The Research Of Reservoir Genetic Mechanism And Distribution Law Of Changxing Formation In Yuanba Area

In Yuanba area of Northeast Sichuan basin,the late Permian Changxing Formation reef facies oil and gas reservoir is a typical marine facies reef reservoir in China,and also developed reef-bank facies reservoir.In recent years,with the exploration and development increase,we obtained a large number of detailed geological data,have a new understanding,hope that this research will make a contribution to the further study on reservoir evaluation and the development area selection.Based on summing up and analysising the previous studied results,and put sedimentary petrology,sequence stratigraphy,reservoir geology,logging geology,geophysics,rock and mineral geochemistry geological theory as a guidance,a lot of modern advanced rock and mineral test methods have been used in this study,including cathodoluminescence,SEM,stable isotopes analysis,trace element and REE analysis,X-diffraction analysis,inclusion analysis,electron microprobe,EDS ect.,use well drilling and logging,cores testing and geochemical data,finish the research on reservoir genetic mechanism and distribution law of Changxing Formation.The following is the main results in this study:?1?The Changxing formation mainly developed tidal flat facies and reef-bank facies reservoir,and reservoir rock types is mainly dolomite and part of the limestone;penetration and storage space is the secondary dissolution pore and late unfilled crack;reservoir porosity between 2%and 5%,permeability is around 0.1×10^-3?m².?2?Various diagenesis types developed in study areas,different diagenesis have different effects on reservoir's pore evolution,reservoir porosity constructive diagenesis evolution are:dolomitization,dissolution and tectonic disruption,tris diagenesis are the key to the reservoir porosity and permeability system of the formation.?3?Hydrothermal geological action.In the early of Changxin formation was in tension stress environment,in the platform margin developed fault activity,deep thermal fluid into the Changxin formation,then the hydrothermal dolomitization and hydrothermal solution developed in Changxin formation.?4?According to the mineral petrological and geochemical characteristics,think that there are three causes and five types of dolomites,then established the models of different types of dolomitization:?1?penecontemporaneous dolomitization is responsible for microcrystalline dolomite and silty-fine allotriomorphic dolomite;?2?shallow-burial environment dolomitization is responsible for silty-fine euhedral dolomite;?3?controlled by the platform margin fault early hydrothermal dolomitization is responsible for silty-fine dolomite?hydrothermal alteration?and medium-coarse grain dolomite?hydrothermal origin?.according to all kinds of dolomite statistical results in the distribution of sequence and sedimentary facies,think that dolomite distribution controlled by early dolomitization,sedimentary facies and platform margin fault.?5?There are four stages dissolution in changxing formation:First stage is meteoric water karstification,the early unstable mineral selective corrosion,formed few pores;Second stage is hydrothermal dissolution in the cathode rays,the solution hole edge is bright,can be filled by asphalt and calcite;Third stage is organic acid dissolution,formed a few pores;Fourth stage is connected with thermal sulfate of dissolution,the pores clean and unfilled.Summarizes and analyzes this four stages of dissolution,put forward four stages of dissolution models,and statistical four stages of dissolution of the contribution of the reservoir that the third and the fourth are the key to the formation of the secondary pore system.?6?Structural and non-structural crack in study area.The non-structural cracks were filled by calcite;there are three stages of structural crack,only the third stage is clean and unfilled,for the reservoir permeability is important.?7?Through the single well reservoir longitudinal anatomy,and multiwall horizontal comparison,found that upper tertiary sequence reservoir whether thickness or porosity and permeability are better than the lower tertiary sequences,mainly affected by sea-level change and the favorable diagenetic facies influence;laterally,the platform margin and the inner reservoir better than in other facies,reservoir distribution is affected by platform margin fault active and sedimentary facies.