New Oil in an Old Reservoir: Prize From a Comprehensive, Multidisciplinary Reservoir-Management Approach
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 93547, "New Oil in an Old Reservoir: Prize From a Comprehensive, Multidisciplinary Reservoir-Management Approach in Sabiriyah Lower Burgan Reservoir in North Kuwait," by M.F. Al-Ajmi, H.B. Chetri, SPE, A.N. Khan, SPE, and E. Al-Anzi, Kuwait Oil Co., prepared for the 2005 SPE Middle East Oil and Gas Show and Conference, Manama, Bahrain, 12-15 March.
Before 2001, the overall potential and viability of long-term development of the lower Burgan sandstone (LBS) reservoir in the Sabiriyah field in northern Kuwait were uncertain. Earlier evaluations often compromised production and potential by focusing on other waterflooded reservoirs and treating this one as a swing producer. It lacked a proper reservoir definition before commitment as a swing producer with no infill opportunities. It is important to develop an accurate reservoir description, a realistic and flexible development plan, and comprehensive management through the joint efforts of the geologists and engineers.

Introduction
Discovered in 1957, first commercial oil production from the multilayered LBS reservoir was in 1964. With active bottom- and edgewater drive, the well spacing varied, with close well spacing in the crestal area and wider spacing in the southern area.
This reservoir is the largest contributor, yielding 40% of the Sabiriyah daily oil production. Lower Burgan oil is the highest-API-gravity crude in the field, helping to meet the crude-quality export requirement for the only gathering center in the field. A significant amount of LBS production has come from the lower part of the reservoir, where the pattern of water influx is very well understood. Most of the production and most of the remaining reserves are in the upper part of the reservoir, where the pressure support and water influx are relatively well understood.

Reservoir Background
The Sabiriyah field, on the crest of the Kuwait arch in northern Kuwait, is an elongated, north-trending, faulted anticline. The fault throws vary from less than 30 to more than 100 ft. Integration of recently acquired seismic data with well data shows that faults dip 45 to 60°, but the sealing/non-sealing nature of faults is not yet understood. Some faults, particularly in the central and northern part of the field, appear to be nonsealing, but the fluid-flow effects are not known. At the lower Burgan horizon, the Sabiriyah structure has a closure of approximately 350 ft.
On the basis of sedimentalogical and pressure studies, the reservoir was subdivided into the massive (M) sand, which produces through vertical aquifer support, and the layered (L) sand, which experiences largely lateral edgewater sweep. The M member, which forms the lower unit of the reservoir, is high-quality sand, and it has produced most of its reserves. The overlying L member has sand quality that ranges from very good to relatively poor, and it contains most of the remaining producible reserves. A significant fieldwide pressure barrier, called the SID4 layer, separates the M and L layers. The lower Burgan reservoir is divided into 13 layers/flow units on the basis of reservoir pressure and flow behavior.