Recovery improved in a brownfield heavy oil well, using inflow control technology
As oil reservoirs age, the optimisation of oil recovery becomes essential, if oil production targets are to be met. This is not least in heavy oil fields, where the challenge is greater, due to the lower reservoir energy and requirement for high reservoir contact.
One of the most important aspects of heavy oil is its viscosity, which can directly impact the recovery and productivity of the reservoir. Although there is no direct relationship between density and viscosity, a reduction in API gravity scale index for heavy oil is generally accompanied by increased viscosity. Heavy oil usually occurs in shallower formations, in marginal geological basins formed by non-consolidated sand. Reservoirs tend to have lower pressures and temperatures in comparison to a light oil reservoirs. This generally results in lower recovery factors. Although this characteristic points to more complex production processes, factors such as high permeability could make the recovery process easier.
Depending on the capillary pressure; gravitational and viscous forces; and the interaction between these elements during oil flow; oil is generally retained in the reservoir. The porous media may then be measured by the mobility ratio. The mobility of the fluids in porous media is defined by Darcy’s Law, which specifies a direct relationship between pressure, permeability and mobility, depending on viscosity and velocity. Due to an unfavourable mobility ratio for heavy oil flow compared to water, the primary recovery technique may leave as much as 70% of petroleum in the reservoir.
To increase the recovery factor and the production rates, supplementary recovery methods—which are generally termed improved oil recovery (IOR) techniques—deploy operational strategies and the supply of additional energy to the well to increase oil recovery. One technique used in horizontal heavy oil wells is the application of an inflow control device (ICD). This is an engineered nozzle or high-friction channel that is typically made from high-erosion resistance material, and installed in the base pipe to create pressure drop. It is used to control the inflow, from heel to toe, by applying higher pressure drop in the heel of the well to balance the inflow in the toe of the well and overcome the friction flow in the length of horizontal completion as shown in Figure 1.
The use of passive ICDs in horizontal wells has been practiced widely in conventional wells, to achieve the balance flux and mitigate early breakthrough of unwanted water or gas in oil wells. The devices are, however, passive in nature, and once water or gas breaks through, the choking effect cannot be adjusted without intervention. Furthermore, the viscosity difference between heavy oil
and water creates an unfavourable mobility ratio, which allows water to flow much faster through the reservoir and into the wellbore. This enables water breakthrough to happen faster, displacing oil production from producing zones.