CHEN M J, CHEN X N, KANG Y L, ,et al.Investigation of reservoir sensitivity evaluation and damage mechanism in deep coalbed methane reservoirs of the Daji Block in Eastern Ordos Basin[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(1):18-28.

doi:10.16186/j.cnki.1673-9787.2025030056

Received:2025/03/25

Revised:2025/07/01

Published:2025-12-03

Investigation of reservoir sensitivity evaluation and damage mechanism in deep coalbed methane reservoirs of the Daji Block in Eastern Ordos Basin

Chen Mingjun1, Chen Xueni1, Kang Yili1, Guo zhidong2,3, Wang Yubin2,3, Shi Yang4, You Lijun1, Dai Wangru1, Yan Maoling1

1.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation， Southwest Petroleum University， Chengdu  610500， Sichuan， China；2.Engineering Technology Research Institute， Petro China Coalbed Methane Co.， Ltd.， Xi’an  710082， Shaanxi， China；3.China United Coalbed Methane National Engineering Research Center Co.， Ltd.， Beijing  100095， China；4.Petro China Research Institute of Petroleum Exploration & Development， Beijing  100083， China

Abstract: Objectives To clarify the sensitivity characteristics and damage mechanisms of deep coalbed methane （CBM），a study on sensitivity evaluation and damage mechanisms is conducted. Methods The deep CBM reservoirs in the Daji Block of the Ordos Basin is investigated in this study. Petrographic thin-section analysis， X-ray diffraction （XRD）， and scanning electron microscopy （SEM） are employed to  characterize the deep CBM reservoirs and identify potential sensitivity-inducing factors. Laboratory experiments are conducted to evaluate the fluid and stress sensitivity of the deep coal samples， thereby elucidating the mechanisms of damage associated with sensitivity effects. Results （1） The coal maceral composition in the study area is dominated by vitrinite， with a low inertinite content and an absence of liptinite. The inorganic components are mainly quartz and clay minerals， with quartz content at 22.60% and clay minerals at 57.05% （predominantly kaolinite）. The pore structure is characterized by abundant cast membrane pores， cellular pores， and gas pores， with well-developed fractures that are mostly filled by clay minerals or calcite. The porosity and permeability are relatively low，and pore connectivity is poor. （2） The CBM reservoir exhibits velocity sensitivity， water， salt， alkali，and stress sensitivity. The velocity sensitivity index is 82.64%，indicating strong damage. The water， salt， and alkali sensitivity indices are 53.90%， 57.00%， and 63.50%， respectively， representing moderately strong damage. The stress sensitivity coefficient ranges from 0.692 9 to 0.938 3， indicating moderately strong to strong damage. However， no acid sensitivity damage is observed， and acid treatment can enhance permeability. （3） The high-temperature， high-pressure， and high-stress environment of deep CBM reservoir leads to low rock mechanical strength， making them highly susceptible to stress sensitivity damage. The high content of pyrite， kaolinite， and illite in the mineral composition tends to autogenous cementation under complex fluid conditions， causing pore and fracture blockage that hinders gas production. Furthermore， high-salinity formation water is prone to salt precipitation and crystallization blockages during drilling and production. Conclusions The findings improve the rationale for designing working fluid systems and production regimes. This is of positive significance for enhancing coal reservoir protection and increasing coalbed methane production.

Key words:deep coalbed methane;reservoir characteristics;reservoir sensitivity;reservoir damage