Production of fluids with high CO2 content in fields undergoing enhanced oil recovery (EOR) can prove challenging due to thermal stability issues. Particularly for wells with gas-to-liquid ratios above 5 Mscf/bbl and liquid rates below 300 BFPD, these issues become acute due to aggressive Joule-Thompson (JT) cooling of CO2. In these conditions, freezing causes excessive paraffin deposition and ice plugs, thereby forming a negative feedback loop through excess pressure drop and even more JT cooling. This application targets the following issues: insufficient downhole separation of gas leading to pump cavitation and premature failure, and excessive paraffin deposition and hydrate plugs requiring expensive interventions and downtime. This paper presents the design considerations and lessons learned from a novel solution using hydraulic jet pumps for such wells.
A novel design utilizing hydraulic jet pumps to mitigate downhole freezing and paraffin deposition issues was deployed in 2016. The system was designed considering two engineering imperatives. First was the common process of hydraulic optimization by sizing the jet pump throat and nozzle combination to reduce bottomhole pressure as constrained by available surface horsepower, well depth, and producing friction. Second was the novel optimization of thermal design by sizing the power fluid injection rate for the requisite latent heat and heat absorption capacity to offset the JT cooling of the produced fluid and maintain thermal stability. This design was successfully deployed in the Permian Basin on multiple producing wells with high CO2 content and subsurface freezing issues from 2016 to 2022.
The thermal design is similar to that of a cross-current heat exchanger. Cool produced fluids are warmed by: a) specific heat of warm power fluid, b) higher heat conduction from warm casing/rock due to higher heat conduction of the power fluid, and c) conduction with warm power fluid in the casing. These temperature phenomena in the tubing and casing were modeled before deployment and measured during field trials, thus confirming the design. The hydraulic jet pumps proved to be a successful mitigant for subsurface freezing issues and led to less frequent failures, less downtime, and higher production enabled by more drawdown. Temperature measurements through the tubing column confirmed successful design and operation. Stable production enabled by thermal stability resulted in decreased work hours required to operate the wells and lower operating expenses for chemical treatments, paraffin cutting, and well repairs. Regular maintenance may include throat-nozzle replacement and chemical treatment through slipstreaming into the power fluid.
A novel application of hydraulic jet pumps improved production and reliability by reducing subsurface freezing of produced fluids containing high amounts of CO2. The novel design and thermal modeling procedure, installation procedure, and long-term learnings from field application are shared in this paper.