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Study On The Origin And Reservoir Characteristics Of Dolostones Of Majiagou Formation 4 Of The Ordovician In Ordos Basin

Posted on:1996-04-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y S ZhangFull Text:PDF
GTID:1100360218456729Subject:Sedimentology
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This dissertatiom, Study on the Origin and Reservoir Charactaristics of Dolostones of Majiagou Formation 4 of the Ordovician in Ordos Basin, is the third grade project, Industrial Mapping of Dolostone Reservoir Bodies and Traps of Majiagou Formation 4 of the Ordovician in the Middle and South Areas of Ordos Basin, which is belong to the major general project of CNPC, Industrial Mapping of Petrography, Sedimentary Facies and Reservoir Bodies of the Palaeozoic in Ordos and its Peripheral Regions, that is undertaken by Prof.Feng Zengzhao, Who is working in University of Petroleum, Beijing.Under the guidance of the theories of sedimentology and geological evolution, based on sedimentary and diagenetic analysis, combined with log and seismic interpretation, standing upon the first -hand qualitative and quantitative data especially the quantitative data from single section study, the division and correlation of Majiagou Group of the whole region were discussed. The origin and reservoir charactaristies of massive dolostones of Majiagou Formatian 4 Were probed. The types of reserving- capping combinations of Majiagou Formation 4 and the.lower member of Majiagou Formation 5 were systematically summed up. Following conclusions were obstained.1. According to sedimentary cycles that were displayed with the shape of the natural gamma log that reflects the change of mud abundance, the division of 6 units of Majiagou Group could be correlated from middle and east Ordos to West or South Ordos.2.According to the crystal boundary, the dolostones of Majiagou Formation 4 were divided into normal-shaped crystalline dolostone and wheat-shaped crystanine dolostone. According to crystalline size, the dolostones were divided into mud- sized crystalline dolostone, mud- silt- sized crystalline dolostone, coarse - silt- sized crystalline dolostone, very fine crystalline dolostone, fine crystalline dolostone, medium crystalline dolostone, dolostone with relict textures, different grade crystalline dolostone. The dolostones can be divided into penecontemporaneous dolostones and post-penecontemporaneous dolostones according to their origin. Penecontemporaneous dolostones include only dolomitic flat type dolostone. Post-penecontemporaneous dolostones include burial thermal water dolostones and burial thermal water abundant with sulfate ions dolostones. For the first time, the homogenization temperatures of inclusions of fine crystalline dolomites in dolostone bodies of Majiagou FormAtion 4 were determinated. The fact that the temperature is above 104℃proved that the formation mechanism of thick massive dolostone of Majigou Formation 4 is burial therrnal water dolomitization.3.Through the study on the reservoir pore space and reservoir characteristics of massive dolostone of Majiagou Formation 4, it is concluded that the major reservoir space is the secondary pores such as intercrystal pores and intercrystal solution pores. The main percolating passages are intercrystal gaps, bedding and network stylolites, polygenetic fractures and microfractures. The principal type of reservoirs is fracture-pore reservoirs.4.The reservoirs of dolostone bodies of Majiagou Formation 4 are of multilayer distribution vertically. The macroscopic distribution was controlled by the condition of lithofacies paleogeography. The last determinate factors of the formation of multilayer reservoirs are thermal water dolomitization and thermal water solution.5.The relationship between porosity and the type of dolostones is that the best is medium crystalline dolostone; the second is fine crystalline dolostones, most of them with relict textures;the third is very fine crystalline dolostones and the worst is coarse-silt- sized crystlline dolostones.thus the target reservoir rocks are fine -medium crystalline dolostones with relict textures that their protolithes are related with bank facies.6.The dolostone bodies of Majiagou Formation 4 were divided into zone A, B and C from west to east. Zone A is confined between Dingtan 1 Well and Shah 56 Well, and the reservoirs are typeⅡ; Zone B is confined between Shah 56 Well and Qican 1 Well, and the reservoirs are typeⅢ; Zone C is comfined between Qican 1 Well and the east rim of the basin, and the reservoirs are typeⅣ.7.There are two types of reserving-capping combinations of Majiagou Formation 4. They are M4(reserving)- M4(capping) and M4 (reserving)- M510(capping). The reservoirs are dolostone bodies with different size. The type of traps is a kind of lithologic trap that is self- generating, self-reserving, top- capped and lateral- closed. Besides,there are also two reserving-capping combination in the lower member of Majiagou Formation 5. They are M59(reserving)- M58 (capping) and M57(reserving)- M56(capping), the type of traps is also a kind of lithologic trap which is self-generating, self-reserving, tap-capped and laterral-closed. These two combination should be paid great attention too.8.The important place of natural gas exploration of Majiagou Group in Ordos Basin should still be located in the range of the Middle Gas Field and its west side next. The target reservoirs are Majiagou Formation 4, M59 and M57 of the lower member of Majiagou Formation 5.
Keywords/Search Tags:Characteristics
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