Reservoir Characteristics Of The Cambrian Qingxudong Formation And Petroleum Entrapment In Southeastern Sichuan Basin

The southeastern part of the Sichuan Basin is estimated to have great potential for the oil and gas exploration according to the source-reservoir-caprock association in the region.The success of the Longwangmiao Formation made the Lower Cambrian carbonate strata in the Sichuan Basin the focus of attention and stimulated the exploration for the Qingxudong Formation.There were few wells drilling across the Qingxudong Formation in the southeastern part of the Sichuan Basin.There are still many problems to be solved in terms of the reservoirs.The reservoir characterization is not enough detail and the main factors of high quality reservoir of the Qingxudong Formation are not yet clear,the mechanisms of dissolution and dolomitization need further exploration.The studies of petroleum entrapment process and model are also relatively weak.In order to clarify the characteristics of the reservoirs,based on the sedimentary petrology,reservoir geology,petroleum and geophysical geology and so on,with the field profile and core observation,thin slice analysis,cathodoluminescence and isotope analysis,we studied the reservoir lithology characteristics,physical characteristics,reservoir space type,reservoir diagenesis type and reservoir diagenetic evolution model and proposed the main factors of high quality reservoir of the Qingxudong Formation.The model of oil and gas accumulation in the study area was dissected based on the analysis of the source-reservoir-caprock association.The main results achieved in this paper are listed as following:?1?The reservoirs of the Lower Cambrian in the southeastern Sichuan Basin are mainly developed in the Qingxudong Formation.It is a set of carbonate reservoir.Micro-powdery limestone,granular limestone,dolomitic limestone developed in the Qingxudong Formation one section;Powdery dolomite and crystalline dolomite developed in the Qingxudong Formation two section.The reservoirs main developed in the Qingxudong Formation two section.?2?The characteristics of porosity type,reservoir space type and horizontal distribution of the Qingxudong Formation were discussed.The reservoir space mainly are intragranular and intergranular solution pores of dolomitization.Porosity is high and average porosity is 3.42%;permeability is relatively low,mostly less than 0.01×10^-3?m².Reservoir storage property was slightly worse from the north to south.?3?It is considered that the influence of sedimentary facies,dolomitization and the number of terrestrial debris contained on reservoir formation is relatively large.Cloud pond,mud cloudy lagoon,oolitic beach and cloudy beach sea provided a material basis for reservoir development.The dolomitization is the great significance to reservoir diagenesis and burial dissolution is the key factor.A large number of terrestrial debris is conducive to the formation of high quality reservoirs.?4?The main source rocks are the Cambrian Niutitang Formation;the reservoir is the Cambrian Qingxudong Formation,which is the main research object of this paper;the gypsum ointment and the gypsum salt are the direct cover of the Cambrian Qingxudong Formation.The type of the Cambrian Longwangmiao gas pool is the reservoir being above the source rock;pool forming assemblage are superior.