Practical Aspects Of Closed-Chamber Testing

Abstract

Abstract Since their inception, closed-chamber testing techniques have been refined to the point where imperial Oil's drill stem tests are almost exclusively designed for closed chamber testing. As in a conventional drill-stem test, the primary objective of the closed-chamber test is to obtain reservoir pressures, confirm reservoir content and define well potential. The build-up of surface pressure is monitored and these measurements, along with estimates of flow rate into the closed chamber, become the basis of the testing engineer's subsequent decisions for flow and shut-in periods. After the initial observations of pressure and fluid influx, the subsequent test procedure can then be optimized. Most importantly, the nature of closed-chamber testing allows a well to be evaluated with maximum safety. This is a distinct advantage in an environmentally delicate area, particularly where the wells are drilled during periods of extended darkness. Introduction The development by Imperial Oil of closed-chamber testing techniques has resulted in one of the most effective evaluation tools for wildcat wells. Closed-chamber drill-stem testing is similar to conventional drill-stem testing in that both are basically a temporary completion of a well. The primary objective of the tests is to obtain accurate information on reservoir pressure, reservoir content and well potential. Accurate pressure determination will be used by the exploration group to aid in selecting follow-up drilling locations in the area and by the reservoir group as a starting point for reservoir studies. Knowledge of the reservoir fluid is important for the design of possible future production facilities. Most importantly, an accurate estimate of well potential is needed to determine the economic feasibility of future production-facility construction, especially in frontier areas. The closed-chamber method of testing has the advantage that the type of reservoir fluid can be identified and an stimate of its flow rate can be made after the initial flow period. Depending on these estimates and the objectives of the particular test, a decision can be made during the initial shut-in periods as to whether the remainder of the test should be conducted closed chamber or in a conventionalmanner. These flow rate estimates will indicate the duration of the shut-in times necessary to obtain a satisfactory pressure build-up and subsequently meaningful Horner pressure build-up plot. Definition of a Closed-Chamber Test A closed-chamber test is quite similar to a conventional drill-stem test. The basic difference is that during a closed chamber test the well is shut-in at the surface when the subsurface tester valve is open, and open at the surface only when shut-in downhole at the formation. The surface equipment for a closed-chamber test is modified to allow the monitoring of pressure versus time. This in turn identifies the fluid influx as gas, oil or water and allows an estimate of the flow rate to be made. Equipment for Closed-Chamber Testing Figure 1 is a schematic showing the surface equipment used for most conventional drill-stem tests. It has no provision for monitoring surface pressures with each opening of the downhole tester valve.