A Research Of The Ordovician Hydrothermal Geological Processes And Its Reservoir Significance In South Of Tahe Oilfield

In the south of the Sichuan Basin,the Cambrian strate possesses the geological conditions of forming high quality reservoirs. But at present, comparing with the great hydrocarbon discovery of the Anyue gas field in the middle of the Sichuan Basin, the exploration achievements of the the Cambrian Strate in the south of the Sichuan Basin is not obvious. Through this study I hope that it can enriche the evolution theories of the Cambrian carbonate reservoirs in the south the Sichuan Basin and accelerate the pace of hydrocarbon exploration in this area.On the basis of the seniors research, the article makes a research which selects Cambrian carbonate reservoirs in the south the Sichuan Basin as the research object, guided by relative theories of sedimentary petrology, reservoir geology,geochemistry, diagenesis, to microscopic observation as the foundation, and combined with geochemical analysis of cathode luminescence, degree of order, carbon and oxygen isotopes, rare earth element, microelement. The research is aims at explaining the geochemical characteristics and the formation mechanism of the Cambrian reservoirs in the south the Sichuan Basin. The specific research results are listed as following:(1)To observe carbonate rock samples and thin section of the three profile, reservoir space types includes: intragranular dissolved pore,intergranular dissolved pore,moldic pore, intercrystalline solution pores, intergranular pores, paste solution pores, dissolved pores, fractures and other. The reservoir is mainly dolomite reservoir,including grain dolomite reservoir of bank facies, dissolved pore-cavity dolomite reservoirs, gypsum dissolved hole reservoir.(2)The study area Carbonate Diagenesis is relatively complex, the diagenesis mainly includes: submarine cementation, dolomitization, dissolution, compaction pressure solution, fracturing and packing and so on. The storage space of reservoirs in the study area mainly through the carbonate deposition, cementation, contemporaneous dissolution, syngenetic dolomitization, buried compaction, burial dolomitization, buried hydrothermal dissolution; filling(asphalt and hydrothermal minerals), organic acid dissolution, tectonic rupture surface deformation and other diagenesis.(3)Geochemical identification marks of various types of dolomite are established through geochemical analysis. Microcrystalline dolomite and powder-fine crystalline dolomite cathodoluminescence shows hair orange light, 18 O mean values were-5.58 per thousand,-6.41 per thousand, which is relatively high,The REE distribution pattern is characterized by weak accumulation of HREE and weak loss of LREE,. Eu and Ce show negative anomalies. Fine crystalline dolomite ordered degree was 0.56 ~ 0.68, 18 O values was-6.85‰ ~-7.2‰, and the average of ?REE is relatively low(18.75×10-6), Rare earth elements with depleted migration Eu and Ce show negative anomalies. The different occurrence of saddle dolomite inclusions temperature distribution range is wide, and rare earth elements Eu show positive and negative anomaly characteristics, revealing the cause of the different shape saddle dolomite is different.(4)Based on the geochemical data of dolomite, the formation mechanism and model of various types of dolomite are analyzed, and two types of saddle dolomite, which are hydrothermal origin and non hydrothermal origin, are put forward. Based on the geochemical data of dolomite, the formation mechanism and model of various types of dolomite are analyzed, and two types of saddle dolomite, which are hydrothermal origin and non hydrothermal origin, are put forward. microcrystalline dolomite and powder fine crystal dolomite are the result of the evaporation pump mode and the seepage reflux mode in the super saline water environment. Fine grained euhedral dolomite is the result of the burial dolomitization. the structural fractures in the saddle dolomite is mainly product of hydrothermal dolomitization, saddle dolomite in the gypsum dissolved pore cave and solution vug may is due to inherited the optical characteristics of the original plaster or absorb too much sulphur ion and saddle dolomite undulatory extinction and the crystal curved surface characteristics.(5)To observe profile samples and drilling take core, thin section,based on the characteristics, found in the region there are four stages of dissolution: syngenetic meteoric water dissolution, hydrothermal dissolution, buried organic acid dissolution, surface meteoric water dissolution.(6)The multiphase dolomitization and dissolution are the main controlling factors of reservoir formation. Syngenetic meteoric water dissolution of intergranular dissolved the intergranular pore and intragranular dissolved pore, shallow burial dolomitization leads to intergranular pore development, the development of the corrosion and dissolution pores along the joint of the hydrothermal solution, organic acid dissolution formed dissolved pore and dissolved pores, the third phase of the rupture role in the formation of fractures is the main permeability space of reservoir.