Production from oil fields can be increased by enhanced oil recovery (EOR) techniques. Among several other EOR methods, the injection of chemicals has been studied since the 1970s.
In that time, anionic polyacrylamides (PAM) have proven to be efficient viscosifiers for moderate field conditions to reduce mobility of the displacement fluid, thus increasing reservoir sweep efficiency. Surfactants mobilize oil that is trapped in formation rock pores by lowering the oil/water interfacial tension.
Polymer flooding is now considered an established technology, which is applied on a commercial scale in several countries. In contrast, the commercial use of EOR surfactants is still limited despite more than 50 years of research history in this area. This can be partly explained by the technical complexity of EOR surfactant projects and the higher cost.
The implementation of a chemical EOR (cEOR) project is often a significant endeavor that not only poses technical challenges but also represents substantial financial risk. In recent years, cEOR projects also target challenging conditions such as high temperatures, high salinity, and demanding locations such as offshore fields.
A multidisciplinary and integrated approach is vital to managing technical, regulatory, and economic challenges with a team of geoscientists, engineers, chemists, and mathematical modelers working together to achieve an increase in incremental oil recovery at the lowest total cost of ownership.
From Laboratory to Full Field
Once the operator has verified that injection of chemicals is a viable option to enhance oil recovery in one of its assets, a laboratory-screening program will start to identify a suitable chemical solution that not only will perform under specific reservoir conditions but also meet financial targets. The principal workstreams of a cEOR project are illustrated in Fig. 1.
EOR-specific application test work is needed, such as rheology evaluations for polymers, or phase-behavior and interfacial-tension measurements for surfactants. The quality of the work will rely considerably on the collaboration of an experienced multidisciplinary team mainly because the experimental evaluations cover a broad range of knowledge fields such as chemistry, physical chemistry, and reservoir and petroleum engineering.
While laboratory research for EOR polymers will focus on measuring rheology, thermal, and mechanical stability, the screening of EOR surfactants in general is more complex. In most cases, a blend of several surfactants is needed to reduce the oil/water interfacial tension by two to three orders of magnitude to an “ultralow” level. These evaluations require extensive solubility and interfacial-tension measurements followed by phase behavior tests.
Ultimately, coreflood studies will be required for all chemicals, polymers, and surfactants to assess injectivity, propagation profile, dynamic adsorption, and incremental oil recovery. The results of porous media flow investigations can be used as input parameters to perform reservoir-simulation studies.
Once the chemical candidate has been identified, it is important in the laboratory phase to work out production and supply concepts to cope with performance requirements and production capabilities at the same time. Results of all mentioned steps in the project development need to be fed back into laboratory work for potential adjustment.
An important but sometimes overlooked property of a cEOR solution is applicability. Using EOR surfactant formulations offshore or at very low temperatures needs a proper design of chemicals and their formulation to not fail in the last step.
For a single-well pilot test, up to a few tons of EOR chemical formulation are needed, which can be produced in a small chemical pilot facility. A multiwell pilot test might demand a few hundred tons of chemicals. Besides timely availability, understanding the interplay between production scales and product performance is of utmost importance to be able to scale EOR operations.
Project dimensions and financial exposure will significantly change once the project progresses to full-field scale. While the operator will start investing in surface equipment and eventually even new wells, the chemical supplier may have to invest in additional production capacity to meet the chemical demand, which could be several thousand tons per year. For standard PAM polymers, production capacity is not as much of an issue. A challenge might exist for specialty surfactants that were tailored toward EOR and for which dedicated production capacity is limited. Availability of raw materials and regulatory requirements need to be considered carefully, as well as established manufacturing processes, to help reduce project risks and cost. Risk-sharing agreements between an operator and chemical partner can help to ease approval processes and manage financial uncertainties.
Making cEOR a Reality
For polymers, anionic PAM, which is well-known in the water treatment industry, is nicely suited to the cost-performance requirements of EOR. But the operation window of such polymers is limited to mild field conditions with temperatures below 70°C and salinities less than 30,000 ppm, which leaves room for innovation.
In contrast, most of the surfactants known from cleaners, cosmetics, and other applications are not perfectly suited for use in EOR. Organic sulfonates, for instance, either did not have the right alkyl chain, or the quality of commercial products was unsteady. This resulted in inefficient surfactant pilot floods in the 1970s. When oil prices eroded in the 1980s, EOR research activities were almost abandoned. Only a few academic research groups continued working in the EOR area, gaining fundamental know-how on the relationship between molecular structure and EOR application performance. This knowledge came into use once oil prices recovered and the interest of the oil and gas industry in EOR was renewed.
Several full-scale polymer flooding projects have been implemented since then, first in China, later in Canada, the Middle East, and several other countries. Over the years, quality has constantly improved so that good solubility and injectivity today are technically achievable. Innovative polymers such as the new class of associative polymers will help to further improve overall project economics. New polymer architectures are being designed for harsh field conditions where standard PAM is not applicable.
Research in the surfactant area also targets more dose-effective structures, but the development of molecules that can withstand harsh conditions is also of interest. It is worth emphasizing that, except for standard PAM, most of the innovative EOR chemicals are still in trial or pilot phase and are not yet fully scaled up to a true commercial size.
A large chemical company with experience in both polymers and surfactants can contribute in several key areas of EOR product development and supply through these methods:
- Product screening, new product development, and scaleup. The key objective is to identify the optimum chemical solution for a given field. In case it is necessary to design new chemicals, a large and experienced chemical partner builds on a profound research and development expertise, which also includes the development of reliable, industrial-scale manufacturing processes.
- Production and quality control. A large, international chemical supplier has all processes in place to ensure the supply of chemicals even in large volumes with an always consistent quality. Analytical support beyond routine quality control measurements can be given during site visits in the startup phase of a chemical flood.
- Registration of new chemicals. This topic is especially relevant for the market introduction of new surfactants and has to be addressed early, as it is not only costly but may take several months or even years.
- Raw materials. The long-term availability of key raw materials at reasonable costs is decisive for sustainable project economics. A large chemical supplier is either backward-integrated in such raw materials or, in case of insourcing, may benefit from a stronger purchase position to keep costs low.
- Supply chain. A strong global presence helps to set up cost-effective supply chain solutions even for oil fields in remote locations.
In summary, close cooperation be-tween the experts of the operating company with those of the chemical partner from an early stage on is vital to making a cEOR project a success.