煤田地质与勘探2024，Vol.52Issue(2)：134-146,13.DOI:10.12363/issn.1001-1986.23.11.0741
深部煤层气游离气饱和度计算模型及其应用
A calculation model of free gas saturation in deep coalbed methane reservoirs and its application
摘要
Abstract
In recent years,breakthroughs have been achieved in the exploration of deep coalbed methane(CBM)in China based on fine-scale geological research and techniques such as multistage hydraulic fracturing using proppants in a horizontal well.As a result,some wells yielded daily gas production of up to 100 000 m3,inspiring confidence again in the CBM industry.However,since deep coal reservoirs occur in a complex geological environment characterized by high in-situ stress,high geotemperature,high pore pressure,and low permeability,there is an urgent need to reveal the typical parameters of coal reservoirs at different depths and the distribution of CBM in varying occurrence forms in the reservoirs,as well as their effects on CBM reserves and production.Based on Langmuir equation of isothermal adsorp-tion,Henry's law,and the material balance principle,this study established a calculation model of free gas saturation of deep CBM reservoirs by considering the effects of adsorption layers and dissolved gas.With the deep CBM reservoirs in the Daning-Jixian block in the Ordos Basin in China as a case study,this study investigated the occurrence forms and distribution of deep CBM at varying depths and assessed the effects of free gas saturation on the reserves,production,and rational production allocation of deep CBM.Key findings include:(1)Free gas appears only when the coal seams'burial depth exceeds the depth corresponding to the dissolution saturation of CBM reservoirs,with the free gas satura-tion increasing rapidly initially and then slowly as the burial depth increases.In the Daning-Jixian block,free gas emerges at a burial depth of 1 875 m,and the free gas saturation reaches 90%at a burial depth of 2 800 m,where the free gas accounts for up to 17.3%.(2)The free gas saturation has significant effects on the reserves calculation,gas produc-tion characteristics,and reasonable production allocation of deep CBM.With an increase in the free gas saturation,the CBM reserves linearly increase,and the cumulative gas production keeps rising,with the increased amplitude gradually decreasing in the late stage.Furthermore,an increase in the free gas saturation is accompanied by an increase in the op-timal production allocation of a deep CBM well,an increase in the drop rate of bottomhole pressure,a decrease in the pressure difference between the stimulated reservoir volume(SRV)and the unstimulated reservoir volume(USRV),and an increase in the producing degree of the USRV.The dominant coal seams to be exploited in the target block are loc-ated at depths between 2 100 and 2 300 m,with free gas saturation ranging from 48%to 68%and a proportion of free gas varying between 10%and 13%.It is recommended that the rational production allocation of gas wells in the target block should be(4-10)×104 m3/d.The results of this study will provide a theoretical basis and methods for the further exploita-tion of deep CBM.关键词
深部煤层气/赋存方式/游离气饱和度/储量评价/产气规律/合理配产Key words
deep coalbed methane/occurrence mode/free gas saturation/reserve evaluation/production law/rational proration分类
天文与地球科学引用本文复制引用
石军太,邓婷,李靖,李相方,曹敬添,徐凤银,熊先钺,黄红星,孙政,贾焰然,马淑蕊,郑浩杭..深部煤层气游离气饱和度计算模型及其应用[J].煤田地质与勘探,2024,52(2):134-146,13.基金项目
国家自然科学基金重点项目(42230814) （42230814）
山西省科技重大专项项目(20201101002) （20201101002）
中石油股份公司前瞻性基础性攻关项目(2021DJ2301) （2021DJ2301）
中国石油大学(北京)优秀青年学者基金项目(2462020QNXZ003) （北京）
