caa a22 4500 605466939 CHVBK 20210128100309.0 cr unu---uuuuu 210128e20151001xx s 000 0 eng 10.1007/s00397-015-0873-8 doi (NATIONALLICENCE)springer-10.1007/s00397-015-0873-8 Structural breakdown and recovery of waxy crude oil emulsion gels [Elektronische Daten] [Guangyu Sun, Jinjun Zhang] The structural breakdown and recovery behaviors of waxy crude emulsion gels were investigated. First, the tests of stepwise increase in shear rate and hysteresis loop were carried out, and the structural breakdown process was further analyzed. Then, the structural recovery behaviors were investigated from the recoveries of apparent viscosity, storage modulus, and yield characteristics. It was found that the thixotropy of emulsion gels weakens with increasing water cut and the structural breakdown process gradually changes from solid-like brittle fracture to ductile failure. The broken-down structure of emulsion gels can only recover partially, and both the recovery rate and the recoverability are related to water cut, precipitated wax content, and pre-shear rate. To be specific, the storage modulus recovers faster with increasing water cut and decreasing precipitated wax crystals, or after pre-sheared at a higher rate, while the effects of water cut and precipitated wax on the recovery rate of yield stress are opposite. The recovery degree of both storage modulus and yield stress decreases obviously with increasing amount of wax crystals but is barely influenced by the water cut. Springer-Verlag Berlin Heidelberg, 2015 Waxy crude nationallicence Emulsion nationallicence Gel nationallicence Structure nationallicence Breakdown nationallicence Recovery nationallicence t : Time (s) nationallicence G ′ : Storage modulus at time t (Pa) nationallicence G 0 ′ $$ {G}_0^{\prime } $$ : Storage modulus at t=0 (Pa) nationallicence G ∞ ′ $$ {G}_{\infty}^{\prime } $$ : Storage modulus at t=∞ (Pa) nationallicence t g : Characteristic gelation time (s) nationallicence d : Stretching exponent in Eq. (1) (−) nationallicence τ y : Yield stress at any rest time t after structural breakdown (Pa) nationallicence τ e : Shear stress in the equilibrium, fully broken-down state, i.e., remaining shear stress at the end of the shearing in step (2) of the yield stress recovery test (Pa) nationallicence τ y∞ : Recovered yield stress at t=∞ (Pa) nationallicence k nb : Recovery rate constant of yield stress in the Nguyen-Boger model (1/h) nationallicence K r : Coagulation rate constant in the Leong model (1/h) nationallicence S th : Area enclosed by the up curve and the down curve (Pas−1) nationallicence S up : Area determined by the up curve and the shear-rate axis (Pas−1) nationallicence S down : Area determined by the down curve and the shear-rate axis (Pas−1) nationallicence S R : Relative thixotropic area (%) nationallicence τ : Total shear stress (Pa) nationallicence γ : Total shear strain (−) nationallicence γ · $$ \overset{\cdotp }{\gamma } $$ : Shear rate (s−1) nationallicence λ : Scaled structural parameter, varying between the values of 0 for the completely broken-down structure and 1 for the fully developed structure (−) nationallicence G 0 : Shear modulus of the completely structured material (λ=1) (Pa) nationallicence γ e : Elastic strain of the continuous network structure (−) nationallicence Δ k : Structure-dependent consistency ( Pa s n 1 $$ \mathrm{Pa}\ {\mathrm{s}}^{n_{\kern0.2em 1}} $$ ) nationallicence k : Completely unstructured consistency ( Pa s n 1 $$ \mathrm{Pa}\kern0.35em {\mathrm{s}}^{n_{\kern0.2em 1}} $$ ) nationallicence n 1 : Kinetic index describing the viscous stress's dependence on shear rate (−) nationallicence p 1, p 2 : Dimensionless parameters related to the viscoelastic property (−) nationallicence n 2 : Positive dimensionless constant (−) nationallicence a : Kinetic constant for structure buildup (s−1) nationallicence b : Kinetic constant for shear-induced breakdown (Pa−msm−1) nationallicence ϕ : Rate of energy dissipation, defined as ϕ = τ γ ̇ $$ \phi =\tau \dot{\gamma} $$ in the simple shear flow (Pas−1) nationallicence m : Dimensionless constant (−) nationallicence s : A characteristic time in the elasto-viscoplastic thixotropic model (Eq. 5) with the value of 1s (s) nationallicence τ y0 : Yield stress when the gel structure breaks down for the first time (Pa) nationallicence τ y1h, τ y4h, τ y8h : Yield stresses when gel structure yields for the second time after rest for 1, 4, and 8h, respectively (Pa) nationallicence Sun Guangyu National Engineering Laboratory for Pipeline Safety / Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum (Beijing), 18 Fuxue Road, Changping District, 102249, Beijing, China aut Zhang Jinjun National Engineering Laboratory for Pipeline Safety / Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum (Beijing), 18 Fuxue Road, Changping District, 102249, Beijing, China aut Rheologica Acta Springer Berlin Heidelberg 54/9-10(2015-10-01), 817-829 0035-4511 54:9-10<817 2015 54 397 https://doi.org/10.1007/s00397-015-0873-8 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00397-015-0873-8 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Sun Guangyu National Engineering Laboratory for Pipeline Safety / Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum (Beijing), 18 Fuxue Road, Changping District, 102249, Beijing, China aut NATIONALLICENCE 700 1- Zhang Jinjun National Engineering Laboratory for Pipeline Safety / Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum (Beijing), 18 Fuxue Road, Changping District, 102249, Beijing, China aut NATIONALLICENCE 773 0- Rheologica Acta Springer Berlin Heidelberg 54/9-10(2015-10-01), 817-829 0035-4511 54:9-10<817 2015 54 397