Abstract

Historical production (spanning almost 30 years) has confirmed that the UG (MO) reservoir receives very little natural pressure support in some areas. This has resulted in a declining reservoir pressure (from 4050 to 3200 psi) and low recovery factor and also, areas of poor water sweeping. The remedial plan is to initiate a full field water injection project to increase reservoir pressure, improve sweep and enhance oil recovery.

A dumpflood pilot project was initiated to prove the viability of and quantify sweep benefits of water injection in the B-zone of the MO reservoir. The dumpflood Pilot aims to prove that water flooding can enable this unswept oil to be produced and provide data to support the design of future Full Field Water Injection Project.

A dumpflood operation is basically injecting water into the recipient reservoir from a water source reservoir by the natural force of gravity and the pressure differential of the two reservoirs using the same well. In the Umm Gudair Dumpflood Pilot, the water bearing source reservoir is the Zubair formation. The recipient reservoir is the B-zone in the MO. And since the Zubair is structurally higher than the MO, and the reservoir pressure of the Zubair is higher than the MO, water was being produced from the Zubair and injected into the MO by the natural force of gravity and the pressure differential between the two reservoirs.

A location in the east flank of east UG field was chosen to allocate the dumpflood pilot well. This was done after going through 4 different locations in the field to allocate the most suitable field location.

Surveillance requirements have been identified for the UG dumpflood pilot. This surveillance plan involves the dumpflood injection well and 4 other observation wells. In addition to regular PLT surveys, to determine zonal injection profiles and ongoing corrosion surveillance in the Dumpflood well, additional pressure surveys on adjacent wells were planned. It was also planned to utilize radioactive tracers to monitor breakthrough and develop an understanding of the pattern of sweep.

Technical Contributions:

  1. Demonstrated the design of a water dumpflood method to analyze injectivity & water sweep.

  2. Established a cost-effective technique to quantify injectivity and water sweep.

  3. Demonstrated the applicability of dumpflood to re-pressurize a constantly depleting reservoir.

Introduction:

The study was initiated by reviewing all relevant and previous data and studies or projects to recommend an appropriate procedure and set a plan assuming a five year dump flood project life.

The primary objective of this project is to study and analyze the long term effect of dumpflood (DF) operation from Zubair aquifer into the Minagish Oolite (MO) reservoir. The injection target zone is in the MO B-zone in the water swept zone. During this process, a full study and analyses of the pressure response in nearby wells and close monitoring of the water movement within the reservoir will be done. The outcome of this (DF) pilot will assist in the design of the full field pressure maintenance scheme. Also, as part of our objectives, is to test A and C zone injectivities.

In this paper, detailed discussions on the process of selecting a well location for the DF pilot purposes and the completion strategy that was chosen for this well. Also, it will discuss the surveillance plan designed for this pilot. The paper also discusses the advantages and disadvantages of each completion design considered for this pilot. The answers to all these issues are discussed in the body of this paper.

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