Variables Controlling Diagenetic Processes
The dependence of sandstone reservoir quality on composition has been recognized in numerous empirical studies (e.g., Hayes and others, 1976; Nagtegaal, 1978; Selley, 1978; Seeman and Scherer, 1984; Scherer, 1987; Smosna, 1989) and in experimental studies (Pittman and Larese, 1991). The composition and relative abundance of detrital components in sands greatly influence both physical and chemical diagenesis and, thus, reservoir quality. The purpose of this chapter is to discuss some of the effects of detrital composition on porosity and permeability and then review evaluation of mineral composition of a potential reservoir prior to drilling.
Evidence purported to document the influence of various controls on diagenetic processes or on reservoir properties abounds in the literature. However, such evidence often consists of simple crossplots in which the influences of only one or, at most, two variables are displayed. In most cases, the influences of other variables to which the same effects might be attributed are not discussed, or they are claimed to have a minimal effect or be held constant. Seldom is the data backing up these claims presented or available to outside workers. As a result, the reader is forced to accept these claims on faith alone, or to base his acceptance on prior knowledge of the unit, area, or relationship being discussed.
It is not the intent here to present incontrovertible evidence regarding the relative importance of each of the factors which control the major diagenetic processes. The data to accomplish that are simply not available. As discussed in Chapter 5, many of the controlling processes are still in question, and even where general agreement exists with respect to the importance of a particular process, the factors that control that process are commonly not fully understood. This chapter will, therefore, review examples of evidence presented in the literature which are claimed to support the importance of a particular control. This will give the reader an overview of those variables which are considered by specialists to play a major role in controlling diagenesis. Some of these factors may indeed be very important, while others may
Figures & Tables
Reservoir Quality Assessment and Prediction in Clastic Rocks
This course is designed to emphasize the following topics: (1) Historical perspective on previous and current empirical, and geochemical methods of reservoir quality prediction; (2) Overview of diagenetic processes which significantly impact reservoir quality and those factors which act as major controls on those processes; (3) Proper design of a comprehensive or limited-focus predictive analysis of reservoir quality; (4) Methodologies for the accurate measurement of all major dependent and independent variables; (5) Data analysis techniques involved in quality control and the assessment of variability prior to performing multivariate regression; (6) Steps involved in the generation of a multivariate regression to insure that the model developed provides maximum accuracy using a minimum number of independent variables; (7) Case histories from a variety of settings illustrating application of the recommended approach to reservoir quality prediction.