Abstract:

The southern Yanchuan Block is a deep, high-rank coal-bed methane reservoir with large buried depth at 800~1 500 m, meagre coal or anthracite, and good gas content at 12 m³/t. The resource conditions are relatively favorable, but the single well productivity level of the gas field varies greatly. Based on the comprehensive study of gas field geological conditions, and by the analysis of the influence of structure on reservoir hydrocarbon generation, porosity and permeability, hydrogeological conditions, coal body structure, and CBM storage, the researches on the control mechanism of structure on CBM reservoir formation are carried out to find out the main controlling factors of coal seam formation and its changing rules. Combined with the CBM development dynamic data, the relation between block structure and CBM well productivity is analyzed, and a structural gas control mode for CBM well productivity is established. The research results show that the buried depth of the coal seam controls the gas-bearing and permeability of the reservoir. The deeper the buried, the better the gas-bearing and the worse the permeability. The control effect of tectonic activities on the formation of coal-bed methane has two sides, the local folds and the development of faults has a significant effect on improving permeability, which is conducive to the enrichment of gas reservoirs, but the excessive tectonic activity on the other hand will also lead to the enhanced hydrodynamic conditions and the escape of coalbed methane. The structure has an obvious control effect on the gas well productivity. The high-yield wells are mainly distributed in the coalbed methane enrichment and the permeability improvement areas at the wing of the local micro-uplift belt with a buried depth of 830~1 280 m. The middle-production wells are mainly distributed in the low-permeability areas with a buried depth of more than 1 280 m, whose structure is gentle and the faults are not developed. The low-yield wells are mainly distributed in local depression areas with severe structural damage and CBM escape areas near fault development belts.

Key words: deep coalbed methane, structure, production capacity, control effect, southern Yanchuan, Ordos Basin