High water production normally becomes a problem late in the production period of a water flooded oil reservoir. This is often due to reservoir heterogeneities. Deep placement of gel may block channels with high water flow and divert the water into other parts of the reservoir. This offers a potential for reduced water production and increased oil production. The objective of this project was to develop gel systems based on innovative chemistry taking nanoparticles into use as cross-binders and where the gelling time can be increased sufficiently to get the chemicals to the desired position. Further, mechanisms for reaction and transport of the gel constituents should be described enabling modelling of gel placement.
The scientific work in the project is done through four sub-projects briefly described below.
SP1: Hybrid materials as sweeping efficiency modifier: Several types of functional nanoparticles (FN particles) have been synthesised and deactivated by adding various groups to the active sites. Synthesis routes and effects of adjusting the synthesis parameters have been evaluated. The reactivity of the resulting FN particles has been tested by measurement viscosity and gel formation as function of time at 80 ? in synthetic sea water.
The results obtained show that it was possible to retard gel formation by blocking of the reactive sites and the subsequent activation by slow hydrolyses. In a second approach where only parts of the active sites were deactivated it was found that by partially deactivation the formation of gel was controlled to vary from several days to several months.
SP2: Nanogels from polyelectrolyte complexes (PEC): This sub-project was conducted in cooperation with Texas A&M University. Samples with only Cr-ions as cross-linker, samples based on the original Texas A&M PEC-Cr recipe and samples with activated nanoparticles were prepared.
By adding Cr3+ ions into PEC particles made after published procedures it was possible to delay gelation for in the order of 20 days for aging at 50 ?. At 80 ? the gelation was much faster, however. When the PEC was modified by changing the original polycation with active FN particles and changing the polyanion, delayed gelation for in the order of 20 days and possible longer was obtained at 80 ?. This indicates that making polyelectrolyte complexes with active FN as polycation may be viable.
SP3: Transport of nanoparticles: Core flooding experiments with nanoparticles and polymer alone and in mixtures have been done. The results indicate that polymer adsorption, retention and inaccessible pore volume (IPV) were generally reduced by the presence of nanoparticles. Adsorption, total retention and IPV were significantly higher in Berea compared to Bentheimer. Adsorbed or otherwise retained polymer during injection was not released during following water floods, while the retained nanoparticles were partly released. Nanoparticles had negligible effect on rock permeability, while polymer significantly reduced rock permeability. In-situ gelling experiments with the most promising system developed in SP1 have demonstrated that strong gel was formed in the porous medium, depending on the gelling time.
SP4: Numerical simulation of the hybrid gel/polymer interaction with water/oil/soil: A mathematical model of 1D two-phase flow with polymers and nanoparticles have been developed, implemented and tested. Results from the core flooding experiments with were used in the testing. Simulations have also been done using a synthetic data set where polymer viscosity depends on polymer concentration and the concentration and age of the nanoparticles.
The formulation includes tracking the age distribution of the nanoparticles in solution as well as the age distribution of absorbed nanoparticles. This means that at each position and time, the composition of the nanoparticles with respect to age is given. The age composition of the particles in solution in turn affects the nanoparticles ability to crosslink and form gel. Consequently, this formulation facilitates simulation of gel forming far away from the injection point. The simulator also includes the standard effects of polymer on water mobility, such as shear thinning, permeability reduction due to adsorbed polymer, and IPV for polymers and nanoparticles.
In a second approach, an alternative 1D model has been established for the transport of the polymer and nanoparticles. Also in this model, the nanoparticles serves as crosslinking agent. A constitutive equation was formulated based on the gelation data for a given set of polymer concentrations, a given type of nanoparticles, and measured gelation times. In the model, a residence time for the nanoparticles was used to link the viscosity of the cross-linked polymer as the mixture was transported. The model has been used for simplified simulations of time delayed gelling to illustrate the functionality of the model and to carry out a sensitivity analysis.
This project will develop competence and technology within in-depth gel placement for water diversion. New hybrid nanogel systems will be developed based on "green" technology. The gel systems will be based on novel multifunctional hybrid polymers prepare d at SINTEF Materials and Chemistry (FunzioNano?) and polyelectrolyte complexes developed at Kansas University. Testing infrastructures at NTNU IPT, NTNU NanoLab and SINTEF Petroleum Research will be used in the experimental work. Numerical simulation inc luding molecular dynamic simulation will be based in competence of SINTEF Materials and Chemistry and SINTEF Petroleum Research.
Following research tasks are included in this project:
SP1: Hybrid materials based on FunzioNano as sweep efficiency modifier
SP2: Nanogels from polyelectrolyte complexes based on systems developed at Kansas University
SP3: Transport of chemical system including nanoparticles in reservoir formations
SP4: Numerical simulation including molecular dynamic simulation of the hybrid gel/polymer interaction with water/oil/rock system.
SP5: Dissimilation and networking
SP6: Project management
The project will edicate 1 PhD candidate at NTNU with focus on applying nano technology within EOR.