53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: During loss of control situations, fracture initiation occurring during the capping stages after uncontrolled fluid discharge, can lead to reservoir fluids broaching to the sea floor. A classic example is Union Oil’s 1969 oil spill in Santa Barbara channel, whose impacts on California’s oil industry are still strongly felt today. Reservoir fluids spewed in the channel at rates of 5,000 bbl/day in the first days. Fracture initiation at five different locations caused thousands of gallons per hour to broach to the ocean floor over a period of a month before it was controlled (Mullineaux, 1970; Easton, 1972). Disasters like this can be prevented if the effects of the uncontrolled discharge and capping stages of loss of well control are incorporated into the wellbore architecture. A critical capping pressure and subsequently a critical worst case discharge rate, below which fracture initiation would occur, during capping can be calculated analytically for a “hard” shut-in. For a “soft” shut-in, two numerical models are built; a geomechanics model simulating the stress loads on the wellbore in the two stages of loss of control and a reservoir model simulating capping pressure build-up. Propagation of this fracture up towards the seafloor can ultimately lead to broaching of reservoir fluids to the sea.
If a kick is not detected and circulated properly out of the well, it can lead to blowouts. In this case, loss of control leads to reservoir fluids gushing out of the wellbore uncontrollably without restriction. Well capping attempts generating pressure build-up in the wellbore, can lead to fractures initiating just below the casing shoe and propagating upwards creating channels for reservoir fluids to flow to the seafloor. The ability to predict these fracture failures will enhance wellbore integrity understanding during loss of control, predict and therefore prevent broaching occurrences (Zaki et al., 2015; Michael and Gupta, 2018; 2019a).
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