Rheological behavior of shear degradable oils: Kinetic and equilibrium properties

Abstract

An investigation of the non‐Newtonian, time dependent, flow properties of various crude oils at or below their pour points is reported. Experimental observations of material response under various shear and stress conditions provide a basis for the development of a kinetic and rheological model which quantitatively describes the shear degradation and equilibrium behavior exhibited by these materials. Preliminary data on the effects of thermal history and aging are also reported, showing the relative importance of these factors to the rheological properties.

Thixotropic behaviour of concentrated bauxite residue suspensions

“…However, reformation of the network linkages of the same characteristics as those initially present may not be feasible unless, of course, the degraded red mud is refiltered. Similar non-reversible nature of structural bond disruption and restoration has previously been reported for certain gelled materials such as greases, plastic paints and waxy crude oils [3,7,28,29,32]. In these systems, complete recovery of the original structure could only be achieved, not by resting alone but by thermal treatments.…”

“…In these systems, either the structure breaks down irreversibly under shear or the structural recovery at rest is slow (compared to the breakdown) and incomplete. Both characteristics may also prevail in a given material [7]. Similar behaviour has been known for some time by workers in soil mechanics where certain highly sensitive clay soils (quick clays), which normally can support large loads, are readily liquefied when sheared and can remain in the fluid state for long periods of time [11][12][13].…”

“…The rate of disappearance of the structure (-&u/dt) at a fixed shear rate. is thus dependent only on (~,-~Ue)-By analogy with a secondorder irreversible chemical reaction, the rate equation may be expressed as [7,36]:…”

“…For this purpose we follow the reaction-kinetic approach previously employed by many workers, e.g. [7,10,[33][34][35][36][37]. The procedure basically involves (i) specifying an appropriate structural parameter to represent the thixotropic structure, (ii) selection of a suitable rate equation describing the time-dependent changes of the structure, and (iii) testing of the model using the experimental kinetic data.…”

“…In concentrated and flocculated suspensions, where the inherent structure can be very complex in nature [6], it is possible that the thixotropic processes involved may not be reversible, at least within the time scales of practical interest. Several examples of irreversible or partially reversible thixotropic materials have been reported in the literature [7][8][9][10]. In these systems, either the structure breaks down irreversibly under shear or the structural recovery at rest is slow (compared to the breakdown) and incomplete.…”