| The Taxinan palaeohigh of Tarim basin is a large scale palaeohigh of Palaeozonicera, it sinked since the Neogene Period. The Taxinan palaeohigh migrated from southto north during the Caledonian-Himalayan tectonic movement and the Maigaiti slopealso inclines from north of early stage to south. The formation,evolution of theTaxinan palaeohigh relates to the accumulation of oil-gas closely in the Maigaitislope. The study area has characteristics of many exploration layers, various oil andgas reservoir types, many types of reservoirs, several accumulation stages,accumulated in the early stage and adjusted later, producted oil in the early stage andcracked later. Against to the complex accumulating character, directed byaccumulating theroy of oil-gas bearing basin of multicycle superimpose, begin withdissect of reservoir discovered,analysis of typical failed well and the staticaccumulating factors,guaided by structural evolution of basin and migration ofTaxinan palaeohigh,started by main oil formation stage of source rock, tracing thedynamic accumulating process of creation, migration,accumulation,conservation,adjustment and destruction of oil-gas, thus shows oil-gasdistributed regulation in Maigaiti slope.During the anlysis of the structure background, the evolution of the Maigaitislope and it’s adjacent region has been divided into six stages:①Sinian period－early Ordovician Period-the stage of passive continent edge;②Middle-lateOrdovician period-Devonian period-the stage of active continent edge;③Carboniferous-early Permian period-the stage of passive continent edge;④LatePermian period-Triassic period-foreland basin period;⑤Jurassic period-OldTertiary-the stage of the inner continent depression;⑥Neogene period-Quaternary Period-the stage of revived foreland basin period. The reform of the basin has beendivided in to five stages; and seven important unconformable surfaces have beenidentified: Cambrian System/Precambrian system;Middle-Upper Ordovician/LowerOrdovician; Silurian system/Ordovician; Carboniferous System/Devonian System;Tertiary syetem/Permian System; Miocene series/lower Tertiary; Pliocene series/Miocene series,and the unconformable surface between the top surface of the buriedmountain of Upper Cambrian-Lower Ordovician and Silurian system, CarboniferousSystem, Devonian System which covered on it is the particular unconformable surfaceof Maigaiti slop,this is the main channel for the oil and gas that come fromMiddle-lower Cambrian system migrating.Using2D seismic data,this paper has analyzed formation,evolution and migrationof Taxinan palaeohigh systematically.Taxinan palaeohigh has experienced fourevolution stages.There are some great differences in the evolving and migratiing ofthe palaeohigh between in east and west Maigaiti slope,the differences played animportant role in controling evolving,migrating,and accumulating of oil-gas of theslope area.During the analyzing of dynamical accumulation process, it’s considered that thematching relationship between time and space domain in the key period have manyfactors in the area:①Matching Relationship between trap formating time and themain producting, expelling time of hydrocarbon;②among channel system consist offaults,unconformities, fractures and caves, during Caledonian-early Hercynain period,it is main the fractures and caves; before Middle-late Hercynain period, channelsystem is main consisted of unconformities, fractures and caves; in laterHercynain-Himalyan, faul, unconformities and fractures is the main pathway, butthere is the primary and secondary. There are many kinds of oil-gas channel:unconformity(before later Hercynain period), fault-unconformity in trap(laterhercynain and after it), unconfornity-fault-unconformity in trap(Himalayan period),pore-cave-fracture system;③Three accumulating periods: oil-gas accumulated anddissipated during the late Caledonian-early Hercyniant，accumulated and dissipatedduring the late Hercynian,migrated from multi-sources and adjusted intensivelyduring the Xishan.The effective accumulating times of modern pools are mainlyduring the Hercynian and Xishan movement.By studying migration and accumulating conditions of Taxinan palaeohigh,keycontrolling factors of main oil formation in Maigaiti slope have been analyzed,Ordovician oil-gas distribution is controlled by development of the reserviors.Thedevelopment of the buried hill crust reservior of Ordovician is controlled by lithologyof buried hill and reformation of the fractures. The reserviors are mainly fracturetypes, reseviors in east solpe is superior to that in west.The advantageous buried-hill reserviors mainly distribute in the area that faults and fractures developed,eapecially inthe north-east area that the faults developed.Analyzed the main control factors accumulation of the main oil-bearing series inMaigaiti slope, Ordovician oil-gas distribution is controled by development ofreservoir. Through to the Ordovician reservoir character analysis, it is considered thatthere are two reservoir type, Ordovician weathering crust limestone fracturereservoirs and inner dolomite fracture and cavity reservoirs. The reservoir predictionresults show that the limestone fracture reservoirs is more development in faultedstructure belt of Maigaiti slope, and the inner dolomite fracture and cavity reservoirsis more development in3D area.The study shows that distributional regulations of the oil-gas in Maigaiti slopeare:①multistage reservoir formation,early oil gas late;②oil distributes in west andsouth maigaiti slope,gas distributes in east and north slope;③distribution ofOrdovician oil-gas is controlled by Taxinan palaeohigh migration and reserviorsdevelopment;④oil-gas distribution is controlled by faults,and fault belts enrichoil-gas best;⑤The time that traps formed controls the distribution of the oil-gas;⑥Taxinan palaeohigh Migration controls reservoir distribution.Based on studying of accumulational conditions and distributional regulation ofoil-gas,two exploration directions have been suggested:①Exploratory domains ofCambrian－Ordovician: crust of thrusted belts in south-east of Mazhatage andMaigaiti slope;②Exploratory domains of multi-target horizons in west Maigaitislope. |
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