Pumping Fluid with High Gas Content

Carlos Matheus, Mechanical Engineer for the Midstream group within NOV’s Completion & Production Solutions segment, spoke with Pumps & Systems about common difficulties for midstream pumping end users and one potential technology solution. Q. What problems was this technology solution developed to solve? A. End users are having trouble pumping fluid from oil wells with very high gas content. For most wells, operators invest in separation equipment at the wellhead, which allows them to separate the gas, liquid and solid components of the fluid; and then treat and transport the three phases of fluid separately. Multi-phase pumping simplifies this process and saves on capital spend, especially for wells with high gas concentration. Q. How did you decide to approach these issues? A. The challenge is to meet the requirements on-site for the gas volume fraction: ensuring we can convey the fluid at a gas concentration of up to 95 percent, so we only need to guarantee that the pump will have liquid at 5 percent at any time. We also needed to obtain the right elastomer from our lab experts as that is essential to providing the means for the pump to handle the high gas concentration. The rubber that goes into the core of the stator will provide the compression fit against the screw that pumps the fluid. That elastomer must make up for all the gas slugs for that 95 percent maximum allowable by the pump. A major factor to consider is the amount of gas the pump will encounter. When there is no gas concentration, there is only water, oil and some solid in the fluid, and a regular progressing cavity pump (a type of positive displacement pump) can be used. Other technologies require more liquid in the pump at any one time compared to the 5 percent that this pump needs. Many end users are trying to develop a solution for pumping multi-phase fluids to avoid spending $2 to $3 million on separation equipment at the wellhead. The savings with the multi-phase pumping are substantial compared to a full separation battery at the wellhead. Q. What kind of maintenance is involved? A. Training is minimal because this pump technology and set up, including geometry and features, is straightforward. The components include: tie-ins, flanges, suction and discharge, gear shaft, and the motor. With regular set-up tools, you can rig down the pump and replace the critical part: the stator, which has a life of 12 to 15 years. Replacing the mechanical seal is an easy process, as is replacing the windings. Q. What sort of pumps does this transfer equipment use? A. The rotor within the progressing cavity pump has a resemblance to a screw. It has a smooth surface with different geometry than typical screw pumps. It is a solid coaxial shaft, in the shape of a screw, with cavities that are formed by the shape of the rotor against the elastomer that is the core of the stator.