Well Design

Well Design

Well Design

The discovery of High Pressure High Temperature (HPHT) fields in Asia Pacific, the North Sea, US land, Gulf of Mexico and numerous other places around the world during the last three decades has led to a new class of ‘critical’ wells. These wells pose significant challenges during the design and well construction phases.
HPHT wells are often characterized by extreme bottom hole pressures (greater than 20,000 psi or 138 MPa) and temperatures (beyond 450 F or 232 C), usually at great depths. These extreme conditions, coupled with small pore pressure-fracture gradient margins, demands that high dimensional efficiency is maintained in casing design. Small radial clearances significantly impact several design and operational aspects such as running casing and liners, equivalent circulating densities (ECD), mud losses, and cementing efficiencies. Furthermore, great well depths give rise to new and unusual loading conditions such as Abnormal Pressure Build-up (APB), slip crushing and severe hydrogen embrittlement problems such that proper material selection is essential to construct these wells.
Innovative solutions and advanced designs involving quantitative risk evaluations are necessary for the more complex casing and tubing designs. This approach combines uncertainty, risk and economics, and is sometimes called Reliability Based Design (RBD). In classical tubular design, reduction in risk results in an increase in initial costs (thicker wall, higher grade material), and reduction in the consequence (casing or tubing failure; or other catastrophic incident) costs. The optimum design, however, is one that minimizes total cost (initial cost + consequence cost). Such an approach is necessary for HPHT critical wells, and one we’ve successfully applied on dozens of projects worldwide.