Operation of directional and horizontal wells at maximum production rates requires placement of a downhole pump inside the horizontal well section. Several special-purpose downhole sucker-rod pump designs intended for operation of directional and horizontal wells have been considered. These are ELKAM’s differential piston pump with plunger mechanical seal provided by Ecogermet-M; downhole pump of Bavlyneft Oil and Gas Production Department of Tatneft PJSC, equipped with a suction valve with self-adjusting gate and conventional ball-type delivery valve; Packer Research and Production Company’s pump provided with suction and delivery valves with self-adjusting gates and, finally, downhole pump designed at TatNIPIneft Institute, consisting of a plunger with controllable delivery valve and a spring-operated ball-type suction valve. Additional tensile load on pump rods in differential pumps is a product of cross sectional area of hydraulic power booster pushrod and pressure determined by the distance from wellhead to dynamic fluid level. Valves are forced open and closed by friction forces: in the suction valve, it is the friction of valve seal on hydraulic power booster pushrod, in travelling valve – friction of plunger seals on pump barrel. Flow rate of such pump is proportional to the difference between cross sectional areas of pump plunger and hydraulic power booster pushrod and is less than the flow rate of conventional pump with similar plunger diameter. Practical applications have demonstrated that with low viscosity of the produced fluid the weight of rod string in nominally vertical well section is typically sufficient to ensure steady downward rod movement in horizontal and directional wells. Results of field tests in wells of Tatneft PJSC are provided. Advantages and disadvantages of special-purpose pump designs for directional and horizontal wells are discussed, as well as lessons learned from real field trials. Recommendations for implementation of different downhole sucker-rod pumps for operation of directional and horizontal wells as well as for oil production from lateral holes are given.
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