High-strength and self-degradable sodium alginate/polyacrylamide preformed particle gels for conformance control to enhance oil recovery

Excess water production has become an important issue in the oil and gas extraction process.Preformed particle gels(PPGs),show the capability to control the conformance and reduce excess water cut.However,conventional PPGs have poor mechanical properties and their swollen particles are easily damaged by shearing force when passing through the fractures in formations,meanwhile PPGs can be also degraded into various byproducts,leading to permanent damage to the reservoir permeability after temporary plugging.Herein,a novel type of dual cross-linked PPGs(dPPGs)was designed and synthesized using sodium alginate(SA)and acrylamide(AAm),cross-linked with N,N’-methylenebisacrylamide(MBA)and Fe^(3+).Results show that dPPGs have excellent mechanical properties with a storage modulus up to 86,445 Pa,which is almost 20 times higher than other reported PPGs.Meanwhile,dPPGs can be completely degraded into liquid without any solid residues or byproducts and the viscosity of dPPGs degraded liquid was found to be lower than 5 mPa·s.A laboratory coreflooding test showed that the plugging efficiency of dPPGs was up to 99.83%on open fractures.The obtained results demonstrated that dPPGs could be used as economical and environment-friendly temporary plugging agent with high-strength,self-degradation,thermal stability,and salt stability,thus making it applicable to a wide range of conformance control to enhance oil recovery.

Determination of Fe and Zn contents and distributions in natural sphalerite/marmatite by various analysis methods

The contents of Fe and Zn in natural sphalerite samples were determined by chemical titration and spectroscopic techniques(portable X-ray fluorescence(P-XRF) spectrometry, electron probe microanalysis with energy dispersive spectroscopy(EPMA-EDS), electron probe microanalysis with wavelength dispersive spectroscopy(EPMA-WDS), and time-of-flight secondary ion mass spectrometry(To F-SIMS)). Besides, the distribution of Fe and Zn in sphalerite samples was analyzed by imaging EPMA-WDS and imaging To F-SIMS. The results show that Fe and Zn contents determined by each spectroscopic technique have good linearity with those determined by chemical titration(R^2>0.77), and the R^2 values of Fe are generally greater than those of Zn. The imaging analysis results revealed that Fe and Zn are not uniformly distributed in the sphalerite.

Temperature effect on the dynamic adsorption of anionic surfactants and alkalis to silica surfaces

Chemical loss such as surfactants and alkalis by adsorption to reservoir rock surface is an important issue in enhanced oil recovery(EOR). Here, we investigated the adsorption behaviors of anionic surfactants and alkalis on silica for the first time as a function of temperature using quartz crystal microbalance with dissipation(QCM-D). The results demonstrated that the temperature dependent critical micelle concentration of alcohol alkoxy sulfate(AAS) surfactant can be quantitatively described by the thermodynamics parameters of micellization, showing a mainly entropy-driven process. AAS adsorption was mediated under varying temperature conditions, by divalent cations for bridging effect, monovalent cations competitive for adsorption sites but not giving cation bridging, pH regulation of deprotonated sites of silica, presence of alkoxy groups in the surfactants, and synergistic effect of surfactant coinjection. The addition of organic alkalis can enhance the overall adsorption of the species with AAS,whereas inorganic alkali of Na_(2)CO_(3) had capability of the sequestration of the divalent ions, whose addition would reduce AAS adsorption. The typical AAS adsorption indicated a non-rigid multilayer,estimated to have between 2 and 5 layers, with a likely compact bilayer followed by disorganized and unstable further layering. The new fundamental understanding about temperature effect on surfactants and alkalis adsorption contributes to optimizing the flooding conditions of chemicals and developing more efficient mitigation strategies.