Main Controlling Factors And Favorable Reservoir Distribution Of The Sinian Dengying Formation Reservoir In Western Sichuan

For a long time,the Sichuan Basin has not obtained valuable oil and gas from carbonate rocks in the Proterozoic,and has not achieved significant results in the exploration of the Sinian Dengying Formation in recent decades.It was not until 2011 that CNPC obtained natural gas from the Dengying Formation in the Gaoshi 1 well in the central Sichuan region.After that,it obtained high production in multiple wells,indicating that the Dengying Formation has good prospects for exploration.Therefore,it is necessary to carry out a detailed investigation of the stratigraphic characteristics and reservoir characteristics(petrological characteristics,physical characteristics,and reservoir space types)of the Sinian Dengying Formation in the Sichuan Basin.Based on outcrop data and some well location data,the following understandings were obtained:(1)According to the outcrop lithology and well location curve,the Dengying Formation is divided into four segments.The lithology of the Dengying Formation is mainly internal clastic dolomite,algal dolomite and grain dolomite,breccia,mudstone,shale Rock,siliceous rock,etc.The sedimentary environment of the Dengying Formation is basically dominated by tidal flats within the platform.The reservoirs are mainly developed in the middle and upper sections of the second and fourth members of the Dengying Formation;mudstone and shale are mainly developed in the third member of the Dengying Formation,which are good landmarks.(2)From the observation under the microscope and the identification of field hand specimens,it can be seen that the storage space type of the Dengying Formation is mainly a combination of secondary holes,holes,and fractures,and the reservoir type is mainly fracture-porosity or fracture-cavity and karst.Reservoir.(3)According to the thin sheet data and physical property data,the Dengying Formation reservoir is considered to be a low porosity and low permeability reservoir with an average porosity of about 2% and an average permeability of about 0.2 m D.The algae dolomite porosity is about 2%,and the fine-grained dolomite has the highest porosity,which is 2.94%.(4)Studies have shown that high-energy sedimentary facies provide a material basis,and superficial karstification and recrystallization increase the possibility of reservoir development,and buried dissolution further increases the development of reservoirs.In addition,recrystallization has improved the physical properties of the reservoir;silicification has reduced the physical properties of the reservoir to a certain extent;most of the fractures generated by the tectonic effect have been filled by non-oil and gas,which mainly improves the permeability of the reservoir.Based on the analysis of the sedimentary environment,lithology,and physical properties of the Dengying Formation,it is believed that the main controlling factors of the Dengying Formation reservoirs are mainly controlled by primary and epigenetic factors: that is,the main controlling factors of the good reservoirs of the Dengying Formation are freshwater leaching during the superficial growth period.Filtration and burial karst in the burial period.The original sedimentary microfacies and lithology control the intensity of karst.The burial dissolution is mainly the expansion of the karst pores or the filling failure.The later structure,recrystallization and other effects are certain.The reservoir has been improved to a great extent.A series of factors make the Dengying Formation suitable for becoming a good oil and gas reservoir,and it also indicates that this set of formations will have huge exploration prospects.