Volume 24 Number 5
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397


Finding new hydrocarbon reserves is not getting any easier. Despite the historically high prices of oil and gas, there remain significant cost pressures to economically and efficiently exploit hydrocarbon reserves accessible to multinational companies. One potentially cost-effective way of adding new reserves and production is via ‘infrastructureled exploration’. This involves exploring for reserves that are deeper or laterally off-set from developed fields and existing production facilities. Both pose significant, albeit different, drilling challenges. It is the challenges associated with drilling in deeper, hotter and more highly pressured environments that are described here. The term ‘HPHT’ is commonly used to describe wells that are hotter or higher pressure than most. The term came into use upon the 1990 release of the Cullen report on the Piper Alpha platform disaster in the UK sector of the North Sea. Here, HPHT is formally defined as a well having an undisturbed bottomhole temperature of greater than 300°F (149°C) and a pore pressure of at least 0.8 psi/ft (ca. 15.3 lbm/gal, or 1.83 g/cc) or requiring a blowout preventer with a rating in excess of 10,000 psi (68.95 MPa). With combined bottomhole conditions of 20,000 psi (137.9 MPa) and 420°F (215°C), Mobile Bay, off the coast of Alabama, USA, still holds the record as the world’s hottest and highest-pressure offshore producing environment. As exploration foci are targeting deeper and deeper formations, a new terminology is developing that further classifies HPHT conditions (Figure 1). Three levels of HPHT severity are defined: Tier I refers to wells with reservoir pressures up to 15,000 psi (103.4 MPa) and temperatures up to 350°F (177°C). Most HPHT wells drilled to date fall into this category. The Tier II category defines the current focus of ‘ultra-HPHT’ wells, defined as having bottomhole fluid pressures of up to 20,000 psi (137.9 MPa) and temperatures of up to 400°F (204°C). Several deep gas wells currently being planned (or being drilled) in coastal regions of the Gulf of Mexico fall into this category. Tier III defines ‘extreme-HPHT’ conditions, with reservoir pressures up to 30,000 psi (206.8 MPa) and temperatures up to 500°F (260°C). Several deep gas reservoirs onshore North America and in the Gulf of Mexico – both on the Shelf and in deep water – would fall into this category - see Figure 2, adapted from Baker Hughes (2005).


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  • Article Type: Research Article
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