Arild Lohne

Silicate Gel for In-depth Placement - Gelation Kinetics and Pre-flush Design

Sodium silicate gel has historically been used in the oil industry for near wellbore water shut-off. Relatively recent application of Sodium silicate gel for in-depth water diversion have generated some interest. Its main advantage is that its mobility is water-like before it gels. For in-depth diversion purposes, the gelation kinetics need to be appropriately modeled for better prediction of gel placement. This paper makes a review of different gel kinetics models found in the literature. To our knowledge, the models presented in the literature are fit-for-purpose, i.e. they are based on correlations that are fitted to the lab data. Although they describe the lab data well, it is challenging to use them to predict field scale operations, where there are significant temperature, pH, and salinity gradients throughout the reservoir. In this paper, we present an improved silicate gel model. Our model takes into account two important rate step in the formation of silica gel from a sodium silicate solution: the nucleation rate of monosilisic acid to form critical nucleus of nanosized colloids and an aggregation rate of the nano-colloids to form a pore blocking gel. It is important to allow for nano sized colloids as these are small enough to be transported a significant distance from the well before they aggregate into larger clusters that can block the pores. The model explains well the experimental observations where the gelation time is sensitive to pH, temperature, silicate concentration and brine composition. We also investigate the preflush volume and concentration that is needed to minimize the indirect rock-brine interaction that can alter the designed gelation time. Results from this simulation shows that the Cation Exchange Capacity (CEC), Mineral distribution and Temperature profile are critical design criteria for the preflush volume and concentration.

Simulation of Sodium Silicate Water Diversion Using IORSim

We demonstrate that it is possible to predict the impact of a sodium silicate injection on oil recovery by using a coupled approach where an industry standard reservoir model, Eclipse, interacts with a simulator for species transport and reaction, IORSim, using file based communication. The main motivation for our approach is that it makes it possible to take advantage of history matched industry standard reservoir models and use these models together with new models for ion transport and geochemical reactions. In IORSim a block sorting technique is used to speed up the computation of species transport and chemical interactions. IORSim also has a thermal model which can be used if the temperature option is not used in the reservoir simulator. The validity of our approach has been checked by comparing with analytical solution and by comparing with an in-house reservoir simulator. Our in-house version solves the multiphase sodium silicate system implicitly. We demonstrate that it is possible to get the very similar results with the sequential IORSim-ECLIPSE coupling and our in-house reservoir simulator by choosing reasonable reporting steps in ECLIPSE. The numerical scheme is improved by using an adaptive implicit numerical scheme and a Cranc-Nicolson method for solving the geochemical reactions.

Mechanical Degradation of Polymers at the Field Scale - A Simulation Study

Polymer flooding is a chemical EOR method which aims to improve the oil recovery by making the water phase more viscous, and hence to increase the macroscopic sweep efficiency of a waterflood. However, the polymers considered for EOR applications are very susceptible to mechanical degradation in regions of high shear, such as in the injection facilities and in near well regions. If the applied flow rate is too high, an injected polymer solution may lose more or less all its viscosifying ability before properly entering the formation. This can be especially difficult to avoid if polymer is injected directly into a heterogeneous reservoir region where high molecular weight polymer species will have to travel through successive contractions and expansions inside small pores. At EAGE-ECMOR XV we presented a new simulation model that is capable of modeling all the commonly observed flow regimes in porous media, such as Newtonian, shear thinning and shear thickening flow, as well as polymer mechanical degradation. Based on simple pore scale models, we derived expressions for the in-situ polymer rheology that can account for spatial variations in important reservoir parameters such as permeability, temperature, and salinity. This allowed us to match the different experiments with most of the input parameters kept fixed. The model captured very well how HPAM polymers of different molecular weights were mechanically degraded when injected into cores and series of cores with an order of magnitude variation in permeability. In this paper we use the model with parameters that was history matched to lab data to study the polymer behaviour in a typical field operation. We investigate how the model scales from the lab to the field. In particular, we simulate flow of polymer near an injector in order to estimate the amount and extent of mechanical degradation as a function of injection rate and reservoir heterogeneity near the injection well. Preliminary results indicate that there will always be some degradation, but that this can to some extent be minimized using reasonable injection rates. In cases of open fractures near the injection well, the risk of degrading the polymer will be greatly reduced.

