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www.slb.com/artificialliftESP technologies for operating in high-gas environments / Title Page

ESP Technologies for Operating in High-Gas Environments

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www.slb.com/artificialliftESP technologies for operating in high-gas environments / Overview

Applications Oil-producing wells with high gas volume

fractions (GVF)

Oil-producing wells with nonvented packers

Gas lift for wells converted to electrical submersible pumps (ESPs)

Dual liftgas lift and ESP wells

Subsea oil wells

Gas wells with liquid loading

Benefits Increased production and field life through

maximized drawdown Increased production through fewer

shutdowns caused by gas locking Extended ESP system run life Reduced operating costs through

elimination of workovers

Features Vortex gas separators capable of greater

than 90% separation efficiency Centrifugal gas handlers capable of

ingesting free gas of 45% at low pump intake pressures

Poseidon multiphase pump systems capable of ingesting free gas of 75%

Superior, patented, abrasion-resistant construction

The application of ESPs is growing rapidly, often

pushing the technology envelope for solutions to higher

temperatures, pressures, abrasives, and gas content.

With the latest advances in gas handling technology,

wells that were previously considered too gassy for

ESP systems can now be pumped successfully.

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Gas is typically associated with most oil-producing wells. As the well is drawn down to achieve production targets, gas

will break out of solution. A portion of the gas will enter the ESP system and affect the operation of the ESP. Natural separation is the portion of the gas that bypasses the ESP intake and travels up the annulus to the surface.

ESP technologies for operating in high-gas environments / Why is gas a problem?

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Why iS gAS A ProBlEm?

Wells are routinely produced below the bubblepoint pressure to maximize drawdown and increase total hydrocarbon production. Higher drawdowns require the pumping system to handle higher volumes of gas. ESP systems can typically manage between 10% and 25% of free gas before performance degradation and gas locking occurs.

how does gas affect ESPs?Extreme differences in the densities of liquids and gases create a low-pressure area in the impeller eye, which results in gas accumulation. Free gas in the stage impellers displaces liquid and restricts the volumetric efficiency of the pump. The accumulation of free gas results in lower lift per stage and a decline in expected production.

Without effective applications of gas technology to prevent excessive gas accumulation, either gas interference or gas locking will occur.

Gas interference is a partial blockage of the impeller flow path, resulting in degraded pump performance and low production. Gas locking is complete blockage of the flow path, requiring a pump shutdown. Gas and gas locking can be detected from pressure fluctuations measured by a downhole sensor or from erratic current fluctuations from an amp chart.

minimizing the effects of gasThe three basic methods to minimize the amount of gas entering the pump are avoidance separation handling.

When gas first enters an ESP system, the amperage becomes unstable, causing interference in the flow. As more gas enters the system, the operation becomes more and more unstable until the ESP system shuts down on undercurrent. Multiple shutdowns from gas interference cause fatigue on the ESP system as well as lost production.



An inverted shroud is a piece

of casing with the opening above the ESP. This system induces natural separation by creating a reversal of the flow path for the fluid to enter into the ESP system, and the gas travels up the well to the surface. This system is limited by drawdown and pump size.

When a portion of the wellbore

extends below the perforations, a sumped shroud is used to install the pump below the perforation, inducing natural separation as the fluid and gas travel out of the perforations and flow down and around the shroud to enter the pump intake.

The Bottom Feeder intake is specifically designed for horizontal wells to allow fluid entry from the bottom portion of the wellbore. It is constructed so that gravity causes the intake ports to orient toward the bottom of the well. This enables the fluid to enter the pump from the bottom and the gas to bypass the intake on the top.

ESP technologies for operating in high-gas environments / Gas avoidance techniques

gAS AvoidAncE TEchniquES

gas avoider intake systems

Gas avoider intake systems feature an eccentric weighted outer sleeve to provide a self-orienting intake with inlet ports at the lower side of the casing annulus. Designed for use in highly deviated or horizontal wells, the light phase (gas) flows past the top of the device while the heavier liquid phase flows into the inlet ports and into the pump or other gas handling devices. The system can also be installed below the ESP on a tailpipe connected to a shroud.

Shrouded systemsShrouded systems are gas avoidance measures that enhance natural separation and reduce free gas at the pump. After shrouding, the gas continues up the annulus and the fluid is diverted into the pump, creating a separation. There are two methods of shrouding. First, a shroud can be used to encase the pump, and the system is placed below the perforations. The shroud can also be inverted and placed above the perforations. These systems usually require smaller-diameter ESP systems and may limit production.



