Swelling of Clay Minerals and Its Impact on Permeability

Open Access
Author:
Aksu, Irem Yasar
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 12, 2014
Committee Members:
  • Zuleima T Karpyn, Thesis Advisor
Keywords:
  • Montmorillonite
  • kaolinite
  • clay swelling
  • clay coatings
  • porosity-permeability relationships
  • X-ray micro-computed tomography
Abstract:
Formation damage has been described as any irreversible alteration, i.e. decrease of permeability, of the hydrocarbon reservoir rock after wellbore operations, which may have a serious economic impact upon the productivity of the reservoir. The presence of clays minerals is often considered as a major cause of formation damage. Thus, clay behavior in porous media needs to be taken into account when evaluating the potential productive capacity of hydrocarbon reservoir sandstones. Since the main mechanisms of permeability reduction, such as fine migration and clay swelling, occur at the pore-scale, in this study we couple permeability experiments with X-ray μ-computed tomography (μ-CT) to visualize and quantify clay behavior in porous media. The selected porous media were packed columns (diameter, d=1.27 cm, average length, L=6.4 cm) of soda lime beads and quartz grains. Various amounts of swelling (montmorillonite) and non-swelling (kaolinite) clays were added as coatings on beads and quartz. The amount of clay in the samples varied from 1.38 to 5.5wt.% in montmorillonite-coated samples and from 2.0 to 6.84wt.% in kaolinite-coated samples. Permeability measurements were performed on each sample to investigate the impact of clay content and grain size on permeability reduction as a result of clay swelling. Permeability changes were monitored as a function of time. Visualization of coated bead and grains columns by μ-CT provided quantitative information on morphological changes of clay grains/coatings among dry and water-saturated samples. All clay-coated samples showed 10-40% decrease in permeability as compared to uncoated samples (K/Ko= 0.6-0.9). In general, the higher the clay content was, the larger permeability reduction was observed. Permeability remained constant within an error after 4 hours of flow experiment in montmorillonite samples. In contrast, permeability of kaolinite samples oscillated with time, possibly due to fine migration. A 39% volume increase of montmorillonite particles was observed by μ-CT immediately after the sample was saturated with water, i.e. swelling occurred almost instantaneously after water-clay contact. However, no further changes in volume were observed after 4 hours of flow. Kaolinite-coated samples showed a 15% volume increase of clay particles, which was attributed to the hydration of clay pellets by water. The calculated porosity reduction associated with clay swelling ranged from 0.4-1.7% including both montmorillonite- and kaolinite-coated samples. This decrease in porosity was estimated to cause only a 2-5% reduction in permeability, primarily due to the high initial porosity and permeability of the selected samples. This study presents a base line to estimate changes in permeability as a result of clay swelling for variable clay content, grain size, and porosity.