A model for non-Newtonian flow in porous media at different flow regimes

Polymeric liquids are of great practical importance for porous media flow as they can be used to improve the sweep of water in the reservoir and therefore improve the recovery of oil. Due to the non-Newtonian behavior of these liquids, they are extremely challenging to model. In this paper, we present a model that is capable of describing the most commonly observed flow regimes in porous media: (i) Newtonian, (ii) Shear thinning, (iii) Shear thickening, and (iv) Mechanical degradation. The novel feature of our model is that the time constants for the shear thinning and shear thickening behavior are related to variations in reservoir properties and conditions, thus making it possible to translate lab results to larger scale without introducing new fitting parameters. Furthermore, we present a way to estimate polymer mechanical degradation in porous media. In our model, the polymer degradation rate is linked to the effective pore radius (using a Kozeny-Carman type equation), shear stress, and polymer molecular weight, Mw. The degradation results in a lower Mw, while the polymer volumetric concentration is unaffected. The model is applied to a series of laboratory core flood experiments conducted with partially hydrolyzed polyacrylamide, HPAM, of different initial Mw ranging from 5 to 20 MDa in seawater, and core permeability varied from 137 to 2019 mD. The flow rate is varied approximately three orders of magnitude and covers the shear thinning, shear thickening, and degradation flow regimes. We show that our model is able to reproduce experimental rate-dependent flow resistance, as well as viscosity of effluent samples. An important aspect supporting the use of the model as a predictive tool is that all the simulations with a given brine have made use of a single set of input parameters to describe the observed shear thickening and degradation behavior. Simulation of a second experimental series using low salinity brine required a separate set of input parameters for the shear thickening and shear degradation. The onset of shear thickening was not affected while shear thickening was reduced and degradation appeared to be slower.

A Model for Non-Newtonian Flow in Porous Media at Different Flow Regimes

The EOR potential of polymer flooding is well documented in the scientific literature. However, it has remained a challenge to create good simulation tools that can be used for predictive purposes. A main limitation with the current models is the insufficient description of the transition between the different flow regimes that characterize the polymer rheology. Typically, Newtonian behaviour is observed at low shear rates, followed by shear-thinning, shear-thickening and shear-degradation regimes at increasing shear rates. Furthermore this is complicated by the fact that the apparent viscosity of the polymer is influenced by a combination of factors, such as adsorption, brine salinity, polymer concentration and molecular weight. In this work we present a core scale simulation model that is capable of describing all the aforementioned flow regimes. The novel feature of the proposed model is the inclusion of an equation to describe polymer (mechanical) degradation. The polymer degradation rate is linked to the effective pore radius (via permeability through a Kozeny-Carman type equation), wall shear stress, and polymer molecular weight, Mw. The degradation results in a lower Mw, while the polymer volumetric concentration is unaffected. The change in Mw over a time step is found using an implicit chord method at the end of each transport time step, and the solution is then used to update the effective polymer properties. The main flow field is computed using a standard sequential algorithm, where a linear pressure equation is solved first, followed by an implicit saturation equation formulated in a fractional flow approach. The model is applied to a series of laboratory experiments. Our model explains the core data very well, taking into account that several experimental factors have been varied such as synthetic polymer types, core length and permeability.

IORSim - A Simulator for Fast and Accurate Simulation of Multi-phase Geochemical Interactions at the Field Scale

Optimal injection strategies for a single core in the lab can usually be found, but there is a significant challenge to translate the lab results to field scale. In this paper we present a simulator, IORSim, that can be calibrated to lab experiments and used together with industry standard reservoir simulator to predict chemical alteration on field scale. Based on the flow velocities predicted by the reservoir simulator, IORSim advects the chemical species in the reservoir, taking into account chemical interactions that may affect the flow of the fluids. As a finer grid than the reservoir simulator and a block sorting technique is used in IORSim, the species transport and rock-fluid interactions can be performed at considerably higher speed and accuracy compared to a built-in geochemical model. The sorting algorithm allows us to solve the whole transport problem implicitly without solving for all blocks simultaneously, and thus greatly improve the stability of the numerical problem. We present two applications (1) simulation of produced water for a sector of the Ekofisk field, which is compared with data, (2) sodium silicate injection in a high permeable zone. IORSim modifies the reservoir permeability due to the gelling and the macroscopic sweep is improved.