Study On Reservoir Characteristics Of Sanshanzi Formation Dolomite In The South Of Ordos Basin

As an important hydrocarbon exploration area in China, which locates in the west of North China Platform, numerous giant and supergiant oil and gas fields have been discovered in Ordos Basin in recent years. Carbonate rocks of Lower Paleozoic have great exploration potentials. Predecessors' research concentrates in the Majiagou Formation of Ordovician System in lower Paleozoic and therefore the study on Cambrian System is relatively imperfect. The study area is situated in the south of Ordos Basin. Though several wells have been drilled and reached Sanshanzi of Cambrian System, taken as a whole, the exploration extent of Cambrian System in the south of Ordos Basin is pretty low. So far industrial gas fields haven't been discovered in carbonate rocks of Sanshanzi in Cambrian System and research on the hydrocarbon geological conditions is still in the initial stage, therefore the study on Cambrian reservoirs' characters is very significant for the hydrocarbon exploration, such as petrology characters, reservoir space types and physical characters. This thesis targets at the reservoirs of Sanshanzi Formation in upper Cambrian, takes the study approaches of field geological investigation, drilling cores observation and description, usual and casting thin sections observation and appraisal, and porosity and permeability test, states the petrology characters, pores evolutionary characters, types and evolutionary phase of diagenesis and figures out the controlling factors of reservoirs. The discoveries in this thesis are as follows:In Sanshanzi period of the study area, appearing ancient central uplift. tidal flat, open- restricted platform, platform margin slope and shelf which surrounded by ancient central uplift turn outward spread. The main lithological strata are powder-fine crystalline dolomite, fine- in the dolomite, dolomite sand debris, gravel crumbs dolomite, oolitic dolomite and so on.Through studying the rock diagenetic evolution of Sanshanzi dolomite reservoir of study area that dolomitization, dissolution as the main constructive diagenesis. Compaction pressure solution, cementation, metasomatism, filling the role, recrystallization and so is not conducive to the development of the reservoir, it is determined that the destructive diagenesis.Based on the types of constructive and destructive diagenesis, and united with the change of burial deepness in the diagenesis, this thesis divides the diagenesis into four evolutionary stage: penecontemporaneous stage, epidiagenesis stage, early diagenesis and late diagenesis stage.The main controlling factors of reservoir development are sedimentary facies, dolomitization, dissolution and tectonic fracture.