Conformance Gel Design for High Temperature Reservoirs

Abstract

Abstract A gel conformance treatment is a complex process that has to be adapted to reservoir conditions such as pH, temperature and salinity. For instance, high temperature and low salinity reduce gelation time making field operations difficult. Understanding the interactions between functional groups of polymers, crosslinkers and retardants is essential to control the gelation process considering kinetic, strength and stability of the gel. The objective of this work is to better understand chemistry mechanisms in gel formation to design an optimal gelation system for in-depth conformance treatment in a high temperature reservoir. The target reservoir conditions are a low salinity water (TDS 6 g/L) and a temperature of 100°C. The ultimate goal is to select a polymer / crosslinker / retardant system with a gelation time above 7h, and Sydansk's gel strength of "G" that is stable over more than one week. This work contains a stepwise process to design a conformance gel based on the understanding of the chemical interactions between polymers and crosslinkers. In a first step, a rheology evaluation of different polymers containing ATBS was performed. Then, a wide range of combinations between polymers and crosslinkers with and without retardants was studied. The study of the formation of gels was carried out in bottle test (Sydansk's gel-strength code) in order to provide information about the gel formation, the gel kinetics, the gel strength and the stability of gel as function of time. Finally, the best gelant solutions were selected to further study the evolution of the complex viscosity over time using a rheometer with a high pressure cell that mimics the reservoir conditions. This study provides new knowledge of polymer gelation at high temperature; the main findings are the following: Gelation depends on the chemical composition of polymer and crosslinker.Gelation time depends on the particular polymer / crosslinker system and not only on whether the crosslinker is organic or not.Concentration plays a very important role in the formation of certain gels.The polymer molecular mass dependence is not as clear as it might be assumed at first. The kinetics of the polymer / PEI crosslinker systems can be delayed by retardants that contain inhibitor groups. This positive laboratory results will be complemented with simulation studies to assess the field implementation of these new conformance gels. The main novelty of this work is the use of thermal resistant polymers that combined with the adequate crosslinkers and retardants allowed the generation of a conformance gel at 100°C. The information provided in this study will be useful for the design of conformance treatment for other field conditions. The close communication and integration between polymer manufacturers and operators was crucial for the interpretation of the results and gel optimization.