Application of TDS technique to developed reservoirs

Well test interpretation methods for a single well in infinite reservoirs may not be suitable for those wells when their pressure is affected by other wells operating in the same reservoir. This effect becomes more significant as both the flow rate and the test duration increase. It is observed in drawdown tests when the well experiences an additional pressure decline due to production from other wells and, also, when the well produces under pseudosteady state before shut-in it for a buildup test. When pressure data are interpreted as recorded, estimation of reservoir parameters may not be accurate. Slider1–3 introduced a technique for analyzing a pressure test that takes into account the effect of nearby active wells. Corrected or extrapolated pressures are obtained by applying the superposition principle to include the pressure decline contribution from the neighboring wells. Traditional semilog plots are then constructed and permeability and skin factor can be estimated, respectively, from the slope and intercept of their linear trend.A new technique, called TDS (Tiab's Direct Synthesis), was designed to analyze pressure and pressure derivative data without using type-curve matching. It uses characteristic features found on the derivative plot, so reservoir parameters are directly estimated. It depends upon how well the pressure derivative is calculated. If derivative is taken to the recorded pressure data the resulting curve will not be properly defined and the estimated parameters may be erroneous. Application of the TDS technique to wells in depleted reservoirs is presented here. The recorded pressure is extrapolated to include the contribution from other wells as suggested by Slider. Once the pressure derivative of the extrapolated data is taken, the TDS technique as discussed by Tiab [Tiab, D. 1993. Analysis of Pressure and Pressure Derivative without Type-Curve Matching: 1- Factor de daño and Wellbore Storage. J. Pet. Sci. Eng. 12 (1995), 171–181.] can be readily applied. It was successfully tested with synthetic and field examples. A comparative analysis was carried out to see the effects when derivative is taken to uncorrected pressure data and the estimation of permeability, skin factor and drainage area.