A Reservoir Study of the Friendswood Field

Abstract

To temporarily stop migration of oil into the original gas cap, the existing gas injection project in this Texas Gulf Coast field was expanded. For the purpose, water turned out to be a more efficient displacing medium than gas. By unitizing the field and then injecting 80,000 barrels of water a day, oil migration can be stopped and 55 million more barrels of oil will be recovered. Introduction The Friendswood field (sometimes referred to as Webster) was discovered by Humble in 1937. It is located on the upper Texas Gulf Coast immediately south of Houston (Fig. 1), and has productive sands originally encompassing more than 4,100 acres. Approximately 215 wells were required to fully develop the field to 20-acre spacing. The sands are very prolific and the average well exhibits a productivity index of approximately 29 B/D per psi productivity index of approximately 29 B/D per psi drawdown. Cumulative Frio sand oil production has been 310 million bbl, and reservoir pressure has dropped only 340 psi since discovery. Principal production has been from upper Frio sands of Miocene age. Although prorated together, these sands have been divided into 17 members for reservoir control purposes. A small amount of oil (2 million bbl) has been produced from the Marginulina sands, which lie just above the Frio. The field contains several fault systems, and, because of fault juxtaposition, communication occurs between some of the sand members. Several studies, resulting in MER hearings, workover programs, and a gas injection program, have been conducted in the past. For the study discussed here, those past programs were reviewed and additional necessary programs were determined. Current fluid contacts for each sand member were ascertained on the basis of conventional neutron logs, pulsed neutron logs, induction electric logs, and well production histories. Oil and gas volumes were then production histories. Oil and gas volumes were then mapped for original and current conditions. Material balance and unsteady-state water influx calculations were used to match past reservoir behavior and to predict future performance. predict future performance. JPT P. 685