羌塘盆地角木日地区中、下二叠统碳酸盐岩成岩作用及储集物性特征

Diagenesis and reservoir physical property of carbonate rock in middle and lower Permian in Jiaomuri of Qiangtang basin

运用岩石薄片、铸体薄片、扫描电镜、阴极发光和物性测试等手段,详细研究了羌塘盆地角木日地区羌资5井中二叠统龙格组、下二叠统展金组碳酸盐岩的岩石学特征及储层物性。岩石类型主要为泥晶灰岩、砂屑灰岩、细晶白云岩及粉晶白云岩,储集空间主要包括晶间孔、次生溶孔、构造缝和溶蚀缝。灰岩孔隙度平均值为0.40%,渗透率平均值为0.016×10-3μm2;白云岩孔隙度平均值为2.73%,渗透率平均值为0.012×10-3μm2,基本上属于低孔低渗致密储集层。综合评价了成岩作用对储层物性的影响,通过对比分析区内龙格组灰岩与展金组白云岩的成岩作用及孔渗参数,认为白云石化作用能够保持甚至提高原有岩石的孔隙度,而去白云石化作用会导致孔隙堵塞,对储层的形成起破坏作用。

Relying on the analytical techniques as rock thin section, cast section , SEM, cathodoluminescence, conventional petrophysical property, etc. , a detailed description of the lithologic and reservoir physical properties of middle and lower Permian carbonate rock is given inside the Qiangzi tang basin . The study shows that the carbonate reservoir is dominated by stone, fine dolomite and silty dolomite. The type of reservoir spaces includes -5 borehole of Jiaomuri area Qiangmicritic limestone, sand-clastic limepores （intercrystalline pore and secondary solution pore） and fissures （ structural fracture and solution fissure）. The average porosity of limestone is 0. 40%. The average permeability is 0. 016 ×10^-3μm^2. The average porosity of dolomite is 2. 73%. The average permeability is 0. 012 ×10^-3μm^2. The interstitial physical property parameters show both limestone and dolomite belonging to a dense reservoir with low porosity and low permeability. This paper also discusses the effects of different kinds of diagenesis on the improvement of the reservoir physical properties on limestone and dolomite. According to the study the pores can be well preserved and even improved due to dolomization. However dedolomitization occludes the pores,which exerts great unfavorable effects on the reservoir.