| It is of great scientific significance to cognize the development and preservation mechanisms of deep/ultra-deep carbonate reservoirs by study on sequence stratigraphy,microfacies and reservoir characteristics of the Lower Cambrian Xiaoerbulak Formation,Tarim Basin.Moreover,this will facilitate the petroleum exploration in the Cambrian subsalt dolomite of the Tarim Basin.Based on comprehensive analysis of outcrops data in the southwestern region of the Tarim Basin,drilling data and seismic data in combination with published research achievements,the sequence stratigraphic framework,the characteristics and distribution of microfacies succession in system tract,and the sedimentary models of the Xiaoerbulak Formation in Bachu-Tazhong area were explored.What is more,the types and characteristics,the development and preservation mechanisms of carbonate reservoir in the Xiaoerbulak Formation were discussed.The Xiaoerbulak Formation in Bachu-Tazhong region was in carbonate ramp sedimentary environment,which developed two integrated 3rd sequences.The lower part of the Xiaoerbulak Formation was composed of middle ramp interior and exterior zone sediments to internal ramp tidal flat and lagoon sediments,while the upper part was composed of large scales of shoal with regional reef developing.It was generally behaved as aggradational-progradational stacking style from north to south.The Xiaoerbulak Formation could be identified with 13 microfacies types,including muddy to micritic dolostone(MF1),silty-fine dolostone(MF2),calcite dolostone(MF3),Peloidic dolostone(MF4),bioclastic dolomite(MF5),thrombolite(MF6),spongiostromata bioistromes(MF7),stromatolite(MF8),laminated microbialite(MF9),intraclast dolostone(MF10),oolite(MF11),clastic dolostone(MF12),gypsiferous dolostone(MF13),gypsum-salt rock(MF14).Horizontally,the distribution of microfacies succession in the first 3rd sequences was of continuity,however for the influenceof paleogeomorphology,water energy and microbial activityin the second 3rd sequences,it kept different.Different microfacies types kept different reservoir space characteristics.The pores developing microfacies types were MF1,MF2,MF4,MF6,MF7,MF8,MF10 and MF11.The intercrystalline pores,intergranular pores,bio-framework pores,holes and little dissolved pores contributed most of the reservoir spaces of the Xiaoerbulake Formation.Kelping-Bachu region mainly developed microbial carbonate reservoirs that were composed of MF6 and MF7,and grain dolomite reservoirs that were composed of MF10.The east of Bachu-Tazhong region mainly developed grain dolomite reservoirs that were composed of MF10 and MF11.High quality reservoirs that kept obvious stratabound andwere regularly stacked in the vertical and comparable in the horizontal,mainly developed in the shoal facies and located in the upper part of the Xiaoerbulak Formation.What is more,the development of the reservoirs was obviously controlled by microfacies succession,sedimentary facies and high-frequency sequence.The porosity development was caused by meteoric fresh water dissolution during penecontemporaneous stage.Furthermore,during burial stage,it was of inheritance and adjustment,whichwere jointly controlled by dolomitization,fluidization,reservoirs control mechanism of microbe and evaporate,along with oil or gas filling. |
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