Fluid Identification And Gas And Water Distribution Rules In Tight Clastic Rock Reservoirs

With the development of unconventional oil and gas resources,more and more attention has been paid to the tight clastic rock reservoirs.However,the tight clastic rock reservoirs have various types of rocks and complex pore structures,features such as mineral composition and reservoir space have strong heterogeneity,complicated gas reservoir formation conditions lead to uneven distribution of gas and water.All of these make fluid identification more difficult.In order to meet the requirements of exploration and development of dense clastic rock gas reservoirs,it is very important to study the appropriate methods of fluid identification and assessment to clarify the developmental locations of effective gas layers in gas reservoirs.In this paper,the tight clastic gas reservoirs in Denglouku Formation in the W Fault are studied,and comprehensively using core description,thin slice,electron microscopy,diffraction,mercury intrusion,NMR,well logging(including dipole shear wave)and other information to in-depth study fluid well identification method,calculation of reservoir physical parameters and the lower limit division and gas-water distribution law.This paper has achieved the following results and understanding:(1)In conventional logging,based on the resistivity curve,porosity-resistivity cross plot,RX-density cross plot and array-induced curve characterization method are compared,it is found that the conventional methods can recognize the gas layer,the water layer and the dry layer to a certain degree.Therefore,the electrical response characteristic mode of tight clastic rock reservoir layer-fluid interpretation is established,but there are application limitations.(2)According to the differences of acoustic logging responses of different fluids,the fluid sensitivity parameters are calculated by using the dipole-shear elastic modulus evaluation method and the elastic parameters reflecting the fluid changes are screened out.The cross-plot of the sensitive parameters and the image pattern with reverse scale envelope are created,thus,the fluid identification is conducted from both qualitative and quantitative aspects.(3)In the aspect of comprehensive forecasting research,the optimal segmentation algorithm is used to automatically stratify the logging curves of Dengloukou Formation and judge the properties of fluids by the logging-fluid phase database established by cluster analysis.Combining the characteristics of fluid electrical response and identification criteria,a fluid identification method based on the double information of "well logging-fluid phase+electrical response standard" under the inter-mezzanine control of gas and water cycle is established.(4)Through the core test and the experimental data of the rock electric field,from the point view of the rock physics model of tight clastic rock,the porosity model is established according to the pore structure type to improve the calculation accuracy.At the same time,the porosity-permeability regression model is used to calculate the permeability.And the gas saturation model of sub-reservoir type is established by Archie formula.Then,the lower limit of reservoir physical properties is established synthetically by means of physical gas test method,direct and inverse statistical method and minimum flow pore throat radius method,which is used to analyze the quality of tight clastic rock reservoir and provide a reliable basis.(5)According to the analysis of core and well logging data,the paper studies the characteristics of interval intercalation layer,and studies the characters of gas and water distribution,and uses the above fluid identification method to evaluate single well.On this basis,the continuous well profile and plane gas-water distribution figure is drawn.Then determine the good physical properties and gas saturation of the tight gas development favorable areas.A series of methods established in this paper can effectively improve the accuracy of well-demarcated clastic fluid well logging identification,and have a good application value in the division of effective reservoirs,exploration of natural gas favorable areas and "sweet spot"prediction.