Development and Evaluation of High-Temperature Conformance Polymer Systems

Abstract

Abstract Conformance polymer systems have been successfully applied for many years to control undesired water production from hydrocarbon wells. However, currently available polymer systems present a number of limitations for high-temperature conformance applications (> 300°F). Based on laboratory research, this paper documents the results of the development and evaluation of polymer gel systems used as sealants to shut off water production in high-temperature environments. The polymer systems were evaluated by their effectiveness to:provide adequate gel time for placement (up to 400°F),limit permeability to water at temperatures up to 375°F in sandpack flow experiments, andprovide long-term thermal stability in sandpack flow experiments at elevated temperature (up to one-year study). A commercially available polymer system that has been successfully used in field applications (up to 275°F) has been modified to extend its applicability up to 375°F. Recently developed base polymer, crosslinker, and retarder were tested successfully to extend the temperature range of applicability of this polymer system. Discussed are:methodology used for gelation time measurement of polymer systems at elevated temperatures, andlaboratory results regarding gelation time of crosslinked polymer systems when varying temperature, base polymer concentration, crosslinker concentration, retarder concentration, salinity of mixing brine, and/or pH of solution. Additionally, this paper discusses and describes the dynamic flow through porous media experiments performed to simulate high-temperature / high-pressure reservoir conditions to evaluate the performance of polymer systems at elevated temperatures (up to 375°F). Specifically, this paper details:the physical laboratory equipment and test conditions used for dynamic flow studies,experimental procedure regarding short-term and long-term testing, andthe effect of temperature versus permeability reduction over time. Introduction Excessive water production from hydrocarbon reservoirs is one of the most serious problems in the oil industry. Watercut greatly affects the economic life of producing wells and unwanted water production is estimated to cost the petroleum industry about $45 billion a year (although accurate records of water production are difficult to obtain).1,2 These costs include the expense to lift, dispose, or reinject this water, as well as the capital cost of surface facility construction, water treatment, and efforts to ensure that environmental regulations are met.1 Remediation techniques for controlling water production, generally referred to as conformance control, include the use of polymer systems to reduce or plug permeability to water. This paper mainly discusses water control in high-temperature environments for treating hydrocarbon-producing wells to reduce water production for applications in which water and hydrocarbon zones are clearly separated. The principle of operation of this technique is to pump the polymer system into the formation around the wellbore and allow it to propagate through the rock matrix. In-situ gelation takes place, plugging pore spaces and channels, thus limiting undesired water flow.3 A variety of techniques for controlling water production have been attempted by the oil industry. Earlier attempts to reduce water production included mechanical isolation, squeeze cementing, solid slurry (clay) injection, and oil/water emulsion. More successful results have been obtained with in-situ polymerized systems, crosslinked polymeric solutions, and silicate-based gels.4 Polymer gel systems have emerged over the last decade as one of the most effective tools for controlling water production. One of the most widely used polymer systems employs polyacrylamides (PAm's) or acrylamide co-polymer and chromium [Cr(III)] as a crosslinker.5 Cr((III) has been extensively used because of its high success rate and relatively low cost. However, the short gelation times of this system at elevated temperatures limit their application to low- to moderate-temperature reservoirs.6 Another polymer system widely used is a water-based gel based on phenol/formaldehyde crosslinker for homo-, co-, and ter-polymer systems containing acrylamide. The loss of phenol by partitioning into crude oil with which it comes into contact has been identified as an important issue for that polymer system.8 The toxicity issues associated with formaldehyde and phenol have been addressed by other researchers.9