| 5-5th sub-member of Majiagou formation of Ordovician in the Eastern of SuligeGas Field is the new horizon for gas exploration in this area. With the breakthrough ofexploration to mid-formation stratum, the study of reserevoir of5-5th sub-member ofMajiagou formation is developed gradually. Based on the former researches, thisthesis takes sedimentary petrology, sedimentary geochemistry and reservoir geologyas its theoretical principles. It analyzes polystomatous drilling core, such as itsdescription, sample analysis and scanning electron microscope. It also combineslogging information and analysis of porosity and permeability to study thesedimentary facies, diagenesis and reservoir characteristics. In addition, the thesistries to research into genetic model and reservoir controlling factor of the dolomiteand gains much result on research horizon.Basin of5-5th sub-member of Majiagou formation is hot and drought and theincrement of fresh water are small. In addition, its evaporation is strong which makesthe sea of survey region be a low energy depositional environment of shallow water,high salinization and easily exposure. It also develops supralittoral zone, intertidalzone and sublittoral zone. Based on the lithologic assemble, sedimentary facies isulteriorly divided into eight sedimentary micro-facies.To combine the observation of thin slice with cathodeluminescence and scanningelectron microscope, diagenetic stage is divided into four strike-slips in total. Themain diagenesis types of the5-5th sub-member of Majiagou formation are dolomization, compaction, pressure solution, recrystallization, dissolution andremoving ointment effect. Among them, dolomization, removing ointment effect anddissolution are good for formation and development of crack. They are constructivediagenesis.The extent of porosity of5-5th sub-member of Majiagou formation in researchregion is about2-9%，and the research region belongs to low permeability layer. Thecrack types of5-5th sub-member of Majiagou formation are intercrystal porosity,bird’s-eye pore, plaster mole hole, intercrystal dissolution pore, dissolution pore,dissolution corrosion and so on. Among them, dissolution pore, dissolution corrosionand intercrystal porosity are the main reservoir space type in the research region. Thereservoir of powder crystal dolostone is the most advanced one. The secondaryporosity, secondary lacune and secondary hole which are formed in exodiageneticstage and buried diagenetic stage are the key factors which can form good reservoir ornot. In addition, the development of structural fracture and how well its preservationalso is the key factors. The subsequent structural fracture improves thestorage-percolation system. By the geochemical prospecting method of X-diffraction,trace element and carbon and oxygen isotope, the genetic model of dolostone inresearch region is divided into two kinds: penecontemporaneous dolostone model andburial dolostone model. Compared with penecontemporaneous dolostone, burialdolostone has rough kernel, high degree of order and high extent of porosity. It alsohas the characteristics of high Mn and Fe, low Sr and Na, low C and O isotope.Crystal grain dolostone by burial genetic cause of formation becomes the mainlithology of dolostone reservoir. However, the storage of gas reservoir in researchregion is directly connected with the thickness of dolostone. In addition, precipitationfacies, diagenesis and tectonization control together, and precipitation micro-faciesand diagenesis are key factors to the development of good reservoir. However, theperfect source-reservoir-seal assemblage is essential condition of deposits. |
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