钙质砂岩-沉凝灰岩组合致密油储层孔隙类型及成因:以二连盆地阿南凹陷下白垩统腾一下段为例

从微观尺度对二连盆地阿南凹陷下白垩统腾一下段3口取芯井55块致密油储层样品开展孔隙类型及成因进行系统研究。利用AM2井,A43井和H20井3口典型井的岩心(100m)、薄片(200片)、背散射(60个)、扫描电镜(18块)、荧光显微镜(150片)及PCAS(6块)等方面资料及方法,对目的层进行了岩石类型、沉积特征、孔隙类型、分布及成因等方面的系统研究。研究结果表明,阿南凹陷腾一下段岩性复杂,发育滨浅湖、浅湖、半深湖、火山灰沉积及重力流沉积等多种类型沉积相。钙质砂岩和沉凝灰岩的油气显示最好,是目的层致密油勘探的重点目标。砂岩储层的孔隙主要包括残余粒间孔、粒间扩大孔和溶蚀孔。沉凝灰岩储层的孔隙以溶蚀孔为主,其次为粒间孔和构造微裂缝。沉凝灰岩的平均面孔率为12.05%,要高于砂岩的平均面孔率9.13%。腾一下段致密油储层孔隙的成因包括压实及脱水作用、溶蚀作用、沉凝灰岩的脱玻化作用、构造应力作用。目的层的沉凝灰岩在地质历史时期遭受了强烈的溶蚀作用并表现为重稀土亏损。目的层砂岩和沉凝灰岩中的长英质、碳酸盐及凝灰质组分普遍发生了强烈溶蚀作用,溶蚀作用是目的层致密油储层孔隙成因的主导因素。

PORE TYPES AND GENESIS OF THE LOWER CRETACEOUS TENG1 TIGHT OIL RESERVOIR OF CALCAREOUS SANDSTONE AND TUFFITE COMBINATION IN ANAN DEPRESSION,ERLIAN BASIN

55 samples collected from 3 drilling holes in the lower Cretaceous Teng1 section tight oil reservoir are studied by means of thin section observation, backscattering analysis,SEM analysis,fluorescence microscopy observation and PCAS analysis, so as to understand comprehensively the lithology, sedimentary character,pore types,distribution and genesis of the target layer.It shows that the Teng1 tight oil reservoir is composed of complicated lithology with development of shore shallow lake facies,shallow lake facies,semi-deep lake facies,volcanic ash deposition and gravity flow facies.Obvious oil and gas shows occur in calcium sandstone and tuffite,which are the key exploration target.Pores in the sandstone reservoir consist of residual intergranular pores,intergranular expansion pores and dissolution pores.The pores in the tuffite reservoir are mainly composed of dissolution pores with minor intergranular pores and microfractures,and the surface rate of tuffite(12.05%) is higher than that of sandstone(9.13%).The genesis of porosity in the Lower Teng1 section includes compaction,dehydration,dissolution,devitrification of tuffite and tectonic stress.Tuffite in the target layer was subjected strong dissolution with loss of heavy rare earth.In the target layer,strong dissolution commonly occurs in the quartz-feldspathic, carbonate and tuff compositions in the tuffite and sandstone.Therefore,dissolution is the dominant factor in the pore formation in the target tight oil reservoir.