A Methodology for Classifying Operating Regimes in Underbalanced-Drilling Operations

Abstract

International audienceThis paper proposes an extension to an existing operating-envelope technique used for underbalanced drilling (UBD) to enhance control of bottomhole pressure and inflow parameters. With the use of an implementation of the drift-flux model (DFM) with boundary conditions typically encountered in underbalanced operations (UBO), a steady-state analysis of the system is performed. Through this analysis, four distinct operating regimes are identified, and the behavior in each of them is investigated through steady-state calculations and transient simulations. In particular, the analysis reveals that a section of the operating envelope previously believed to be unstable/transient is, in fact, stable/steady when a fixed choke opening is used as an independent variable in place of a fixed wellhead pressure (WHP). This results in the steady-state operating envelope being extended, and gives an increased understanding of the well behavior encountered in UBO toward enabling the introduction of automated control. Finally, we investigate the mechanism behind severe slugging in UBO and argue that the cause is different from that of the slugging encountered in production and multiphase transport

Two-Sided Boundary Stabilization of Heterodirectional Linear Coupled Hyperbolic PDEs

“…To ensure safety and efficiency of operations, it is desirable to monitor at all time the amount of gas inside the well. This is a difficult task since sensors cannot be placed all along the drillpipe, and the dynamics of multiphase flow are known to be complex [3]. The presence of gas, in particular, makes the distributed, delay-like nature of the dynamics predominant and may generate instabilities, such as severe slugging.…”

“…Along with closure relations, this yields a set of three nonlinear transport PDEs with appropriate boundary conditions. The model can be linearized around a given equilibrium profile, which yields a system of the form (1)-(3) with n = 2 and m = 1 (see, e.g., [3]).…”

Review of two-phase flow models for control and estimation

“…Due to the high level of complexity encountered when deriving two-phase models from 1st principles, using black box or step response models are an attractive approach, The downside is that it might be difficult to identify and handle situations when the two-phase system exhibit changes in qualitative response, see Aarsnes et al (2016).…”

“…Models that strike the right balance between complexity and fidelity are sometimes referred to as fit-for-purpose models, and have been employed in control (Stamnes et al, 2011a) and monitoring (Willersrud, 2015) of drilling processes in one-phase flow regimes. Obtaining such simplified models becomes significantly more difficult for gas-liquid two-phase dynamics due to the significant complexity and distributed nature of multiphase pipe-flow (Aarsnes et al, 2014b(Aarsnes et al, , 2016. This makes the reduction to fit-for-purpose models for scenarios such as gaskick incidents, and underbalanced operations, challenging.…”

State and Parameter Estimation of a Drift-Flux Model for Underbalanced Drilling Operations

“…Especially for underbalanced wells producing gas, the magnitude of the production index has a significant impact on the dynamics of the UBD and thus on the control problem as well [4]. Hence, accurate estimation of the production index and reservoir pressure are important for an UBD operation.…”