Degree

Doctor of Philosophy (PhD)

Department

Craft & Hawkins Department of Petroleum Engineering

Document Type

Dissertation

Abstract

Fluid-driven fracture initiation from oil and gas wells is examined in detail. The dissertation covers three subtopics: drilling, completion (stimulations), and post-blowout capping-induced fracture initiation.

Drilling-induced tensile fractures (DITFs) are located in an azimuth orthogonal to wellbore breakouts and are observed from image logs obtained during drilling operations. Fully analytical criteria for the orientation of DITFs initiating from wells in porous, permeable media are derived considering fluid infiltration from a pressurized wellbore. DITF orientation (longitudinal or transverse-to-the-wellbore) is used to constrain the magnitude of the local maximum horizontal principal stress. The range of the possible stress states is indicated on dimensionless plots vis-à-vis a given DITF orientation and in-situ stress regime.

Completion-induced hydraulic fractures (CIHFs) are initiated from perforated wells during stimulation practices, aimed at improving the permeability in the near-wellbore region. For application in low permeability formations, such as shale reservoirs, transverse fractures are more desired from a productivity perspective. A horizontal well with multiple transverse fractures outperforms the same horizontal well with a gigantic longitudinal fracture. Closed-form analytical approximations from the literature for the longitudinal and transverse fracturing stresses are modified to incorporate pore pressure effects and then used to develop a criterion for the orientation of fractures initiating from perforated wells. The validity of this criterion is numerically assessed and found to overestimate transverse fracture initiation, which occurs under a narrow range of conditions; when (i) the formation tensile strength is below a critical value, and (ii) the breakdown pressure within a “window.” At a known breakdown pressure, the fracture initiation pressure can be determined semi-analytically.

Following blowouts after mismanaged loss of well control situations, tensile fractures can initiate during capping stack shut-in. Upward propagation of these fractures can provide a broaching pathway for reservoir fluids towards the seafloor leading to an ecological disaster. Being able to predict fracture initiation, a-priori to post-blowout capping, thus preventing broaching from taking place is of considerable importance. Capping stack shut-in procedures can be optimized using the post-blowout discharge flowrates. A deepwater Gulf of Mexico case study is performed, extended to a comprehensive stability analysis of the casing-cement sheath-rock formation system.

Committee Chair

Gupta, Ipsita

DOI

10.31390/gradschool_dissertations.5423

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