The objective of this paper is to address the challenges related to well control and highlight the successful implementation of deep transient tests (DTT) operations in an offshore well located in Southeast Asia that was carried out by PETRONAS with the help of a dynamic well control simulation platform. The paper aims to provide insights into the pre-job simulation process, which ensured a safer operation from a well control perspective. Additionally, a comparison between simulated and actual sensor measurements during the DTT operation will be presented.
The latest DTT technology enables a higher volume of gas or hydrocarbon to be pumped into wellbore compared to formation tester (FT) operation. During the DTT operation, the pumped formation fluids are mixed with mud that is pumped from surface through a circulation sub into the annulus, and the mixture of fluids is then circulated out from annulus simultaneously to the surface during the drawdown period. To ensure well control safety, it is crucial to have a comprehensive understanding of the processes involved. Therefore, a dynamic multiphase flow simulator that takes into account the interactions between downhole pumped hydrocarbon and drilling fluids is important to better simulate the pressure downhole throughout the DTT operation.
In this case study, simulations were conducted prior to the job execution, considering several sensitivities, to ensure that the operation stayed within a safe operating mud weight window while meeting the surface gas handling limits. During DTT execution, real time downhole measurements were sent to a cloud-based platform, where they were plotted on a graph alongside the simulation data for monitoring purposes. Any changes in observed formation fluid, downhole flow rates and mud circulation rates during the DTT operation were quickly reflected in the simulation, this enabled effective communication between the PETRONAS project and execution teams ensuring a safe well control condition throughout the operation.
As a result, the DTT operation was conducted successfully and safely, with the measured data aligning well with the simulations. The accurate wellbore dynamics simulator allowed for quantification of changes in drilling fluid design, circulating rates, hydrocarbon composition, downhole pump rates, and pump duration for various formation testing design sequences. It also facilitated predictions of downhole well pressure, free-gas distribution along the well geometry, and gas rate on the surface. This valuable insight provides PETRONAS with more flexibility in understanding and planning advanced FT operations, while enabling larger volumes of hydrocarbons to be pumped downhole. Furthermore, adopting an advanced pressure transient testing method like DTT is in line with both industry and PETRONAS's efforts to reduce carbon dioxide emissions.