When a moderate amount of gas can be effectively sepa-rated from the liquid at the desired drawdown, the Vortex

gas separator uses an inducer and propeller to induce slippage between the phases. The heavier liquid naturally moves to the outside, and the gas stays near the center. As the fluid separates and travels up the gas separator, the gas is expelled back into the annulus and the fluid enters the pump intake.

ESP technologies for operating in high-gas environments / Gas separation

The vortex gas separatorThe Schlumberger Vortex gas separator is a dynamic gas separation device that uses a natural vortex action created by a specially designed inlet configuration, axial flow inducer, propeller, retention chamber, and discharge crossover. It provides greater efficiency over a broader range of flow conditions than earlier rotary separators.

The Vortex gas separator features a patented compliant-mount zirconia radial-bearing technology to enhance reliability in sandy and abrasive conditions. To further extend life expectancy, the design sends very little energy to the solid particles that are produced through the separator. The advanced hydraulic design of the Vortex gas separator uses state-of-the-art computational fluid dynamics and solids modeling technology. The improved hydraulics enable more effective gas separation at higher fluid flow rates.

gAS SEPArATion

Natural gas separation occurs because of the differences in density and buoyancy between the gas and the liquid phases. A number of factors make it difficult to estimate the efficiency of natural gas separation.

Mechanical gas separators are classified as either static or dynamic. Static gas separators are designed to keep free gas from entering the pumpwithout applying any additional mechanical force. They provide a tortuous path that turns the fluid stream and moves it down toward the inlet ports. Some of the free gas accompanies the liquid to the intake and a portion is separated, limiting overall separation efficiency. Dynamic gas separators, on the other hand, actually impart energy to the fluid to separate the vapor from the fluid.

Factors impacting natural and mechanical separation include

casing and equipment size free gas volume percentage pump intake pressure and temperature hydrocarbon composition bubblepoint pressure casing pressure flow rate obstructions or restrictions operating frequency.



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Gas locksESP failurePower interruption

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Gas-handling solutions for ESP operations fall into the following two technology groups: advanced gas handler systems with high-

specific-speed centrifugal gas handlers for the gassy ESP market up to 45% GVF at low intake pressures

axial flow technology for ultrahigh-gas-cut ESP market with GVF up to 75%.

The AGH* advanced gas-handling device was designed to improve the overall lift efficiency of a submersible lift installation by maintaining a higher gas-to-liquid ratio in the tubing string. The systems higher GVF reduces the hydraulic horsepower required to lift fluid to surface. The AGH system uses a unique centrifugal stage design to alter the pressure distribution of the impeller, creating a homogenized mixture with reduced gas bubble size. This conditioned fluid behaves as a single-phase fluid before entering the pump.

Proven field resultsAn AGH system installed in a European wellwith all other downhole equipment remaining the sameincreased production from 800 bbl/d, with a GOR of 925 ft3/bbl, to 1,250 bbl/d. The gas locking was also eliminated and 23% of free gas was produced through the pump. In addition, eliminating cycling resulted in a longer-than-expected equipment run life.

The AGH advanced gas handler is a high-speed centrifugal pump that homogenizes the gas and fluid. As the gas and

fluid enter into the AGH system, the impellers break the bubbles into smaller and more manageable sizes and compress some of the bubbles back into solution, so the ESP system can pump the mixture.

As reservoir pressure is depleted and gas breaks out of solution, producing the wells becomes increasingly difficult. By using the Poseidon gas-handling system, the producer can extend the field life and continue producing the wells beyond their previous economic limit, thus adding to the recoverable reserves.

With the ability to manage more gas through the pump comes the require-ment to implement a new way of operating. By installing a thermocouple in the motor winding and using a sensor to transmit the data to surface, the ESP system can be shut down using motor temperature to protect the ESP system and enable the system to ride through gas slugs.

ESP technologies for operating in high-gas environments / Gas-handling solutions

gAS-hAndling SoluTionS

Oil Production

Conventional Gas Handling System

Poseidon System

Time



The Poseidon multiphase pump operates on the same principles as the large seabed multistage pumps. An axial

stage accelerates the gas and fluid into the ESP system and, by forcing the mixture through the pump in the process, prevents the first few stages of the ESP from becoming gas locked.

