Abstract
Optimum development of a giant offshore field requires the best strategy and maximum reservoir knowledge. Any information gained in advance will improve the development strategy and allow for taking timely corrective measures to optimize production and recovery. Amongst many alternatives to get early information, a long term injectivity test is considered to be a good method to determine injection sustainability and reservoir connectivity – transmissibility. This paper presents the background and methodology to implement a long term injectivity test in an offshore field, the challenges faced during the initial phase of injection, and the preliminary results of the test in the two reservoirs included in this project.
The subject field development consists of two main reservoirs that were characterized to have a transition of the oil column from the typical Arabian Heavy medium viscosity to very Heavy Oil zone at the flanks of the reservoirs, and lower rock properties in the western flank of the field. Thus, a long term injectivity test in the field was planned to give early information on some of the identified uncertainties; its aim is to evaluate the sustainability of the injection rate at depths very close or inside the Heavy Oil zone and transmissibility towards the crestal sector of the field from the injector wells located in the western flank of the structure. Additionally, the test will allow us to evaluate the vertical communication within the shallower reservoir as we have identified two very good permeability zones separated by a very low permeability rock in between which could act as a barrier in the flanks and as a baffle in the crest under dynamic conditions.
Main drivers for these tests were:
Few wells drilled in the west sector during initial development and production period
Well tests and core data indicate low permeability along the west flank
Current Earth model reflects the estimated lower permeability in west flank of the field and simulation results suggest the need of many wells in this flank to compensate withdrawal rates
Evaluate vertical connectivity across and within the reservoirs
Based on above, early interference tests were designed to evaluate this transmissibility and optimization of the field development including injectors’ well placement. The selected wells were proposed to get good sector coverage to better understand the reservoirs which includes two wells in the deeper reservoir and one well in the shallower one.
