Polymer Selection for Sandstone Reservoirs Using Heterogeneous Micromodels, Field Flow Fractionation and Corefloods

Abstract

Incremental oil recovery due to polymer flooding results from acceleration of oil production along flow paths and improving sweep efficiency. To achieve favorable economics, polymers should have a high viscosifying power and low adsorption. However, in addition, incremental oil production from various rock qualities needs to be maximized. We developed a workflow using a layered micromodel, corefloods and Field-Flow Fractionation (FFF) to determine the Molecular Weight Distribution (MWD) for the selection of polymers addressing heterogeneous reservoirs. We have designed micromodels consisting of two layers with different permeabilities, one four times larger than the other. The micromodel structure is based on the characteristics of a real sandstone core, with the dimensions 6 cm × 2 cm. These micromodels were used as preliminary screening of the polymers incorporating heterogeneity effects. Subsequently, single- and two-phase core experiments were performed to determine injectivity effects and displacement efficiency of the selected polymers. In addition, FFF was used to measure the molecular weight distribution, gyration radii and conformance of the polymers. Based on the workflow a polymer was selected. All polymers were tested at target viscosity at 7 1/s shear rate. Micromodel experiments showed that tested polymers are leading to improved sweep efficiency of heterogeneous structure. The displacement efficiency within the higher permeable layer was similar for the investigated polymers whereas the oil recovery from the lower permeable layer showed differences. FFF revealed that the MWD's of the tested polymers were different. The MWD of one of the polymers showed a large number of larger molecules compared with the other polymers. This polymer did not lead to the highest oil recovery in the micromodel. Injectivity and propagation of the higher MW polymer in both single- and two-phase core-floods was falling behind the other polymers. Measurements of the MWD of the core effluent showed that for all tested polymers the larger molecules are initially retained more than the smaller molecules. The polymer with the smallest molecules and narrow MWD showed the best propagation characteristics in the core. Owing to the good performance of this polymer in terms of sweep efficiency improvement, injectivity, and propagation, this polymer was selected for a field application. Therefore, the novelty presented here can be summarised as follow: Heterogeneous micromodels were used to screen polymers for one-dimensional displacement efficiency and sweep efficiency effects Single- and two-phase core floods in combination with Field-Flow Fractionation revealed the impact of the molecular weight distribution (MWD) on polymer injectivity, propagation and retention Selection of polymers need to include MWD to find the most effective polymer Polymer selection needs to take near-wellbore and reservoir effects (micro- and sweep efficiency in heterogeneous reservoirs) into account

Evaluating Factors Impacting Polymer Flooding in Hydrocarbon Reservoirs: Laboratory and Field-Scale Applications

“…These polymers can be applied under highly acidic conditions such as in the presence of high concentrations of hydrogen sulfide or carbon dioxide or when the crude oil has a high total acid number. It is important to note that these types of polymers are usually much more costly than other conventional polymers [ 48 , 49 , 50 ]. Salinity: When referring to salinity, there are two main categories of interest: monovalent cations and divalent cations.…”

“…It is therefore extremely important to measure the molecular weight of the polymer prior to injection. It is also important to note that the molecular weight of the polymer can change over time due to polymer degradation [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. Polymer Cost: The overall cost of a polymer flooding operation relies on multiple components, including the cost of the polymer itself.…”

“…It is therefore extremely important to measure the molecular weight of the polymer prior to injection. It is also important to note that the molecular weight of the polymer can change over time due to polymer degradation [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ].…”

Microvisual Investigation on Steam-Assisted Heavy Oil Extraction Behavior in Heterogeneous Porous Media

“…Immiscible liquid displacement in the porous medium affected by viscous fingering and capillary fingering synergistically promotes the injection fluid quickly entering into the production well along the water channels before heavy oil is largely displaced . Many researchers have focused on the effect of viscous fingering, realizing that increasing the viscosity of the injection fluid can greatly improve sweep efficiency. , As for the fingering phenomenon caused by the difference of pore size, various improvement methods are always implemented to change the viscosity of injected fluid . Therefore, it has become important to study the influence of capillary fingering generated by different pores on the sweep effect in heavy oil reservoirs.…”

“…6,7 As for the fingering phenomenon caused by the difference of pore size, various improvement methods are always implemented to change the viscosity of injected fluid. 8 Therefore, it has become important to study the influence of capillary fingering generated by different pores on the sweep effect in heavy oil reservoirs. Owing to viscous fingering, capillary fingering, and chemical effects of injection fluid, a comprehensive investigation of the intricate distribution of injection fluids requires the utilization of diverse research methods.…”