Proven Technology Yields High Impact Results - A Case History of Water Shut-Off in the PNZVs South Umm Gudair Field.

Summary

The South Umm Gudair (SUG) Field is a large, anticlinal, primarily edge water drive reservoir located in the Partitioned Neutral Zone (PNZ) between Kuwait and Saudi Arabia. A successful water shut-off program was implemented in SUG's Ratawi Oolite reservoir during 1994/95. This program relied on zonal isolation tests, spinner surveys, thermal decay logs, and correlations with surrounding wells to identify watered-out intervals. Since the field produces using electric submersible pumps (ESP's), surveys were run through a downhole bypass tool. A comparison was made between thermal decay logs run under static and dynamic conditions in an analogous reservoir to evaluate invasion by kill fluids. Remedial action including cement plugbacks, reperforations, additional perforations, and acidizations were implemented based on the interpretations. The techniques presented in this paper are applicable to reservoirs requiring water shut-off analysis.

Introduction

The SUG field was discovered in 1966. The field produces from the Ratawi Oolite reservoir of Lower Cretaceous age. The reservoir straddles the boundary line between the PNZ and Kuwait. It Is operated by Joint Operations In the PNZ and by KOC in Kuwait. Joint Operations is an organization comprised of personnel from Saudi Arabian Texaco and Kuwait Oil Company.

When the water shut-off program was initiated in July 1994, there were 17 producing wells located on 320-acre spacing. Field development coincided with the workover program. An additional twelve infill wells were drilled in SUG, with the first well activated in November 1994. Figure 1 provides a structure map and well locations. The production history for the entire field is shown in Figure 2. Although this paper will focus on the workover results, production from the infill drilling program is included in the graph.

Approximately nine workovers for water shut-off were performed prior to 1994; the last of which occurred in 1987. Prior to the workover program, oil production averaged 31,000 BOPD and was declining at 3%/yr. The water cut had gradually increased to 48%. Cumulative production through December 1995 was 420 MMBBLS.

Thirteen wells were worked over during the 1994/95 program. Figure 3 shows that the workovers doubled oil production in these wells from 20,000 BOPD to 40,000 BOPD and decreased water production by more than 50%.

Reservoir and Fluid Properties

The average depth of the producing horizon is -8200' SS or 8825' TVD. The original oil-water-contact (OWC) is -8450' SS. The reservoir is 200' - 300' thick and consists of wackestones and packstones. P. 406

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