FloFuse in fractured carbonate reservoirs
FloFuse – Rate limiting control device
Carbonate reservoirs hold approximately 60% of the world’s proven conventional oil reserves, of which about 50% feature natural fractures, with significant accumulations across the Middle East in particular.
Common challenges of these carbonate reservoirs are high heterogeneity caused by complex pore and fracture systems, oil wet rock, and low reservoir energy resulting in low recovery factors. The optimum drainage strategy is frequently horizontal production bores to increase reservoir contact, and water injection wells to improve oil sweep. The benefits of water injection can be diminished by the presence of highly conductive fractures or fracture corridors in the injection well within the reservoir. These can create thief zones connected to production wells, reducing sweep efficiency and resulting in early water breakthrough in the production wells.
In response to these challenges, Tendeka has launched FloFuse – a new technology to optimise water injection. As an addition to an extensive range of advanced inflow control technology, FloFuse can increase oil recovery by improving injected water conformance in fractured reservoirs or by ensuring effective placement of matrix stimulation acids.
Injection Control Devices (ICDs) have been proven in application to improve water conformance by balancing frictional losses and reducing outflow into large fractures. Figure 2 illustrates an outflow profile for:
1. A barefoot completion with no outflow control
2. An ICD completion with uniform ICD setting across the well
3. An optimised ICD completion with the flow area adjacent to the fractures reduced by a factor of 10.
It can be observed that without control a significant portion of the outflow occurs into the two fractures with rates of 9 m3/d/m for the case modelled. Introducing ICDs with a uniform setting does not provide adequate control due to the high permeability contrast encountered and results in a similar outflow profile. However, the use of highly restrictive ICDs across the fractures enables the flow to be effectively distributed. In this case, flow to the fractures is reduced to 2.5 m3/d/m with more than 90% of the injected water entering the reservoir matrix.
Fractures may be identified during drilling as loss zones or with image logs but due to the complexity of the reservoirs and the extent of natural fracturing, there is inherently a high degree of uncertainty in attempts to identify thief zones prior to completing the wells. This results in a high risk of a non-optimised completion leading to poor water conformance and ineffective sweep.
One method commonly applied to overcome this issue is to integrate sliding sleeves with ICDs to enable the thief zones to be isolated. This requires the well to be logged to identify the sleeves to be closed and then a shifting tool to be deployed to close the sleeves, eliminating flow to the fracture compartments entirely.