煤田地质与勘探2023，Vol.51Issue(11)：24-33,10.DOI:10.12363/issn.1001-1986.23.04.0168
二连盆地巴彦花凹陷煤层气成因类型及生气潜力
Genetic type and gas-generating potential of coalbed methane in the Bayanhua Sag,Erlian Basin
摘要
Abstract
The Bayanhua Sag in the Erlian Basin is a critical experimental area for coalbed methane(CBM)develop-ment from low-rank coals in Inner Mongolia.However,the relatively low exploration level and the limited understand-ing of the CBM origin in the sag restrict the CBM exploration and development to some extent.This study tested the gas components,stable isotopes and hydrochemistry of the gas and water samples from CBM wells in the Bayanhua Sag.It also conducted radioisotopic dating for these samples.By combining the classic charts for the identification of natural gas origin,this study clarified the gas origins,further analyzed the gas-generating potential,and identified the critical gas-generating factors.The results show that the CBM from the sage is characterized by C1/C1.5 ratios greater than 0.99,CO2-CH4 coefficient[CDMI=φ(CO2)/φ(CO2+CH4)×100％]roughly less than 5％,drying coefficient(C1/C2+)between 104-5 540,high CH4 contents,and low heavy hydrocarbon and CO2 contents.Furthermore,the δ13C(CH4),8D(CH4),and δ13C(CO2)values of the CBM range from-51.80‰ to-67.70‰,from-226.20‰ to-291.00‰,and from-20.30‰ to-37.60‰,respectively,suggesting the characteristics of continental biogenic gas.In the identification charts,the CBM samples mostly fell within the biogenic gas zone,indicating that methane originated from acetic-acid and methyl fermentation and that CO2 is primarily the associated product of microbial methanogenesis.Coalbed water,originating from meteoric water,is NaHCO3 type of slightly alkaline water primarily,with δ13CDIC and δ18O(H2O)values of-2.6‰ and-16.4‰,respectively.Based on these findings,as well as the 14C dating results,the coalbed water is inferred to be the Quaternary water and modern mixed water rather than primary water.By combining the analysis of the structures and hydrogeolo-gical conditions in the Bayanhua Sag,it can be concluded that the runoff areas in the sag are favorable for gas produc-tion from acetic acid fermentation and that areas with weak runoff are conducive to the enrichment and accumulation of biogenic gas.The low-rank coal reservoirs in the sag exhibit high pore permeability,suitable geotemperature,and superi-or hydrogeological conditions,which are beneficial for the generation of biogenic gas.Furthermore,biogenic gas reser-voirs of the hydraulic sealing type have developed in the confined area.Therefore,hydrogeological conditions,which play a vital role in the formation of biogenic gas,should be emphatically concerned in selecting CBM exploration tar-gets in the sag.关键词
二连盆地/巴彦花凹陷/低阶煤/煤层气/成因类型/生气潜力Key words
Erlian Basin/Bayanhua Sag/low-rank coal/coalbed methane/genetic type/gas-generating potential分类
地质学引用本文复制引用
孟芹,李玲,李杰,田文广,林海涛,李恒..二连盆地巴彦花凹陷煤层气成因类型及生气潜力[J].煤田地质与勘探,2023,51(11):24-33,10.基金项目
中国石油天然气股份有限公司"十四五"重大科技项目(2021DJ2303) （2021DJ2303）
中央引导地方科技发展资金项目(2022ZY0018) （2022ZY0018）
