Gel Treatments in the Matrix
Effective gel placement in the matrix is essential for controlling unwanted water production in non-fractured or mildly heterogeneous reservoirs. While much attention is often given to fractures, matrix treatments present unique challenges—including rock permeability, lithology, and gel-fluid interactions—that significantly impact the success of conformance control efforts. This section presents key technical publications focused on understanding and optimizing gel behavior in porous media.
Fundamental studies by Seright and others explore how rock type (sandstone vs. carbonate) and permeability levels influence gel propagation, placement efficiency, and long-term blocking performance. For example, resorcinol-formaldehyde and Cr³⁺-xanthan or Cr³⁺-HPAM gels show different resistance behaviors depending on the pH during gelation and the velocity of fluid injection. These variables directly affect residual resistance factors and the extent of permeability reduction.
Another important mechanism examined is spontaneous imbibition (SI)—where aged polymer gels lose water to a water-wet matrix, leading to gel dehydration, shrinkage, and a decrease in blocking effectiveness over time. Laboratory tests demonstrate how factors such as matrix surface area, fluid boundary conditions, and gel age impact the rate and severity of gel dehydration. These insights are critical for evaluating long-term performance and durability of gel treatments in the field.
Additionally, the rheological behavior of crosslinked xanthan solutions is reviewed, illustrating how chromium ions increase viscosity and resistance in porous rocks, making them suitable for in-situ gelation strategies in water shut-off treatments.
Whether you’re planning gelant injection in a sandstone injector or evaluating matrix conformance solutions for chalky reservoirs, these technical papers offer essential data and guidance to design robust, field-ready treatments.
Explore the resources below to deepen your expertise in matrix-targeted gel placement, rheology, and performance prediction in diverse lithologies.
Table of Contents
This paper investigates the effects of rock permeability and lithology on the performance of four gel systems: resorcinol/formaldehyde, colloidal silica, Cr(III)-chloride-xanthan, and Cr(III)-acetate-polyacrylamide. Attention is paid to pH effects on gelation, gel performance as a function of fluid velocity, and tracer measurements of pore-space gel occupancy. The study demonstrates that gel performance cannot be adequately characterized using single-permeability rock — effectiveness must be assessed across the permeability range of the target formation to determine whether a treatment will enhance or harm oil production.
This paper tests key assumptions used in calculations of non-Newtonian gel placement in injection wells for Cr(III)-xanthan gels in Berea sandstone. Three assumptions are tested: whether pre-gelation porous-media rheology is unaffected by Cr(III) addition; whether post-gelation residual resistance factors are independent of fluid velocity; and whether gel is immobile under flow. Results: Cr(III) at 90 ppm does not significantly alter xanthan rheology before gelation. After gelation, residual resistance factors are NOT velocity-independent — they increase at higher velocities. The validity of this assumption in prior gel placement calculations is thus challenged
Resorcinol/formaldehyde gels demonstrate that gel performance in porous rock depends critically on gelation pH. At pH 9, a strong, clear red gel forms with no free water; as pH decreases toward 7, gel becomes weaker, opaque, and orange-white with residual free water. Gels generally reduced permeability more in low-permeability sandstone than in high-permeability sandstone. Residual resistance factors can be greater in sandstones than in less-permeable carbonate cores, demonstrating that lithology affects gel performance independently of permeability. A mathematical model assesses whether pH effects can be exploited to optimize gel placement in injection wells.
This work investigates dehydration of Cr(III)-acetate-HPAM gel by capillary imbibition of water from gel into strongly water-wet chalk matrix. In fractured chalk reservoirs, spontaneous imbibition of water from fracture-filling gel into oil-saturated matrix causes gel shrinkage, potentially reopening gel-filled fractures to flow. Spontaneous imbibition rate was much slower from gel than from brine, and decreased with increasing matrix-volume-to-open-face ratio. A dehydrated gel layer on the core surface lowered subsequent imbibition rate. Severe dehydration and gel shrinkage up to 99% volume were observed, suggesting gel treatments may lose efficiency over time wherever significant imbibition potential exists.
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