Study On Reservoir Characteristics Of The Upper And Lower Ordovician Yingshan Formation In The Middle 5-7 Well Area Of ​​Tazhong Area

Based on the principles of carbonate sedimentology and reservoir geology, result of well drilling, well logging, test and seismic prediction, sedimentary characters, control factors and distribution of carbonate reservoir of Yingshan Formation (Middle-Lower Ordovician) in Zhonggu5-7borefield (Central part of Tarim basin) are docunmeted by detailed petrographic investigations and integrated core, thin section, SEM, cathodoluminescence, with results of seismic data analysis. The main understandings and progresses are summarized as follows:Strata of Yingshan Formation in study area are belt shaped bodies parallel to the Tazhong1st break area in slope, and are devided into four mebers as Ying1,Ying2,Ying3and Ying4members from top to buttom. The Formation thickness of stratum of Yingshan Formation are commonly stable and lateral continous except the difference denudation of the top of Ying1member. Moreover, the thickness is gradually decrease and denuation degreeis increase from north to south. The thickness part of maximum residue is there, where near the Tazhong1st break area in slope (T1BS); The thickness part in western part is thin and eastern part is thick where parallel toT1BS.Fluctuations of relative sea-level commonly observed throughout Yingshan successions are represented by transgressive-regressive cycles across the study area. Open platform facies(OPT) in the study area can be divided into subfacies such as high energy of arene beach(HEAB), ocean between beaches(OBB), and low energy of arene beach(LEAB) et al.Vertically,internal platform(IPB) and OBB are assemble by multicycles. In Yingl member.theHEAB near the TIBS are main distributed near the east of well ZG5and ZG1, the LEAB are porphyritic and linear parallel to TIBS distributed in the area of well ZG5-1,ZG4,ZG7. Whereas in Ying2member, the HEAB are main NW to SE direction widespread distributed, the LEAB and OBB are belt shaped bodies parallel to the TIBS.The rock types of carbonate reservoirs in Yingshan Formation are complex and porosity is gruandully decrease from dolomite to limestone. Resevoir space types are main concludes with macro-pores such as dissolution cavities and secondly are vug and fractures, and micro-pores such as intergranular pores, inner pores, intercrystalline pores, intercrystalline solution pores, secondly are micro-fractures and dissolution fractures. Reservoir that has been most developped within the3nd and5nd layer of Ying1member, and are formed Ⅱ-Ⅲ typesreservoirs. The Yingshan Formation was slightly contrlled by eustatic change,diagenesisand intensely affected at tectonic movement in buried condition. During these times, complex dolomitization, concomitant leaching and fractures increased porosity of the reservoirs, formed effective Vuggy and fracture-vuggy reservoirs.Favorable area of Yingshan Formation in study area are main distributed along the areahere the fractures and carst developped. Overall, the satisfactory areaes are in the Southeastern of well ZG7,ZG7-Hl,ZG702,ZG7-2, and well ZG6to ZG6-2, and well ZG518to ZG434where the southern of the study area.