This paper reviews the design and implementation of a full-field interwell tracer program for a giant onshore oil field in Abu Dhabi. The field is under peripheral waterflooding in order to maintain reservoir pressure and provide a mechanism to sweep the oil. However, the existence of strike-slip fault planes juxtaposed across the reservoirs added a variable to the complexity of waterflood management. To improve the understanding of reservoir heterogeneity and reduce the uncertainties associated with major faults, a full-field water-tracer program has been designed.
On the basis of the streamline model, unique chemical tracers have been injected in 21 water injectors covering all the peripheral areas; dozens of associated offset producers across the field were selected to monitor the tracer movement. The design of the program is explained in the complete paper in terms of tracer selection and capability tests, chemical-volume calculation, injection-well and monitoring-well selection (made on the basis of the streamline model), and design of the comprehensive monitoring plan. Ultimately, the results of this tracer program will be used in combination with other reservoir-surveillance tools to facilitate better management of the reservoir.
The subject field is located approximately 110 km to the southeast of Abu Dhabi Island. The field was discovered in 1965, with first production in 1973 and first water injection in 1976. The main oil-bearing zones are X, Y, and Z. These zones are in communication through faults. Each zone is bounded at the top and base by a dense argillaceous limestone and further subdivided by the occurrence of stylolite-bearing dense intervals. Of these, Zone Y, the subject of this study, contains more than two-thirds of the field’s original oil in place.
Zone Y is an undersaturated, heterogeneous, and highly stratified reservoir with an average porosity of 30%. It is divided into five subzones. The Upper Y contains the higher-permeability zones in excess of 700 md, while the Lower Y has a lower permeability of approximately 10 md. The current development scheme, with selective injection and production under peripheral water injection, was implemented in 1982.
The existence of major faults in Zone Y resulted in splitting the reservoirs into 12 main sectors. Among the major monitoring tools and techniques, tracer injection is one of the most important for monitoring the effectiveness of a waterflood project because of the lack of direct information on flow from individual injection wells. Tracer injection can be used to determine early water breakthrough in different areas, crossflow between zones, and the degree of water slumping caused by reverse coning....
A Full-Field Interwell Tracer Program on a Giant Carbonate Oil Field
21 August 2016