Evaluation of a low salinity water flooding with polymer gel treatment in Trinidad and Tobago

Abstract

Trinidad and Tobago (TT) has a rich history of crude oil production and is still one of the largest oil- and gas-producing countries in the Caribbean region. The energy sector contributes approximately 35% of GDP to its economy; however, economic headwinds due to steadily decreasing oil production, low commodity prices and increased competition worldwide have highlighted the need for more economical methods of enhanced oil recovery (EOR) techniques. Although the use of low salinity polymer flooding for EOR has had success in other countries, critical information relating associated flooding system parameters such as soil type, additive type, adsorption characteristics, rheological (flow) characteristics, pH and salinity is not available and is critical if this type of EOR is to be implemented in TT. The nature and inter-relationship of these parameters are unique to a particular reservoir, and studies in this regard will provide key input data for simulations to produce near realistic projections of this EOR strategy. These projections can be used to evaluate the usefulness of a low salinity polymer flooding in TT and guide for the proper implementation of the strategy. The EOR 33 wells located in the lower Forest sands in Southern Trinidad was selected for study as they satisfied the screening criteria. Laboratory studies of the adsorption of xanthan gum concentrations of 0 to 4000 ppm in combination with NaCl solutions (0–40,000 ppm) onto gravel packed sand found that the mixture of 1000 ppm polymer containing 1000 ppm NaCl exhibited the lowest adsorption capacity. The Langmuir coefficients were derived for each salinity, and together with results from the viscosity studies were inputted within the simulation models. Simulations of a sector of the EOR 33 projected that the highest oil recovery occurred using NaCl < 2000 ppm was 11% greater than water flood. A combination of brine (NaCl < 2000 ppm) with gel technology (1000 ppm polymer) produced the highest oil recovery factor (54%), almost twice that of water flooding, the highest average reservoir pressure and lowest water cut value. The improved performance characteristics observed using low salinity water flood with xanthan gum gel for injection can be associated with improved displacement efficiency and improved the sweep efficiency suggesting the strategy to be a technically feasible option for the EOR well in Trinidad.