致密砂砾岩成储界限及分级评价标准——以松辽盆地徐家围子断陷白垩系沙河子组为例

Reservoir limits and grading evaluation criteria of tight glutenite:a case study of Cretaceous Shahezi Formation in Xujiaweizi Fault Depression,Songliao Basin

徐家围子断陷下白垩统沙河子组砂砾岩储层是松辽盆地深部重要的致密气藏储层,其孔渗关系复杂,给成储界限的厘定和储层分级评价带来挑战。针对沙河子组砂砾岩储层,采用水膜厚度法、充注动力法、试气产能法和力学平衡法厘定了理论下限、成藏下限、有效渗流下限和成储上限,根据不同成岩作用主控因素下的孔渗关系确定成储界限物性值。在此基础上,结合储层微观孔隙结构差异划分储层类型,建立致密储层分级评价标准,并利用测井资料将分级评价标准进行应用,为研究区致密气甜点区优选提供依据。将沙河子组砂砾岩分为常规储层、Ⅰ—Ⅳ级致密砂砾岩储层和非储层,成储界限与分级评价结果具有很好的匹配关系。其中,常规储层孔隙度大于9%,渗透率大于0.05×10^(-3)μm^(2);Ⅰ级致密储层孔隙度为8%~9%,渗透率为(0.01~0.05)×10^(-3)μm^(2);Ⅱ级致密储层孔隙度为5%~8%,渗透率为(0.001~0.01)×10^(-3)μm^(2);Ⅲ级致密储层孔隙度为3.5%~5%,渗透率为(0.2~1)×10^(-6)μm^(2);Ⅳ级致密储层孔隙度为2%~3.5%,渗透率为(0.05~0.2)×10^(-6)μm^(2);非储层的孔隙度小于2%,渗透率小于0.05×10^(-6)μm^(2)。致密砂砾岩气产量受控于致密储层类型;Ⅰ级、Ⅱ级致密储层是致密气高产的有利层段;徐家围子断陷北部安达—宋站地区有利储层厚度较大,为致密气勘探开发甜点区。

The Lower Cretaceous Shahezi Formation glutenite reservoirs in the Xujiaweizi Fault Depression are important tight gas reservoirs in the deep strata of the Songliao Basin.Their complex porosity and permeability relation-ships pose challenges to determining reservoir boundaries and evaluating reservoir grades.For the Shahezi Forma-tion glutenite reservoirs,the water film thickness method,charge dynamics method,gas testing productivity method,and buoyancy balance method were used to determine theoretical lower limits,gas accumulation lower limits,effective flow lower limits,and reservoir-forming upper limits.The petrophysical values of the reservoir boundaries were determined based on the porosity and permeability relationships under different diagenetic controlling factors.On this basis,reservoir types were classified according to differences in microscopic pore structures,and a grading evaluation standard for tight reservoirs was established.This standard was then applied using logging data to provide a basis for selecting sweet spots in the tight gas exploration areas.The Shahezi Formation glutenite was divided into conventional reservoirs,ClassⅠ-Ⅳtight glutenite reservoirs,and non-reservoirs.The reservoir boundaries and classification evaluation results were well matched.Conventional reservoirs had porosity greater than 9%and permeability greater than 0.05×10^(-3)μm^(2).ClassⅠtight reservoirs had porosity of 8%-9%and permeability of(0.01-0.05)×10^(-3)μm^(2).ClassⅡtight reservoirs had porosity of 5%-8%and permeability of(0.001-0.01)×10^(-3)μm^(2).ClassⅢtight reservoirs had porosity of 3.5%-5%and permeability of(0.2-1)×10^(-3)μm^(2).ClassⅣtight reservoirs had porosity of 2%-3.5%and permeability of(0.05-0.2)×10^(-6)μm^(2).Non-reservoirs had porosity less than 2%and permeability less than 0.05×10^(-6)μm^(2).The gas production of tight glutenite was controlled by the reservoir type.ClassⅠand ClassⅡtight reservoirs were favorable high-yield layers.The thick-ness of favorable reservoirs in the Anda-Songzhan area of the northern Xujiaweizi Fault Depression was large,making it a sweet spot for tight gas exploration and development.