Polymer design to optimize Enhanced Oil Recovery by polymer flooding

T. Broekhuis, D. Wever, F. Picchioni
UNiversity Groningen,
Netherlands

Keywords: polymer, design, enhanced oil recovery

Summary:

Chemical products are known to require long lead-times, in particular when new product functions demand that new constituents and technologies have to be designed and developed. To reduce this lead-time, a structured approach for their design, engineering and manufacture has been proposed and developed, and several universities have included Chemical Product Design and Engineering (CPD&E) as part of their engineering education programs. At our university, this introduction resulted in a public-private collaboration with the aim to design and develop improved water-soluble polymers to be used in enhanced oil recovery. Polymer flooding is considered as the most important technology to enhance oil recovery by chemical methods. Usually, it is applied following water flooding of a reservoir and based on flooding with a semi-dilute solution of a high molecular weight polymer, such as hydrolysed poly-acrylamide (HPAM) or xanthan gum. Although recovery enhancements up to 8% have been reported with these systems, significant practical problems occur due to unpredictable viscosity-changes caused by polymer shear instability, gradual hydrolysis, and sensitivity to brine composition and concentration. To tackle these issues a series of new polymers have been designed and tested with the aim to generate basic understanding regarding the relation between molecular structure and reservoir performance. Linear, star and comb-like polyacrylamides (PAM) have been prepared by atomic transfer radical polymerization (ATRP). The influence of the molecular architecture of PAM on the rheological properties in aqueous solution has been investigated. The theory of increased entanglement density by branching for polymers in the melt has been applied to polymers in the semi-dilute water solutions. We demonstrated this by investigating the rheological properties of PAM of similar molecular weights with different molecular architectures. Interestingly, the solution viscosity of a comb-PAM is higher compared to its linear and star analogues. In addition to the pure viscosity, we also demonstrate that the visco-elastic properties of the polymeric solutions depend significantly on the molecular architecture of the employed PAM. The potential of the branched PAMs in improving oil recovery was evaluated. The oil recovery was investigated in a 2D flow-cell and in low permeable sandstone cores. The observed higher oil recovery by the branched PAMs appears to be caused by their inherent higher viscosity and a more pronounced elastic response.