A UNIFIED APPROACH FOR FALLOFF AND BUILDUP TESTS ANALYSIS FOLLOWING A SHORT INJECTION/PRODUCTION TIME

This study presents a general methodology for analyzing falloff/buildup tests, particularly with short injection/production time; this methodology consists of a simultaneous match of the pressure drop, superposition derivative, and the normalized impulse derivative, by using the first and second drawdown derivative. Furthermore, a new radial composite model with a fractal transition zone (RCMFT) is also proposed for falloff tests; the RCMFT considers an intermediate region with fractal behavior between the invaded zone by the injected fluid and the non‑invaded homogeneous zone. New short‑, intermediate‑, and long‑time approximations for the pressure response are introduced. Application The methodology is general for analyzing falloff/buildup tests, but it is particularly suitable in those cases where neither the conventional semi‑log nor modern methods based on first derivative, can be applied. The RCMFT is helpfully for falloff tests in low mobility reservoirs, since it honors the dynamic of flow occurring when an injected fluid displaces another one with lower mobility. Results, Observations, and Conclusions It is important to distinguish the cases in which the superposition derivative matches with the second drawdown derivative and the normalized impulse derivative, in order to have a good control on the model selection, and on the parameters determination. In falloff tests, it is necessary to take into account the intermediate transition zone, since it has a sound influence on the pressure response of the system. Therefore, if it is ignored, then the skin factor could be overestimated. From the field cases presented, we have evidence of the fingering phenomenon at greater scales than those ones of laboratory experiments. Significance of Subject Matter The proposed methodology is promising, since it facilitates the well test interpretation in many practical situations. Therefore, it is recommendable to incorporate it into the transient pressure analysis workflow.