The Structurally Feature And Petroleum Geologic Evaluation In The Southeast Region Of Tarim Basin

The southeast part of Tarim Basin consists of the Southeast Tarim Depression and South Tarim Uplift,which is surrounded by Cherchen Fracture as north boundary,Aerjin,Kunlun Mountains as the south, Cele as the west and Ruoqiang as the east.The area is about 1000km long from east to west and 100km wide from south to north.There are four prospecting wells in the study area.Amongthem, the well Ruocan1 which locates in the Washixia sag has gained the well gas survey indication,the other wells such as the well Luobei1 and Mincan1,which locate in the Luobuzhuang salient and Minfeng sag respectively, have drilled to the Precambrian basement below the sea level 2229m and 4015m which passes through Palegene and Carboniferous ,but no gas survey indication.The paper is one part of the《The exploration targets'selection and appraisement in new region and domain of Tarim Basin》which is the project of BGP in 2005.The paper applied the advanced acknowledge about petroleum geology,structural geology,seismic survey theory and comprehensive evaluation methods to reveal the strata distribution,basin characteristics,tectonic evolution and fracture characteristics of the study area. In this basis, we marked off the secondary-order structure zones and pointed out the main blocks and tectonic zones of the next step's exploration.The result of the paper will provide the basal study results and significent referrence for the oil and gas exploration of the study area.The study results have basilicly theoretical and practical significence. 1,The study area's strata distribution characteristicsThe southeast part of Tarim Basin is a uplift zone of Precambrian metamorphic basement.The stratigraphic section don't have outcrops from the surface in this area. Prospecting wells drilled through the Proterozoic,Carboniferous,Permian,Jurassic,Paleogene,Neogene and Quaternary. The stratum was the deepest in Jurassic but lost in Silurian,Devonian,Triassic and Cretaceous.2,The study area's structural featureSoutheast Tarim Depression conbined with South Tarim Uplift is called by a joint name"Southeast Tarim Uplift". According to the tectonic framework and the defference of strata distribution and tectonic evolution characteristics, Southeast Tarim Uplift is recompartmentalized four secondary-order structure units.From west to east ,they are Minfeng sag,Qiemo salient,Washixia sag and Luobuzhuang salient.The stress which formed the Southeast Tarim Depression has mainly three stages.The stress roots in the collision and tension of Southeast Tarim Depression and each south blocks.In Late Caledonian-early Hercynian period,Tarim basin block collided with Middle Kunlun block to close the Kudi Ocean and form the palaeo Aerjin fracture and palaeo Cheerchen fracture. The Southeast Tarim Depression derived a series of NE-SW trending thrust fractures.The front of thrust fold belt locates the line of Tanggu1-Gucheng4-Luobei1 wells nowadays;In Hercynian-early Indosinian,Tarim block and south blocks was in the movement of divergence. The Southeast Tarim Depression formed a series of NE-SW trending tensional fractures on the action of the stress.In Cretaceous,the collision of Tarim block and south Qiangtang block make the tensional fractures formed in the early period reversed to the thrust fractures.In late Himalayan,due to the Indian plate collision,Aerjin fracture reversed to a big left lateral slip fracture.In this period,the strike-slip fracture has a little effectiont to the preformed fracture system. In the effection of three stages mainly stress, The Southeast Tarim Depression formed the nowadays two stages fractures.They are early tensional fractures system in Hercynian-early Indosinian period and transpressional fractures system in late Indo Chinese epoch-Yanshan period.the fractures system were mainly the NE-SW trending,associating a series of parallel minor fractures.Tarim Basin is a large composited and superimposed basin.The tectonic evolution in the southeast part of Tarim Basin can be roughly divided into five periods including①late Eopaleozoic peripheral foreland compressive inversion period;②Carboniferous-early Permian craton-margin depression period;③late Permian-Triassic post arc forland thrust decken upthrow period;④Jurassic-Paleogene intracontinental downfaulted-depression basin period;⑤Neogene-nowadays strike slip tensional basin period.3,qualification of oil geologyThere are two sets of generating rocks in the study area.According to the outcrop and seismic data,it is speculated that in the Minfeng sag Jurassic generating rocks is mainly distributed and Carboniferous rocks is likely to have oil-forming conditions in certain cxtent.Outcrops and drilled wells show that there are four sets of revervior seal assemblages in lengthways of the southeast part of Tarim Basin .The sets of revervior seal assemblages in Jurassic is the most important assemblage.There are two sets of roof rocks distribute in the southeast part of Tarim Basin: Paleogene mudstone and Middle Jurassic gray mudstone.Several sets of revervior beds and roof rocks were developed in the southeast part of Tarim Basin.They are compartmentalized seven sets of revervior seal assemblages from Carboniferous to Paleogene.4,The ragion compartmentation and estimationAccording to the same or similar tectonic evolution of the fracture and trap assemblage of petroleum accumulation condition,we mark off the new twelve structure zones of southeast part of Tarim Basin from west to east.On the basis of nowadays understanding degree,the paper appraised the twelve structure zones of the study area. According to the petroleum accumulation condition including trap,oil source,revervior bed,roof rock,assorted conditions and retention conditions and so on,the paper utilize the uniform parameter and appraision standard to comform the oil potential of study area and for the base of sequent resource calculation and compositive appraision.the final appraision is three best oil-gas provinces,three better oil-gas provinces and seven good oil-gas provinces.