Kuwait Case Study: Integrated-Reservoir-Management Approach Offsets Effects of Reservoir Heterogeneity, Injectivity Challenges, and Delayed Waterflood

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 111472, "Integrated- Reservoir-Management Approach Beats the Impact of Reservoir Heterogeneity, Injectivity Challenges, and Delayed Waterflood in Upper Burgan Reservoir in North Kuwait - A Case History" by H.B. Chetri, SPE, Abd Aziz El-Sabry, Mishal Al-Mufarej, and Ealian Al-Anzi, SPE, Kuwait Oil Company, prepared for the 2008 SPE North Africa Technical Conference and Exhibition, Marrakech, Morocco, 12-14 March. The paper has not been peer reviewed. The Upper Burgan is a multilayered reservoir in the Sabiriyah field of northern Kuwait, currently undergoing the initial phase of waterflood development. The reservoir is highly complex with respect to reservoir heterogeneity, connectivity, and structural compartmentalization. Early waterflood performance was too poor to achieve the targeted injection rates. Detailed channel mapping enhanced the subsurface understanding to add value to the ongoing drilling, production, and injection plans. The integrated-reservoir-management (IRM) approach, with a strategy for depletion and pressure support for each segment, increased short-term production and is sustaining the rates. The current and short-term drilling plans target reservoir segments with higher pressures for well placement. Introduction The Upper Burgan reservoir in the Sabiriyah field was discovered in the 1950s. The reservoir comprises a complex series of tidal, estuary, deltaic, valley-fill, and shoreface sands interbedded with semicontinuous shales. The first facies is carbonaceous sand, fine- to medium-grained sand with porosity of 22 to 25% and permeability greater than 400 md. The thickness can reach 40 ft, with 10 to 20 ft being typical. The second sand-prone facies is bioturbated sand, a very-fine- to fine-grained facies with variable reservoir quality. The thickness averages 20 ft. The third facies is heterolithic sand and typically is very-fine- to fine-grained. This facies type is abundant in the Upper Burgan. Reservoir quality is erratic because of its laminated nature, and vertical permeability is low. The reservoir was subdivided into five mappable layers (UB1 through UB5) in 1992. This zonation scheme was reviewed and modified where appropriate by the Upper Burgan Team in 1997. Average net-pay thickness is 60 to 100 ft. The initial reservoir pressure was 3,800 psia, with a bubblepoint pressure of 1,500 to 2,450 psia. The current reservoir pressure ranges from 2,600 to 3,500 psia. Reservoir Heterogeneity Key lessons from analog reservoirs suggest the necessity of flexible development planning. Connectivity was reviewed in terms of stratigraphy, structure, and pressure, with the following general conclusions.In many analogous reservoirs, the paralic depositional environment proved more complex than originally thought. Closely spaced wells can exhibit drastic changes in sand character—continued infill drilling most likely will be necessary in some parts of the field in the future.Most peripheral floods in paralic environments are converted to pattern floods.Small faults in the Upper Burgan can cause nonjuxtaposition of productive layers.Structure, channel architecture, and stratigraphy likely will play a significant role in the waterflood performance of the reservoir.