Keeping your fluids flowing

Multiphase Wiki

Glossar zu den wichtigsten Begriffen in der Öl und Gas Industrie mit besonderem Fokus auf Multiphasenanwendungen

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API Gravity

 

A specific gravity scale developed by the American Petroleum Institute (API) for measuring the relative density of various petroleum liquids, expressed in degrees. With increasing gravity the viscosity of fluids is decreasing.

Multiphase pumps can be operated beneficially in oil and gas fields producing oil or condensate of virtually any API grade. The lower the API grade the better for Twin Screw Multiphase pumps, as their performance increases with lower viscosity.

Artificial Lifting

 

Different methods focusing on giving energy to the fluids of a well, with the aim to improve its production. Multiphase boosting forces the well fluids to overcome system back pressure. Multiphase pumps are usually installed close to the wellhead, on the surface, which is different to most other lifting technologies. However, this makes it one of the most efficient artificial lifting technologies, due to very high uptime of up to 98 % (and more), easy maintenance and high pump efficiency.

 

Darcy

 

Named in honor to Henry Darcy. It measures permeability, the ability of fluids to flow through rough stones, sand or rocks, etc. It has a number of input factors which makes it a good indicator for artificial lifting solutions and well head pressure considerations.

 

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Bottomhole Pressure

The pressure at or close to the depth of perforation. The bottom hole pressure is usually measured in psi and is determined at different well conditions, for example at shut-in or flowing well. In these cases it is called shut-in bottomhole pressure (SIBP) or flowing bottomhole pressure (FBHP).

The FBHP is the essential value to determine the effectiveness of an artificial lifting technology!

Multiphase Boosting reduces the flowing bottom hole pressure by reducing the wellhead flowing pressure, typically by 250 psi or even more.

Brownfield

A reservoir of oil or gas that has matured. It is producing at production plateau or has even progressed to a stage of declining production.

The end of natural plateau production is the right time to install Multiphase Boosting equipment at the surface.

Multiphase Boosting is one of the most effective technologies to extend the life of brownfields. It can easily and very economically be combined with other artificial lifting technologies. Thus, once the reservoir is further depleting, Multiphase Pumps support the use of other technologies installed downhole like electrical submersible pumps, sucker rod pumps, jet pumps or velocity strings.

Bubble Point

The bubble point defines the pressure and temperature conditions at which the first bubble of entrant gas comes out of the oil. In any hydrocarbon reservoir the oil contains some natural gas. With decreasing pressure this gas evolves from the liquid.

Multiphase Boosting reduces the wellhead pressure and subsequently the flowing bottom hole pressure. Under normal production, the liquids flowing to surface pass the bubble point somewhere in the completion. The use of Multiphase Pumps shifts this point to a lower level and the gas evolves at a lower point in the well, generating an additional gas volume and reducing the average density of a fluid column in the tubing. This enhances the production and creates an additional drive of liquids to the surface – similar to a gas lift.

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Engineered Rotors

Multiphase pumps based on twin screw pump technology are available with two different designs of rotors: engineered and solid. The latter means ‘machined from one piece’.

Engineered rotors consist of a shaft with two screws and locking nuts. The screws are fixed to the shaft by using the locking nuts and are tensioned accordingly. The advantage is having different materials for shaft and screws as well as lower costs for replacements as shafts can be reused and only screws have to be replaced.

Enhanced Oil Recovery (EOR)

Enhanced Oil Recovery, also named the third stage of oil recovery or tertiary recovery, consists of methods which change the properties of the oil in the reservoir. There are different techniques available and the one used is depending on the current reservoir conditions.

Multiphase boosting helps to extract the hydrocarbons from the well, once they have reached the well, due to improved mobility caused by EOR.

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Gas / Liquid Ratio (GLR)

GLR is the ratio of the volume of gas in relation to the volume of produced liquids, measured in SCFD/bbl. Produced liquids are the sum of produced water and oil. This value may vary on different temperatures and pressures.

This is a sensitive value indicating the behaviour of a well. It can be used to plan and control artificial lifting solutions like water injection.

Gas / Oil Ratio (GOR)

The ratio of the volume of gas in relation to the volume of produced oil at standard conditions. This value varies with time but not pressure, different to the GVF.

This value is used for the design of Multiphase-Installations based on first data over a longer period of time, i. e. during Multiphase Added Field Development (MAFD).

Gas Volume Fraction (GVF)

The Gas Volume Fraction is the ratio of gas volume flow to the total volumetric flow rate of all fluids at actual conditions.

This is the most important value for multiphase boosting, as it significantly varies with pressure, due to the fact that the gas volume is changing whereas the liquid volume can be considered constant. It determines the suitability of different multiphase pump technologies as well as their performance and efficiency. Thus it is a very essential figure for each multiphase application as it determinates pump type, size and execution. Furthermore, it has a high influence on the efficiency of the Multiphase System and on design details such as mechanical seals and liquid re-circulation.

