Research On The Triple Porosity Model Of The Fractured-vuggy Oil Reservoirs

Carbonate oil reservoirs are widely distributed and have good exploitation potentials.Its reasonable development and effective utilization are of great significance to the national energy supply strategy and national economic development.There are fractures and vuggys in carbonate reservoirs,and their seepage laws are different from those of reservoirs with only one porosity.In order to reflect the reservoir characteristics of carbonate reservoirs,carbonate rocks are simplified as triple media composed of matrix system,fracture system and vuggy system.Considering the stress sensitivity of reservoirs,the effect of temperature on viscosity and fractal characteristics of reservoirs,the mathematical models of triple porosity and triple permeability have been constructed.The mathematical models are nonlinear partial differential equations with variable coefficients,which are discretized by fully implicit finite difference schemes,solved by Newton-Raphson iterative method based on self-developed programs;According to the calculation results,the dimensionless well bore pressure and pressure derivative curves are plotted.And the sensitivities of parameters are analyzed.Meanwhile,the effects of various parameters on the calculation process are analyzed;In order to describe the anisotropic reservoirs,the elliptic flow model has been established,and the pressure variation characteristics of the better permeability and the worse permeability are compared and analyzed;According to the different temperature characteristics at different depths,the mathematical model has been established.And the pressure variation characteristics of different depths are compared and analyzed.The main conclusions of the study are in the following sections:(1)Considering well bore storage and skin effect,the preesure response in triple porosity reservoirs with constant pressure boundary can be divided into six redimes:1.Pure well bore storage regime;2.Skin factor influence regime;3.Inter-porosity flow regime of vugs and fractures;4.Inter-porosity flow regime of matrices and fractures;5.Inter-porosity flow regime of matrices and vugs;6.Stable flow regime.(2)The increase in dimensionless permeability modulus,dimensionless inter-porosity transfer parameters,dimensionless well-bore storage coefficient,dimensionless viscosity factor and fractal dimensions will make the numbers of iterations grow.With the increase of skin factor,the numbers of iterations of calculations of pressures in vugs and matrices will decrease,but the numbers of iterations of calculations of pressures in fractures will increase before skin factor increases to 3.And the numbers of iterations of calculations of pressures in fractures will decrease when skin factor is greater than 3.(3)Elliptic flow model can describe anisotropic reservoirs.Because of the constant flow production,in order to achieve a specific velocity at well bore,the directions of poor permeability need more pressure,but the velocities of pressure transmissions do not change.(4)Considering that the reservoirs have different temperature at different depths,the pressures value are larger with the increase of depth.However,the pressures at different depths have the same trend with time.(5)The theoretical model presented in this paper shows that the dimensionless pressure has a certain deviation from the measured curve in the early stage due to the uncertainty of the production site.But the calculated results in the later stage fit well with the measured data.The field data of pressure derivative also deviate from the theoretical results in the early stage,and the time of inter-porosity regime of matrices and fractures is very short.This phenomenon may be related to heterogeneity.