ESP technologies for operating in high-gas environments / The Poseidon system

The Poseidon system is a multiphase, axial flow gas-handling device installed below the main production pump to allow the production pump to efficiently handle higher percentages of free gas. The system can be installed either above a gas separator when gas can be vented into the cas-ing, or it can be installed above a standard intake if all the produced gas has to go through the pump. In many wells with high gas volume, the Poseidon system can increase production and extend the use of submersible pumps in gassy oil wells where production is limited by the cen-trifugal pumps ability to handle gas. The Posei-don gas-handling system is designed to improve pumping stability in gassy wells, provide better slug handling in horizontal wells, and increase the production rate, recovered reserves, and ESP effectiveness. It can also be used in wells with nonvented packers that are typically found in subsea and offshore completions.

System developmentThe Poseidon system was developed by Institut Francais du Petrole (IFP), Total, and Statoil as the next step in the historical evolution of advanced gas handling. Schlumberger uses the Poseidon system to enhance production in oil and gas wells with gas-locking problems.

Most gas-handling systems currently rely on centrifugal force to transfer energy to the liquid/gas mixture. If there is a high percentage of free gas in the vanes, the liquid and gas will separate, lowering energy transfer efficiency.

When enough gas accumulates, the pump gas locks and prevents fluid movement. The Poseidon gas-handling system is a multiphase helicoaxial pump installed between the intake (or gas separator) and the pump. The specially designed axial flow stages prime the main production pump and push the gas-liquid flow stream through the ESP stages. Gas volume is reduced by compression. In laboratory tests and field trials, the Poseidon system operated successfully in the ultrahigh-gas ESP market, with GVF up to 75%, exceeding the 40% to 45% GVF limitations of existing gas-handling devices. Combination systems can be used with GVF up to 95% to further reduce the GVF entering the pumping system to acceptable levels.

Because of its special design, the energy transfer of Poseidon axial flow stage is more efficient, resulting in trouble-free operation at a high GVF. The Poseidon system maintains a high boosting pressure with increasing amounts of gas fraction and handles up to 75% of free gas ingested into the pump without gas locking.

ThE PoSEidon SySTEm



*Mark of Schlumberger. Other company, product, and service names are the properties of their respective owners. 09-AL-0042 Copyright 2009 Schlumberger. All rights reserved.

Products and Services Advanced Lifting Services Variable Speed Drives Vortex Gas Separator AGH Advanced Gas Handling Device Poseidon Multiphase ESP Gas Handling

System

case Studies Advanced Lifting Services Dramatically

Increases Production Phoenix MultiSensor Monitoring System

Motor Temperature Protection Prevented ESP Failure

Poseidon Pump Increases Oil Production and Life of Gassy Well for Canadian Operator

ESP technologies for operating in high-gas environments / A new way of operating

visit the gas Solutions Web Site.

A nEW WAy oF oPErATing rElATEd rESourcES

unconventional wisdomWhen operating in high-gas environments, the conventional wisdom of using amperage to protect the motor does not apply. Because high-gas environments generally have extremely volatile flow regimens, the load on the motor has wide swings, which causes erratic amperage readings. For this reason, downhole monitoring systems, variable speed drives (VSDs), and remote montitoring and control systems are useful tools.

downhole monitoringAll submersible pumps in high-gas environments should be equipped with downhole monitoring tools. These tools are equipped to monitor motor winding temperature through a thermocouple attached directly to the motor winding. This protection for the ESP system uses more stable, faster acting, measured data. In addition, these tools protect the downhole equipment and are valuable sources for providing operational and production data and for monitoring pump intake pressure, pump discharge pressure, wellbore temperature, internal motor winding temperature, current leakage, and vibration. Using the motor winding temperature mode for ESP protection enables riding through gas slugs and unstable production periods. In addition, using the pump intake pressure allows for current mode operation and further extends uptime.

variable speed drivesVSDs are used as the surface control package in all wells with high volumes of gas because they provide pump operational flexibility for flow rate and total dynamic head generation. Another key benefit is the VSDs ability to control and manage startup and operations in gassy environments. Current, frequency, and pressure modes provide three modes of operation for the operator to use the downhole monitoring system to keep the well producing longer through gas slugging flows. Combining the downhole monitoring system and the VSD is a highly effective method of operating ESPs in gassy environments.

monitoring and controlHigh-GOR wells are unstable and unpredictable and, therefore, should be closely monitored. By connecting to the espWatcher Web-hosted surveillance and control system, a well can be monitored from any computer that has connectivity. This system has the capability to allow for adjustments in operation as well as to shut down and start up. A previously challenging well can be effectively produced by implementing a holistic approach.

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The Poseidon systemGas Handling SolutionsGas SeparatorsGas Avoidance TechniquesWhy is gas a problem?ESP Technologies for Operating in High-Gas Environments

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