deeper water. For example, in the 1960s digital sound recording and processing greatly enhanced the quality and interpretability of seismic data. In the 1970s advances were made in digital, three-dimensional seismic imaging, and in the 1980s use of computer workstations enabled faster processing of the data generated in geologic surveys. Those and other technological advances dramatically enhanced industry’s accuracy in locating productive wells. Improved accuracy was a critical factor, given the multimillion dollar cost of drilling an individual well in deep water. Between 1985 and 1997, the success rate of offshore exploratory wells for the major companies in the United States increased from 36 to 51 percent (EIA 2008).

New generations of rigs were developed that enabled drilling at water depths of 5,000 to 10,000 feet, and from 20,000 to 30,000 feet of subseafloor depth. Advanced drilling techniques allowed the direction of an individual well to be changed from vertical to horizontal for greater adaptability to geologic conditions. Techniques were also developed to obtain information (such as position, temperature, pressure, and porosity data) from within the borehole while the well was being drilled.

By 1990, most of the oil and gas from the Gulf of Mexico came from wells drilled through an average production-weighted depth of about 250 feet of water. By 1998, the average production-weighted depth of water was greater than 1,000 feet. At that point, deepwater production (at about 700,000 barrels of oil and 2 billion cubic feet of gas per day) surpassed that from shallow water for the first time.

Global deepwater production capacity increased by more than threefold from 2000 to 2009 (from 1.5 million barrels per day in water depths over 2,000 feet to more than 5 million barrels per day). In 2008, total oil and gas discovered in deep water globally exceeded the volume found onshore and in shallow water combined.

CHALLENGES IN DESIGNING AND CONSTRUCTING OFFSHORE WELLS

Geologic structures beneath the deep water4 of the Gulf of Mexico provide a harsh and unpredictable environment of high-temperature and high-pressure hydrocarbon reservoirs that typically contain significant amounts of dissolved natural gas. These factors require additional precautions in the design and construction of wells.

The formation fracture pressure (the pressure at which a hydraulic fracture forms at the wellbore and propagates out into the formation) usually increases

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4 For this report, the committee did not identify a specific depth to distinguish between shallow water and deep water. Although various depths have been identified by other organizations as a transition point, depths greater than 1,000 feet are often considered to define deep water.



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