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Heavy Oil

The American Petroleum Institute denotes oils with a gravity below 22,3° API as heavy oils. Typically these oils also have high viscosities. Due to high viscosities, heavy oil has relatively bad flow characteristics, many require down hole artificial lifting solutions, like rod pumps, to produce the crude to the surface.

Multiphase pumps reduce the back pressure for the down hole pumps and the downhole pressure simultaneously.

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Multiphase Pumps

Multiphase pumps are designed to handle the untreated flow from wells without the need of any separation. They handle gas, liquids (like oil & water) and solids (like sand) coming from a single or from multiple wells. The operating conditions are unpredictable due to slug flow from tubing, raiser or flowlines, causing rapid changes of GVF, pressure and temperature and thus a challenge for the pump design.

Multiphase pumps are located close to the wells and reduce the wellhead flowing pressure to defined values, ideally close to atmospheric conditions.

Multiphase Boosting installations improve the productivity of reservoirs from the very beginning and increase the net present value of such assets by:

  • Disconnecting wells from the back pressure of downstream systems
  • Lowering the flowing wellhead and subsequently the flowing bottom hole pressure
  • Providing defined operating conditions for secondary artificial lifting at a later stage of well life, reducing the costs and risks for the management

Multiphase pumps are used for:

  • Oil / gas well boosting
  • Boosting of header production, e. g. in clusters
  • Boosting of complete field production
  • Brownfield development
  • Marginal field development
  • Tie in of remote fields

They are suitable for on- and offshore installations as well.

Multiphase Pumps mainly include positive displacement pumps because their performance does not depend on the density of fluids. In helicoaxial pumps, the design principal of rotating impellers and fixed diffusors is adapted in such a way, that these pumps have a higher tolerance against low fluid density.

Multiphase Pumps are usually based on these pump types:

  • Twin Screw Pumps
  • Progressive Cavity Pumps
  • Piston Pumps
  • Helicoaxial Pumps
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Primary Recovery

Primary Recovery is the first stage of producing hydrocarbons from a reservoir, driven by the initial reservoir pressure. In the beginning of a well’s life this reservoir pressure can be sufficient to drive fluids up to the surface. However, with declining reservoir pressure caused by shrinking volumes, artificial lifting technologies are required to lift fluids from the wellbore to the surface at reasonable rates.

Multiphase Boosting is the first Artificial Lifting Technology to be implemented once naturally flowing wells are not producing at sufficient rates anymore. It significantly reduces the bottom hole pressure and basically disconnects these wells from the upstream system, pressure wise.

Later on, once the wells drain further, additional artificial lifting measures may be required. In this case the Multiphase Boosting Pumps create defined production conditions, optimizing the use of these technologies. Secondary artificial lifting solutions are:

  • Sucker Rod Pumps
  • Electrical Submersible Pumps
  • Jet Pumps
  • Gas lift
Productivity Index (PI)

The Productivity Index describes the gain of production when reducing the flowing bottom hole pressure given in bbl/psi.

For Multiphase Applications the productivity index is a very good indicator to evaluate the profitability of the installed multiphase pumps. The PI is used by the asset management to determine incremental production as well as additional overall recovery and related commercial benefits for the net present value.

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Recirculation

Recirculation of fluids is a standard procedure for multiphase pumps in order to ensure sufficient liquid at pump inlet for a proper operation of multiphase pumps. Multiphase Pumps require liquid to regulate the GVF at inlet conditions, for different reasons. This can be achieved internally or externally of the pump. The main challenge is to recirculate liquid only, i. e. no free gas or solids. German Legacy achieves this with a Liquid-Recirculation Management System.

Recovery Factor

The Recovery Factor describes the recoverable amount of hydrocarbons compared to the amount initially in place. Increasing the recovery factor is a major step to overcome the worldwide shortage of natural resources.

Multiphase boosting increases the recovery factor by lowering the bottom hole pressure while allowing significantly more hydrocarbons to flow into the well.

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Secondary Recovery

Secondary Recovery combines methods where fluids are re-injected into the reservoir with the objective to maintain reservoir pressure. Furthermore the injected fluids shall drive the reservoir fluids towards the producing wells. Common technologies are gas injection and water flooding.

Multiphase pumps support secondary recovery methods by decreasing the flowing bottom hole pressure and increasing the differential pressure between reservoir and well, which is the driving force for reservoir fluids.

Steam-Assisted Gravity Drainage (SAGD)

Steam-assisted gravity drainage is a thermal production method for heavy crude oil. It uses steam to heat the reservoir up reducing oil viscosity so that the fluids drain into a lower production well. These wells are usually maintained by sucker rod pumps (SRPs).

Multiphase Pumps (MPPs) are often used in these applications, it is a common technology especially in Canada. The producing wells are typically designed as an open completion with the MPP suction connected to the annulus of these wells, called Vapor Recovery Units (VRU). The MPP lowers the flowing bottom hole pressure to achieve a better inflow performance.

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Water Cut

Water Cut is the ratio of produced water compared to the produced volume of all liquids: 

Multiphase Pumps are designed to be very tolerant to changing water cut values. Normally there is no additional equipment needed.

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