.The research results show that the deep CBM resources in Guizhou are mainly distributed in many syncline units of the Liupanshui,North Guizhou and Zhina coalfields.Sedimentary differentiation and structural zoning lead to regional differences in the geological conditions of deep CBM reservoirs.The Liupanshui coalfield is characterized by“obvious overpressure,low temperature and high stress”,the Zhina coalfield is characterized by“overpressure,high temperature and low stress”,and the northern Guizhou coalfield is characterized by“overpressure,high temperature and high stress”.The permeability of deep CBM reservoir is low,and the permeability of 1000 m deep will be generally lower than 0.1×10^(-15)m^(2).The CBM content of the coal reservoir is relatively high.The average CBM content of the middle-rank coal reservoir represented by the Liupanshui coalfield is 10.03 m^(3)/t,and the average CBM content of the high-rank coal reservoir represented by the Zhina and Qianbei coalfields is 14.51 m^(3)/t,and the deep supersaturation phenomenon is more obvious at 400 m.Based on the prediction model of free gas and adsorbed gas,considering the change of coal rack,it is predicted that the overall gas content in the deep part will further increase,and the supersaturation phenomenon will be more obvious,and the proportion of free gas will increase.At about 2000 m,the proportion of free gas will generally reach 10%-25%,and the proportion of free gas in medium-rank coal is higher than that in highrank coal.On this basis,the geological resources of CBM in the key synclines of Guizhou Province with a depth of more than 2000 m are calculated.Based on the calculation results,the geological resources of CBM in Guizhou Province is 3.85 trillion m^(3),of which the geological resources of CBM in the depth of 1000 m reach 1.90 trillion m^(3),and the deep CBM resources in the Liupanshui and northern Guizhou coalfields account for a large proportion.Considering the scale and abundance of resources comprehensively,the development sequence is proposed.The Panguan-Tucheng-Zhaozihe-Jiupu'an syncline and the Gemudi syncline are the preferred development units.The above synclines are large gas fields with high abundance.