Diagenesis Of Dense Reservoirs In Intra - Continental Rift Basins

The tight reservoirs of Permian Lucaogou formation of Jimsar sag in eastern part of the Junggar basin of Xinjiang formed in a rift-fault depression of salt lake with stong volcanic activities,and the mantle derived magma hydrothermal fluid participates in this sedimentary process,with the characteristics of high thermal evolution conditions, excess pore pressure, high geotemperature,fractures and rich in organic matter of rocks. The particular sedimentary environment of Lucaogou formation lead to the special dia-genesis and diagenetic processes of Lucaogou formation,that is alkaline,acidic fluid alt-ernate diagenesis,and at the same time,it has an important impact on porosity evolutio-n of diagenesis and tight oil formation.By the observation of the large number of cor-es and thin sections,combining with X-ray diffraction,electronmicroprobe, laser Raman, scanning electron microscopy,rock-mineralogy and geochemistry and experimental analy sis of vitrinite ref-lectance,and aiming at the tight reservoir with alkaline volcanic mat-rial involved in the salt lake basin sedimentary characteristicsin Permian Lucaogou for-mation,we study the main rock types characteristics of diagenesis of main rock types (tuff rocks and tuffaceous rocks) and pore evolution,and establish a diagenetic sequen-ce,namely alkali corrosion of early quartzand feldspar,analcime â†'early lowmaturity of organic matter (hydrocarbon filling),resistance to compactionâ†'acid corrosion feldspar a-nd carbonatesâ†'sparry calcite cementation,calcite replacing feldspar,dolomite,ankerite ce-mentationâ†'rock salt â†'irondolomite metasomatic calcite;The subject of Lucaogou form-ation is in a stage of A diagenesis,the organic matter in some layers may form low-mature oil in early diagenesis with the influence of the heat.The low-mature oil enters into the pores and inhabit the compaction,not only retaining the original holes,but al-so producing corrosion and forming secondary pores,and expanding storage space;The rock types(for example:Tuff,tuffaceous rock classmicritic dolomite) of high content of tuffaceous develop remaining intergranular pores+corrosion and intergranular holes+inte-rgranul arholes and icrocracks,and the micritic dolomite containing tuffaceousor purified micritic dolomite develop dolomiteintercrystal porosity,pressure solution seams and stitc hingwire;With the control of many factors such as alkaline and acidic fluid alternate reconstruction,rock-mineralasse-mlage and petrophysical of rocks,the formation of seco-ndary pore have chracteristics of multiple stackingin the study area,and the enabling p orestrips preferably coincide with the upper and lower oil layers rich in tuffmaterial in Permian Lucaogou formation of Jimusaer sag.