摘要
Abstract
Longhupao Field Area is located in the Songliao Basin. The Gaotaizi Oil Bed belongs to the second and thirdsections of Lower Cretaceous Qingshanqkou Formation in Longhupao Field Area. The reservoir rocks mainly de-posited in distributary month bar and front thin sand sheet of lacustrine delta. The current geotemperature is 65 to90℃, and the geothermal gradient is 3.9℃/100 m for Gaotarzi Oil Layer in Longhupao Field Area.
Most reservoir rocks are lithic arkosic siltstone. The framework grains consist of 80％ to 90％ of reservoirrocks by volume. The framework composition is 20％～37％ quartz, 23％～41％ feldspar, and 14％～35％ lithicrock fragments. Most rock fragments are of sedimentary and volcanic rocks. Sometimes carbonate particles are pre-sent. The carbonate particles, which is mainly ostracodes skeletons, are present in minor to trace amount, makingup usually less than 5％ of reservoir rocks. All clasticg rains are less than 0.5 mm in diam are believed to have.
Compaction, cementation, dissolution, change of clay minerals, and displacement modified the sediments.
The rocks are buried in 1 537～2 402 m. Compaction produled influence on sediments to a medium ou highdegree because of fine clastic grain, poor sorting, some content of matrix and plastic carbonate particles. As a re-sult of compaction, grain contacts are dominantly of long and concavo- convex types, and reduction of originalpores is obvious. Compaction caused loss of 61.32％ to 78.59％. Calcite is the most abundant authigenic minerals.Authigenic days are rarely present Authigenic quartz is comrnon, but present in trace amount. Authigenic feldsparis much less than authigenic quartz. Most calcite, among which clastic grains float, occurs in poikilotopic cement.values of calcite cement range from 1. 358‰ to 7. 165‰ and - 21. 428‰ to - 11. 662‰, andaverage 2. 958‰ and - 19. 351‰ (PDB), respectively. Thevalues of calcite cement change irregu-larly with depth, suggesting that burial diagenesis only slightly effect on calcite cement. The low values and nar-row range ofsuggest that calcite cement formed early before maturation of organic material. Feldspar and intermediate/basic volcanic rock fragments are dissolved in different degree, forming variouswpes of pores. Dissolution of quartz is often present, but weak, and only small dissolution pits are present in rimsof quartz grains. Dissolution of calcite is also weak, and occurs only in cement of ostracoda coelomata. Illite is mainclay mineral, and chlorite is present only in minor amount. Kaolinite basically disappeared. Smectite mostlychanged to illite or mixed - layered illite/smectite.Vitrinite reflectance (Ro) rages from 0.61％ to 1. 39％, sug-gesting that organic material has already matured.
Ancient geotemperature is higher than current geotemperature. Diagenesis proceeded to middle late stage.Compaction and cementation are the principle processes contributing to reduction of porosity. Dissolution offeldspar and intermediate/basic volcanic rock fragments made porosity increase to some degree. Compaction andcalcite cementation prevented growth of authigenic quartz and formation of secondary porosity zones. Partialpreservation of original pores and development of feldspar dissolution are due to framework consisting of clasticgrains and calcite cement of early precipitation.
关键词
储集岩成岩作用孔隙演化Key words
reservoir rocks diagenesis porosity modification分类
天文与地球科学
