Real Time, Low Cost, Diagnostic Tool for Understanding Oil and Gas Well Performance
Authors: Alexander L.G. 
Published: March 2010

New rapid methods for testing oilwells are presented based on modified closed chamber theory. The tests are of great assistance in solving pumping problems. In the case of a sudden drop in production, the tests define the problem in real time. Tubing leaks, pump failure, defective check valve or flowline failure can readily be detected at the time of the test and remedied in a cost effective manner The tests are of short duration (twenty minutes or less). They have minimum equipment requirements (i.e., a critical flow prover, a high-resolution pressure recorder and a laptop computer). Several tests can be conducted in a single day, travel time included. The mass balance theory and relevant equations behind these tests are developed and explained with emphasis on the practical aspects. Test procedures are described with step by step detail in field examples. One of these examples obviated the need for a previously ordered service rig. Another example shows how a simple, non-quantitative visual scan of the pressure response can be used to immediately recognize problems (in this case the problem was a severe foam buildup). Some other applications of the method are mentioned, including gas well testing, workover and completions, surface casing vent tests and nitrogen cushion drill stem tests.

Introduction

Closed chamber testing techniques for drillstem tests were first developed and described(1-4) in the early 1970s and 1980s. These same techniques were extended to include pumping well analysis, first published in 1980(5), and other later papers(6-10). As the name suggests, all flow rate measurements were measured under closed chamber conditions. That is, the surface valve was closed when measuring inflow rates during a drillstem test. Similarly, the casing was closed while measuring inflow rates for pumping wells. The technique has now been modified to enable measurements of inflow rates in any non-closed chamber situation: i.e., whenever the surface valve is open. The method of testing described uses the same mass balance equations developed forclosed chamber testing, but extends their application. The extensions remove the assumption that the flowrate is constant when the prover is being vented. They also provide the ability to calculate reservoir inflow rates at the same time the well is flowing at surface.

Applications and Definitions

Some applications for this new technique are:Pumping oil well: Venting the annulus of a pumping well to evaluate the wellbore gas volume, the annular gas rate and the inflow rate of gas and oil when the pump is deactivated.Gas well testing: Determining sandface gas influx rates as a gas well is being produced at surface. Present practice is to report the surface flow rate as though it were equivalent to the downhole sandface rate. This is seldom true. For this reason, reservoir computations utilizing surface rate data are frequently incorrect. This problem is overcome with the new testing technique which calculates adjusted sandface rates directly.Nitrogen cushion DST: Measurements of downhole inflow rates during flow periods of drillstem tests where a nitrogen cushion is simultaneously being vented at surface.