Study On Reservoir Characteristics Of Zhangxia Formation And Sanshanzi Formation In The Southeast 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 northeast of Ordos Basin. Though several wells have been drilled and reached Cambrian System, taken as a whole, the exploration extent of Cambrian System in the northeast of Ordos Basin is pretty low. So far industrial gas fields haven’t been discovered in carbonate rocks of 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 Zhangxia and Majiagou Formation in upper and middle 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:Upper and middle Cambrian system in the northeast of Ordos Basin mainly develops powder-fine crystalline dolomites, fine-microcrystalline dolomitic limestones, sparite-microcrystalline bioclastic calcarenite, microcrystalline limestones, micritemicrocrystalline silty muddy dolomites, oolite limestones and fine crystalline residual calcarenite, etc.The constructive diagenesis of study area’s reservoirs are mainly dolomitization, karstification(dissolution); the destructive diagenesis are mainly compaction-pressolution, cementation, cavity filling, metasomatism, recrystallization,etc.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.Pore types are mainly intracrystalline pores, intracrystalline solution pores and a little dissolved intragranular pores, dissolved intergranular pores, dissolution fractures and tectonic fractures. The main reservoir space is various secondary pores while the main flowing channels are various fractures.The main controlling factors of reservoir development are sedimentary facies, dolomitization, dissolution and tectonic fracture.