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Effects of Near-Wellbore Supercharging and Hydro-Mechanical Coupling on Pressure Response for Formation Testing While Drilling

Formation testing while drilling (FTWD) shows a great potential for characterizing reservoir type, estimating reserves, and determining reservoir energy. With the increasing in unconventional reservoirs, however, the utilization of FTWD has encountered some challenges. The near-wellbore formation prior to conducting the formation testing is usually supercharged due to the mud filtrate invasion during drilling. The supercharged pore pressure can directly influence the pressure response of FTWD. If the pressure response curves are misinterpreted, it may bring some mistakes or risks to engineering design. In addition, the formation testing process is a hydro-mechanical (H-M) coupling process, and the variation of pore pressure in formation can change the porosity and permeability of the rock, which will in turn affect the pressure response of formation testing while drilling. To clarify the effects of near-wellbore supercharging and H-M coupling on pressure response of FTWD, a three-dimensional simulation model of FTWD was built andthe pressure responses with different parameters wereanalyzed. The simulated results indicated that: In thesupercharged condition, the initial probe pressure ishigher than the original pore pressure. And during thepressure recovery stage, the probe pressure rises abovethe original formation pressure in the early part of thebuildup and then decreases to reach the equilibrium state.Also, the supercharging effect can result in theoverestimation of the original formation pressure. TheH-M coupling can produce an extra coupling skin on thepressure response of FTWD, and H-M coupling cancontribute to the underestimation of the originalformation mobility. The results of this paper can help usto understand the pressure response behavior andimprove the formation parameter interpretation accuracyof FTWD.