Study On Cenozoic Sedimentary Facies And Reservoir Characteristics Of Qianxi Area In The North Edge Of Qaidam Nasin

By using seismic, well drilling/logging, core sampling and some relative data and conferring former study achievements of other researchers, this paper examines the Cenozoic sedimentary facies and reservoir characteristics of Qianxi area in the north edge of Qaidam basin and forecasts the favorable reservoir and facies belt in this area based on the theory of Sedimentology and Petroleum geology.The Cenozoic sedimentary facies of Qianxi area is divided into alluvial fan, braided channel and lacustrine facies, and then subdivided into 7 subfacies and 9 microfacie based on the seismic and well drilling/logging data, core observation and the analysis of the core samples. Sedimentary facies of Palaeocene- Eocene series are braided channel and lacustrine facies, Sedimentary facies of Oligocene series are alluvial fan, braided channel and lacustrine facies, Sedimentary facies of Miocene series are braided channel and lacustrine facies.Through the methods of core observation, core sampling, microcosmic imaging analyses, mercury penetration test and other experimental analysis, it is found that the Cenozoic reservoir in Qianxi area has undergone some diageneses like compaction, cementation, metasomatism, dissolution and cataclasis. The diagenetic stage is in the early period of B to the medium of A. Dissolution and cementation are the mainly diagenesis, which results in the pore to be the dominant reservoir type. The intragranular and interparticle dissolution pore formed by feldspar, lithic and carbonate cement are the main reservoir space types. The content of carbonate cement has much influence on the reservoir property. The illite and illite/smectite formation on the surface of detrital particles have bad influence for reservoir permeability.The reservoir of this area is porous type.The pores of reservoir are primary interparticle pore, secondary intragranular pore, oolimolds, interparticle dissolution pore, particle brink dissolution crevice.And the majority pore are secondary pore deformed by the dissolution and denudation of feldspar and carbonate cement. The reservoir of Xiaganchaigou group is extra small-small pore and fine throat, The reservoir of Shangganchaigou group is extra small pore and fine-middle throat. According to the physical properties of reservoir, it is observed that the majority of Cenozoic reservoir in this area is typy III and IV, few for II, I , and rarely I.Integrated the sedimentary facies and reservoir characteristics, it is concluded that favorable reservoir are mainly developed in channel bar of braided stream, sandbank of lacustrine facies and braided stream of alluvial fan facies.