Study On Evaluation Of Pore Structure And Permeability Of Tight Sandstone Reservoir By Nuclear Magnetic Resonance Logging

With the continuous deepening of exploration and development,more attention has been paid to the tight sandstone reservoir.Tight sandstone reservoir is a typical reservoir with low porosity and low permeability,which has strong anisotropy and complex pore structure.In the vertical,permeability change is relatively large.The fine interpretation of reservoir pore structure and permeability can deepen the understanding of reservoir,and better determine the main production layer.Therefore, the study on the pore structure and permeability evaluation of tight sandstone reservoir can provide guidance for reservoir fracturing and so on,which has certain significance. With taking A and B two tight sandstone reservoirs as an example,this paper systematically studies the evaluation methods of pore structure and permeability of tight sandstone reservoir,and the following results were obtained:?1?Based on the analysis of experimental data of mercury injection and nuclear magnetic resonance,a qualitative and quantitative evaluation method of pore structure based on nuclear magnetic resonance logging is established,and a new parameter which reflect the pore structure and the corresponding evaluation method are presented.The method is derived of unit model and linear scale pseudo capillary pressure curve construction method,and this paper proposed spectral area parameters.Because having certain theoretical basis,the spectral area parameters obtained by this method are compared with those of the traditional mean pore throat radius and Swanson parameters,it is more closely related to permeability,and in the actual assessment it is no need to construct the continuous pseudo capillary pressure curve,and only evaluate by using T₂ spectrum conveniently.?2?Based on the analysis of experimental data of mercury injection and physical property,a method for predicting permeability of cores based on mercury injection experimental data is developed for tight sandstone reservoirs.In this method,the average pore throat radius parameters sorting coefficient were determined by mercury intrusion experimental data,and the genetic algorithm is used to establish the optimal model with porosity parameter.By comparing with the available method using experimental data of mercury injection to determine the permeability of cores,it is concluded that the method is more accurate and can accurately calculate the core permeability.At the same time,this paper also analyzes the reasons of the low precision of NMR logging permeability model based on continuous pseudo capillary pressure curve and prediction model of core permeability by mercury injection.?3?In view of the problem that permeability calculation accuracy is not high in existing tight sandstone reservoir due to the complex pore type and pore structure,from the two aspects of rock physics and algorithm,the permeability evaluation method of NMR logging based on the unit cell model and the permeability evaluation method of NMR logging based on hybrid intelligent algorithm and T₂ full spectrum are proposed.For the permeability evaluation method of NMR logging based on the unit cell model,firstly,the pore network in the formation is simplified into a tortuous capillary model,and the equation of permeability and T₂ spectrum of nuclear magnetic resonance logging is deduced,it determine the optimal parameters by genetic algorithm and thefinal model.For the reservoir with dominated induced porosity and diverse pore types and structure,the relationship between the full spectrum of T₂ and the permeability is obtained for the first time by physical derivation,through which it illustrate the reason that the evaluation results of the existing NMR logging permeability models are not very satisfactory for complex tight sandstone reservoirs.And it present a model that using all porosity components of T₂ full spectrum as input,permeability as output,the model of hybrid intelligent algorithm as prediction algorithm proposed in this paper,it determine the relationship between T₂ spectrum and permeability by hybrid intelligent algorithm,and evaluate the new wells.After putting forward the two models,this paper analyses to explain the application conditions of the two models.These two models can be used to help evaluating the permeability of tight sandstone reservoirs.