In the past, the challenging environments of High Pressure/High Temperature (HP/HT) wells were considered uneconomic, but as technologies and experiences evolve, tapping these reservoirs has become a reality.
An HP/HT well is considered so when the conditions of the well are hotter or more pressurized than typical wells. In HP/HT wells, the botomhole temperature, or the temperature at the total depth of the well, is higher than 300 degrees Fahrenheit (149 degrees Celsius) and pore pressure reaches at least .08 psi per foot.
Being able to develop and produce from HP/HT wells is a relatively new concept for the upstream industry. Typically, HP/HT wells were not considered economically viable until the mid- to late-1990s. In fact, the term HP/HT was only first coined within the industry in the mid-1980s.
Typically found offshore in the North Sea, deepwaters of the Gulf of Mexico and China, wells with HP/HT characteristics are a small number of wells drilled and completed every year, but that number is growing. Because operators are continually pushing the boundaries in order to replace more easily obtained reserves, service companies have formulated innovative solutions to develop these formally marginal fields.
By their very nature, high-pressure fields contain more hydrocarbons than those with normal conditions. As long as the fields boast large enough reservoirs, the development of HP/HT wells is economical.
In addition to being expensive to overcome, HP/HT conditions are extremely dangerous and add exorbitant risk to drilling, completion and workover operations. The most extreme risk, HP/HT conditions can cause blowouts.
Designed to close off a well before a blowout occurs, a Blowout Preventer (BOP) with a rating that exceeds 10,000 psi is required on all HP/HT wells now. BOPs comprise a series of large valves on the surface of the well that recognizes predictors called "kicks,"or changes in formation fluid flow, and acts immediately to thwart blowouts. Usually comprised of a number of different BOPs, called a BOP stack, BOPs can be either be annular or ram preventers, which describe the way that the well is sealed from the forming kick. While ram preventers create a seal across the end of the pipe, ram preventers cork the wellbore.
Furthermore, HP/HT conditions wreak havoc on equipment designed for less extreme environments. The high-pressure, high-temperature settings add stress to components, and over time and increased exposure, this stress is compounded.
Historically, engineers and drillers working on HP/HT wells enclosed equipment within HP/HT-resistant flasks to overcome the elements, but as wells have become more challenging, new techniques and equipment had to be developed. There are a number of propriety solutions that oil service companies offer operators working in HP/HT environments, and more revolutionary technologies are being developed every day.