Experimental Study of the Gelation Behavior of a Polyacrylamide/Aluminum Citrate Colloidal-Dispersion Gel System

Abstract

This paper (SPE 52503) was revised for publication from paper SPE 37220, first presented at the 1997 SPE International Symposium on Oilfield Chemistry held in Houston, 18-21 February. Original manuscript received for review 18 February 1997. Received manuscript revised 27 June 1998. Revised manuscript approved 5 August 1998. Summary The gelation behavior of a polyacrylamide/aluminum citrate colloidal-dispersion gel (CDG) system was investigated in sandpacks at frontal advance rates of 2 ft/D. A gelatinous mass formed where the gelant encountered a change in flow medium. Permeabilities of homogeneous media were reduced only by factors that were similar to those obtained with a polymer displacement alone. A laboratory investigation of a polyacrylamide/aluminum citrate CDG system was conducted to determine whether the system develops in-depth permeability modification in unconsolidated sandpacks. The study includes flow of the polymer and in-situ gelation behavior of the gelant in porous media and aggregate growth during the gelation reaction in beakers. Flow experiments were conducted in long unconsolidated sandpacks in which the gel solution was mixed in-line before injection. Injection rates were designed to provide adequate residence time for the gel solution to develop in-situ flow resistance during displacements based on bulk gel characterization tests. Residual resistance factors were determined following a static rest period in which the sandpack was left saturated with the injected gel solution. For comparison, apparent viscosity and residual resistance factors were also determined for the polymer flowing through unconsolidated sandpacks. Membrane dialysis was used to study the aggregate size distribution of the gel system at selected times after mixing. In-depth in-situ flow resistance did not develop when the gelling solution was injected into the sandpacks at frontal advance rates of 2 ft/D. Propagation through the sandpack was similar to a polymer solution. Flow resistance was characterized by the formation of a gelatinous filter cake, which formed when the injected solution encountered a change in flow medium, such as a screen placed at the ends to retain sand in place, the interface between the 50-mesh coarse sand layer at the inlet and the rest of the sandpack, and void spaces. Delaying injection by 2 hours after mixing in-line (to simulate field conditions) resulted in severe front-end stripping of gel aggregates. In all cases, residual resistance factors for the gel solution were similar to those obtained with a polymer displacement alone. Effluent fractions from gel solution displacements never developed a gel structure, and their viscosities were significantly lower than the injected solution. In the study of gel size distribution, aggregates were not detected at reaction times of 4 and 8 hours. P. 337

Network Modeling of EOR Processes: A Combined Invasion Percolation and Dynamic Model for Mobilization of Trapped Oil

“…Most studies have focused on propagation of gel in porous medium and finding ways to delay the gelation time. The gelation behavior of colloidal dispersion gel system was studied by Ranganathan et al (1998) and Rocha et al (1989) with the aim to understand the performance of CDG on in-depth permeability modification. Dong et al (1998) performed extensive displacement experiments and also studied CDG structure and rheology using atomic force microscopy (AFM) and dynamic rheological methods.…”

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

“…[124][125][126][127][128]155,156 That is, they are NOT super-polymer flooding agents. In particular, researchers from the University of Kansas 125,126 , the University of TX 124 , and New Mexico Tech 156,157 found that resistance factors (effective viscosities) provided by aluminum-citrate-HPAM colloidal dispersion gels within cores (i.e., beyond the inlet core section) were the same as those provided by polymer solution alone (i.e., containing 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.…”

“…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.…”

“…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.…”

“…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.…”