Underdeveloped Oil Fields in Upper Pennsylvanian and Lower Permian Carbonate Reservoirs of Southeastern New Mexico: Initial Development Missed Major Reserves

Ronald F. Broadhead
New Mexico Tech, Socorro, NM

Upper Pennsylvanian and Lower Permian carbonate reservoirs in the Permian Basin of southeastern New Mexico, U.S.A. are significant reservoirs for oil and gas. The 400 fields that have produced from these reservoirs have yielded a cumulative production of 490 million bbls oil (MMBO; 78 million m3) and 3.2 trillion ft3 (91 billion m3) gas. Sixteen of these fields have been identified that were underdeveloped at some stage in their history. Although initially underdeveloped, subsequent redevelopment of these 16 fields added significantly to reserves and production. Mathematical analysis of production decline curves was used to estimate reserves developed during initial drilling of these fields and during subsequent discrete phases of redevelopment. For the 16 fields studied, redevelopment accounted for a total of 65% of developed reserves and varied from 16% to 99%. Redevelopment in these fields was generally in undrilled portions of the fields, and not in bypassed pay zones. The fields are formed by stratigraphic traps but most were initially thought to be structural traps and were initially developed on structural culminations. Because initial development was based on the premise of structural entrapment, the majority of reserves in these fields remained unproduced until redevelopment. Redevelopment generally resulted in a fivefold to tenfold increase in numbers of producing wells and productive acreage. Because 91% of Upper Pennsylvanian and lower Wolfcampian fields have less than 10 producing wells and because exploratory prospects have generally been drilled on structures, it would appear that significant reserves may remain undeveloped in already discovered fields.