致密砂岩气藏不同岩石相孔喉结构对气水相渗特征控制机理:以鄂尔多斯盆地东胜气田J72井区下石盒子组储层为例

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

为了明确致密砂岩气藏储层微观孔喉对气水相渗特征的控制机理,更好地指导气田增储上产,以东胜气田J72井区下石盒子组储层为研究对象,综合多种分析化验资料并细分岩石相探究了微观孔喉参数对气水渗流能力的影响,揭示了不同岩石相对含气性及产能的控制作用。研究结果表明:J72井区下石盒子组岩石相可以归纳为砾岩相、砾质砂岩相、含砾粗砂岩相、中细砂岩相、泥岩相五大类,其中含砾粗砂岩相、砾质砂岩相为优质岩石相;孔隙类型主要为次生粒间溶孔,平均占比达48.5%,含砾粗砂岩相、砾质砂岩相、中细砂岩相的粒间溶孔比例依次减少,三类岩石相均具有多重分形的特征,大孔比例逐渐降低,其中优质岩石相的物性好、综合分形维数小;优质岩石相的黏土矿物含量低、平均孔喉半径大,气体渗流时的可动气体孔隙度和最大有效气相渗透率较大,含气性好。综合研究认为优质岩石相是控制气井高产稳产的关键因素,深入剖析岩石相的微观特征可以为致密砂岩气藏的高效开发提供有力指导。

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.