Reservoir Characteristics And Diagenetic Evolution Of Lower Cretaceous Clastic Rocks In The Aer Depression,Erlian Basin

The exploration and development history of Erlian Basin has a long history.In recent years,as new depressions have been discovered,the value has gradually increased.Since the discovery of the Aer Sag in 2008,large-scale reserve replacement areas have rapidly formed.Clastic rock reservoirs have become the main reservoir type.The predecessors have made detailed exploration and research work on the sedimentary environment,stratigraphic features,reservoir features,oil and gas development,etc.of the Aer Sag,but nobody focused on diagenesis and reservoir lithology.With the deepening of exploration,the prediction and evaluation of high-quality reservoirs are particularly important.It is necessary to combine the geological structure of the Erlian Basin,the type of sedimentary facies and its distribution,and the physical characteristics of the reservoir from the perspective of the interaction between diagenesis and pore evolution research.In this paper,based on the theory of mineralogy and reservoir sedimentology,combined with well logging,core slices,scanning electron microscopy,XRD,and physical property test data of rock samples,the preliminary exploration data is synthesized and the following results are achieved:(1)The drilling revealed that the clastic rocks in the Aer Sag developed three sedimentary facies including fan delta,braided river delta and a few lacustrine facies,and further identified six types of subfacies and thirteen types of microfacies.Then analyzed the characteristics and their plane distribution.(2)The clastic reservoirs in the study area include three types: tuff,conglomerate and sandstone.The tuff is mostly gray crystal tuff and a little gray glass tuff;conglomerate is complex conglomerate.Most of them is debris,next is terrestrial debris,and least is interstitial material;sandstone is mainly detrital feldspar sandstone and feldspar detrital sandstone,the composition is relatively low in maturity,and the content of terrestrial debris is high.(3)Analyze the pore types and structural characteristics of clastic rocks in the study area,and think that the clastic rock reservoirs have low porosity and poor physical properties,and can be divided into ultra-low porosity and ultra-low permeability reservoirs,ultra-low porosity and ultra-low permeability Reservoirs,ultra-low porosity and ultra-low permeability reservoirs,low porosity and ultra-low permeability reservoirs,ultra-low porosity and low permeability reservoirs,low porosity and ultra-low permeability reservoirs,low porosity and low permeability reservoirs,low porosity and medium permeability reservoirs,9 types of mesopore and medium permeability reservoirs.(4)The clastic rock reservoir in Aer Sag is in A-B stage of diagenesis.According to the symbiotic relationship,metasomatic order and contact relationship of minerals,the diagenetic sequence in the study area is considered as follows: terrestrial clastic deposition ? early compaction,fracturing ? early dissolution ? sericite metasomatism ? fine-grained quartz cementation ? chlorite cementation ? Kaolinite cementation ? pressure solution,quartz secondary increase,new quartz crystallites appear ? illite cementation ? kaolinite is gradually replaced ? calcite cementation ? later dissolution ? iron calcite cementation ? dolomite cementation.(5)Through porosity inversion and quantitative calculation,the pore evolution model of the clastic rock reservoir in Aer Sag was established.The initial test porosity experienced early compaction reduction pores,early cementation-alternation reduction pores,secondary dissolution pore increase pores and In the middle and late stages of cementing-representing pore reduction,the relative errors between the calculated porosity and the measured porosity are between 1.57% and 13.54%,and the average relative error is 4.45%.The error is within the controllable range,and the results are credible.