A novel water-injectivity model and experimental validation with CT-scanned corefloods

Injectivity decline is an issue during produced-water reinjection (PWRI) for water disposal in aquifers, waterflooding, chemical enhanced oil recovery, and geothermal-energy exploitation. A novel model for injectivity decline under flow conditions reminiscent of PWRI was developed taking into account deep-bed filtration and buildup of external filter cake. A distinct feature of the model is that it describes particle-retention kinetics responsible for internal filtration by an exponential decaying function of the retained-particle concentration. The corresponding nonlinear governing partial-differential equations were solved numerically and coupled with a known analytical model for external filtration with the concept of transition time. Coreflood experiments consisting of the injection of brine containing suspended hematite particles (volume fractions in the range of 2 to 6 ppm) were also performed. Computed-tomography (CT) scans of the core were taken to obtain deposition profiles along the core at different times. In addition, effect of various parameters (particle concentration and number of grids) on injectivity was investigated. From CT-scan and optical-microscope analyses, it was found that surface deposition in the porous medium and face plugging at the injection face of the core were responsible for decline in injectivity. The transition time from pure internal to external filtration was accurately determined from the CT-scan and pressure data. The newly proposed model and experiments were found to be in excellent agreement, indicating that the adopted retention function is a good heuristic description of particle retention.Ramesh Chandra Yerramilli, P. L. J. Zitha, Sanjay Surya Yerramilli, Pavel Bedrikovetsk

Novel Insight into Polymer Injectivity for Polymer Flooding

Abstract A considerable portion of world reserves are located in mature and viscous oil reservoirs having thickness less than 15 m. Polymer flooding is a mature technology and is the most important EOR method based on full field case histories. Accurate assessment of injectibility of viscous polymer solutions into these reservoirs without induced fractures is a major challenge. Therefore, the objective of this study is to experimentally investigate and model polymer injectivity in porous media using unfiltered partially hydrolyzed polyacrylamide (HPAM) solutions for wide range of polymer concentrations (125–5000 ppm) and salinities (5–20 g/L) in high permeability sandstones. Data from rheological measurements and single phase linear core flood studies carried out as a part of this study were utilized for understanding the key microscopic (pore level) mechanisms and for quantifying the injectivity. Based on the experimental analyses, it was found that viscous nature of polymer solutions and their retention in porous media were the main mechanisms for loss in injectivity. Data obtained from the experiments were used to validate and fine tune the model. Subsequently, with the help of the Langmuir adsorption isotherm, filtration theory, permeability reduction model, Non-Newtonian viscosity and Darcy laws numerical modeling was performed for predicting the injectivity losses during polymer injection. A good quality match was obtained with experimental data. Finally, sensitivity of polymer concentration and salinity on injectivity was studied. Further, the results from this study, will serve as an auxiliary input for field scale simulations, will help operators in the selection, design and execution of the field projects and will stand as guidelines for extending the polymer flooding technology for heavy oil reservoirs.</jats:p

Cloud point and thermodynamic parameters of a non-ionic surfactant heptaoxyethylene dodecyl ether (C₁₂E₇) in presence of various organic and inorganic additives

1284-1290Cloud points (CPs) of heptaoxyethylene dodecyl ether (C12E7) in the presence of varying concentrations of additives such as inorganic salts, alkanols, diols, glycols and their ethers, hydroptopes and short chain tetraalkylammonium salts are measured and the increase/decrease in CP is discussed. While inorganic anions decrease the CP due to the “salting out” (dehydration) effect and follow the Hofmeister series, an increase in CP by CNS- and I- ions is governed by the “salting in” effect. Short chain alcohols (4), diols (6) and ethylene glycol ethers, diethylene glycol, propylene glycol, dipropylene glycol (4) increase the CP whereas a decrease is seen in the case of higher homologues. This increasing/decreasing effect of alcohols and diols and their monoalkyl ethers is ascribed to their function as a cosolvent/cosurfactant for C12E7 micellar systems. Both hydrotropes and short chain tetraalkylammonium salts increased CP of C12E7 to 100 °C at very low concentration. The thermodynamic parameters of these mixtures are also calculated at varying additive concentrations.<span style="mso-fareast-font-family: AdvGulliv-R;mso-bidi-font-family:AdvGulliv-R;letter-spacing:-.1pt;mso-ansi-language: EN-IN;mso-fareast-language:EN-IN" lang="EN-GB"> <span style="letter-spacing: -.1pt;mso-ansi-language:EN-IN" lang="EN-IN">As the solubility of non-ionic surfactant containing heptapolyoxyethylene hydrophilic chain is highest at the cloud point, the thermodynamic parameters are calculated at this temperature. The results show that the standard Gibbs free energy change (ΔG), the enthalpy (ΔH) and the entropy (ΔS) at the cloud point are positive or negative depending on the nature of the additives. </span