Extended Polymer Injectivity Test in a Medium Viscosity Sandstone Oil Reservoir, Sultanate of Oman

Abstract

This is an extended polymer-injectivity-test where the main objectives are to prove that polymer solution can be injected at acceptable conditions and injectivity can be sustained for a considerable time period. Other objectives include determining the need for certain protective additives, evaluating the possibility of oil gain in producing wells around the test injector and providing some input to the process of flood pattern optimization. A nine-month's polymer injectivity test has been implemented in HRD sandstone reservoir (Karim Small Fields’ Cluster, Sultanate of Oman) as part of the ongoing chemical flood evaluation. Selected polymer and desired concentrations are based on extensive laboratory test programs. The subject reservoir has been producing for over thirty years, mostly on primary conditions but with a successful waterflood (using inverted, irregular seven-spot patterns) during the last seven years that is still ongoing. Reservoir oil is highly under-saturated, 29° API gravity with initial viscosity of about 15 cP. Average depth is 1,200 mMD and absolute permeability is in the range of 250-500 mD. Chemical flooding is selected as the appropriate EOR method and is currently being evaluated in order to determine the optimum process design that can provide maximum incremental oil recovery over the ongoing waterflood. Preliminary results from the polymer injectivity test confirm that injection rate of about 150 m3/d can be sustained at maximum surface injection pressure of around 4,000 kPa. Polymer break-through (at low traces) is observed in two of the six surrounding producing wells. Oil gain observed in surrounding producing wells is in the range of 0 - 5 m3/d/well which is lower than the values predicted by the simulation model. The reasons leading to low oil gain and general reservoir behavior within the injectivity pattern are discussed in the paper. The discussed reasons and behavior are essential design aspects of a potential chemical-flooding pilot that can be implemented for analogous fields.