地质科技通报 (May 2023)
Controlling mechanism of pore-throat structure of different lithofacies on gas-water relative permeability characteristics of tight sandstone gas reservoir: A case study of the Lower Shihezi Formation in the Well J72 block of the Dongsheng Gas Field, Ordos Basin
Abstract
To understand the controlling mechanism of pore-throat characteristics on gas-water relative permeability characteristics of tight sandstone gas reservoirs and better guide the increase in gas reserves and production, taking the Lower Shihezi Formation reservoir in the J72 well block of the Dongsheng Gas Field as a research object, the effects of microscopic pore-throat parameters on gas and water transport properties were studied by combining various analytical data and lithofacies division. The controlling effect of rock lithofacies on gas content and productivity was revealed.Results show that the lithofacies of the Lower Shihezi Formation in the J72 well block can be classified into conglomerate rock, gravelly sandstone, pebbly coarse-grained sandstone, medium- and fine-grained sandstone, and mudstone lithofacies, of which the pebbly coarse-grained sandstone and gravelly sandstone lithofacies are the high-quality lithofacies. Pore types are mainly secondary intergranular dissolved pores, with an average proportion of 48.5%. The proportion of intergranular dissolved pores in pebbly coarse-grained sandstone lithofacies, gravelly sandstone, and medium- and fine-grained sandstone lithofacies decreases successively.Pore space in the three lithofacies is multifractal, and the proportion of large pores gradually decreases. The high-quality lithofacies has superior physical properties and small comprehensive fractal dimensions. The high-quality lithofacies also has low clay mineral content, large average pore-throat radius, large movable gas porosity, maximum effective gas permeability during gas transport, and high gas-bearing capacity. A comprehensive study shows that high-quality lithofacies is the key factor in controlling the high and stable production of gas wells. The in-depth analysis of the microscopic characteristics of lithofacies provides useful guidance for the efficient development of tight sandstone gas reservoirs.
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