Productivity Evaluation By Finite Element Method And Underbalance Pressure Determination For Perforated Oil Wells In Naturally Fractured Reservoirs

Underbalance perforating has been widely accepted as a standard for perforating to abtain the optimum perforating performance. However, almost all studies about perforating optimization did not take into account the presence of natural fracture reservoir. The productivity evaluation of perforated oil well becomes very complicated in the presence of natural fracture in reservoirs, the mathematical model has been established in this paper based upon the given three-dimensional physical model describing the characteristics of seepage flow in the naturally fractured reservoir and continuity equation. The equation of variation for the finite element derivation has been deduced for obtaining the solution of the elliptical boundary value problem. The study has acquired the quantitative analysis results about the influence of different perforation and formation parameters towards the productivity of oil well in the naturally fractured reservoir through mesh subdivision, finite element numerical modeling and quadratic regression analysis in orthogonal designing. In addition, A comprehensive approach for method of reasonable underbalance pressure design has beed completed. By mean of finitie element analysis(FEA) and coupling models study of rock mechanics and hydrodynamics theory, new models for underbalance pressure had been carried out. The important points abtained are very nutritious to direct the operation of perforating completion in natural fracture reservoirs and improve the efficiency of single-trip perforating completion operations.The main contents of this thesis are listed as as follows:(1) The phsical models describing fracture structure have been put forward based on the detail analysis of phsical characteristerics of the naturally fractured reservoirs.(2 )The method to depict face configuration of fracture wall has been evaluated, and model predicting fracture width has been set up.(3) The 3D mathmatical models essentially governing the fluid flow in fracture formation have been established. Its differential equations for the fininte element solution has also been derived.(4) The methods of grid meshing and solving for the finfite element equations have been reasonably carried out, the computer FEA programs have been also workedout.(5) The influence of perforating parameters on well productivity has been analyzed, the result shows the same perforation parameters have different effects to the well productivity in the naturally fractured reservoir with the varied network model. The productivity of model with the two groups of vertical fractures or three groups of orthogonal fractures are greater than that of only with one group of horizontal or vertical fractures.(6) Lots of results have been acquired by running each test according to orthogonal designing, the computer codes of quadratic regression analysis haved been programmed, the relative importance of perforation parameters on the well productivity has been obtained for the each physical network model.(7) The transient back surging performance during underbalance perforating has been studied by the FEA method, the method for determining the minimum underbalance pressure based on critical renolds number has been proposed according to the clean-up mechanism in the compacted zone around perforation tunnel.(8) The models coupling rock elastoplasticity mechanics and non darcy flow equations have been developed for determining the maximum underbalance pressure based on mechanism of perforation stabilization and critical equivalent plastic strain.(9) The method for determining the minimum and maximum underbalance pressure fully incorporated the effect of properties of formation and fluids, properties of rock mechanics, and the type or performance of shaped charges. It take a essential progress than previous empirical models and have wide practical importance.(10) It is the first time in abroad and home that the correlation of perforation parameters versus oil well productivity could be accomplished by mean of FEA method, it is of great importance to guide the design of perforating job in in naturally fracture reservoirs. Theme: Productivity Evaluation by Finite Element Method and Underbalance Pressure Determination for Perforated Oil Wells in Naturally Fractured Reservoir...