Broaching Analysis During Post-Blowout Capping Following Worst Case Discharge: A Gulf of Mexico Case Study

Abstract:

Unsuccessful attempts for capping an offshore well undergoing worst case discharge (WCD) may lead to fracturing and subsequent hydrocarbon broaching on the seafloor, breeding an ecologic disaster. Following a blowout, efforts to mitigate and cease uncontrolled subsurface discharge involve the placement of a capping stack over the compromised blowout preventer (BOP) of the discharging well. During the capping stack shut-in process, pressure build-up can occur in the wellbore, exposing locations of possible fracture initiation, such as directly below the casing shoe and sites of casing collapse (which can occur during the preceding WCD period) to highly-pressurized fluid. Broaching refers to hydrocarbon migration through the generated fractures, across stacked geological formations to seafloor. The driving force of the propagating fracture is delivered through the energy of the discharging reservoir. The 1969 Union Oil blowout in Santa Barbara, California is the quintessential example of fracture broaching during post-blowout capping.

Fracture propagation during post-blowout capping can be modeled numerically using inputs from the preceding post-blowout discharge (WCD). A hypothetical case study is performed replicating typical deepwater Gulf of Mexico (GoM) parameters considering rate-dependent fluid injection into the fracture opening. Vertical fracture containment is investigated with fracture height as the main dependent variable. The casing shoe depth is the primary prevention measure (line of defense) against broaching with reservoir depletion being an effective remediation factor, hindering fracture growth.

Research reported in this publication was supported by an Early-Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine.