Investigations And Field Observations On The Occurrence Of Flashing Phenomena During Sucker-Rod Pumping Of Hot Fluids From Thermal Processes
Authors: Coates R. , Toma P. , Lam V. , Nguyen D. 
Published: March 2010

Flashing of high-temperature, near-saturation, aqueous oil emulsions and inflow of steam and volatiles produced during the thermo-recovery process of heavy oil are decreasing the efficiency of conventional sucker-rod pumping systems. This paper describes novel laboratory methods aiming to allow direct observations of this phenomena and assess the rationale and effectiveness of external speed control and better valve design to improve pumping efficiency. A 1:1 operational replica of a sucker-rod pump in which the pump barrel and valve cages have been constructed from Plexiglas, was used for laboratory simulations and room temperature visualization of effects induced by gas inflow and vapor flashing. Mixtures of Freon 114 and oil were used to simulate at room temperature flashing of high-temperature, high-pressure fluids, and a laser Doppler anemometer was used to measure the velocity within the pump.

The presence of gas, either from inflow or by generation of vapor flashing resulted in a decrease of the pump efficiency. Visual observation of the occurrence of flashing within the pump could be directly related to regions of critical velocity peaks. The design of valves studied created image dimensional velocity fields with areas of high velocity reversing and stagnant flows, resulting in the flashing occurring at uneven intensities within the valve. The experimental rig and investigative methods developed offer a tool to assess pump operating strategies and designs for improving the pumping efficiency during adverse thermo-recovery conditions.

Introduction

The processes used for the recovery of hydrocarbons from oil sand and heavy oil reservoirs often results in the production of hot multiphase fluids. The current downhole artificial lift systems, which have been transferred from conventional operations, are not well adapted to pumping thermal, near saturation fluids. In certain situations a mixture of liquid oil emulsions, steam and non-condensable organic volatiles enters the pump and, as a result of local pressure and velocity distributions in the pump chambers and their oscillatory variation during the stroke, flashing of hot fluids occur. These situations can decrease the efficiency of a standard sucker-rod pumping system and can often lead to vapor lock and fluid pound conditions, equipment damage and drop of production rates.

Additionally, production fluids are frequently laden with considerable solids that can cause costly shutdowns and well workovers. To improve the pumping process, a great need exists for assessing and understanding the effect of local velocity distributions to irreversible phase-change and solid-liquid-gas phase phenomena.

New investigations methods are first assessed and then used for testing rationale equipment modifications and suitable operating strategies.

This paper describes and assesses novel experimental apparatus aiming to allow direct observations and measurements of multiphase transport during the pumping process. The apparatus consists of a 1:1 operational sucker-rod pump in which the barrel and cages are made of Plexiglas allowing direct visualization of the flow within the pump. The following experimental procedures are assessed in a preliminary experimental program:—use of a laser Doppler anemometer to measure the velocity field within the pump,—use of a Freon-oil mixture to simulate high-temperature, high-pressure fluids and produce flashing induced perturbations at room temperature.