Well Control Simulation Model of Oil-Based Muds for HPHT Wells

Abstract

Abstract A kick is defined as an unscheduled flow of formation fluids into a wellbore. Kick control is crucial for safe drilling in high pressure high temperature (HPHT) wells. During drilling with oil-based mud (OBM) in these conditions, it is difficult to detect and control a kick because of high gas solubility and mud density change with pressure (P) and temperature (T). The main objective of this paper is to simulate behavior of kicks in HPHT conditions in offshore wells with OBM. To simulate kick behavior more accurately, it is necessary to consider mud density change with P and T. We select Standing-Katz correlation for base-oil density among three typical methods by comparing them with experimental data available. With the correlation, we update OBM density by use of Hoberock et al.'s compositional model in HPHT conditions. In this paper, by updating OBM density in Choe and Juvkam-Wold's modified two-phase well-control, kick behaviors are analyzed more realistically. We analyze several cases in 20,000 and 30,000 ft offshore wells with OBM. Under the condition of simulations, mud density decreases as well depth increases because temperature is more dominant than pressure. Pit volume does not always increase as the kick rises to surface because of combined effect of gas solubility, P, and T on kick volume. If we consider the density change of OBM, more surface choke pressure is needed for constant bottomhole pressure with deeper vertical depth and HPHT condition. By applying the proposed method, we can have realistic modeling of wellbore pressure profile and kick behaviors.