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A bit of history. I first encountered jet pumps for field geophysical surveys (FGS) in 2002 when I was working at TNG-Group (Usinsk). Since then I have been captivated by the simplicity and elegance of this equipment. During my years of work in geophysics, I have faced the tasks of well development and exploration, which helped me to gain experience in working with these pumps. Since 2010 I have been developing this technology from scratch at Nekko (the company was introducing a new line of business), and with a team of geophysicists who joined me at the same time, we took well development and exploration to a whole new level. Y.V. Shanovsky, who supplied pumps at that time, actively shared his experience. Over time, we modernised Shanovsky pumps, increasing their reliability and efficiency, while remaining within the unified constraints of serial production.

Since 2017, I have been developing jet pumps for various applications. This resulted in two series of jet pumps: the JPR research and the MJP development. They have advanced functionality for solving tasks of any complexity.

EneGro jet (ejector) pumps are available in two series:

1. Development and production jet pumps MJP (jet vapour in discharged inserts). MJP is intended primarily for development and production. The MJP-1 model has become the base model and has capabilities for geophysical surveys and hydrodynamic studies on wells with AHFP (abnormally high formation pressure).
2. Well testing jet pumps JPR (jet vapour in a casing run on tubing). The JPR-3 and JPR-4 models are designed for field geophysical surveys, but also perform well in development applications. The models JPR-1-mg and JPR-2 are used for development, have a very simple design and do not require highly qualified personnel when used at the well.

A little about the purpose and physics of the process

Drilling and well preparation techniques often result in a significant reduction of formation permeability in the bottomhole zone. Various complications also occur in the bottomhole zone during well operations. Therefore, it is important to correct the negative effects of previous operations during the well development process. The time allocated for well development is counted in hours and days, and the time of future well operation is counted in tens of years. Poor development quality means low well productivity and unreliable well performance for years to come.

The purpose of development is to restore the natural permeability of the reservoir to its potential. Fluid flow into wells is caused by the difference between formation pressure and bottomhole pressure. All operations to induce flow and develop the well are reduced to creating underbalance, i.e. pressure below reservoir pressure, at the bottom of the well. In stable reservoirs, this depression should be large enough and achieved quickly; in friable reservoirs, on the contrary, it should be small and smooth.

Disadvantages of existing technologies

By inducing flow by swabbing or compressing, highly permeable reservoirs can be tested with confidence. A limitation of these methods is the difficulty of inducing flow from low-permeability, confined formations and low-pressure wells.

During compressor development, the tested reservoir at the initial stage of level reduction is subjected to overpressure (before triggering of start-up clutches), which leads to absorption of downhole fluid by the reservoir, thereby reducing the permeability of the bottomhole zone for the hydrocarbon phase. It is not possible to regulate the created depression during compressor development.

Well development by swabbing has the disadvantage that the underbalance is created discretely and not instantaneously, as it takes some time to lower and raise the swab. In addition, when welding a low-productivity target, it is not possible to achieve stable steady-state production withdrawal with flow rate and bottomhole pressure relief.

There are no such disadvantages when developing a well with a jet pump. On the contrary, there are a number of advantages:

• exceptional reliability due to the simplicity of design and the absence of moving parts, as well as the ability to operate steadily under influences that interfere with normal fluid injection;
• easy to start, stop and change operating parameters over a wide range without compromising stability;
• minimal sensitivity to gas and solid inclusions in the pumped medium, which is important when pumping gas-containing and contaminated liquids, including aggressive and radioactive liquids;
• combining energy exchange processes occurring in the mixing chamber of the jet pump with chemical and thermal processes reduces the duration of technological operations and increases their intensity;

Purpose of jet pumps

Jet pumps are designed to create underbalance and induce inflow from the reservoir, while solving various tasks – development after drilling, hydraulic fracturing, perforation, chemical, physical treatment of bottomhole formation zone, production of reservoir fluid, hydrodynamic and geophysical studies.

Today, jet pumps are one of the components of complex solutions for time-optimised solutions.

