Surface and Subsurface Requirements for Successful Implementation of Offshore Chemical Enhanced Oil Recovery

Abstract

Summary Chemical enhanced oil recovery (EOR), including polymer and surfactant-based processes, is a method that operators consider to maximize oil recovery from onshore and offshore reservoirs. Because of the logistical, operational, and environmental differences and the footprint and required weight needed for additional injection and production equipment, offshore chemical EOR processes are challenged by greater complexity and costs as compared with onshore applications of the same technologies. Chemical EOR commonly requires large volumes of injection chemicals, as well as demulsifiers to break produced-water/oil emulsions and inhibitors to control scale, resulting in high shipment and storage costs. The use of seawater and/or produced water for injection of the chemicals into offshore fields mandates stringent processing of both streams to allow optimal injectivity, sweep efficiency, and chemical effectiveness in the reservoir. Offshore production of saleable oil and clean water requires space- and weight-efficient oil/water-separation equipment. Currently, conventional methods for processing produced fluids fall short in both efficiency and compactness. High offshore drilling costs lead to relatively large well spacing and more difficulty in monitoring the EOR subsurface process, and lead to restrictions on the number of disposal wells. Finally, environmental restrictions limit the overboarding of toxic or poorly biodegradable EOR chemicals. The industry is currently investigating the limiting factors pertinent to offshore chemical EOR. As a result of these efforts, new enabling chemistries and technologies are being examined for improving surface operations to allow cost-effective offshore chemical EOR to be performed in an environmentally sound and safe manner. Some of these recent chemical- and fluids-processing developments are described in this paper. Subsurface challenges to implementing offshore chemical EOR are also highlighted, along with potential solutions.

Recovery rates, enhanced oil recovery and technological limits

“…This has most often been achieved using high molecular weight water-soluble polymers of 2-propenamide (acrylamide) and 2-propenoic acid (acrylic acid) as the partly neutralized sodium salt in a ratio of about 70:30 of polymer to acid by weight [60,61]. The polymers typically have a molecular weight (or relative molecular mass) of 9–25 million daltons.…”

“…When dissolved in water, the solutions have a viscosity that depends on the polymer concentration, polymer molecular weight, temperature, water salinity and the concentration of divalent ions. Other polymers, such as xanthan gum [60,61], have been used for the benefit of the improved viscosity yield in more saline water, but these have often been consumed by anaerobic sulfate-reducing bacteria resident in oil reservoirs causing the generation of dissolved hydrogen sulfide (commonly known as known as ‘souring’).…”

“…Like polymer flooding, ASP flooding can significantly improve RFs [73–75] with incremental costs quoted to be as low as $2.42 per incremental barrel for an onshore field [76]; however, like polymer flooding, there are a number of difficulties which have limited widespread field application, especially offshore [61]. Operational difficulties include the large volumes of chemicals that have to be transported to remote sites and then stored on platforms where space is limited.…”

Scientific research and field applications of polymer flooding in heavy oil recovery

“…Polymer flood in offshore fields faces more challenges than that onshore (Raney et al 2011). These challenges include costs to transport chemicals, space for mixing facilities on platform, large well spacing, and reduced polymer viscosity when mixed with sea water.…”

Oil–water separation property of polymer-contained wastewater from polymer-flooding oilfields in Bohai Bay, China

“…These problems make polymer-containing wastewater treatment become one of the restricting factors of the large-scale application of polymer flooding in offshore oilfields, which also is a worldwide problem of wastewater treatment. [8] Nowadays, in China offshore oilfields, the wastewater treatment apparatus is adopted from that of land oilfields. [9] However, the existing process, apparatus and reagents of wastewater treatment cannot perform well on the polymer-containing wastewater treatment.…”