A Joint Venture Evaluation of Closed Chamber Testing On Pumping Oilwells

Abstract This paper presents the results of a Joint Venture applications research project between Petro-Canada Resources, Imperial Oil Limited, and Alexander Pressure Instrumentation Ltd, to evaluate the accuracy of a closed chamber surface technique for calculating bottomhole flowing pressure in pumping oil wells. For comparative purposes, high resolution electronic pressure gauges were run directly below the downhole rod pump. In addition, acoustical and dynamometer methods of calculating bottomhole pressures from surface information were evaluated and compared to both closed chamber data and downhole pressure measurements. Production volumes of oil, gas, and water were measured over one minute time increments with a special trailer mounted test separator. Data comparison and analysis summaries are presented, along with final conclusions reached. Introduction Closed Chamber Testing was developed in the early 1970's by Lloyd Alexander of Imperial Oil Limited, for application on drill stem testing in the Canadian Arctic. In 1980, Alexander and Associates extended the theory for use in analyzing pumping oil wells2. However, it wasn't until 1988, with the development of high resolution pressure transducers with digital output, that closed chamber testing on pumping oil wells became practical in the field. By early 1991, both Petro-Canada Resources and Imperial Oil Limited each had independently run closed chamber tests on several pumping oil wells, on an ad hoc basis. At this point, a joint venture was established between Petro-Canada, Imperial Oil Limited and Alexander to evaluate the accuracy of closed chamber tests in determining flowing bottomhole pressure, annulus gas flow rate, and wellbore fluid inflow rate on a pumping oil well.Reference 1,Reference 2(References are given at the endd of the text.) What is Closed Chamber Testing? Closed chamber testing on a pumping oil well involves installing a critical flow prover to the open side casing annulus of a pumping well, as shown in Figure 1 A high resolution pressure transducer is connected to the annulus between the casing valve and the critical flow prover shut-off valve. In Figure I, a transducer is also shown connected to the tubing flowline, to monitor tubing pressure. Output signals from the transducer(s) are input to a lap top computer, with appropriate software to record pressure versus time data. Generally, the test procedure consists of the following steps:Close flowline side casing valve and monitor pressure for three to four minutes.Open flow prover and vent gas for two to three minutes. An alternate method (for sour wells) is to hook up a nitrogen bottle and inject nitrogen through the prover, into the annulus, for two to three minutes.Close prover and monitor pressure for two to three minutes.Shut-down pump jack and monitor pressure for two to five minutes.Open prover and vent gas for two to three minutes.Start-up pump jack and end test. Example output is shown in Figure 2. The slopes of the graph developed in Steps 1 and 2 are used to calculate bottomhole pressure and annulus gas rate.