What is important to know about jet pump applicability

When using ejector systems, we need to remember that we have three media areas separated from each other. Let’s evaluate them on the basis of pressure.

The first medium (working flow) is the high-pressure area created by the working flow due to the operation of the power unit. The second medium (mixed flow) is a zone of normal hydrostatic pressure, where the mixed working fluid and the extracted fluid are carried in a common mixed flow. The third medium (suction flow) is the area of pressure below the static (or formation) pressure from where the fluid is extracted (suction flow).

What’s important to know when planning to use a jet pump for well development and well testing

Let’s highlight three important points:

1. Static level is an important parameter for understanding the minimum pressure required to induce inflow.

Note: When filling a well to the static level volume, it must be realised that it must be compensated for by the operation of the propulsion system. And only the force expended in excess of this compensation will go to operate the jet (ejector) pump.

2. The capability of the power unit (pump unit) is the decisive parameter, which sounds like the question: What maximum operating pressure and fluid flow rate during the desired development time can the unit generate? This parameter will determine the feasibility of the pump unit and hence the jet pump.

Against our wishes:

• pumping units have technical limitations;
• tubing and EC are limited by the maximum possible applicable pressure;
• the ability of a pump unit to generate and maintain a continuously specified flow rate and discharge pressure is not unlimited in time.

Note: Poor pump unit performance is for the most part one of the main factors for the low application and utilisation of jet pumps today. This factor is primarily related to the basic current need of technological processes, few of which utilise prolonged injections at high pressures.

3. Production casing (PC) pressurisation pressure and its tightness is a parameter of the possibility to work in this casing. Tightness is necessary so that the circulating fluid does not escape into the leaky areas and it is possible to estimate the current flow rate. EC pressure test – will provide insight into the feasibility of development or geophysical surveys with downhole injection.

Note: At geophysical surveys with jet pump and injection of working flow along the annulus there is no excessive pressure drop at the sealing unit in the form of injection pressure, which makes it possible to create a large depression (the limitation becomes the pressure of EC pressure test).

With these three parameters, it is possible to quickly assess the feasibility of jet pumps in any given application.

Working in Nekko I have adapted a calculation algorithm to quantify downhole parameters. Subsequently, I wrote a design programme (calculator) estimating downhole parameters at different injection modes. Withdrawing the questions arising in advance, I will say that the programme is an estimation programme and the discrepancy with practical data (10-20%) is explained by the presence of complex multiphase medium and not always up-to-date data provided for calculation. Despite the low accuracy, this estimate is sufficient to assess the possibility of working with a jet pump and to estimate the required development mode (required depression value).

Currently, in order to maintain the level of liquid hydrocarbons production, oil reserves formed by fields with viscous, high-viscosity and extra-viscous oil (hereinafter referred to as “viscous oil”) are included in development. Most of these fields are located in regions with developed infrastructure, so their development today becomes a real task and a necessary condition for the development of oil business.

The reserves of fields with oil viscosity over 10 centipoise have been depleted in our country by only 10-30 per cent (depending on the degree of viscosity). According to GKZ RF estimates, reserves of such oil by ABC1+C2 categories in Russia amount to about 1.7 billion tonnes, i.e. about 10 per cent of the country’s total black gold reserves. And initial reserves exceed 5 billion tonnes.

The challenges in developing fields with viscous oil are associated with extracting it from the reservoir and transporting it from the reservoir to the refinery. To solve them, special methods of stimulation are used. These include thermal (steam displacement, vapour gas, combination of horizontal drilling and vapour gravity (SAGD), in-situ burning), physical (hydraulic fracturing), chemical, special waterflooding methods, and microbiological. Implementation of the above methods involves significant energy costs, difficulties in technical implementation, which leads to lower efficiency and higher production costs.

Acoustic stimulation of the reservoir can be used to increase the efficiency and reduce the energy consumption of the methods used. Acoustic stimulation can also be used as a stand-alone reservoir treatment.

