Studies investigating the validity of the conventional description of two phase immiscible flow are reported. Laboratory techniques for relative phase immiscible flow are reported. Laboratory techniques for relative permeability determination have been applied in well controlled permeability determination have been applied in well controlled experimental conditions to strongly wetting systems. The tests enable a definite description of drainage and imbibition displacement processes. Concurrently a numerical model, based on the conventional macroscopic flow equations was developed to simulate the dynamic displacement tests. The purpose was threefold; 1) To study the concept of relative permeability purpose was threefold;
To study the concept of relative permeability
To simulate the physical processes occurring during unsteady state displacement tests
To use the model to assist in the provision of laboratory data more relevant to reservoir simulation.
The results show the relative permeability concept is valid for drainage displacement. For imbibition processes the concept is not strictly valid and the macroscopic flow equations are limited in their ability to describe the physical process. Consequently the relevance of laboratory data derived using this conventional theoretical framework is limited and its applicability to the reservoir will depend upon the selection of the appropriate tests. Guidelines as to the selection of the laboratory tests suitable for the different occasions are given and illustrated with a small number of field cases.
Relative permeability is used to describe quantitatively the simultaneous transport of two or more immiscible phases through a porous medium. Inherent in the concept are the assumptions that each fluid remains continuous (in complete pressure communication) and that all flow is in the same direction. Thus use of the concept is only strictly valid under these conditions.
Determination of relative permeability for a given rock-fluid system can be by one of two laboratory methods; dynamic displacement tests or the steady state flow method. Unfortunately the results can often appear different. A variety of reasons may explain why and this paper attempts to identify the major ones. For example, data derived from dynamic displacement tests is often obtained using the simplified non-capillary Buckley-Leverett theory. This theory neglects the potential effects of capillary pressure and may thus give distorted data. Also it has been suggested that the different nature of the tests may lead to alternative fluid distributions during the two types of flow. Our goal is to provide a strong experimental and theoretical basis for recommending which laboratory tests, provide the data most applicable to the precise reservoir situation under consideration.
Fluid flow tests on drainage (wetting phase saturation decreasing) and imbibition (wetting phase saturation increasing) systems were conducted using unsteady state and steady state methods. In addition capillary pressure and wettability data for these systems was also generated. pressure and wettability data for these systems was also generated. The effects of flow rate and sample length on recovery and differential pressure from dynamic displacement tests are illustrated. This provides pressure from dynamic displacement tests are illustrated. This provides a basis for understanding the physical processes occurring in each of the two extreme wetting cases.
A numerical model based on Darcy's Law and the continuity equation was developed to simulate these processes. The effects of capillary pressure were included in the model which takes into account the contribution to flow of capillary pressure and also by applying boundary conditions quantifies laboratory scale capillary pressure effects. The recovery and pressure data can thus be predicted from the model which requires input pressure data can thus be predicted from the model which requires input relative permeability and capillary pressure data. Comparison of experimental observations and these theoretical predictions has enabled an assessment of the limits to the validity of the relative permeability concept to be made. Thus through the study of drainage and imbibition cases (the limits of reality) a consistent framework based on an understanding of the physical processes has been developed and is applied to some real wetting systems.
In order to clarify effects that may be quite small, a rigorous experimental procedure has been used and is described in detail below.
