Mechanistic Aspects of Polymeric Relative Permeability Modifier Adsorption onto Carbonate Rocks

Abstract

Relative permeability modifiers (RPMs) are chemicals that can be injected into a reservoir to change its fluid/gas transport characteristics. For example, RPMs can reduce the relative permeability to water in a subterranean reservoir while having minimal impact on hydrocarbon production. Most commercially available RPMs are specifically designed for silica surfaces which are dominant in sandstone reservoirs. However, the concentration of silica in carbonate rocks is very low and many of these RPMs are unsuitable for carbonate reservoirs (which hold a significant portion of the remaining 60% hydrocarbon reserves). Furthermore, carbonate reservoirs tend to have more complex permeability and porosity characteristics and as such few research publications report the utilization of RPMs in the reservoirs of this type. The main mechanism of RPMs is either chemical adsorption onto, or functionalization of, a rock surface. However, as carbonates have distinctly different chemistry compared to silica, a new RPM formulation is required. The approach reported here overcomes this obstacle by using sodium silicate to functionalize the carbonate rock surface thereby converting it into a surface that in many ways exhibits the chemistry of silica. This has been confirmed by sodium silicate adsorption tests and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis. The other components consist of an amine-containing silylation reagent which reacts with the newly formed silicate surface, a polymer containing amine functional groups, and a linker molecule that reacts with the amines on the silane immobilizing the polymer. The chemistry is confirmed using five different chemical solutions to investigate their adsorption onto carbonate rocks using static tests. The results show that carbonate particles treated by the RPM have the highest adsorption weight, 7.33 mg/g and according to the measurements of X-ray photoelectron spectroscopy (XPS), the atomic percentage of Si 2p and N1s is 9.89% and 7.51% respectively, indicating the adsorption of RPM onto carbonate particles. To further verify the performance of RPM under reservoir conditions (1500 psi and 60 °C), three core flooding tests have been conducted. The results show that relative permeability to water decreased much more than oil. RRF to water in sample indinana-2 can reach up to 5.21, but RRF to oil is less than 2. The disproportionate ratio (RRF brine /RRF oil ) is 3.1, indicating the good performance of RPM under reservoir conditions. This work first introduced sodium silicate and APTES to make polyacrylamides as a new RPM material strongly stabilized onto carbonate rock surfaces, which provided further insights into the effectiveness of this approach applied in carbonate reservoirs.

Further Insights into the Performance of Silylated Polyacrylamide-Based Relative Permeability Modifiers in Carbonate Reservoirs and Influencing Factors

“…Generally, the concentration of uncross-linked polymers used in sandstone reservoirs is less than 0.3 wt %; higher concentrations of polymer can lead to undesirably large reductions in the permeability for both oil and brine. , Given that carbonate core samples contain narrow pores with a small average pore radius and generally weak pore connectivity compared to typical sandstone core samples of similar permeability/porosity, the polymer concentration will likely need to be less. The RPM formulation we used in a previous study had a higher concentration of a polymer of 0.6 wt % (and correspondingly higher amounts of formaldehyde, sodium silicate, and APTES) and a higher viscosity; however, there was a concern that 0.6 wt % might cause a blockage of high-permeability channels in the carbonate core sample when PAM-co-AA is immobilized onto the pore walls after the RPM flooding. As a result, for all the RPM formulations used in this study, a polymer concentration less than 0.3 wt % was used.…”

“…Regardless of the precise mechanism, to date, very little research has been done utilizing RPM formulations in carbonate rocks. , This can be attributed to the significant differences (i.e., mineral compositions, pore structure, and permeability characteristics) between carbonate rocks and sandstones. Aiming at making a new RPM applied in carbonate rocks, based on our previous studies, , we have shown that we can efficiently functionalize/immobilize polyacrylamides onto the pore surface of carbonate rocks. ,, In our previous study, sodium silicate was used to functionalize the carbonate surface with silicate groups, and then, 2-aminopropyltriethyoxysilane (APTES) reacted with the Si–O bonds to functionalize the surface with amine groups. ,, An organic linker such as formaldehyde can then be used to attach the polyacrylamide to the surface (i.e., the amides within the polyacrylamide would attach via the organic linker to the amines on the rock surface).…”

“…Aiming at making a new RPM applied in carbonate rocks, based on our previous studies, 31,33 we have shown that we can efficiently functionalize/immobilize polyacrylamides onto the pore surface of carbonate rocks. 31,33,34 In our previous study, sodium silicate was used to functionalize the carbonate surface with silicate groups, and then, 2-aminopropyltriethyoxysilane (APTES) reacted with the Si−O bonds to functionalize the surface with amine groups. 31,33,34 An organic linker such as formaldehyde can then be used to attach the polyacrylamide to the surface (i.e., the amides within the polyacrylamide would attach via the organic linker to the amines on the rock surface).…”

Comprehensive Review of Polymer and Polymer Gel Treatments for Natural Gas-Related Conformance Control

“…This phenomenon ideally aims to selectively reduce the water permeability, while causing a minimal effect on the oil/gas permeability. The polymer adsorption on the rock pore walls is considered to be the underlying reason for this phenomenon [ 58 , 59 , 60 ]. Besides polymer adsorption, several mechanisms that contribute to polymer selectivity, including swelling/shrinking [ 61 ] fluid partitioning [ 62 ], lubrication, and steric and wettability effects [ 63 ], have been discussed and debated among scholars.…”

Rock/Fluid/Polymer Interaction Mechanisms: Implications for Water Shut-off Treatment

“…Excessive water production is a major challenge in the oil and gas industry as water production can subsequently cause a significant reduction in hydrocarbon productivity − and increase the operational costs related to surface water treatment and handling. ,− Three different types of methods (i.e., chemical, mechanical, and biological) can be applied to regulate or decrease water production. ,,,, This review will focus on chemical treatments which have been extensively utilized to reduce water production. One class of chemical materials that have received widespread attention, − due to their potential performance, low cost, and ease of implementation, , are relative permeability modifiers (RPMs) that can selectively reduce the permeability to water while ideally having minimal effect on oil/gas permeability.…”