The proposed method is based on a gentle and prolonged impact on the formation by acoustic vibrations, which are accompanied by significant alternating loads, which gives:

1. Increased fluid withdrawal. Due to the “piston” effect, the filtration volume of the mobile fluid is increased;
2. Intensification of oil extraction. By overcoming the viscoplastic forces holding the fluid in the filtration process, the still fluid is involved;
3. Reducing oil viscosity and reducing water cut of products. Due to depolarisation of molecules and weakening of intermolecular bonds, the rheological structure of oil is destroyed, as a result of which its phase permeability increases, whereas for water it remains unchanged;
4. Increase of oil displacement coefficient with water. By reducing the wetting angle between water and oil, surface tension forces are overcome;
5. Redistribution of oil saturation and more complete oil recovery. Due to acceleration of gravitational separation of phases of different densities in the acoustic field, segregation (separation) of oil and water in highly watered formations takes place;
6. Increased reservoir permeability and oil recovery rate. Due to the seismoelectric effect, which destroys the walled immobile layers of fluid (oil) that are electrostatic in nature, the effective cross-sections of pore and perforation channels are increased. Thus, they are cleaned from mechanical impurities, viscous deposits and disruption of surface fluid layers, as well as involvement of stagnant reservoir zones in the filtration process.

Pilot tests on acoustic influence on the formation with simultaneous induction of inflow by a jet pump in order to clean the bottom-hole zone of the formation gave positive results. The work was carried out at Rosneft, Lukoil and Gazprom Neft divisions. The acoustic transmitter was lowered on a geophysical cable and the bottomhole formation zone was treated (1 hour per 1 metre interval, f= 10-11 kHz) while the jet pump was operating at a stable mode; in parallel, the change in inflow from acoustic treatment was assessed. The average effect was an additional 4 tonnes per day, with effect duration ranging from 4 to 18 months.

Despite the positive results of acoustic treatment subsoil users are wary of acoustic impact. This is due to the peculiarities of the technology:

• The technology is science-intensive and requires coordinated work of various specialists (scientists, engineers, geologists);
• the technology is “capricious” and requires a detailed study of the geological structure of the sites for compliance of the applied processing parameters with the real geological conditions;
• few industrial trials (lack of statistical evaluation of application experience);
• high cost, which today is due to sporadic work.

The systematic use of acoustic processing technology on the basis of a geophysical enterprise will significantly reduce the cost of these works. Using a geological and geophysical approach to the candidate wells to be selected will address the “capriciousness” of the technology.

The conducted works on cleaning of bottomhole formation zone gave an impetus to the possibility of using acoustic impact in a constant mode in the production of hydrocarbons, including viscous oil. Both independently and in combination with existing methods of viscous oil production, acoustic impact will increase efficiency by reducing energy consumption, preventing formation bottom-hole zone colmatisation, increasing the overhaul period of downhole pumping equipment, and increasing oil recovery. In summary, acoustic stimulation becomes one of the steps towards reducing the production cost of viscous oil, which is an important factor in today’s world.

To select the required optimum operating mode of the well, an acoustic complex and a jet pump can be used. This will allow hydrodynamic studies to be carried out:

• at different operating modes of the acoustic complex by regulating the time and power of acoustic treatment of the formation;
• over a wide range of downhole pressures by adjusting the injection pressure of the working fluid at the jet pump inlet.

Hydrodynamic studies will allow selection of deepwater pumping equipment, necessary operational parameters of reservoir operation and its acoustic treatment, which is very important when working in multiphase media.

The acoustic complex will improve the efficiency of existing methods to optimise energy consumption for transporting viscous oil from the reservoir to the place of its processing.

Our laboratory tests on viscosity reduction were carried out with oil emulsion (30% water cut). The oil emulsion was acoustically treated at 17 kHz for 60 and 300 seconds. The treatment resulted in a 30% reduction in viscosity and a 38% reduction in the load on the electric motor of the transfer pump, while maintaining the temperature regime. Recovery to initial viscosity parameters was 5 hours. Moreover, the processing time did not affect the result. After acoustic treatment a homogenised oil emulsion with reduced viscosity was obtained with a time of gravitational separation into oil and water within 8 hours (the original oil emulsion has 1-2 hours). In the laboratory tests, the effect of temperature was excluded in order to evaluate the effect of acoustic exposure. The energy expended to operate the acoustic radiator is 30-40% of the energy consumed and 60-70% is spent on heating. It is advisable to use the processed oil emulsion for cooling, which will additionally lead to reduction of its viscosity due to heat exchange.

