No abstract

The Days Chapel area of the Slocum oilfield was investigated as a target for conducting a polymer flood using heated water. The crude oil in the Carrizo zone of the Slocum oilfield is a heavy oil with an API gravity of about 19 degrees and a viscosity of about 1000 cp. The Carrizo formation is a shallow sand with high porosity and permeability. A new well was drilled for the purpose of obtaining log and core data needed to characterize the target area. Simulations using these data were used to assess its potential in this area of the field. Polymer flooding using heated water is significantly more complicated than conventional polymer flooding with respect to the surface facilities, the design and prediction of the flood, the operation of the flood, and the reservoir performance. One of the most important variables is the temperature of the heated water. Higher temperature results in lower oil viscosity, but it also results in higher heat losses from the wellbores and reservoir, and higher energy costs to heat the injected polymer solution. Injection and production rates are also key variables. Another important design variable is the duration of hot water injection before starting hot polymer flooding. Preliminary results indicate this innovative approach to polymer flooding of heavy oil zones is promising and should be evaluated in other heavy oil reservoirs.

The work described in this paper details the development of a single stimulation package that was successfully used for treating an offshore horizontal polymer injection well to improve near wellbore injectivity in the Captain field, offshore UK. The practice was to pump these concentrated surfactant streams using multiple pumps from a stimulation vessel which is diluted with the polymer injection stream in the platform to be injected downhole. The operational challenges were maintaining steady injection rates of the different liquid streams which was exacerbated by the viscous nature of the concentrated surfactants that would require pre-dilution using cosolvent or heating the concentrated solutions before pumping to make them flowable. We have developed a single, concentrated liquid blend of surfactant, polymer and cosolvent that was used in near-wellbore remediation. This approach significantly simplifies the chemical remediation process in the field while also ensuring consistent product quality and efficiency. The developed single package is multiphase, multicomponent in nature that can be readily pumped. This blend was formulated based on the previous stimulation experience where concentrated surfactant packages were confirmed to work. Commercial blending of the single package was carried out based on lab scale to yard scale blending and dilution studies. About 420 MT of the blend was manufactured, stored, and transported by rail, road and offshore stimulation vessel to the field location and successfully injected.

In this work, we present the development and deployment of high activity liquid polymer that improves logistics for field deployment in supply chain constrained locations. Such polymers show superior performance in terms of dissolution times, increased neat polymer stability, and improved injectivity during tertiary oil displacement in comparison to traditional emulsion polymers. The initial screening process comprised of testing for viscosity yields in the desired brine, filterability, and long term injectivity corefloods in surrogate rocks. Additional tests included long term aging studies with contaminants to measure shelf life of the neat polymer. Finally, yard scale tests were conducted to identify mixing configuration and system pressures for optimal mixing conditions to scale up for field deployment. The liquid polymer developed for this application shows superior performance with rapid viscosity yields both in lab scale and yard scale mixing tests. Long term injection shows good injectivity (stable pressure for greater than 25 PV injected). Aging tests demonstrated the improved shelf life and higher stability of the neat material in the presence of iron. Application of mechanical shear and imposing temperature vaiations to the neat polymer did not affect the quality of the diluted polymer solution. QA/QC of field supplied batches indicate consistent quality of commercial scale polymer production thus demonstrating the applicability of liquid polymer for piloting at the field scale. The developed liquid polymers improve upon the limitation of traditional emulsion polymers with higher activity, better injectivity, faster dissolution times and better neat polymer stability. These features combined lead to enhanced product performance thus further de-risking polymer flooding in logistically challenging environments.