Study On Sedimentary Micro-facies Of Majiagou 5 Member Of Ordovician And The Impact Of Gypsum Deposit On The Formation Of Oil & Gas Reservoir In Jingbian Area

Combined with the principle of sedimentory of carbonate,sequence stratigraphy and lithofacies and paleogeography etc, Majiagou 5 member was researched in the studying area. According to the information and data we collected in local area and the cores observation, slices analysis and logging data getting from our laboratory, we describe characteristic of petrology and the sedimentary structures. Studying on the plane distribution characteristics and the evolvement pattern of microfacies in this area, the depositional model of Majiagou 5₄¹ sub-member in north Jingbian area was established and the favorable sub-faces areas of Majiagou 5₄¹ reservoirs was proposed. The issues of sedimentary facies, microfacies, characteristics of gypsum salt rock and under-salt reservoir have been focus on in this thesis. At last, we get some conclusions:According to characteristics of microfacies in this area, Majiagou 5 member was divide into 8 sub-facies : (1) argillaceous dolostone of upper tidal flat, (2) dolostone of upper tidal flat, (3) evaporative gypsum of upper tidal flat, (4) limy dolostone of upper tidal flat, (5) argillaceous limestones of upper tidal flat, (6)limestone of middle tidal flat, (7) dolostone of upper tidal flat , (8) limy dolostone of upper tidal flat.23 lithology microfacies could be reduced to 10 microfacies types: (1 ) microcrystal dolostone(2 )microcrystal-powder dolostone(3)grained clastic dolostone (4) microcrystal-powder limy dolostone (5) powder-aplite dolomited limestone (6) micrite limestones (7) marlite (8) argillaceous dolostone (9) gypsum rock and gypsum breccia (10) plaster dolostoneMapping the lithofacies -paleogeographic map of Majiagou 5₁ to Majiagou 5₅ .Contrasting the horizontal diversification of sedimentary facies to Majiagou 5₄¹ sub-member, we draw 8 microfacies section with wells and mapping the lithofacies -paleogeographic map with predominance mapping methods. We believe the water depth should be increase , and argillaceous dolostone of upper tidal flat, dolostone of upper tidal flat, limy dolostone of upper tidal flat and limestone of middle tidal flat distribute in turn from north-west to south-east in studying area. The depositional model of Majiagou 5₄¹ sub-member in north Jingbian area was established and thefavorable sub-faces areas of Majiagou 5₄¹ reservoirs was proposed.Characteristics of gypsum salt rock are analyzed in this area. In the line with the research actuality we affirm that the cause of gypsum salt rock formation is related to environment of evaporation.in the end , we the distribution of under-salt reservoir to Majiagou member have been summarized, including it's physical property, such as characteristics of lithology, porosity, porosity , pore types and pore structure.