The viscosity reduction and homogenisation is due to the cavitation phenomenon. In fact, it is the formation and collapse of gas bubbles in a liquid medium. This results in the decomposition of high-melting high-molecular-weight paraffins during high-intensity treatment, which changes the physical and chemical (operational) properties of the oil. Also, cavitation effects, which occur during acoustic treatment of oil, prevent polarised associates from combining into large structures, dispersing them into smaller groups of molecules.

The results of laboratory works show the possibility of using acoustic treatment in a constant mode during the transport of viscous oil from the reservoir to the place of its processing as an independent method of influence and in combination with existing ones. For example, when chemical reagents are added, the reaction will occur faster and with less reagent consumption, better homogenising the mixture.

Today there are projects of development of equipment for acoustic influence on pumped viscous oil emulsions, which require industrial execution and testing. Feedback from the developers will improve the technology and reduce the cost of equipment production through optimal selection of operating parameters and mass production.

Mass application of the acoustic complex in the production and transport of hydrocarbons will allow us to talk about a new turn in the development of fields with viscous oil.

Known physical effects often require practical confirmation so that psychologically we can accept them. The same applies to the effect of acoustic effects on the change in viscosity of liquids. In the course of laboratory studies, we obtained a decrease in the viscosity of oil emulsion (oil + formation water) due to the destruction of its rheological structure and homogenisation.

Laboratory investigations were carried out in three phases, evaluation:

• of the original viscosity;
• influence of acoustic treatment on the load of an oil emulsion pump before and after treatment;
• reduction of oil emulsion viscosity after acoustic treatment and time of initial viscosity recovery.

A glass vessel with a 4 mm outlet opening was used for viscosity estimation. The volume of samples to be taken is 100 ml. The oil emulsion flow time was estimated based on the flow rate of 75 ml sample. All samples were kept in a room with a temperature of 22 C. When the sample was heated during acoustic treatment, it was cooled down to 22 C, after which the viscosity was measured.

The test bench is represented by an ultrasonic reactor (rod radiator with a magnetostrictor in a cylindrical vessel) and a UZG-5 generator. The coolant circulation is provided by a circulation pump.

1 STEP. Measurement of the flow rate of the initial oil emulsion sample from the viscometer. The temperature of the emulsion is 22 C.

Sample	Measurement	Volume, ml	Temperature, C	Expiration time, sec
original emulsion	1	75	22	92
	2	75	22	94
	3	75	22	92
	4	75	22	98

The viscosity of the initial oil emulsion sample was estimated. The average flow rate was 94 seconds at the initial sample temperature of 22C (absolute error +/-2 seconds, relative error 2%).

2 STEP. Circulation pump load evaluation tests at initial viscosity and after ultrasonic treatment.

The aim is to evaluate the load on the circulation pump at initial viscosity and after acoustic treatment while maintaining the temperature of the treated sample.

The temperature of the original and treated samples is 22C. The sample volume for acoustic treatment is 800 ml.

Measurement of the pump load while circulating the original sample.

Measurement	U, В	J, А	Temp, C	Power, W
1	24	2,76	22	66
2	24	2,8	22	67
3	24	2,87	22	69
4	24	2,84	22	68

Average value of current J=2.817 A, power 68 W. Absolute error +/- 0.0375 A, relative error 1.3%.

Measurement of pump load while circulating the ultrasonically treated sample for 60 seconds.

Measurement	U, В	J, А	Temp, C	Power, W
1	24	1,7	22	41
2	24	1,73	22	42
3	24	1,76	22	42
4	24	1,8	22	43

Average current J=1.747A, power 42W. Absolute error +/- 0.0325 A, relative error 1.2%.

