| The red bed of Es4x-Ek in the southern gentle slope of Bonan sag has rapid sedimentary transformation and complex diagenetic transformation,resulting in strong heterogeneity of the reservoir in the study area.Aiming at the problems faced by the target layer in the oil and gas exploration in the study area,this paper makes use of core observation,thin section identification,combined with logging data,as well as various analysis and test data such as temperature and salt measurement of inclusions,carbon and oxygen isotope analysis and electron probe microanalysis to analyze the lithology,physical properties and The diagenetic fluid transformation and the formation mechanism of effective reservoir are analyzed,and the main controlling factors and development mode affecting the favorable reservoir on the south slope of Bonan sag are defined.The reservoir on the south slope of Bonan sag has poor physical properties and belongs to low porosity and low permeability reservoir.The main types of reservoir space are residual primary intergranular pores and secondary dissolution pores dissolution fractures.For reservoirs with different lithology in the study area,compaction and cementation are the main reasons for the densification of clastic rocks.The pore reduction of 85% of sandstone samples in the study area is greater than 50%of the total pore loss,and the clastic particles are closely arranged in medium strong compaction;The amount of cemented pore reduction is more than 30%.The common cements include calcareous,siliceous,iron and clay cements,which seriously damage the reservoir space;Dissolution is the main pore increasing diagenesis.The dissolution of unstable components such as feldspar and rock fragments,with an average dissolution pore increasing rate of more than 5%,has effectively improved the reservoir performance of the target layer.Systematic analysis of reservoir quality control factors on the south slope of Bonan sag shows that lithology,lithofacies and sedimentary facies control the initial porosity of the reservoir,and the medium and coarse-grained lithic arkose of braided river channel subfacies in the study area is the most favorable reservoir;The burial process determines the diagenesis and pore evolution path.The transformation of structural factors leads to the development of fault system in the fault step slope zone in the study area,which provides a good communication channel for acid fluid and is a favorable structural zone for the development of secondary pores;The compaction intensity and fluid transformation are the key to determine the current porosity.The burial depth of different sedimentary structural units in Bonan sag varies greatly(2000-5500m),and the compaction intensity has significant differences.The burial depth of the southern basin margin belt and the fault step slope belt is relatively shallow,and it is obviously transformed by acid fluid,and the reservoir physical properties are good.The diagenetic response characteristics of different fluids are studied: the alkaline fluids controlling calcite cementation in the study area include calcium rich fluid derived from salinized Lake Basin(near Salt Lake),deep upwelling thermal fluid(near volcanic vein),calcium rich fluid dissolved by limestone debris(near basin edge),calcium source provided by plagioclase and volcanic debris alteration(developed in the target layer),interlayer water released by mineral transformation(near argillaceous layer);Acid fluids controlling corrosion transformation include atmospheric fresh water,acid removal by thermal evolution of organic matter and acid removal by transformation of clay minerals.Summarize the development characteristics of effective reservoir: far away from calcium source,adjacent acid source,effective allocation of source reservoir at appropriate time,and hydrocarbon supply through fracture / unconformity window.Four kinds of effective reservoir development models of "early alkali cementation,three source acid control and stepped distribution" are comprehensively established,reservoir evaluation criteria are formulated,and favorable reservoir distribution is predicted. |
