Chemical Interactions of Aluminum-Citrate Solutions with Formation Minerals

Abstract

In order to test the effectiveness of complexing agents for in-depth cross-linking and mobility control in polymer and waterfloods, we investigated the transport of aluminum citrate solutions in sandstone and limestone cores. The study was prompted by experimental observations indicating that crosslinking attempts cause plugging of the inlet end of core sections unless special precautions were observed. The plugging was caused by poor transport of the aluminum citrate solutions, which, in turn, was caused by precipitation of aluminum hydroxide in limestone cores, and of both aluminum and ferric hydroxide in sandstone cores. The formation of these precipitates, and the poor transport of the aluminum citrate solution was confirmed experimentally and modeled quantitatively by a geochemical flow simulator. We then used the flow simulator to design injected solutions that would avoid precipitation, generally by raising the injected pH and by using a larger citrate to aluminum ratio. By using these solutions the precipitation could be avoided, and the aluminum citrate could be transported in an unretarded fashion. Polymer cross-linking treatments using solutions designed to eliminate precipitation generally showed more uniform mobility reduction, and an absence of the plugging observed in the first set of flow experiments.

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

“…The University of TX 124 and the University of Kansas 125 reported results consistent with our results, where the gel caused substantial permeability reduction only in the first section of a core. Both sets of researchers also extensively studied the ability of aluminum to propagate through porous rock.…”

“…For these cases, the aluminum was probably either removed (by adsorption on rock) or was present in concentrations too low to allow crosslinking-so the polymer could propagate through the formation and provide some benefit as a polymer flood. This scenario is very consistent with the laboratory findings from the University of TX 124 and the University of Kansas. 126 Since the aluminum provided no benefit for this scenario, the money spent on aluminum citrate would have been more effectively spent on more polymer.…”

“…If gelation is stopped sufficiently early or if gels are sufficiently sheared so that gel particles remain significantly smaller than pore throats, the gel suspensions can propagate through porous rock; however, the level of mobility reduction (residual resistance factor) is generally small (less than 2). 16 Independent studies at several locations (the University of Kansas, 125,126,155 the University of TX, 124 New Mexico Tech, 156,157 Stavanger College, 128 and BP 127 ) confirm that aluminum-citrate-HPAM gelants and gels behave like other gelants and gels.…”

“…They found that effective propagation required high citrate/aluminum ratios and appropriate pH values. 124,125 Aluminum precipitation and ion exchange played important roles in inhibiting aluminum propagation.…”

“…For conditions that allowed effective propagation of aluminum, researchers 124,126 found that resistance factors (effective viscosities) provided by aluminum-citrate-HPAM colloidal dispersion gels within the core (i.e., beyond the first core section) were the same as those provided by polymer with no crosslinker. This observation suggests that either the gel particles were too small to interact significantly with pore throats or the crosslinking reaction did not take place to a significant extent.…”