The effect on the load of an oil emulsion pump was found, with acoustic treatment for 60 seconds reducing the load by 38%.

3 STEP. Conducting tests to evaluate viscosity as a function of acoustic exposure while maintaining a constant temperature. Estimation of viscosity recovery time.

The aim is to establish the dependence of oil emulsion viscosity change on acoustic impact and to estimate the time of viscosity recovery (relaxation).

The temperature of the original and treated samples is 22C. The sample volume for acoustic treatment is 800 ml.

Measurement of the viscosity (flow time) of the oil emulsion after 60 seconds of acoustic treatment.

Time after RCD, hour	0	1	2	3	4	5
Initial viscosity at T=22C	94	94	94	94	94	94

Acoustic treatment 60 seconds, T=22C

Measurement 1. Expiration time, sec	65	69		75	84	97
Measurement 2. Expiration time, sec	67	71	64	73	82	93
Measurement 3. Expiration time, sec			70
Average value, sec	66	70	67	74	83	95

Absolute error +/- 2 sec, relative error 2%.

Acoustic treatment 300 seconds, T=22C

Measurement 1. Expiration time, sec	62	65	65	93	93
Measurement 2. Expiration time, sec	68	64	64	91	91
Measurement 3. Expiration time, sec		68	68
Average value, sec	65	66	66	92	92

Absolute error +/- 2 seconds, relative error 3%.

The 3 stage tests found a 30% reduction in viscosity after treatment for 60 and 300 seconds. The decrease in viscosity is purely due to acoustic effects, as all measurements were made at the same temperature. Viscosity recovery begins after 2 hours of settling, with the longer acoustic treatment not producing a greater reduction in viscosity and showing a faster recovery to the initial state. Also in the course of the experiment it was found out that the stability of the emulsion is maintained for about 10-12 hours.

Key Findings:

1. During the tests, the effect of heating the oil emulsion by acoustic influence was excluded. Energy losses for heating will give an additional effect due to heat transfer to the oil emulsion.
2. After treatment, a stable emulsion was obtained with the condition maintained up to 10-12 hours, with viscosity lower by 30% with recovery within 5 hours.
3. A 38% load reduction on the transfer pump was obtained, the effect was achieved without heating the oil emulsion.
4. When processing oil emulsion in weak acoustic obtained a faster separation of water and oil.
5. A transmitter with an acoustic power of 1kW was used There are more powerful loudspeakers that can be used in industrial settings.
6. Additional tests with acoustic treatment with exposure times of less than 1 minute, at higher frequencies and with more powerful acoustic radiators should be carried out.

Focused acoustic stimulation (FAS) of the bottom-hole formation zone (BHZ) is an environmentally friendly technology for increasing injectivity in injection wells and stimulation of production wells.

Decrease in bottomhole permeability is mainly due to:

• penetration of drilling fluid filtrate, mechanical impurities of injected fluid or killing fluid into the pore space of the formation; deposition of high-viscosity oil components and clay particles on the surface of pore and perforation channels;
• formation of fixed liquid films on the surface of pore channels, which include adsorption and partially diffusion sub-layers.

The effectiveness of acoustic impact on the bottomhole formation zone is due to the creation of significant inertial forces in the fluid, intense currents at solid-liquid interfaces, which are implemented in the reservoir in the form of intra-pore turbolisation of the fluid, which leads to the detachment of mechanical particles and high-viscosity deposits from the surface of perforation channels and pore space. In addition, the generation of transverse magnetohydrodynamic pressure allows increasing the effective cross-section of pore channels due to the disruption of stagnant surface liquid films. Thus, acoustic stimulation can restore or increase the permeability of the bottomhole formation zone.

The FAS technology is based on acoustic impact on the bottom-hole zone of the well and reservoir by frequencies of sound and ultrasonic ranges and promotes cleaning of perforation channels and bottom-hole zone of the reservoir from colmatising material, disruption of surface liquid layers, increase of waterflooding coverage, increase of oil displacement intensity by displacing agent, change of fluid phase permeability, acceleration of gravitational separation of oil and water.