Reservoir Characteristics And Main Controlling Factors Of The Carboniferous Karashayi Formation In The Southern Part Of The Tahe River

Tahe oilfield in Tarim basin is located at the south of Tianshan Mountain and the north of the Taklimakan desert in Xinjiang province.Its research area lies in the southwest slope of the Akekule uplift which is the secondary structure unit in the southeastern Shaya uplift.After the acquirement of the industrial oil run from the S106-2 and S111 wells,the Huyang 1 and the Huyang 2 wells have got achieved recently,furtherly evidenced the carboniferous reservoir,one of the main clastic reservoir in Tahe oilfield,having exploited a new area in salt body.However,the sand shale interbedded,rapid lateral variation of thin sand body and strong anisotropy of Kalashayi group blocked the further exploration.As a consequence,a further study in the characteristics of reservoir and the impacts of main controlling factors on reservoir development is of great significance.This essay use the Kalashayi group in southern Tahe basin as the main research object,utilized the drilling data and previous research results enough at the base of the work of important core observations,thin section descriptions and sample tests and analysis in studying sedimentary facies,reservoir characteristic,diagenesis and diagenetic evolutionary sequences,to name but a few,proposes the main controlling factors on reservoir development from the aspects of sedimentary facies and diagenesis,classifies the sand shale section of the Kalashayi group and predicts the distribution of advantageous reservoir.The research shows that southern Tahe basin carboniferous Kalashayi mud faces provide provenance for the shallow braided river delta which is the tidal flat facies sedimentation controlled by tidal actions.The sedimentary facies of southern Tahe carboniferous Kalashayi group is a sedimentary deposited alternately by braided river delta facies and tidal-flat facies,where its north area is mainly dominated by the delta facies and its south area by tidal flat facies.Its lithology is mainly composed of feldspar quartz-sandstone,debris quartz sandstone,feldspar debris sandstone and debris feldspar sandstone,and characterized by a medial-poor sorted and rounded,low maturity rock constituent.Diagenesis,including compaction,cementation,dissolution and diagenesis development,has reached the phase of late diagenesis A-B period.The main type of the pore is the interparticle dissolution pore,with intragranular dissolved pores and residual intergranular pores as the other two types.The average permeability of the research area is 9.8%,ranging between 6?15%,and the average porosity is 42.89×10-3?m2,concentrating in the range of 1?10×10-3?m.At large,the permeability takes the form of low-medial pores,low-high permeability reservoir while the porosity takes the form of medial pores with small throats and small pores with fine throats and bad connectivity between pores and throats.The high quality reservoir is primarily produced in tidal-flat faces' tidal-flat sand bodies with coarse grains,well-sorted,well-rounded and low matrix content,which was double controlled by sedimentary and diagenesis.Combining the petrologic features,distribution patterns,mercury-injection curves and parameters of pore structure,this essay develops the standard of classification and evaluation in reservoir study.The primary reservoir type is the second type reservoir while the secondary reservoir is mainly the first and third reservoir.Carbonate cemented is the most important controlling factor that affects the physical property of reservoir,yet the dissolutions taking place in the later phase,provides a number of secondary pores which are the keys to the development of reservoir.