The objective of this paper is to present well control challenges, and results of utilizing wellbore dynamic simulation to achieve safer formation tester (FT) sampling and deep transient tests (DTT) operations that was drilled by PETRONAS. Insight will be provided based on the first implementation in a Southeast-Asia offshore well, with focus on pre-job simulation that is validated with measured data to help improve understanding of gas/hydrocarbon interaction with wellbore mud during and after FT pump-out operations.

FT involves obtaining formation pressure, pressure transients, and downhole fluid samples, and the latest DTT technology enables larger gas/hydrocarbon volumes to be pumped into the wellbore which requires a comprehensive understanding of the processes involved. Wellbore dynamics simulation was utilized to accurately predicts the interactions between downhole pumped hydrocarbon and drilling fluid using a dynamic multiphase flow simulator. For the sampling operation, a maximum allowable downhole gas volume is evaluated prior to operation and simulations are compared to surface gas observation obtained during a wiper trip (mud circulation). During DTT operations, pumped formation fluids are routed to a circulating sub, where they are mixed with circulated mud and the mixed fluids are simultaneously carried to surface. Downhole wellbore pressure measurements are sent to a real time cloud-based dashboard and compared with simulations, which is monitored by both PETRONAS project and execution teams to ensure a safe well control condition. The ability to weigh measurements against simulations creates a comprehensive understanding of well control scenarios and helps operation team to ensure a safer execution of FT operations than conventional methods.

For wireline FT operation, post job comparison showed that the simulation matched well with surface observations during the wiper trip. The simulator accurately predicted the surface free gas arrival compared to mud-gas logging measurements, which confirmed that gas stayed dissolved in the Synthetic Based Mud (SBM) downhole without migrating upwards. For DTT, wellbore pressure measurements were sent in real time to a cloud-based dashboard and are compared to simulations and simulations could be quickly re-run to account for changes in observed formation fluid, downhole flowrates or mud circulation rates. As a results, both the FT and DTT operations were conducted successfully and safely and in both cases the measured data agreed well with the simulations.

With the accurate wellbore dynamics simulator, changes in drilling fluid design, circulating rates, hydrocarbon composition, downhole pump rates, and pump duration for various FT design sequences are quantified, and the downhole well pressure, free-gas distribution along the well geometry, and gas rates on surface can be predicted. This insight provides more flexibility for PETRONAS to understand and plan advanced FT operations and enables larger volumes of hydrocarbon to be pumped downhole. Furthermore, adopting an advanced pressure transient testing method like DTT also aligns with the industrial and PETRONAS's effort of reducing carbon dioxide emission footprint.

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