Semester of Graduation

Summer 2021

Degree

Master of Science in Petroleum Engineering (MSPE)

Department

Petroleum Engineering

Document Type

Thesis

Abstract

Broaching is defined as the uncontrolled release of hydrocarbons to ocean seafloor after a loss of subsurface well control event. Failed attempts to cap the offshore wells undergoing worst case discharge may lead to hydraulic fracture initiation and subsequent propagation, leading to renewed release of hydrocarbon to the seafloor. During the capping stack shut-in process, pressure build-up will occur along the wellbore, exposing locations of possible fracture initiation to overpressurized fluid, such as directly below the casing shoe, and critical points along the well casing. Shall there be enough build-up pressure to exceed the minimum horizontal stress in an exposed layer, a fracture will initiate and may propagate as energy is provided from the movement of fluids in the wellbore. This can lead to a severe environmental impact on marine ecology if the fracture broaches to the seafloor. A quintessential example of fracture broaching during post-blowout is the Santa Barbara Channel Alpha Well 21 blowout in 1969 which resulted in an oil slick discovered near the discharging well. To help evaluate the possibility of such an event occurring in offshore waters of the Gulf of Mexico, numerical modeling is performed on a hypothetical case study using deepwater parameters examining the propagation of a “longitudinal” (i.e., parallel to the axis along the center of the wellbore) fracture during the containment or capping shut-in period. A workflow is developed for Worst Case Discharge (WCD) calculation, assessment of fracture initiation, propagation, and broaching during the capping shut-in period, and relief well heavy-mud injection strategy. A transient wellbore model accurately captures the fracture properties as they grow in height and length. The results of this study show that the growth of a fracture initiated from the side of the wellbore is sensitive to depth of the casing shoe where the fracture had initiated, young’s modulus of overburden rocks, and the duration of the preceding discharge period. In xiv addition, sufficient mud density, and pump rate are needed to compensate the oil column and successfully kill the main wellbore.

Date

5-31-2021

Committee Chair

Gupta, Ipsita

DOI

10.31390/gradschool_theses.5339

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