September 2, 2012
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№ 6 (June 2012)

Downhole Wave Process Stimulates Oil Recovery

   The pulsed hydroimpact technology developed by the Mining Institute of the Siberian Branch of the Russian Academy of Sciences has made it possible to produce a small-sized downhole equipment used to make a vibro-wave impact on oil reservoirs for the purpose of oil-recovery factor raising, well stimulation, and also for bottom-hole zone cleaning up.

By Viktor N. Oparin, Boris F. Simonov, Andrey V. Savchenko, Alexander L. Nikonov, Magomet Ya. Deniev

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   The on-site maintenance of this equipment can be easily performed with standard field facilities and by existing personnel.  

   Before that, many different countries attempted to develop similar equipment but failed to produce anything worthwhile. The offered technology is unique in producing hydroimpact in a pre-discharged volume thus giving rise to the wave-impact energy of not less than 30-40 kJ. Practically, it is a next-higher order in comparison with all known systems.

   The new technology is being field-introduced by the Center of Vibro-Seismic Technology formed by the Mining Institute of the SB RAS and ROMAN CAPITAL Plc. By now, the respective design has been optimized and the manufacture of pilot batch of the modified vibro-seismic equipment has been started.
The equipment is compatible with the currently manufactured sucker rod pumps and is a small-sized seismic wave generator attached to a sucker rod pump and lowered together with the pump into the well. The energy source for the generator is the sucker rod pump itself.

   The proposed technology provides for an increase in oil recovery (by up to 40%) in wells located at distances of within 1.5 km from the generator. Equipment performance is not weather dependent.

   The advantages of this technology include the possibility of operating the equipment without the permanent presence of service personnel and the possibility of combining the equipment with other reservoir treatment methods, e.g. chemical treatment.

   The optimum conditions for the application of this technology are as follows:
water blockage of most wells should be within 95%, while some wells should have 40-60% water blockage;
formation depth to 2000 m.

   Placed downhole in the immediate vicinity of an oil reservoir, the pressure pulsator is actuated by energy of a hydraulic liquid flow impact. The liquid, flooding the tubular annulus, strikes the end of the pulsator cylinder, herewith the reciprocally moving plunger periodically generates under-pressure in the cylinder cavity. The impact energy depends on the liquid column height in the tubular annulus, cylinder diameter, and a plunger stroke. The impact force is transmitted through a mechanical or hydraulic waveguide and an oscillator to a bottom-hole formation zone and then to an oil stratum. Reciprocal motion of the pulsator plunger is provided by a pump jack.

   The schematic diagram of the system for the wave excitation in a productive stratum is presented in Fig. 1.

   The cased well 1 intersects an oil reservoir 2 at some depth with perforation, performed at the oil-reservoir zone. Well 1 is flooded with a liquid up to Nzh height relative to a pump. Pump cylinder 4 is mounted on the pumping-compression tube 3, plunger 5 is placed inside pump cylinder 4, plunger 5 is connected through rods 6 to a pump jack 7 to actuate reciprocal motion of the plunger. Pump 4 is connected to pulsator 8, producing the periodical pulse loads, to be transmitted through wave-guide 9 and oscillator 10 to a productive oil stratum in order to generate elastic fluctuations in it. Packer or splitter 11 can be provided in the system.

   The operation principle involves production of a low-pressure volume in the under-plunger chamber as compared to the annulus pressure. Depressurization of the chamber is followed by flooding of the internal volume with a liquid under pressure. The resultant hydroimpact is transmitted to a liquid column in the well or through a mechanical wave-guide to a borehole bottom as it is specified by the configuration of the system. The generator operation is controlled relative to the pump plunger position.

   The liquid pressure at a hydroimpact moment is 5-12 times higher than the static liquid-column pressure on the borehole bottom. The maximum acting force reaches 120-200 kN, and the force, transmitted to the productive stratum, generates elastic fluctuations in it.

   Hydroimpact process for generation of pressure pulses in exploitation wells provides the wave effects of at least 30 kJ in energy, depending on a dynamic liquid level in a well. This parameter actually exceeds by an order the similar parameter for well-known systems, moreover, an oil stratum appears under influence of concurrent hydraulic and seismic effects.

   The downhole generators produce multiple high-energy effects of a wide frequency range directly at the oil-stratum depth with no losses, specific for the pulse transmission through long wave-guides or a thick rock mass.

   In practice, the production well is converted to the wave-emission mode by substituting a respective size-type pulsator for a submersible oil pump.
The full-scale tests of prototypes and pilot batches of approximately 30 modifications, manufactured and certified at OAO ”Izhneftemash” pertaining to standards API and GOST, have been practiced at Mancharovskoe (Bashkiria) and Oshvortse-Dmitrievskoe (Udmurtia) deposits since 2003. The test data showed:
100% performance;
high operation life – up to two years exploitation;
high, viz., actually by an order higher as compared to this parameter for conventional methods, energy intensity and wide band of emitted fluctuations, providing the influence of high-frequency subspectrum on the bottom-hole formation zone and low-frequency subspectrum on oil reservoir in the range of up to 1.5 km;

   the proposed process and the respective apparatus improves oil recovery by 12-30% with lower water blockage in the impact zone.

   Seismic pulses, generated by the new apparatus in an oil reservoir, have been detected in the full-scale tests. Figure 2 demonstrates a seismic pulse, produced per one operation cycle of the new system. The maximum amplitude corresponds to a higher-pressure impulse in a well at the moment of hydroimpact generation with subsequent fluctuations of the liquid column under action of the forward and backward waves.

   Advantages of the sucker rod pump systems actuated by a pump jack in production wells are:
high energy of a seismic impulse excitation and incomparably high efficiency of the process due to an operation of the excitation source in the close proximity from a productive oil reservoir without energy losses, specific for pulse transition through long, mechanical, hydraulic channels or through a thick rock mass;
applicability of practically proven components of the commercial rod pumps. The equipment set for the downhole excitation of seismic effects mainly consists of standard modules and components of oil-production equipment, meeting standards API and GOST (more than 90%).  The commercial oil-production machinery and accessories, suitable for the downhole wave excitation, are available in the petroleum industry; the current technical, technological, maintenance skills of the working personnel enable to introduce the new-developed technology with no special training;
simple in maintenance with available, field oil-production instruments; applicability of available complex control and diagnostic processes: dynamometry, echoscopy of the dynamic liquid level in annulus, pressure measurement in the discharge line at the well mouth; the low cost of the equipment and opportunity for the large-scale ongoing implementation; The new-developed apparatus is proposed to replace a standard sucker rod pump;
It is also beneficial that the downhole technology does not require the constant presence of an operator and is compatible with other, for example, chemical treatment methods used to influence an oil stratum. The performance of the new complex does not depend on local weather or climate conditions.

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