Evaluation of the Effect of the Water Formation Salinity in the Performance of Gels for Water Shutoff

Abstract

In this work a gel of an acrylamide based polymer crosslinked with organic reagents was studied. This gelling system was one of the commonly used in water conformance treatments. Once formed in bottle tests the gel was placed in contact in several proportions with water of various salinities. The tests where carried out at 266°F, and the changes were registered as a function of time. It was found that the gel swelled until a constant final volume. This value depende the difference between the salinity of the water used to prepare the gel and the added water. The performance of this gel in porous media was evaluated by coreflood experiments in Berea sandstone at 266°F with water prepared with the same compositions evaluated in the bottle tests. The results indicated that the RRF values are lower if the salinity of the reservoir water is similar to water salinity used to prepare the gelling mixture; while the Residual Resistance Factor (RRF) increased if the salinity of the reservoir water was much higher than the salinity of the preparation water. These findings show that it is important to take into account the difference between the water salinity used to prepare the gelling system and the water reservoir in the design of water conformance treatments with polymeric gels. Introduction The aqueous gels prepared from crosslinking reactions of water-soluble polymers are nowadays used to reduce the formation permeability in water conformance treatments. Despite, there are still many questions about the behavior of the gels inside the porous media. One of these questions is how the fluids present in the reservoir affect this gel. The aim of this work, as a contribution to the available information, is to study the influence of the difference between the salinity of the reservoir water and the water in which the gelling system has been prepared. The gels are an intermediate state between a liquid and a solid. As a result of this dual character they can show intermediate properties between the cohesion of the solid and the transport of the liquids. The polymer network holds the liquid in place, and the liquid prevents the networks from collapsing into a compact mass2,4,6. They have the capacity of swell or shrink according to the external media against they are put in contact. A gel can swell or shrink when there are changes in the variables of the external environment like pH, temperature, salinity, etc.1,2,4. The studies on gel swelling have demonstrated that small changes in the external conditions as ionic strength, and external electric field can induce drastic changes in the state of the swollen network. In particular, it is well known that under certain conditions polyelectrolyte gels may undergo a discontinuous volume change. The volume of gel is influenced by osmotic pressure7,8. The osmotic pressure is the sum of the following three components; interactions between the polymer strands and the solvent, the pressure relates to the elasticity of the individual resistance to stretching or bunching, and the hydrogen ion pressure, which is associated with the ionization degree of the polymer network9. The magnitude and direction of the components of osmotic pressure in cnjunction each other govern whether a gel swells or shrinks. In this work the interaction between the reservoir water of reservoir and the water in which the gel was prepared was studied in bottle tests and by coreflood experiments in Berea sandstone. Experimental Gelling mixture preparation. The gelling system was prepared dissolving a water-soluble polymer in water of the composition shown in column A in Table 1. Then a mixture of organic crosslinkers was added and the pH was adjusted adding NaOH.

Exploring Potential of Gellan Gum for Enhanced Oil Recovery

“…Anyway, the experimental results presented above prove that gellan gum provides sufficiently high-pressure gradients (around 50 psi/ft = 1 MPa/m = 0.2 MPa/0.2 m) in 1 mm-width fractures during the post-flush with high salinity brine (150 g/L) (Figure 12). This is a remarkable result because post-flush brine salinity greatly influences the stability of HPAM gels in fractures [63]. For example, the authors of [64] found out that HPAM + Cr +3 gel failed at 0.45 MPa/m (20 psi/ft) during the post-flush with 8% salinity brine; as a consequence, there was no redirection of fluids accomplished.…”

“…Based on the information presented above, when there is an ample supply of fresh water and the budget is not restricted to 4 USD/kg of dry powder, gellan gum may prove to be a preferable alternative to HPAM. Furthermore, the samples of gellan gum gels obtained during the Kumkol pilot test (2013) were aged for 5 years without any evidence of gel degradation [63]. In reservoir conditions, microbial degradation of biopolymers may also be prevented through the appropriate use of biocides [80].…”

Laboratory Investigation on Gelation Behavior of Xanthan Crosslinked With Borate Intended to Combat Lost Circulation

“…There is a breakthrough of water injected for pressure maintenance or enhanced oil recovery. Llamedo et al (2005) explained the effect of salinity of formation water on performance of a gel system for water shut-off. Residual resistance factor (RRF) was lower when the water used for preparation of gel and formation water had similar salinity.…”