Expected Developments in Transient Testing

Abstract

Summary. This paper discusses the developments expected in six areas of pressure-transient testing during the next 50 to 10 years (advances in measurements, new models, computer-aided analysis, integration with other reservoirdescription methods, standardization, and new testing methods). Its purpose is to stimulate discussion purpose is to stimulate discussion among those working in well-test analysis about the developments needed in this area of technology. Introduction Transient tests are used in all areas of petroleum engineering to provide useful petroleum engineering to provide useful information about the well/reservoir system. For example, they can be used to evaluate the types of fluids discovered and the potential of wildcats and development wells by drilstem tests; to estimate the completion efficiency after perforating, gravel packing, or fracturing of a well; to monitor the changes in reservoir pressures and wellbore skin throughout the well's life; to determine the communication among several wells by interference and pulse test s; to provide information about injection wells through step-rate and falloff tests; and to play an important role as one of the reservoir-description methods. Transient testing is a rigourous, reliable, and relatively well-understood tool of the trade. Use of transient information is widespread for several reasons.They provide information needed to manage oil and gas reservoirs (e.g. permeability, reservoir pressure, and effective permeability, reservoir pressure, and effective fracture length).They are relatively simple to run (in some cases, we need only a surface pressure gauge and a valve). pressure gauge and a valve).The results from these tests are not tool-dependent (i.e., we don't need different interpretation methods for pressure gauges from different manufacturers if their accuracy, precision, and resolution are in the same range).Interpretation models are available in the literature (probably because several of these models were developed at academic institutions and service companies). From time to time, papers that summarize the state of the art of discuss the use of current technology are presented. This paper looks to the future. It points out areas paper looks to the future. It points out areas where technical advances are needed to solve existing problems in reservoir description and management. Areas of expected development were determined on the basis of the current st ate of technology and the forces that most likely will dictate the directions of the work. Although transient testing is considered to be a "mature" area of reservoir engineering, it is still is one of the most active areas of interest in research, development, and field operations. The high level of activity is expected to continue because (1) several technical problems have not been solved (e.g., rigorous analyses of tests in hetergeneous formations or reservoirs undergoing secondary or tertiary recovery are needed); (2) computer and communication developments have provided more capabilities to transfer, to process, and to analyze data; (3) the industry is becoming aware of the benefits of comprehensive reservoir description, which requires integration of several characterization methods where transient testing is proving to be a key element; and (4) results from work in this area have been successful in the past. Therefore, it is likely that resources will be allocated to develop the needed technology. The key word describing the expected developments is "evolution" . While a revolutionary development is could occur, it is more likely that small, steady steps will contribute to well-test-analysis development in the next few years. Advances in Measurements Flow rate and pressure are the two parameters monitored and used in well testing. parameters monitored and used in well testing. Flow rate originally was used as the controlling variable and pressure response was measured vs. time. The name "pressure-transient analysis: reflects this procedure. The flow rate usually was changed at the surface. The pressure response was measured either at the surface or downhole. Now, either flow rate or pressure is used as the controlling variable, and the response of the other parameter is measured (we have not only PD vs. tD type curves, but also 1/qD vs. tD type curves). Thus, "well-test analysis" is a more appropriate name than pressure-transient analysis. Analysis pressure-transient analysis. Analysis methods that use the transient behavior of the flow rate and pressure simultaneously also are available. Nevertheless, more tests are run by changing the flow rate at the surface and measuring the bottomhole-pressure (BHP) response vs. time. JPT P. 898