鄂尔多斯盆地延长组致密砂岩储层微观孔喉特征差异及其成因

为分析不同沉积与成岩作用改造下致密砂岩储层的孔喉类型及其参数差异,利用物性、铸体薄片、扫描电镜、恒速压汞、图像粒度与X衍射实验结果,对比了鄂尔多斯盆地合水地区延长组长8储层和薛岔地区延长组长6储层的孔喉类型,定量评价了孔喉参数,揭示了形成原因。结果表明,合水地区长8储层孔隙更为发育,粒间孔、溶蚀孔、晶间孔和微孔、弱压实成因缩颈状喉道和溶蚀成因、粘土胶结成因管束状喉道含量高;薛岔地区长6储层的孔隙类型少且发育程度较差,压实成因片状、弯片状喉道含量高。两个区块的孔隙参数差异小,喉道参数差异大,前者大喉道更为发育,喉道差异大,孔喉比大,对渗透率起贡献的喉道分布范围更宽。相同渗透率条件下,前者的平均喉道半径、主流喉道半径和孔喉比大于后者。沉积水动力条件、粒度、碎屑组分、填隙物、成岩作用类型及其改造程度是两个研究区孔隙发育程度不同、喉道类型差异和孔喉参数表现出不同特征的主要原因。

Differences and origin of micro-pore throat characteristics for tight sandstone reservoir of Yanchang Formation,Ordos Basin

By adopting quantitative evaluation of pore throat parameters under different depositional and diagenetic conditions,and with reference to the test results of physical property,casting section,SEM,constant speed mercury injection,particle size and X diffraction,the pore throat types of Chang 8 reservoir of Heshui Region and Chang 6 reservoir of Xuecha Region in Ordos Basin were analyzed,contrasted and reasons for how they were formed were revealed.Results show that the pores are better developed in Chang 8 reservoir in Heshui Region,with a high quantity of intergranular,dissolved,intercrystalline and micro pores,as well as necking down throats with weak compaction,tube-shaped throats with dissolution and clay cementation; while pores are less developed in terms of both types and range in Chang 6 reservoir of Xuecha Region,with high quantity of lamellar and curved lamellar throats with compaction.For the two studied reservoirs,the differences in pore parameters are not as significant as those in throat parameters.Compared to Chang 6 reservoir,Chang 8 reservoir developed better and larger throats with apparent differences,bigger pore-throat ratio,and wider distribution of throats that are conducive to permeability.Under the condition of same permeability,the average throat radius,main flow throat radius and pore-throat ratio of Chang 8 reservoir are all bigger than those of Chang 6 reservoir.It can be concluded that the hydrodynamic conditions in sediments,particle size,detrital component,interstitials,diagenesis types and their respective influence degrees,are the main reasons for the differences in the development of pores,throat types and pore throat parameters.