Taking the Proper Action to Gas Influx during Constant Bottom-Hole Pressure Technique of Managed Pressure Drilling

Abstract

Managed Pressure Drilling (MPD) techniques rely on precisely controlling annular pressure profile and hence enabling us to overcome challenges due to narrow mud window in offshore and deep-water drilling. In a Constant Bottom-Hole Pressure (CBHP) MPD the bottom-hole pressure is kept relatively constant which allows circulating small influxes out of the well without shutting in. However, during circulation, annular pressure must not exceed the fracture pressure of the weak zones and maximum allowable surface pressure. Therefore, accurate prediction of the annular pressure profile is vital in the decision making process. It enables us to decide whether to continue drilling, shut in the well or take another action such as increasing the pump rate or mud weight.Most of the annular pressure prediction methods during entrance of an influx rely on simplifying assumptions that can cause a significant error and a faulty well design. This issue becomes more important during drilling with Synthetic Based Mud (SBM) in which solubility of gas in the mud cannot be ignored.We attempt to present a transient model for an accurate prediction of annular pressure profile during well control operations in CBHP technique of MPD. The presented model is developed based on the conservation equations and it takes the solubility of gas in synthetic based mud into account. The validity of the model has been tested against the available experimental data from the field scale low-pressure flow loop (8" X 4.5", 90' long) available at The University of Tulsa.Annular pressure profile and maximum surface pressure (casing peak pressure) during circulation of a gas influx are calculated by the introduced transient two-phase model. A chart based methodology and a simple algorithm are developed by which, the proper action could be taken according to the simulation results. This provides a powerful decision making and design tool in MPD operations that ensures delivery of safer wells with lower Non Productive Time (NPT).

Development and application of transient gas‐liquid two‐phase flow model considering sudden density change

“…For conventional drilling, Rommetveit et al and Xu et al developed gas‐liquid two‐phase flow models, which were established for water‐based mud. For deepwater drilling, Sun et al and Yu et al developed gas‐liquid two‐phase flow models for oil‐based mud and synthetic‐based mud, respectively. For underbalanced drilling, Lage et al and Song et al developed a gas‐liquid two‐phase flow model and proposed the idea of combining the first‐order Lax‐Friedrichs scheme and the second‐order MacCormack scheme to solve the model.…”