EXACT SOLUTION AND ITS BEHAVIOR CHARACTERISTIC OF NONLINEAR DUAL-POROSITY MODEL

A nonlinear dual-porosity model considering a quadratic gradient term is presented. Assuming the pressure difference between matrix and fractures as a primary unknown, to avoid solving the simultaneous system of equations, decoupling of fluid pressures in the blocks from the fractures was furnished with a quasi-steady-state flow in the blocks. Analytical solutions were obtained in a radial flow domain using generalized Hankel transform. The real value cannot be gotten because the analytical solutions were infinite series. The real pressure value was obtained by numerical solving the eigenvalue problem. The change law of pressure was studied while the nonlinear parameters and dual-porosity parameters changed, and the plots of typical curves are given. All these result can be applied in well test analysis.

Modeling of multiphase flow in low permeability porous media:Effect of wettability and pore structure properties

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications.However,a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability.To address this issue,based on the digital rock of low permeability sandstone,a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process.In addition,a dual-porosity pore network model(PNM)is constructed to obtain the water-oil relative permeability of the sample.The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties.Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability.The injected water breaks through the outlet earlier with a large mass flow,while thick oil films exist in rough hydrophobic surfaces and poorly connected pores.The variation of water-oil relative permeability is significant,and residual oil saturation is high in the oil-wet system.The flooding is extensive,and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces;thus,water relative permeability is lower in the water-wet system.While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity.Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance,and a large microporosity corresponds to low residual oil saturation.This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

Numerical simulation of two-phase flow in fractured porous media using streamline simulation and IMPES methods and comparing results with a commercial software

Streamline simulation is developed to simulate waterflooding in fractured reservoirs. Conventional reservoir simulation methods for fluid flow simulation in large and complex reservoirs are very costly and time consuming. In streamline method, transport equations are solved on one-dimensional streamlines to reduce the computation time with less memory for simulation. First, pressure equation is solved on an Eulerian grid and streamlines are traced. Defining the "time of flight", saturation equations are mapped and solved on streamlines. Finally, the results are mapped back on Eulerian grid and the process is repeated until the simulation end time. The waterflooding process is considered in a fractured reservoir using the dual porosity model. Afterwards, a computational code is developed to solve the same problem by the IMPES method and the results of streamline simulation are compared to those of the IMPES and a commercial software. Finally, the accuracy and efficiency of streamline simulator for simulation of two-phase flow in fractured reservoirs has been proved.

Carbonate rocks resistivity determination using dual and triple porosity conductivity models

The rocks may be classified as Archie rocks or Non-Archie rocks,depending on the link between pore structure and resistivity of the rock.For carbonate rocks,keeping this factor in view,the applicability of Archie's law tends to be unreasonable and employing Archie's equation will ultimately lead to inaccurate estimates of the water saturation.Numerous investigators have reported models that forms a link between laboratory results and field well logs to determine water saturation in intricate pore systems.In case of complex systems,Archie's law fails to correctly define the resistivity-index curves.In addition,it is imperative to carry out investigations at lower saturation values in order to elaborate the non-Archie characteristics.This brings the dual and triple porosity conductivity models into the equation.As these models are essential in defining the considerable changes of the resistivity-index curves,both qualitatively and quantitatively.The linkage between the two models is depicted electrically in series or in parallel.Moreover,it is possible to have a combination of the two configurations.As a result,the experimental results can be modeled accurately using least parameters.This work presents two models to determine water saturation in carbonate rocks,containing dual and triple porosity systems.This study also investigates the impact of different influential parameters such as saturation exponents,conductivity ratios,and pore volume fraction of each network systems,on the new models.Finally,the effect of each parameter is individually studied and the sensitivity analysis on the RI curves is produced.A new approach to apply these models is also explained which requires the use of NMR log,mercury injection capillary pressure(MICP)measurement,and simple plotting techniques to determine the water saturation.The proposed new models help petrophysicists to estimate water saturation in Non-Archie rocks,containing double and triple porosity network systems.