Executive Summary

This month, we have 30 new publications. The first category covers eight papers on Chemical Flooding (including flooding with polymer, surfactant, and/or low-salinity water). The first article investigates “elastic turbulence” as an explanation for apparent viscosity of hydrolyzed-polyacrylamide (HPAM) polymer solutions increasing with increased velocity in porous media. Previous work explained the phenomenon using polymer elongation concepts. By use of a broad range of methods, the second paper demonstrates that hydrophobically modified HPAM polymers can show complex behavior in porous media that depends strongly on permeability, flow rate, and distance of penetration. The performance of these polymers may be difficult to control in field applications if they are not matched well with the chosen reservoir. The third manuscript uses X-ray computed-tomography scans and nuclear-magnetic resonance to characterize spontaneous imbibition in oil-wet cores. It concludes that chemically enhanced imbibition into nonwater-wet matrix is several orders of magnitude slower than imbibition into strongly water-wet rocks. The fourth paper demonstrates the use of atomic-force microscopy as a rapid screening tool to pin-down the appropriate water composition for low-salinity enhanced-oil-recovery (EOR) flooding in a given core material. The next three papers use UTCHEM to simulate low-salinity waterflooding and gravity stable surfactant flooding. The final paper in this category is not chemical flooding EOR, but it discusses use of a preflush, surfactants, co-surfactants, and alkali to optimize scale-inhibitor-squeeze treatments in oil-wet carbonates.

   The second category, Gas Flooding, includes seven publications. The first contribution uses production optimization to maximize net present value for water-alternating-gas (WAG) and surfactant-alternating-gas (SAG) during simulated CO2 flooding. To improve characterization of the WAG process, the second paper compares gas, water, and oil relative permeability in two- vs. three-phase flow during experiments in water-wet and mixed-wet cores. In the third manuscript, simulations indicate that mineral dissolution, permeability, and injectivity in a carbonate reservoir should be highest for simultaneous water and CO2 injection, less for WAG injection, and least for continuous CO2 injection. The fourth paper uses a bead pack and carbonate blocks to experimentally model gravity drainage, reinfiltration, and mixing for gas/oil and solvent/oil in fractured systems. The fifth paper in this category uses simulation to argue that temperature variations during near-miscible CO2 flooding have a significant impact on oil recovery. In hopes of providing better flexibility and predictability compared with conventional equation-of-state methods, the sixth contribution examines reservoir simulation coupled with molecular dynamics to model CO2 sequestration (using up to one billion cells). The final paper in this category studies mass transfer associated with CO2 dissolving in oil when injected gas displaces a viscous crude oil in a capillary tube.

   Six contributions on Numerical and Analytical Analyses constitute the third category. The first paper develops an upscaling procedure for oil/gas compositional flow simulation. The method computes upscaled parameters and functions for individual coarse-scale interfaces or wellblocks on the basis of a global fine-scale compositional simulation. The second manuscript examines the feasibility of applying nonlinear multigrid methods for reservoir simulation, using a “full-approximation scheme.” The methods are compared with conventional global linearization that uses Newton’s method. A third contribution investigates whether an unregularized adjoint-based optimization scheme can identify the location and magnitude of flow barriers from noisy wellbore pressures and flow rates when flow is slightly compressible. The fourth paper uses an ensemble-Kalman-based history-matching framework to directly incorporate crosswell time-lapse seismic and electromagnetic data. By use of this method, permeability estimates were approximately 25% better compared with a standard history matching with only production data. The fifth paper evaluates the impact of flow geometry on sandface temperature behavior under conditions of high drawdown when Joule-Thompson effects are significant. Transient analyses demonstrated that temperature changes occur earlier in radial flow geometries than in linear (hydraulically fractured) geometries. The sixth manuscript presents a direct-simulation Monte Carlo study of methane gas flow in a simulated Berea sandstone over a range of Knudsen numbers.

   The fourth category focuses on Fractures and Low-Permeability Reservoirs, with seven contributions. The first paper develops a procedure that maximizes net present value when developing a low-permeability gas field by use of nested optimization. The outer-optimization shell decides the number of wells, fractures per well, and amount of proppant, whereas the inner optimization maximizes the productivity index by selecting optimal fracture dimensions. The second paper analytically solves flow inside a fractured porous medium by accounting for nonplanar geometry, aperture size, and special location of the fracture. The effective porosity and permeability are derived that show the influence of the fracture on the flow behavior. The third paper describes two different phase-field fracture-propagation models and presents a technique for coupling these to a fracture-poroelastic-reservoir simulator. The fourth paper uses a 3D fracture-propagation model that captures the coupled deformation of the rock with fluid flow in a horizontal wellbore and within fractures. The model is used to predict simultaneous propagation of fractures from multiple perforation clusters in horizontal wells. For multiscaled fracture systems, the fifth paper develops two alternative hybrid approaches that are aimed at combining the advantages of multicontinuum and discrete-fracture/matrix representations. One model handles the extreme contrast in conductivity between a small-scale fracture network and ultratight matrix. The second model uses an upscaling technique for cases in which a detailed prior model is available for the complete fracture network. The sixth paper extends a previously developed semi-analytical model for a complex fracture (with constant width) to simulate production from planar and nonplanar fractures with varying width. The final paper presents a reservoir simulator for coupling thermal, hydrological, and mechanical phenomena in porous media.

   In the final category, we have two papers on Acidizing. The first paper experimentally confirms that AlCl3 can retard the reaction of hydrofluoric acid with kaolinite, bentonite, or illite at 75 and 200°F, improving permeability of Berea sandstone (over mud acid without AlCl3). The last contribution investigates polymer-assisted emulsified acid as a means to improve acidizing efficiency in limestone. Coreflood results are argued to indicate that the polymer-assisted emulsified acid was an effective wormholing fluid at low injection rates while maintaining a high viscosity of the acid system for zonal coverage.

                                                                                                                               Randy Seright, Executive Editor,  New Mexico Institute of Mining and Technology