While production from the shallow-water Gulf of Mexico shelf has been declining since the 1980s, reservoirs found below 15,000 feet are adding new punch to this mature area. Some industry estimates peg ultimate recovery from deep shelf reservoirs at as much as 10 trillion cubic feet of gas. In a recent study, IHS Energy teamed with PetroSolutions Ltd. to analyze 94 existing fields in the Gulf of Mexico that are beneath less than 1,000 feet of water. Although the shelf has many attractions for operators-relatively low well costs, established infrastructure, and generous government incentives-its challenges include compartmentalized reservoirs and hazy seismic results. The IHS-PetroSolutions study highlighted fields that produced from true vertical depths greater than 15,000 feet. It found that cumulative monthly production from 126 active wells currently exceeds 30 billion cubic feet equivalent (Bcfe). Deep fields on the shelf are primarily overpressured, wet-gas reservoirs with limited aquifer support. Gas fields are six times as common as oil fields. Flow rates vary by type of reservoir, with completions in aggradational reservoirs averaging 40 million cubic feet per day; those in structural reservoirs some 21 million per day; and those in submarine fans, 12 million per day. Additionally, progradational reservoirs average daily flow rates of 9 million cubic feet. The median field in the study contained two wells. The study also considered decline rates: of the 30 active gas-well completions that were analyzed, annual decline rates ranged from 25% to 100%, with an average rate of 83%. The deep Gulf of Mexico shelf has more deep active fields and producing wells than any comparable offshore environment worldwide, and the resource base is growing. The industry has enjoyed a fourfold increase in maximum flow rates during the past 40 years, and a threefold increase in monthly production volumes during the last decade, notes IHS Energy. One well has produced 200 Bcfe of gas, and 14 other completions have made more than 50 Bcfe apiece. -Peggy Williams