Jeff Saponja, Oilify
Justin Conyers, CRC
Rod pumping has been challenged by solids contained in produced fluids, as they reduce pump run-life. For horizontal wells solids risks have dramatically escalated, as hydraulic fracturing has exponentially increased in terms of number of stages and the amount of proppant pumped. EOR schemes can also escalate solids in produced fluids. To combat solids in the produced fluids reaching a pump, control methods have included solids separators and filtering screens. Both methods have realized limitations and therefore have not effectively resolved solids risks to acceptable levels.
Solids separators have typically been gravity and/or cyclonic based. Risk limitations with solids separators has been their ability to separate solids over broad solids particle size and flow rate ranges (a wide turn down ratio). Both cyclonic and gravity-based solids separators struggle to efficiently separate finer particles, such as 100 mesh frac sand, particularly when flow rates range from zero percent to 100 percent during a rod pump cycle. Cyclonic separators also face the reliability risk of erosion due to their inherent angular momentum solids separation design.
To effectively separate solids over a broad size and flow rate range, filtering is required. Risk limitations with solids filtering include filter screen plugging (from solids and scale) and from erosion. Eventually all filtering screens will plug off if flows are in the same or in one direction. For example, if flows are always in one direction, there is no place to contain the filtered solids other than on the filter screen itself. Running more filter screens for more filter screen surface area can extend the run life before plugging, but cost economics quickly come into play. Installing a filter screen bypass, for if in the event it becomes plugged, just exposes the pump to damaging solids once again. Solids can cause erosion, so filter screen designs need to minimize fluid velocities and use erosion resistant materials, which can escalate costs. Scale risks must also be controlled by designing for very low-pressure loss and drops through the filter screen and likely in combination with chemical treating – this means that filter screens placed upstream of a gas separator will likely be ineffective for preventing scale deposition due the expected high multiphase flow velocities.
A downhole self-cleaning filter system was developed to resolve these risk limitations. Proven surface facility self-cleaning filter screen system technology was re-designed to be deployed downhole.
The engineered system components were as follows:
• a filter screen engineered to hold and release solids down to 120 micron particle size; solids do not get retained in or on filter screen when fluid flow ceases during the pump’s downstroke,
• placement of the filter screen sequentially after the gas separation stage and inside the uppermost mud joint – in this location, solids laden liquid’s flow path U-turns from downwards to upwards through the filter screen and allows solids to be contained out of harms way into standard mud joints,
• continuous self-cleaning of the filter screen is achieved with a specially designed rod pump with a standing valve that back flushes the filter screen each pump stroke – a reverse pressure pulse wave and a back flush liquid volume each pump stroke dislodges solids from the filter screen and settles them downward into mud joints during the pump’s downstroke, and
• the filter screen is open-ended for allowing bypass in the event of filter plugging.
Field trials have recently been implemented with early time promising results for extending pump run life. The concept, design, field implementation and results will be shared.