Observations of wellbore failure in the Toa Baja well - Implications for the state of stress in the North Coast Tertiary Basin, Puerto Rico

Journal Article · Fri Mar 01 04:00:00 EST 1991 · Geophysical Research Letters (American Geophysical Union); (United States)

DOI:https://doi.org/10.1029/91GL00408· OSTI ID:5399687

Moos, D ^[1]; Morin, R H

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1. Stanford Univ., CA (United States)

Borehole televiewer (BHTV) and 4-arm caliper (dipmeter) logs were obtained in the Toa Baja well (drilled to a depth of 2,704 m into sediments of the North Coast Tertiary Basin, Puerto Rico) from 704 to 2,676 m depth. The only observations suggesting that stress-induced wellbore failure (breakouts) had occurred were small intermittent features at a depth of approximately 2,600 m with azimuths of 70{degree} and 250{degree} and the fact that, during drilling, wellbore stability became a problem near total depth. An increase in mud weight to 10 lb/gal required to stabilize the deteriorating wellbore was accompanied by loss of drilling fluid into the formation, suggesting that hydraulic fracturing or the reopening of preexisting near vertical fractures had occurred. A series of vertical fractures at a variety of azimuths (averaging N31{degree}W) was detected by the BHTV. The loss of circulation due to an increase in mud weight, combined with the absence of well-developed breakouts, enables one to estimate stress magnitudes near the well for reasonable values of rock strength: S{sub 1} = S{sub v}; S{sub 3} = S{sub hmin} {approx} 0.5S{sub v}; S{sub Hmax} {approx} (0.55-0.63)S{sub v}, and an associated incipient normal faulting stress regime. This stress regime is consistent with focal mechanisms determined for earthquakes with epicenters near the drillsite.

• OSTI ID: 5399687
• Journal Information: Geophysical Research Letters (American Geophysical Union); (United States), Journal Name: Geophysical Research Letters (American Geophysical Union); (United States) Vol. 18:3; ISSN 0094-8276; ISSN GPRLA
• Country of Publication: United States
• Language: English

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