Numerical Evaluation of Dynamic Core-Scale Experiments of Silicate Gels for Fluid Diversion and Flow-Zone Isolation
Authors: Hatzignatiou Dimitrios G. , Helleren Johan , Stavland Arne 
Published: March 2015

Silicate gels have been used in the oil industry mainly for near-well treatments to combat unwanted water production. This technology could be used for mitigating unwanted supercritical carbon dioxide (CO2) leakage out of the storage formation and/or diverting injected CO2 within the reservoir to enhance storage mechanisms and reduce leakage risks. A field test was recently planned and executed by a major operator in a Norwegian Continental Shelf (NCS) oil field to technically qualify the potential use of silicate gels for deep placement to shut off produced water. To optimize the planned silicate-injection test, several experiments were conducted on silicate gel to study the bulk gelation, including dynamic coreflood experiments to determine the reaction kinetics and the strength of the silicate gel. The data obtained from these experiments were used to model the coreflood experiments to obtain a better understanding of the behavior of the gel in porous media. A commercial numerical simulator was used for this purpose. Gel-modeling capabilities are based primarily on a defined chemical reaction, and subsequently, the adsorption/retention of a defined pure blocking gel.

The chemistry and polymerization process of silicate gels are complex. The gelation time of silicate gel is affected by several parameters such as pH, temperature, and concentration of the components. The formation of gel in the model is dictated by the chemical reaction implemented into the simulator and the reaction rate of the reactants. Gel modeling yields a significant amount of gel that is created before the predicted gelation time. To solve this issue, critical gelation time andz critical gel-concentration terms were introduced to reach the maximum gel-adsorption level at the predetermined gelation time. The blocking effect in the model is controlled mainly by the reduced water-permeability factor Rkw, which is affected primarily by the residual resistance factor (RRF) (i.e., the amount and strength of the retained gel).

The dynamic corefloods were modeled to study the parameters affecting the gelation process, including the gelation time, the gel retention in the porous space, and the gel strength. In the dynamic coreflood experiments, the relative effluent concentration and differential pressure were sampled/measured during fluid injection. The observed differential-pressure behavior as a function of fluid injection was simulated by characterizing the gelation process with a simplified chemical reaction, using the experimental bulk-gelation measurements to define input values for gelation reaction (reaction rate, stoichiometric coefficients), determining the gel adsorption/retention vs. concentration simulator-input data to conform with the experimentally determined gelation time, and defining the RRF value to history match the observed differential-pressure increase at the sandpack-formation plugging time. The measured relative-effluent ion concentrations matched well with the simulation results at high injection rates. For lower injection rates, a better match could be obtained by adjusting the reaction order of the reacting components.