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:
- 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).
- 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).
