A field-wide interference test was recently conducted to delineate the hydraulic communication between two large carbonate reservoirs separated by a thick non-reservoir formation. The reservoirs were newly developed with peripheral water injection for pressure support. This initial development stage provided an opportunity to take advantage of the undisturbed state of the two reservoirs during field commissioning to conduct this interference test prior to production. The injection start-up was, therefore, designed to inject into one reservoir while monitoring pressures at various parts of the other reservoir. Several observation wells across the field were designated to record the pressure changes during the initial water injection stage to provide the field coverage. The injection rates were also closely monitored and modified throughout the test period to record the rate of pressure change in the observation wells.
The field was developed with the state-of-the-art permanent downhole monitoring systems (PDHMS) which provided the means for comprehensive monitoring of this field-wide interference test. The test showed some interesting findings within the reservoirs themselves, areas of communication were indentified and the extent of the lateral connectivity was observed. Additionally, the dynamic data acquired during this interference test will complement the static data for building improved geological and engineering models.
This paper describes the test design, implementation and presents the results and findings. The test was concluded but monitoring is continuing utilizing the intelligent field (I-field) infrastructure and the results will, in future, be incorporated into reservoir simulation models for production/injection strategy optimization and accurate field performance forecasting.
The field consists of two large carbonate reservoirs, referred to in this paper as Reservoir A and Reservoir B, stacked one on top of the other and separated by a thick non-reservoir formation. The field was produced in the past. Pressure data that were collected from both reservoirs during these past periods were analyzed and showed pressure match between the offset wells in the two reservoirs. The only fact known at that time was that the reservoirs are in hydraulic communication, but the media of the communication and the areas where they communicate were not well identified. The two reservoirs were developed recently using peripheral water injection to support oil and gas production from both reservoirs. The primary concern of the development was that some injected water might migrate from one reservoir into the other and negatively impact the productivity of the producing wells. The key was to understand the communication mechanisms, delineate the areas of communication dynamically, and set the proper plan, to minimize any adverse effects of inter-reservoir communication, to maximize hydrocarbon recovery.1
