Research On Reservoir Characterization And Key Controlling Factors Of Middle-lower Ordovician Carbonate Reservoir In Bachu-maigaiti Region

Based on the comprehensive analysis of drilling well information, coreinformation, thin section analysis information and geochemical test information, andcombined with the theory of reservoir geology, reservoir geochemistry, petroleumgeology and sedimentary facies etc, this paper conducted a series of studies on thecharacteristics of sedimentary facies, sedimentary mode, reservoir characteristics andthe key controlling factors of Middle-Lower Ordovician carbonate reservoir inBachu-Maigaiti region. The paper summarizes the features of sedimentary facies,depositional model, rock characteristics, and the formation mechanism of reservoir.Through the research, mainly made the following points:①The sedimentaryenvironment of Early Ordovician in Tarim basin has diversity, Bachu-Maigaiti regionmain has restricted platform facies, open platform facies, platform marginal facies,slope and shelf facies from the northeast to southwest, the platform marginal isrimmed type;②Through the core observation, thin section identification and loggingdata analysis; the types of reservoir space including pore, cave and fracture, thecombination types of reservoir space main including intercrystalline pore-dissolutionpore-crack-cave, crack-dissolution pore, crack-dissolution pore-cave;③Cracksystem has an important significance to improve reservoir property of Middle-LowerOrdovician carbonate reservoir in Bachu-Maigaiti region; The middle and lowerOrdovician strata Bachu-Maigaiti region experience Hercynian tectonic movement,Indosinian tectonic movement, the Yanshan tectonic movement, Himalayan tectonicmovement, formed millions of fault and fracture zone, some fracture only developedin single layer or distributed in a small area, and some faults run through multilayerstrata or distributed in many areas of the basin, these breaks are interwoven to formdifferent fault system, and these fracture system greatly improve the reservoirproperty.④The Middle-Lower Ordovician carbonate stratum in Bachu-Maigaitiregion subjected to the reform of multiple karstifications during geological history, themain karstification is weathered crust karstification, followed by burial karstification and syngenetic karstification. The weathered crust karstification has an importantsignificance to improve reservoir property of Middle-Lower Ordovician carbonatereservoir in Bachu-Maigaiti region, while the burial karstification and syngenetickarstification have a lesser impact on reservoir property;⑤The most importantdolomitization for the dolomite of Middle-Lower Ordovician in Bachu-Maigaitiregion is burial dolomitization, secondly is penetration reflux dolomitization, then isevaporative pumping dolomitization and hydrothermal dolomitization;⑥Dedolomitisation has a positive effect on reservoir property. On one hand, thedolomite grain that occur dedolomitisation keeps the original crystal morphology, theporosity of dolomite will not reduce for the dedolomitisation; on the other hand, partmagnesium ion of the dolomite that occur dedolomitisation will separate out from thegrain, these magnesium ion can participate in the dolomitization of the residual ashrock, if so, these magnesium ion have important significance on burial dolomitization.