Case Histories of Analyses of Characteristics of Reservoir Rock from Drill-Stem Tests

The presented case histories of analyses of characteristics of reservoir rock from drill-stem tests illustrate that drill-stem test analysis may be used to evaluate a formation within the vicinity of a wellbore. The examples presented show that an analysis will determine to a practical degree such properties as true pressures and potentiometric surfaces, transmissibilities, actual and in situ producing capacities and permeabilities, productivity index, damage ratio, production rates, distance to any apparent barrier interferences near the wellbore and the approximate drainage radius during a test. The properties thus determined are dependable enough to enable an operator to decide just what is going on in a particular formation, if a formation is worth any effort and expense to complete for production and if a treatment of some type may be needed during completion. They are dependable enough to make comparisons of the rock matrices of different well locations in a reservoir, aiding in a determination of the degree of reservoir homogeneity. The pressures and potentiometric surfaces determined are dependable enough to determine reservoir continuity between wells and to determine which reservoirs are within the same pressure system. Utilizing pressure-elevation graphs, gas-oil and oil-water contacts (which may not be obvious by other means such as electric logs) may be determined from the pressures obtained. In many cases the extrapolated pressures are the initial reservoir pressures, and the drill-stem test is the only means by which they are obtained. Introduction Four case histories were chosen to illustrate the practical usefulness of a drill-stem test analysis to determine a reservoir's characteristics and to show the limitations of an analysis. The case histories chosen illustrate the different types of drill-stern tests which may be taken. The methods and calculations used to make the analyses are presented.