Gelation Kinetics of an Organically Cross Linked Gel at High Temperature and
Pressure

Carbonate reservoirs’ extreme heterogeneity in the form of fracture corridors and super-permeability thief zones present challenges to the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Foam-based conformance control is a relatively new technology especially its use for in-depth diversion in high salinity high temperature conditions. In this work, a laboratory study was conducted to develop and evaluate a foam-based conformance control technology for application in a high salinity and high temperature carbonate. Foaming agents were first screened for their suitability with regard to reservoir temperature and salinity where properties such as foamability and foam stability were measured. The best performing surfactants were then used to study the mobility reduction across a core composite at reservoir temperature and pressure. Foam stability and decay were also investigated in those permeability reduction experiments. Brine and crude oil were injected after foam formation and pressure drops and sustainability of mobility reduction were quantified. The improvement in reservoir contact and hence oil recovery were examined by oil displacement experiments conducted in specially prepared heterogeneous composites. For the studied conditions of high salinity and high temperature, foaming agents of the amphoteric family as well as a special blend were found suitable in terms of salt tolerance and foam stability. The mobility reduction due to foam was 12 times without oil and 6 times in the presence of oil. Oil recovery improvement with foam application was also found to be significant. These results demonstrate the potential of the identified foam system and its favorable impact on sweep efficiency despite the harsh salinity and temperature conditions of the studied carbonate reservoir.

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The Study of Gel Conformance Control Effect within Carbonates with Thief Zones by Advanced NMR Technique

Alshehri

Wang

Kwak

et al. 2017

Day 2 Tue, October 10, 2017

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Carbonate's extreme heterogeneity in the form of fracture corridors and super-permeability thief zones challenges the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Gel-based conformance control has been successfully applied on both sandstone and carbonate reservoirs. Achieving effective in-depth conformance control in high-temperature reservoirs, however, remains a challenge due to severe gel syneresis and significant reduction in gelation time. The first step to improve the performance of gel in these challenging environments is the accurate understanding of gel conformance control mechanism inside reservoir rocks. In this work, a laboratory study was conducted to evaluate a polyacrylamide/chromium gel system for application in a high-temperature and high-salinity (HTHS) carbonate reservoir. Oil displacement experiments on carbonate core samples, combined with nuclear magnetic resonance (NMR) measurements were performed to demonstrate oil recovery improvement by gel treatment and illustrate the mechanisms of the improvement. In these tests, the gel solution was injected into specially prepared heterogeneous carbonate composite core samples, in which different configurations of high-permeability channels were created. Gel treatment was conducted after waterflooding and was followed by chase waterflooding. Oil recovery improvement by gel treatment was 18% of original oil in core (OOIC) in the composite core with high permeability channels extending mid-way through the composite while the improvement was 38% OOIC in the composite core with channels extending all the way through the composite. Detailed spatial fluid variations inside the core samples before and after gel treatment were closely monitored using advanced low-field NMR techniques. Heavy water (D2O) was used in place of water to enhance the contrast between oil and brine for NMR by eliminating the protons in the aqueous phase. NMR measurements indicated that the bypassed oil during waterflooding was effectively recovered after gel treatment. Results in this study demonstrate the potential of the studied gel system and its favorable impact on sweep efficiency improvement application in HTHS carbonate reservoirs. The NMR study enhances our understanding of how gel helps improve sweep efficiency of subsequent floods through blocking/reducing the permeability of highly-conductive zones.

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Gelation Kinetics of an Organically Cross Linked Gel at High Temperature and Pressure

Cited by 4 publications

References 22 publications

A rheological investigation of a high temperature organic gel used for water shut-off treatments

A rheological investigation of a high temperature organic gel used for water shut-off treatments

Development and Evaluation of Foam-Based Conformance Control for a High Salinity and High Temperature Carbonate

The Study of Gel Conformance Control Effect within Carbonates with Thief Zones by Advanced NMR Technique

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