Interference Testing of Horizontal Producers and Injectors in the Huntington Field

Abstract

Abstract This paper describes the design and interpretation of interference tests conducted between injectors and producers in the Huntington oilfield. The field is located in the UK Central North Sea and developed with four horizontal producers and two inclined water injectors. Water injection provides reservoir pressure support and mitigates the uncertainty of aquifer strength and its connectivity to the oil leg. This ensures adequate pressure maintenance in support of hydrocarbon recovery. It is important to understand effective communication between the wells. This is required to improve the forecasts of water breakthrough, to plan preventative actions and to optimise field operations and reservoir management. Therefore, a series of modified pulse tests were performed during the clean-up and well test campaigns to minimise disruption and delay to the drilling schedule. Data were recorded using permanent down-hole gauges installed in the horizontal producers, and the analyses of the results were performed using both analytical and numerical models. The modified pulse tests confirmed good communication between the producers tested. A reasonable match between the modified pulse test data and simulation model predictions is demonstrated in this paper, where reservoir properties such as permeability and porosity estimated for the inter-well areas show good agreement with the well test results. The test between injector and producer was also used to match the pressure response and can be used to predict injection water breakthrough. In the test, water was injected into two different intervals, the Upper and Lower Forties. Comparison of the injection test results with numerical simulation data suggests that no communication exists between these two intervals. This is a practical example of interference testing which provides insight and assurance on effective reservoir properties on an inter-well scale. This kind of data, before field start-up and free from the influence of other producers, is very useful for the field performance prediction and also rarely available in the literature. Introduction Interference tests were first introduced by Jacob (1940) for water wells and later demonstrated for use in petroleum engineering by Elkins (1946). Driscoll (1963) then outlined the use in the petroleum industry to obtain average areal reservoir transmissibility, storativity and degree of communication between wells. For interference testing of horizontal wells, Malekzadeh and Tiab (1991) provided type curves and direct analysis methods for an isotropic medium. Johnson et al. (1966) introduced pulse tests; a modification of interference tests, where the active well flow rate is changed several times to form a series of alternate flow and shut-in periods instead of a single producing constant rate. This was analysed using the tangent method to determine the time lag, tL and response amplitude, ?p. It was initially believed that durations for pulse tests would be shorter compared to interference tests. However, Kamal (1983) showed that the testing times remained the same for both pulse tests and interference tests if the same type of pressure gauges were used but the shut-in time for pulse tests is less. This is the main advantage of the pulse tests, where a long shut-in duration is not required to record pressure data.