泌阳凹陷下第三系核桃园组砂岩成岩作用研究

DIAGENESIS OF THE LOWER TERTIARY HETAOYUAN FORMATION SANDSTONES IN THE BIYANG DEPRESSION

泌阳凹陷是我国东部的一个中新生代富含油气的小型断陷盆地,其中下第三系核桃园组砂岩为主要储集层。研究表明:核桃园组砂岩不同矿物成分含量变化较大,岩石类型丰富,其主要特点是不稳定矿物含量较高。凹陷内不同区域核桃园组砂岩的成岩作用历史也有很大的不同,双河油田的砂岩成岩作用要比侯庄地区的砂岩复杂得多。它们的孔隙类型也大不一样,双河油田砂岩以次生孔隙为主,侯庄地区的砂岩以原生孔隙为主,而油气的运聚与砂岩中次生孔隙的形成关系极为密切。

The Biyang depression is a down-faulted lake basin filled with Tertiary continental deposits. It is one of the basins containing the largest petroleum reserves per unit area in China.The Hetaoyuan Formation sandstones are the main reservoir rocks,and the oil shales and mudstones of this age are the main hydrocarbon source rocks in the basin. Petrographic study shows that the Hetaoyuan Formation sandstones have highly variable mineral composition,including fine-grained to coarse-grained,poorly-sorted to well-sorted quartzo -feldspathic sandstone,arkose,lithic arkose and feldapathic litharenite.The diagenesis of the Hetaoyuan Formation sandstones varies greatly from place to place in the basin.Diagenetic minerals include relatively early-formed grain-coating chlorite,quartz and feldspar overgrowths,and poikilitic carbonate cements and relatively late-formed pore-filling barite,pyrite,kaolinite,smectite and euhedral calcite crystals.The porosity in the Hetaoyuan Formation sandstones is also quite variable,ranging from 0 to 29%;most of the pores are secondary in origin.Porosity reduction is due to compaction and authigenic mineral cementation,while enhancement of porosity resulted from the dissolution of both carbonate cements and unstable framework grains.Sandstones with secondary pores are main hydrocarbon reservoir rocks.