Quality of well testing in highly productive reservoirs directly depends on the pressure-gauge placement in the wellbore. This paper documents the impact of the placement of downhole gauges on pressure transient analysis (PTA) for high-productivity reservoirs. The article illustrates cases where this late-transient behavior is strongly influenced by temperature effects, which can lead to significant errors if not considered during the interpretation process.
Although the correction of measured pressure to datum is possible by proper modeling of the influence of non-isothermal effects on the test string and the produced fluids caused by temperature changes, it is preferable to avoid this situation by suitable gauge placement. This greatly facilitates a more accurate interpretation of data using PTA with a reduced uncertainty in the definition of the appropriate reservoir model to use. Proper modeling during the test design of these temperature effects on the correction of pressure to datum also allows the determination of the resulting uncertainty pressure variations and the selection of the optimal test-string design, with consideration made to the expected temperature changes, fluid present in the wellbore, and range of productivity. Reconstruction of pressure is also possible despite a high level of resulting uncertainty.
A workflow for reconstruction of pressure data taking into account temperature effects is proposed. We emphasize that such corrections cannot substitute the correct pressure measurement for successful well-test data interpretation. Present gauge technology allows proper test design and correct placement of pressure and temperature gauges in close vicinity of the interval of interest, to avoid or minimize potential problems related to the reconstruction of the measured pressure to datum.