Highly Deformable Nano-Cross-Linker-Bridged Nanocomposite Hydrogels for Water Management of Oil Recovery

Conventional poly­(acrylamide) (PAM)-based hydrogels suffered from mechanical instability during water flooding, which markedly reduced their performance for water management and oil recovery. In this report, divinylbenzene (DVB) nanostructured cross-linker-bridged nanocomposite hydrogels with high elasticity were described to increase hydrogel mechanical integrity. Precipitation polymerization of DVB monomers generated well-defined DVB nano-cross-linkers having styrenyl moieties on the surfaces, as demonstrated by proton nuclear magnetic resonance analysis. Frequency sweeps of the hydrogels confirmed the formation of covalent junctions between PAM chains and DVB nano-cross-linkers within the network. The nanocomposite hydrogels with covalent cross-links showed a high degree of extensibility, greater than 40 times compared to self-cross-linked <i>N</i>,<i>N</i>′-dimethylacrylamide hydrogels with elongation of 14 and <i>N</i>,<i>N</i>′-methylenebis­(acrylamide) cross-linked PAM hydrogel having stretchability less than 2 times. The concentration of ammonium persulfate initiator showed a greater effect on mechanical robustness than DVB nano-cross-linkers. The increase in the initiator significantly increased hydrogel extensibility upon stress. In addition, nano-cross-linker-based hydrogel displayed slow swelling kinetics in brine in comparison to commercially available LiquiBlock 40K gel. Low-cost DVB monomer-based nano-cross-linker-bridged highly deformable hydrogels with excellent elasticity rendered hydrogel production in industrial-scale feasible. High deformation characteristics facilitated hydrogel propagation through pore throats for in-depth fluid diversion

Schematic of micromodel apparatus.

<p>1-Micromodel; 2-Bottom light physical model chamber (iosthermal controllable); 3-Micro pump; 4-Video camera; 5-Computer.</p

Etched glass micromodel.

<p>Etched glass micromodel.</p

Development of Thermotransformable Controlled Hydrogel for Enhancing Oil Recovery

A novel thermotransformable controlled polymer system (tPPG) is developed that can be injected into fractures or fracturelike features as a millimeter-sized particle gel (100 μm to a few millimeters) and acts as a plugging agent, then dissolves into linear polymer at a designated period (e.g., 6 months), because of the reservoir’s temperature. The dissolved polymer seeps into the depth of the formation and performs as a mobility control agent with high viscosity. Working together with permanent cross-linking the polymer, polyethylene glycol diacrylate 200 (PEG-200) entails the role of controlling dissolution time which has been added into the tPPG as a labile cross-linker. The polymer’s viscosity will not be influenced by the shearing stress during pumping or salinity in the reservoir. The time tPPG requires for transformation is dependent primarily upon the reservoir temperature and labile cross-linker concentration. This strategy offers a facile and economic approach to fabricating a promising dual-functional polymer system. In order to evaluate our proposed approach, main properties of the tPPG polymer are probed, including the swelling ratio, mechanical strength, and thermostability before transformation, viscosity, moving ability, and mobility control ability after transformation

Amoeba effect I.

<p>(a) Foamed gel distribution in micromodel; (b) Dumbbell-shaped foam; (c) Dumbbell-shaped foam; (d) Foamed gei distribution after placement.</p

Synthetic brine composition.

<p>Synthetic brine composition.</p

Study of Displacement Efficiency and Flow Behavior of Foamed Gel in Non-Homogeneous Porous Media

<div><p>Field trials have demonstrated that foamed gel is a very cost-effective technology for profile modification and water shut-off. However, the mechanisms of profile modification and flow behavior of foamed gel in non-homogeneous porous media are not yet well understood. In order to investigate these mechanisms and the interactions between foamed gel and oil in porous media, coreflooding and pore-scale visualization waterflooding experiments were performed in the laboratory. The results of the coreflooding experiment in non-homogeneous porous media showed that the displacement efficiency improved by approximately 30% after injecting a 0.3 pore volume of foamed gel, and was proportional to the pore volumes of the injected foamed gel. Additionally, the mid-high permeability zone can be selectively plugged by foamed gel, and then oil located in the low permeability zone will be displaced. The visualization images demonstrated that the <i>amoeba effect</i> and Jamin effect are the main mechanisms for enhancing oil recovery by foamed gel. Compared with conventional gel, a unique benefit of foamed gel is that it can pass through micropores by transforming into arbitrary shapes without rupturing, this phenomenon has been named the <i>amoeba effect</i>. Additionally, the stability of foam in the presence of crude oil also was investigated. Image and statistical analysis showed that these foams boast excellent oil resistance and elasticity, which allows them to work deep within formations.</p></div

Visualized waterflooding.

<p>(a) Saturated by crude oil; (b) Displacing to residual saturation; (c) Before foamed gel treatment; (d) After foamed gel treatment.</p

Flow Behavior Characterization of a Polyacrylamide-Based Friction Reducer in Microchannels

Horizontal well and hydraulic fracturing have been proven to be effective technologies for increasing the recovery of shale gas reservoirs. During a fracturing treatment, a pair of main fractures is first generated perpendicular to the wellbore direction. As fluids continue to be pumped, more microsized fractures are generated near the main fractures and form a fracture network. This micrometer-sized fracture network has much more contact area with the matrix than a traditional single pair of fractures and holds the majority of the productivity potential of shale gas. Friction reducer (FR) is one of the primary components of this fracturing fluid. It is used to decrease the flowing friction in pipeline. Flow loop tests in lab and field applications have addressed this issue thoroughly. However, the flow characteristics of friction reducer solutions in microfractures are not clear. This study used capillary tubes to represent microchannels, and the flow behavior of FR solutions in these microchannels was systematically studied. With FR solution flowing in the microchannels at various velocities, the impact of different FR concentrations, microchannel sizes, and microchannel surface wettability on the FR flow behavior was investigated in detail. It is found that the friction reducer is a slight shear-thinning fluid with properties that can be expressed by a power-law equation. Its residual resistance factor to water was also specified, which is closely related with the fluid flowback. Finally, the experimental results were compared with the data in a flow loop experiment. Its flow resistance was found to be increased in microchannels rather than decreased as was observed in the centimeter-sized tubing

Good oil resistance of foamed gel(magnified 300x).

<p>(a) Foaming trapping; (b) Oil film on foam surface.</p