Integrated Gas Management to Maximize Well Potential and Reserves within a Mature Oil Field
Authors: Gunasan Erkan , Pearce Adrian , Blondeau Christophe 
Published: May 2016

Total has been operating oil and gas production from a series of heterogeneous reservoirs offshore Abu Dhabi since 1974. Today, maximizing oil production is critically dependent on how the facilities can cope with handling the associated gas and water rather than treating the oil itself. The nature of these 40-year old facilities and the variable and sometimes erratic performance of individual wells mean that decisions have to be made on a daily basis regarding allocation of available gas for injection into the reservoir for enhancing oil recovery versus its use for gas lift. The decisions have to be made on the basis of predicted incremental oil but in the context of surface gas and water handling constraints.

This paper will describe how a holistic approach seamlessly integrates historical reservoir and well behavior, the daily surface constraints and provide a means to easily and automatically allocate any gas that is available to optimize oil production. A well prioritization list is updated regularly to explicit to which well gas should be allocated and whether it should be used for lifting high water-cut wells or injecting into the reservoir to provide tertiary gas injection for enhancing oil recovery.

This approach has led to a virtually constant level of oil production over the past 3 years; which for a mature oil field that would normally decline at 10–15% per year has been a major success. In addition, the successful full-field Tertiary Gas Injection project has resulted in a recovery factor of over 50% in the main reservoir; a top class achievement for a carbonate reservoir. Today, 15 years after implementation, the TGI effect contributes over 30% to the oil production from the reservoir.

INTRODUCTION

The field was brought on-stream in 1974, less than two years after sanction; and was developed rapidly to reach the plateau early. It was launched on the basis of achieving a 16% recovery in the poorest reservoirs and 38% in the best. Despite the initial view that the field would be uneconomic beyond the mid 1990s, the application of innovative and cost-effective technologies has extended the field life. Following a series of safety and technical upgrades that were carried out on the limited 1970s field architecture, production is still thriving and is expected to carry on economically for many years to come. Today individual layer recovery factors fall between 30 to 65% which is excellent for a heterogeneous, carbonate reservoir of this type in the region.

This best in class results were obtained due to efficient reservoir management utilizing the in-depth knowledge of the reservoir and a good medium/long term planning to maintain economic production potential. Geological and operational challenges faced during the development of the field were solved using innovative technologies. The field has passed through a number of development stages and currently is in a very mature state. The latest technological developments were screened and utilized in the field throughout its life if they were found applicable and economically viable. Classic secondary production mechanisms have been supported by EOR (Tertiary Gas Injection) as well as Multi-lateral wells of which over 30 exist on the field today.