Numerical modeling of fracture propagation during post-blowout capping in offshore wells

Document Type

Conference Proceeding

Publication Date

1-1-2020

Abstract

Seafloor broaching of reservoir fluids following a blowout can lead to a severe environmental impact. The growth of a fracture initiated from the side of the wellbore is sensitive to reservoir pressure depletion during the preceding discharge period and other geomechanical factors. Numerical modeling is performed on a hypothetical case study using typical deepwater Gulf of Mexico parameters examining the propagation of a longitudinal fracture during post-blowout capping conditions. In-situ stress and Young's modulus contrasts between the sand formation the fracture is propagating in and the barrier shale formations, as well as presence of a micorannulus in the cement-rock interface are dependent variables shown to control fracture height, which is the monitored dependent variable. Sensitivity studies are performed using a model developed with PETEX's REVEAL. A three-layer shale/sandstone/shale environment was used assuming the fluid in all formations to be water. Fracture propagation is dominated by the energy provided by the reservoir. An understanding of the reservoir dimensions and geomechanical properties is paramount in modeling fracture growth. Although inconclusive towards in-situ stress contrasts (for the investigated range), the simulation results show high shale/sandstone Young's modulus contrast to suppress fracture height growth, while the presence of a microannulus is shown to accelerate fracture height growth. The casing shoe depth is the main countermeasure to broaching events following extreme loss of well control situations. Further discussion on other factors that can influence fracture growth (and hence potential for broaching), involves the presence of natural fractures, rock and fluid compressibility, and thermal effects induced from temperature gradients between the fluid in the fracture and the surrounding rock.

Publication Source (Journal or Book title)

54th U.S. Rock Mechanics/Geomechanics Symposium

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