Well Management: Use of Permanent Downhole Flowmeters for Pressure-Transient Analysis

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 90316, "The Boris Field Well-Management Philosophy - The Application of Permanent Downhole Flowmeters to Pressure-Transient Analysis: An Integrated Approach," by E.J. Coludrovich, SPE, J.D. McFadden, SPE, and M.R. Palke, SPE, BHP Billiton; W.R. Roberts, SPE, Oilfield Production Consultants USA LLC; and L.J. Robson, SPE, BHP Billiton, prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Considering the large capital investments and returns for high-rate completions in overpressured unconsolidated-sandstone reservoirs, a testing method with defined objectives, designed to define acceptable risk levels for rates of individual completions, was necessary. Critical parameters, such as permeability and skin, are dynamic properties in these types of reservoirs and require frequent measurement. A program was implemented in the Boris field that relies on the use of permanent downhole pressure gauges and flowmeters. Field Description The Boris field comprises two wells in the Green Canyon area of the U.S. Gulf of Mexico with a water depth at the field of approximately 2,400 ft. First oil production from the Boris-1 well was in February 2003, and from the Boris-2 well in September 2003. Production from Boris-1 travels approximately 7,000 ft through a multi-phase flowline to a subsea manifold where production from Boris-2 is commingled with the stream. From the manifold, production travels approximately 5 miles to the Typhoon host facility. The 5-in. multiphase flowline has an erosional flow-rate limit of approximately 20,000 STB/D. Formation-pressure and performance data indicate that the Boris wells are hydrodynamically connected through a large aquifer that provides ample pressure support. Initially, the field was highly overpressured (0.75 psi/ft, or 10,400 psi) and relatively undersaturated, with a saturation pressure of approximately 6,700 psi. The crude is light and sweet with a gravity of 33°API, initial gas/oil ratio of 1,550 scf/STB, and in-situ viscosity of approximately 0.59 cp. No whole cores were taken from the Boris wells. Completion designs were based on empirical permeability estimates made with log and sidewall-core data. Average reservoir permeability of approximately 1 darcy was observed. Coupled with the low viscosity of the undersaturated oil, high initial pressure, and a relatively low skin factor achieved through careful completion planning, high-rate-potential wells were achieved as indicated by the initial productivity indices (PIs) of 25 and 30 STB/psi-D. Permanent downhole flowmeters (PDHFMs) were installed to assist production allocation and completion management. The use of PDHFMs was accepted by the U.S. Dept. of Interior Minerals Management Service for metering the commingled production. The completion interval consists of two clean-sand packages (B4 upper and B4 lower) separated by a shale interval that generally is 10 to 15 ft thick. The Boris-1 interval has 75 ft net thickness, and the Boris-2 has 115 ft net thickness. Initial pressure-gradient information indicated that the sands shared a common pressure regime and contact, and performance data do not clearly indicate whether the sands act isolated under producing conditions.