| Tight sandstone reservoirs have low porosity,low permeability,little contribution of oil and gas to logging response,small difference in resistivity of oil(gas)and water layers,and difficult identification of conventional logging fluids.Nuclear magnetic resonance(NMR)logging can directly detect the fluid in the reservoir,and can provide information on the porosity,permeability,and saturation of each component of the tight sandstone reservoir,which has irreplaceable advantages.However,the data processing of nuclear magnetic resonance logging is all researched under water wetting conditions.Therefore,this article attempts to start from the nuclear magnetic resonance relaxation mechanism under different wetting conditions,and use nuclear magnetic resonance logging technology to carry out data processing methods and fluid identification research for tight sandstone reservoirs.In this paper,the deep tight gas reservoirs in the Tarim Basin and the complex oil-water reservoirs in the Ordos Basin are the research objects,combined with rock physics experiments,to improve the NMR logging data processing method in the research area.In the deep Cretaceous fractured tight gas layer in Kuqa,Tarim Basin,it is difficult to identify fluid types and calculate porosity and other parameters.Based on density and nuclear magnetic porosity calculation methods,light hydrocarbon correction studies are carried out on tight gas-bearing sandstone reservoirs,and the difference between the porosity calculated by the density and the porosity calculated by the nuclear magnetic field is used to construct a fluid identification chart.The Chang 6 and Chang 8 reservoirs in the Ordos Basin have the characteristics of low porosity and low permeability,and the relationship between oil and water is complicated and the wettability is greatly affected.Existing time domain analysis(TDA)methods of nuclear magnetic resonance logging are usually aimed at water-wet formations.For tight sandstone reservoirs under oil wetting and mixed wetting conditions,the existing methods cannot be applied.Based on the petrophysical characteristics of oil wetting,water wetting and mixed wetting conditions,this paper analyzes the NMR relaxation theories under different wetting conditions,and derives the NMR response under long and short waiting time conditions.The nonlinear relationship between echo difference and fluid pore structure and fluid content is established.The thesis uses an ideal rock model to explore the influence of the oil wetting scale factor on the NMR relaxation machine.The genetic algorithm and simulated annealing algorithm are used to solve the nonlinear inversion problem,and the oil and water volume and saturation of the flushing zone of tight sandstone reservoirs under different wetting conditions are calculated.Aiming at the tight sandstone reservoirs after flooding in the study area,the study on the identification and division of water flooded layers by nuclear magnetic resonance logging was carried out using the cross-graph method.After correction for light hydrocarbons in tight gas-bearing sandstone reservoirs,the calculated porosity is consistent with the core porosity,and the constructed fluid identification chart has a good application effect in the study area.The numerical simulation results of the ideal model verify that the lateral and longitudinal relaxation time and oil volume of the oil calculated by the new method are consistent with the preset model,which is more accurate than the original TDA analysis method.The example application shows that the cross-plot of oil saturation in the wash zone constructed by combining the array induction resistivity can effectively realize the fluid identification of tight sandstone reservoirs with different wettability.The constructed intersection map for identification and division of water-flooded layers has a high coincidence rate in the study area.Based on the NMR double TE logging data,the remaining oil saturation after the reservoir flooding is calculated. |
PDF Full Text Request