Jet pump technology for artificial lift in oil and gas production

The barren desert environment is as far removed from Finland as it could possibly be. One should nevertheless not be surprised if the jet pump technology and equipment used there to pump oil to the surface is provided by a company based in Pori on the west coast of Finland. Wellquip Ltd (WQ) has quietly made a name for itself in developing state-of-the-art oil and gas production equipment packages and software (FloWQ systems) and in supplying turnkey deliveries worldwide. Development of its own oil and gas surface and downhole equipment and technology began in 2004. In this article we highlight some of the development phases and technological advances of this remarkable journey into the unknown.

What makes WQ’s specialisation in oil and gas technology even more surprising is that Finland does not have its own oil and gas reserves and consequently the culture in this area is very thin or non-existent. There are also no faculties at Finnish universities that offer studies in the field.

In 2004 WQ nevertheless took up the challenge and began studying feasible areas in oil and gas field development technology. Their efforts were focused on identifying future trends and related requirements. At the time the development team identified the need to produce wells with high paraffin, sand and gas content and the production of heavy oil as growing future needs in the FSU market.

According to Wellquip Managing Director, Sakari Oja, the surface equipment package has been under continuous development since they decided to enter the field in 2004.

“In the beginning the equipment package was based mainly on foreign technology and both the analysis work to define the equipment configuration best suited for each well and the actual equipment was mainly contracted from the USA. We realised very soon that we needed to develop our own technology in order to gain a better understanding of related phenomena and to reduce the risks associated with dependence on external suppliers”, explains Oja.

“We also needed to develop software to determine the optimal equipment configuration for each separate oil well. We cooperated with the Tampere Technical University to create our own software for this purpose.”

Diagram 1. A schematic presentation of the testing package. Pump 1 (180 l/min 130 bar) produces the working fluid flow and pressure and Pump 2 (140 l/min 80 bar) the flow and reservoir pressure of the produced fluid. Both have suction from the water tank. Gas can be added to the produced fluid from the nitrogen bottle battery before reaching the jet pump.

Testing equipment to analyse hydrodynamic flow inside jet pump

In order to analyse the hydrodynamic flow inside a jet pump the pressure reduction factors at the nozzle, throat and diffuser for each nozzle/throat combination have to be determined. There are, however, a vast number of possible combinations and taking the required measurements is extremely time-consuming.

“For this reason we tried to identify dependencies between pump pressure reduction factors and other factors such as the nozzle/throat diameter ratio, spacing between the nozzle and throat, gas presence and Reynolds number etc. With the help of this information the software could automatically use the correct pressure reduction factors once the pump geometry and liquid properties were defined”, Oja explains.

See diagram 1 for a detailed overview of the test equipment setup.

All the testing procedures were controlled with the operator’s PC. The measurements taken from 18 measuring points every second were saved in the PC memory. See diagram 2 for the operators process view.

The WQ laboratory testing device used to simulate oil well features

What is artificial lift and when is it required?

In oil production artificial lift is required when the natural pressure in the underground oil reservoir is not sufficient to push oil to the surface in a self-flowing system. Most oil wells require artificial lift, which is generally provided by a pumping mechanism. Beam pumps are the most common and constitute about 80% of all pumps used in artificial lift production. Jet pumps are worth noting as they have no moving parts, which again means an advantage concerning down-time in production.

How does a jet pump function?

In essence a jet pump is an ejector, located at the bottom of an oil well, modified for oil and gas production in order to ensure easy operation. It mainly consists of a nozzle, throat and diffuser. The working fluid from the surface is pumped through the nozzle, which creates suction for produced fluids. The working fluid and produced fluids are mixed in the throat after which the mixture continues through the diffuser to the surface. The nozzle/throat combination is crucial in determining jet pump performance. Each oil well needs to be analysed separately and finding the optimum nozzle/throat combination from the 150–200 possible standard and tailor-designed combinations with optimum equipment on the surface is a complex task. An extensive software package is required to make the necessary calculations.

Diagram 2. The operator’s process view

Diagram 3. The practical efficiency of the nozzle/throat combination as a function of M

Overcoming challenges

Initially testing produced unexpected results while the automation system proved to be unstable. The cavitation plane had a few surprises in store for the testing team too. The work fluid discharge pressure showed variations despite the installation of pressure dampers. Over time the testing team’s know-how and accuracy, however, increased until proper results were achieved.

“This is what engineering and research is all about. We had to figure out what to do and how to do it. We found solutions to all these challenges”, Oja says proudly.

The immediate test result allowed a performance curve to be drawn for the nozzle/throat combination in question. The curve showed the practical efficiency of the nozzle/throat combination as a function of M. See diagram 3.

The next step included saving the measurements on the computer and manipulating them with a custom-made software program, which calculated all the necessary pressure reduction coefficients in the jet pump. An example of the measurements taken is displayed in Table 1.

Table 1. An example of measurements taken (20.3.2012) from 12 sensors once a second. The location of sensors shown in Diagram 2.

Software developed to select optimal equipment configuration

While the measurements were being taken and results analysed the software to select the optimal subsurface and surface equipment was also developed.

“The program is ready now to be used as a practical tool and it has been tested in real conditions and the results are very encouraging. It contains many quality features such as vertical two-phase flow with gas compressibility and analyses of extreme conditions”, says Oja.

“Actually of most value to us now is that we know exactly how the system works. The entire development process has provided us with a deeper overall understanding of oil production. Originally we thought that we would concentrate purely on pumping the fluids from the reservoir to the surface, but we noticed very quickly that the characteristics of the reservoir could not be ignored. Our clients are often interested in the special features of the reservoir, which now can be addressed and presented. We now have a better understanding of parameter influence on the system efficiency and economy. The program has been loaded onto our server and is ready for use by our clients”, Oja concludes.

What is artificial lift and when is it required?

In oil production artificial lift is required when the natural pressure in the underground oil reservoir is not sufficient to push oil to the surface in a self-flowing system. Most oil wells require artificial lift, which is generally provided by a pumping mechanism. Beam pumps are the most common and constitute about 80% of all pumps used in artificial lift production. Jet pumps are worth noting as they have no moving parts, which again means an advantage concerning down-time in production.

How does a jet pump function?

In essence a jet pump is an ejector, located at the bottom of an oil well, modified for oil and gas production in order to ensure easy operation. It mainly consists of a nozzle, throat and diffuser. The working fluid from the surface is pumped through the nozzle, which creates suction for produced fluids. The working fluid and produced fluids are mixed in the throat after which the mixture continues through the diffuser to the surface. The nozzle/throat combination is crucial in determining jet pump performance. Each oil well needs to be analysed separately and finding the optimum nozzle/throat combination from the 150–200 possible standard and tailor-designed combinations with optimum equipment on the surface is a complex task. An extensive software package is required to make the necessary calculations.

Elomatic acquires share of Wellquip

In May 2014 Elomatic acquired a share of Wellquip Ltd after which Elomatic and Wellquip’s Offshore operations were integrated. The company continues to operate under the Wellquip name. Wellquip provides offshore technology, oilfield solutions and services with a focus on major hydrocarbon production regions. It has strong experience oil and gas related activities in arctic offshore and demanding onshore climates. According to the agreement Elomatic has an option to acquire a majority share in the company during 2014.

The original text was published in our 1/2014 Top Engineer magazine