The No.8 coal seam in the Nalinhe area,Ordos Basin,with a burial depth exceeding 3 000 m,exhibits reservoir temperature and pressure fields significantly different from those of shallow to moderately coal-rock gas reservoirs.Investigating the coal-rock gas accumulation characteristics of this coal seam holds great significance for deep coal-rock gas exploration.This study systematically analyzes the geologic factors controlling deep coal-rock gas accumulation in the Nalinhe area,delves into the geological characteristics concerning coal quality,reservoir characteristics,temperature and pressure fields,gas-bearing properties,and coal-rock gas preservation conditions in the area.Using data from well M1H,which has undergone prolonged coal-rock gas production,we analyze the production characteristics and predict the coal-rock gas productivity of the Nalinhe area.The results indicate that the coal-rock gas reservoirs in the No.8 coal seam at burial depths exceeding 3 000 m exhibit characteristics significantly different from shallow coal-rock gas reservoirs at burial depths less than 1 500 m,which feature low pressure,porosity,and permeability and gases dominated by undersaturated adsorbed gas.The specific characteristics of the No.8 coal seam are as follows:(1)This coal seam is thick and mainly composed of semi-bright coals,and of the medium to high rank;(2)Under compaction and coalification,the medium to high-rank coal reservoirs are dominated by micropores smaller than 2 nm,which account for up to 79.8％of the total pore volume.Additionally,micron-scale endogenetic microfractures,which remain open under deep in-situ stress field,are well-developed in these reservoirs,leading to a high matrix permeability of up to 3.949 × 10-3 μm2;(3)At burial depths exceeding 3 000 m in the Ordos Basin,the formation temperature and pressure reach up to 97 ℃ and 32 MPa,respectively.The formation pressure tends to exert stabilized impacts on the adsorption capacity of coals,which predominantly hinges on the negative effect of temperature.Consequently,the adsorbed gas in the coals is in supersaturation,with free gas accounting for approximately 30％;(4)The deep coal reservoirs in the study area are situated in a confined aquifer zone,while the coal seam itself manifests a low water-yielding capacity.The formation water produced is identified as the primary depositional water remaining in the roof and floor of the coal seam;(5)The consistency between the production curve characteristics of well M1H and the traced coal-rock gas geochemical characteristics demonstrates the stable production and great exploitation potential of coal-rock gas in deep reservoirs at burial depths exceeding 3 000 m.
关键词
排采/成藏地质特征/煤岩气/纳林河地区/鄂尔多斯盆地
Key words
dewatering and production/accumulation-associated geological characteristics/coal-rock gas/Nalinhe area/Ordos Basin
维普
万方数据