Analysis and Design Methods for Vertical Well Testing

Abstract

Two methods, each modifications of a technique proposed by Prats, are recommended for analyzing vertical well tests for horizontal and vertical permeability. The methods are derived and presented, and their permeability. The methods are derived and presented, and their applicability is demonstrated using simulated vertical pulse test data. Information is provided on the behavior of vertical pulse tests in one- and two-layer reservoir systems. Vertical Well Testing Provides Important Reservoir Data Vertical well testing between two perforations in the same wellbore, including interference and pulse testing, provides a mechanism for estimating both horizontal and vertical permeabilities near the well. Those permeabilities are important in reservoir analysis because they can indicate if there is communication between zones or behind the pipe of if tested zones are separated effectively. Such knowledge is essential for selective flooding and vertical conformance control.This paper presents information about vertical well testing techniques, analysis, and design. Both interference and pulse tests are discussed. A future paper will describe field evaluation of the paper will describe field evaluation of the techniques, with a case history.Vertical well testing is accomplished by isolating the upper and lower portions of the wellbore and using one portion as a pressure observation location and the other as an active (injection or production) location. Either production or injection production) location. Either production or injection can be used at the active perforation, but an injection-type test usually is easier to run. All vertical well tests are a class of interference test because pressure is measured at a location other than the injection or production location. A vertical well test is a special type of vertical interference testing that uses alternating (usually equal) periods of injection (or production) and shut-in repeated for several cycles. Because of its periodic nature and the resulting ease in periodic nature and the resulting ease in recognizing test response, pulse testing generally is the preferred technique.Two methods have been devised for analyzing vertical pulse and interference tests. The methods are based on the same flow equation and give comparable results, although the mechanics of using them are somewhat different. Both rely on computer programs that normally would be used for single-well transient tests or multiwell interference tests. The two methods were tested using simulated test data and gave reasonable estimates of formation properties. This paper explains the methods, provides theory for the methods, and illustrates their applicability in analyses of test cases.The only method in the literature for analysis of vertical pulse tests without a computer (proposed by Falade and Brigham) is limited to situations with negligible wellbore storage. In such cases it appears to work adequately.The vertical well test analysis methods given her can be applied when there is significant wellbore storage at both the pulsing and observation perforations. That situation specifically is excluded perforations. That situation specifically is excluded from most published analysis methods. P. 505