Study On Reservoir Characteristics Of The Lower Ganchaigou Formation In Western Part Of The Northern Margin Of The Qaidam Basin

This paper researches on the northern margin of the Qaidam Basin, western part of the Lower Ganchaigou Formation (E3) Sedimentary facies and reservoir characteristics of the analysis described by taking the theoretical guidance of sedimentary facies and reservoir sedimentology, combined with the related information of drilling (logging) wells, core samples and thin sections test analysis and so on. Then makes an opportunity for the Classification and evaluation of reservoir region based on the previous results.By using the related information of drilling (logging) wells, core observation and analysis of the sample tests and so on, the Lower Ganchaigou Formation (E3) of the western part of the North Qaidam Basin sedimentary facies are divided into five categories: alluvial fan, fan delta, braided river, braided river delta, lakes. Sedimentary facies distribution of the different regions are different, alluvial fan mainly developed in Nan baxian - Mahai and Lenghu region, fan-delta mainly developed in Lenghu area, braided river main developed in Nan baxian - Mahai region, braided river Delta mainly developed in Nan baxian-mahai and E-Bo Liang region, while the lakes in the study area are developed almost part.By using the core observation, thin section, scanning electron microscopy, X diffraction and mercury testing tools, we found the Lower Ganchaigou Fomation (E3) of the western part of the North Qaidam Basin reservoir with low compositional maturity, Moderate-poor textural maturity, and the main types of sandstone reservoir are feldspar sandstone, lithic-feldspathic sandstone, feldspathic-lithic sandstone and lithic sandstone. Rich lithic, feldspathic and poor quartz is the matrix components features. And the mainly cement is carbonate. The reservoir rock has mainly withstanded with compaction, cementation. To the reservoir, compaction makes the negative effect and dissolution play a positive role, while the cementation of carbonate cements and chlorite film have the constructive and destructive double effect to the reservoir properties of the transformation. Diagenetic stage mainly between in the A period of early diagenetic stage and B period of late diagenetic stage.The primary porosity is the main reservoir space, secondary porosity is followed, and there also is few small amount of micro-cracks. The better pore structure parameters such as Permeability and porosity is in the E32 Formation reservoir. The development extent of pore and the accumulation property have apparent deviation in different tectonic belts. Both the development extent of pore and the accumulation property in Mahai-Nanbaxian area are best, and produced mainly primary intergranular pores. The reservoir has high porosity and middle permeability. The development extent of pore is very good - good and the accumulation pro- perty is good in Lenghu tectonic belt, and produced mainly primary intergranular pores. The reservoir has mid-low porosity and mid-low permeability. Reservoir porosity and accumulation property are relatively very poor in Eboliang tectonic belt, and merely has a few relict intergranular pores and secondary solution pores, and the reservoir has estremely low porosity and extremely low permeability.We can make sure that E31 can be divided into three classâ… most favorable areas (Saishiteng belt, Mahai-Nanbaxian structure) and four Classâ…¡favorable areas (Kunâ…¡, Kunbei slope, Qianfu structures, Eboliangâ… ,â…¡and Nanbaxian structure); E32 can be divided into three classâ… most favorable areas (Lenghu 4th, and Mahai-Nanbaxian structure) and 6 classâ…¡favorable areas (Lenghu 5th, Qianfu structures, Eboliangâ… ,â…¡, Kunâ…¡, Kunbei slope and Lenghu 6th, 7th constructions), by doing the comprehensive assessment of the sand layer thickness, percentage of sandstone (sand than that), reservoir properties, sand, and a combination of factors on sixty one wells targeted reservoir sandstones. Finally, comprehensively evaluated the final results of different structural zones, the result was: favorable reservoir areas of the Lower Ganchaigou Formattion (E3) of the western part of North Qaidam Basin mainly consists three categories:Nanbaxian - Mahai is the most favorable area for typeâ… , E-Bo Liang, Qianfu, Saisteng,the 5th lenghu and Kunâ…¡- the Kunbei slope region are Classâ…¡favorable area, the 4th,6th,7th Lenghu belts are the classâ…¢favorable areas.