The Study On Well Test Analysis Method Of Low-permeability Reservoir

Based on the former theory, the author has constructed a new well-test theory of low permeable reservoir and presented a log interpretation method of non-dependent beeline character of radial fluid in this paper. This method is different from the one that used beeline character of well-test curve for interpretation now. The new method can be used in low permeable reservoir of permeability in any spacing interval well-test, it can be used for pressure descent and for recovering pressure.Instable well-test analyses can determine the reservoir character for long time. Reservoir geophysist have done many studies in determining homogeneous reservoir pressure distribution for several years. Hurst and Muskat constructed a model of sing end flow in homogeneous reservoir. Muskat first studied reservoir of various permeability.The aim of this paper is presenting a new well-test analyse method of non-dependent beeline character of radial fluid. The method can know heterogeneous reservoir pressure data in any spacing interval permeability and can get permeability distribution, pressure distribution and so on in strata. The author didn't only research the pure radial fluid problem that is permeability changes with the radial distance while porosity is a constant,but also investigated the log analyse problem that porosity is not a constant.In Chapter 1, we probe the heterogeneous reservoir forward problem that permeability changes with the radial distance and with the horizontal surface. Carslaw and Jaeger together studied the thermal conduction problem in which the thermal conductivity changes with the square of the radial distance. They get the analytic solution by using Laplace transform. Loucks supposes that permeability changes with the square of the radial distance and he gives limit well diameter and line source solutionwhen pressure is known. Hantush probes the vadose problem in which stratum thickness changes with the power of X while no changes with Y. He both give the the analytic solution in Laplace space and in real space. All above analytic solutions are supposed stratum parameters change with one direction. So far, no one gives the the analytic solution of the heterogeneous reservoir in which permeability changes with the radial distance.Recently, Oliver studies the vadose problem of the heterogeneous reservoir in which permeability changes with the radial distance. At the same time he supposes permeability changes a little with "reference permeability", using disturbing theory and Laplace transform he gives the approximately analytic solution of pressure and its derivative in instable well bottom. But it's suppose has a lot of difficulty in real use.Also in Chapter 1, we study the general GPDS. This one is a correct of Oliver's. Through real use, it has no dependence with "reference permeability" , predigest GPDS and make GPDS in wider real use. GPDS is got in instable pressure descent, and can be used in the interpretation of pressure recovering through stacked pressure. Otherwise in this paper analytic solution is given when surface is closed and flux expression is given when output in well bottom of given pressure. When given output we can get: 1. stable pressure solution, 2.average stratum pressure, 3.characteristic function, 4.exact expression of stable permeability in equivalent homogeneous reservoir. At the same time we develop the analytic solution of infinity effctive pressure and its derivative in two different flow profile condition. Comparing with above four approximately analytic solutions, we design a numerical fliter of the heterogeneous reservoir and use it to get the well bottom pressure and stratum pressure distribution in any condition.In Chapter 2, we study the non- isotropic oil deposit well test explanation question which the penetration coefficient changes continuously. Kamal has carried on the appraisal to the oil deposit value simulation research work, and exhaustively discussed Shan Jing and the multi- wells well test in the oil deposit description application question. Pressed the degeneration based on the Kamal bottom of the well, Oliver has produced the computation radial direction permeability distribution approximate method using the Backus-Gilbert law. Oliver used this method to analyze a tertiary compound oil deposit well test data, finally indicated: Calculates the permeability distribution isequal to the actual permeability distribution smoothness, and confirmed the counter-question multi- solutions. Rosa and the Home two people have studied using the pulse well test data with the Oliver same question, they draw the conclusion: When excited well current capacity change, the inspection shaft pressure response was more sensitive to the stratum anisotropism, produces one kind to have the two dimensional permeability distribution oil deposit the well test explanation method, calculated each region through the non-linear return method the penetration coefficient, but it to divided the region quantity the request, has received the very big limit in the actual oil deposit description application. Yeh and Agarwal produced descended the data computation fluid fluidity distribution method using the water-injection well shut-in pressure, they thought figured out the fluidity from the instant bottom hole pressure derivative idea for the bottom of the well to survey radius volume weighted average, and has produced when the computation customs police pressure distribution method.Also in Chapter 2 and Chanpter 3, two analytical methods have been provided for calculating the distribution of the stratum permeability directly by the pressure derivative. One method, educed by the GPDS solution in chapter 2, is applicable for both of the oil reservoir with a large variation of the permeability and the pressure data smaller than the semi-log straightway, by which the distribution of the stratum permeability has been calculated by the recursive algorithm. The other one is gained by correcting the Yeh-Agarwal method. The right distribution of the stratum can be got by both of the two methods, however, the result by the first method is more exact At the very beginning, both of the two methods based on the condition of the pressure descending, by correcting the production time for the pressure recovery data, the right distribution of the stratum can also be obtained by explaining the pressure recovery data which have been corrected using the two methods. The instance of the descending and recovery of the pressure, enumerated in this text, approved that the Yeh-Agarwal method can be used to calculate the strata pressure distribution of single-phase flowing oil reservoir pressure recovery at the moment of closing the well. Meanwhile, some other methods have been given in this text, as well, and the analysis for the instances approved the veracity and security of the methods, such as the method for calculating the pressure distribution of the strata in the quasi-steady state, and the method for calculating theaverage stratum pressure^ the production index and the equipollent homogeneous permeability. The main purpose of this text is to study two aspects: one is the problem of undiluted radial flow with the porosity as a constant and the permeability varying with the change of the radial distance, and the other is the influence of the change of the porosity and the permeability taking on the distribution of 2-d plain to the explanation to the test shaft.In the Chapter 4, the problem has been studied that the analytical technique, put forward in this text, has been applied into the plane heterogeneous reservoir with the variable rate of permeation in the radial direction and with the angle (or in the X ^ Y direction ).The result showed that some parameters can be gained using this method, such as the equipollent distribution of the permeability in the radial direction, the average stratum pressure of the reservoir and the production index etc.. The study in this text has been fully summarized in the Chapter 5, and the conclusion also has been given, as well as the study orientation for the future being indicated.So to sum up, the main contributions of this thesis is that it established a new theory on anisotropic reservoirs well which has provided a new method to explain the pressure test materials for anisotropic reservoirs. This new method used in the well test analysis do not depend upon radial flow line characteristic, which is a breakthrough for the former explaining method used till today which generally use the straight line breakthrough for the former explaining method used till today which generally use the straight line characteristic of the curvaraence for the test well to conduct the analysis. It also provides a analyzing method for smaller than the semi-log straightway therefore this thesis is not only of theoreitical value but also of practical value.