The Boris Field Well Management Philosophy- The Application of Permanent Downhole Flowmeters to Pressure Transient Analysis: An Integrated Approach

Abstract

Abstract Considering the large capital investments and returns for high rate completions in overpressured, unconsolidated sandstone reservoirs, a testing methodology with defined objectives, designed to define acceptable risk levels for rates of individual completions is necessary. Critical parameters, such as permeability and skin, are dynamic properties in these types of reservoirs and require frequent measurement. BHP Billiton has implemented a program in the Boris Field that relies on the use of permanent downhole pressure gauges and flow meters. The well management philosophy and integration of pressure transient results is described, and our approach and experiences since first oil will be reviewed. Our program relies on several novel well test approaches.Intermittent, unplanned build-ups can be analyzed to arrive at a continuous history of permeability and skin.Permanent downhole flowmeter data allows for analysis of unplanned build-ups which otherwise would be uninterpretable.Methods to quality control the results such as specialized trend plots of skin and permeability are reviewed. Wellbore management is constrained by limits established by drawdown, flux, water handling, and flow assurance. Surveillance is performed by corroborating the instantaneous well performance from the permanent flowmeters with the most recently interpreted properties. Observations are presented about the utility of intermittent, unplanned shut-ins compared to planned tests. This process is evolving and requires the advancement of available industry tools with regard to data handling and the use of classical analytical pressure transient techniques combined with numerical methods. Historical data files for individual completions using continuous downhole data are very large which makes manual manipulation of the files undesirable. Management of the data and the impact on the methodology is reviewed. Boris Field Description The Boris field consists of two wells drilled in Block 282 of the Green Canyon area of the federal waters of the Gulf of Mexico. Water depth in the field is approximately 2,400 feet. Boris # 1 was drilled in the second half of 2001, and included several sidetracks that helped to delineate the field and identify the regional pressure gradients. Boris # 2 was drilled approximately a mile north of Boris # 1 in the summer of 2002, shortly before Boris # 1 was completed. The location of the Boris wells is identified on Figure 1. First oil occurred from Boris # 1 in February of 2003, and in September of 2003, production from Boris # 2 began. Production from Boris # 1 travels through a multi-phase flow line approximately 7,000' where it is joined by production from Boris # 2 at a subsea manifold. From the manifold, production from the two wells is commingled and travels approximately 5 miles to the Typhoon TLP host facility in the Green Canyon 236 block. The 5" i.d. multiphase flowline has an erosional flow rate limit of approximately 20,000 stbpd. The Boris reservoirs are located in the Typhoon mini-basin that formed as a result of salt withdrawal and diapirism during the Pliocene and Pleistocene. The upper lobe of the B4 interval is 1 or 2 basin wide turbidite events. The lower and thicker B lobe is comprised of amalgamated, stacked turbidite lobes. Both the A and B lobes are highly correlatable across the mini-basin. The Boris wells penetrate two seismic amplitude anomalies located along the eastern rim of this mini-basin and are on-lapping deposits at the basin margin with dips ranging from 40 to 50+ degrees. Figure 2 is a type log illustrating the B4 sand package exploited by the Boris wells. Formation pressure and performance data indicate that the Boris wells are hydrodynamically connected through a large aquifer that provides ample pressure support. The Boris Field was initially highly overpressured (0.75 psi/ft, 10,400 psi) and relatively under-saturated with a saturation pressure of approximately 6,700 psi. The crude is light and sweet, with a gravity of 33 degree API, initial GOR of 1,550 scf/stb and in-situ viscosity of approximately 0.59 cp. There was no whole core taken during the drilling of the Boris wells. Completion designs were based on empirical permeability estimates using log and side wall core data.