The Application Of Mapping And Statistical Methods For Defining Reservoir Heterogeneity
Authors: Owens W.W. , Murphy Robert P. 
Published: December 2007

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Abstract
In reservoir fluid injection operations to accomplish improved recovery, a knowledge of the permeability and porosity distribution within the reservoir is a prerequisite to selection of an optimum well arrangement and to either prediction or interpretation of reservoir performance. Many of the methods available for analytical characterization of reservoirs do not permit definition of continuous oriented trends or avenues of permeability which lead to fluid channeling. This paper describes a statistical and mapping technique that can be used to define and study both areal and vertical permeability and/or porosity trends within a reservoir. An imaginary three-dimensional rectangular coordinate or grid system is imposed upon the reservoir, with the "'horizontal" grid generally parallel to formation bedding, to define the location of known values of permeability from core analysis. Statistical techniques are used to study the frequency distribution of permeability within each grid plane. The areal distribution of permeability in each individual horizontal grid plane is defined by contouring. These individual grid planes are "stacked" to provide a three-dimensional picture of the distribution of permeability within the reservoir. A computer technique for contouring values within each horizontal, grid plane is presented. Results of a study of this type on a reservoir compare favorably with fluid movement patterns established during the early life of a waterflood.

Introduction
More thorough exploitation of known reservoirs to increase oil and gas reserves is a current trend in the oil industry. Improved recoveries from present producing reservoirs are being sought through the application of one or more fluid injection processes at some time during the economic life of the reservoir. In the planning of such operations, knowledge of the heterogeneity of permeability distribution within the reservoir is a prerequisite. Some reservoirs may be so randomly heterogeneous that they, in effect, become homogeneous to the movement of in-place and injected fluids. Recent experiences by the industry as a whole, however, indicate that the distribution of permeability within many reservoirs is not completely heterogeneous or random, there often being continuous trends or avenues of high or low permeability that can have serious and sometimes disastrous effects on the efficiency of fluid injection for improving recovery.