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SPE-172615-MS

Production Enhancement And Assurance Using Surface Jet PumpTechnology

Sacha Sarshar, and N. Beg, Caltec, U.K

Copyright 2015, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE Middle East Oil & Gas Show and Conference held in Manama, Bahrain, 811 March 2015.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents

of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect

any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written

consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may

not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

Almost 67% of worlds oil and gas is produced from mature fields, Which are facing a significant drop

in the reservoir pressure. There are also other challenges such as production from satellites, increase in

water-cut, fragmentation of reservoir and deterioration of the inflow characteristics of wells which restrict

production and total recovery from these fields. A boosting system is therefore required to maintain

production and to ensure that maximum total recovery from the field is achieved.

Surface jet pumps are amongst the most cost effective ways to revive liquid loaded wells and boost

production from low pressure oil and gas wells. This paper describes the principle of their operation and

refers to a number of field examples worldwide. The paper focuses particularly on revival of oil and gaswells which have unstable production or have seized production.

Economics play an important role in selection of the production boosting techniques. For this reason,

the oil and gas operators wish to minimize their risks and the capital and operation costs of the boosting

systems when the production has declined. This paper also covers the effect of multiphase flow and how

to cope with this aspect of the production from LP oil and gas wells, and the use of solutions which

involve surface jet pumps.

Introduction

Recent reports reveal that almost 67% of world oil and gas is produced from mature fields. There is no

formal definition of what is defined as a mature field. Some sources define field maturity when production

has reached 50% of the plateau rate. Some consider a field reaching maturity after 10 years of production.There are of course other criteria which affect the field maturity and selection of the solutions to maintain

production. These include water-cut, status of the field infrastructure, and whether the field is onshore,

offshore or whether it has major subsea completed systems.

In the UK, all production came from only seven fields in 1977. Today, 1.4 MMboe/d comes from 346

fields.

In many fields, if nothing is done in response to the drop in reservoir pressure and other changes to the

productivity of wells, total recovery of oil or gas from the field may be limited to around 35%.

With advances in production boosting techniques, up to 60% to 75% of reserves should ideally be

recoverable before the field is abandoned.

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The industry also faces other challenges such as the drop in the price of oil and gas, related tax regimes,

inflation, and increase in the cost of equipment, personnel, drilling and maintenance operations.

In many fields, long term, life of the field, consideration has been limited and short term solutions have

been adopted. In this case, near the end of the field life, major investments to extend the life of the fields

are avoided. In some fields major operators pass the field to small operators who may be able to take

further risks and extend the life of the field more economically.

The subject of this paper is on the use of a low cost, low risk system which is ideal for marginal ormature fields. The system or solution involves the use of surface jet pumps (SJPs) to revive LP wells,

which applies to both oil and gas fields.

What is surface jet pump (SJP)?

Jet pump is a passive device which uses an available high pressure (HP) fluid to boost the pressure of low

pressure (LP) fluids. Figure 1 shows the key features of the SJP and the pressure profile through the

system. Jet pumps are also known by names such as eductors, ejectors or jet gas compressors. These

names refer to the same product, but have been used in different industries, including the oil and gas

industry by some operators and suppliers of this equipment. In this paper, surface jet pump or SJP term

is used to distinguish it from downhole jet pumps.

In principle, HP fluid passes through the nozzle of the SJP where part of potential energy (pressure)

is converted to kinetic energy (velocity). As a result, the HP pressure drops significantly in front of the

nozzle. It is at this point that the LP fluids are introduced and are carried through the mixing tube with

the HP fluid. It is within the mixing tube where transfer of energy and momentum between HP and LP

fluids takes place. The mixture then passes through the diffuser section, where the velocity of fluids is

reduced gradually and further recovery of pressure is achieved. The outlet pressure of the SJP will be an

intermediate pressure between the HP and LP pressure. The amount by which the LP pressure is increased

depends on major factors such as HP/LP pressure ratio and mass flow ratio.

Figure 1Profile of the velocity and pressure of HP and LP gas passing through the SJP

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Figure 2shows typical graphs for gas production applications where both HP and LP fluids are pure

gas. There are also other factors such as molecular weight of HP and LP gas, the operating temperature,

properties of gas such as Z factor and Cp/Cv value, and presence of liquids in the HP or LP gas which

affect the performance of the SJP.

In some applications, particularly for prevention of flaring very low pressure gas, if no HP gas source

is available, a high pressure liquid phase such as HP oil or water may be used as the motive flow.

Figure 3shows the performance of the SJP handling LP gas and using HP water as the motive flow.

It is worth noting that using a HP liquid phase can achieve a much higher level of boost for the LP gas,

but a relatively high flow rate of HP liquid is needed for each MMscfd of LP gas.

Figure 2Performance of the jet pump in gas production applications

Figure 3Performance of the SJP, using HP water to boost the pressure of LP gas

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Gas production applications

The applications of SJPs in gas production include;

Boosting the pressure of LP gas

Prevention of flaring very low pressure gas

Replacing intermediate compressors

Boosting production from LP gas wells De-bottlenecking compressors

An alternative to re-wheeling compressors

Revival of liquid loaded gas wells

There has been numerous successful applications of each case, most of which have been covered in

previous technical papers. Seereference 1.

This paper focuses on boosting production from oil and gas wells, and the revival of liquid loaded oil

and gas wells.

Revival of gas wells

Many mature gas wells produce some liquids (oil, condensate or water). As the production of gas declines,

or the flow rates of liquids increase, the velocity of gas through the wellbore becomes insufficient to

transport the liquids to wellhead. The gradual buildup of liquids in the well bore results in erratic

production and, if nothing is done, it leads to the final seizure of production.

There are a variety of solutions involving the use of downhole solutions such as using velocity strings,

gas injection, injection of foaming agents, and use of ESPs, plunger lift pumps, PCPs, rod pumps or

hydraulic pumps. These are generally referred to as artificial lift (AL) systems. For some reasons,

generally, lowering the flowing wellhead pressure (FWHP) is not counted as an artificial lift solution,

although in many cases, it may revive liquid loaded wells without having to use the costlier AL solutions.

The SJPs have been used successfully in many cases to revive liquid loaded gas wells. Figure 4,5 and

6 show a few field examples of such a case where the cost of the system has been a fraction of theconventional and more complex AL systems.

Figure 4Use of the SJP to revive stranded subsea wells

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The effectiveness of the use of the SJP system is based on three main factors;

The HP source and to what extent it can reduce the FWHP of the well

The inflow characteristics of the well and the severity of the liquid loading

Architecture and depth of the well

The up-to-date inflow characteristics of the well can be established reliably by allowing the well to flow

at a lower FWHP, which is normally dictated by the production manifold or pipeline pressure. In some

onshore fields the operator may open the well to a burning pit temporarily to establish the inflow behavior

of the well. In some offshore fields, the test separator may be used to operate at a low operating pressure

by temporarily flaring the gas and sending the liquids to the closed drain system (if allowed).Figure 7shows an alternative solution for using the test separator. This system which uses SJPs or a

booster pump for the liquid phase, prevents flaring the separated gas or sending the liquids to the closed

drain. The viability of this system depends on the availability of the HP source to handle the separated LP

gas, and by what extent it can reduce the operating pressure of the test separator.

Figure 5Use of SJP to revive satellite LP wells

Figure 6Revival of 16 gas wells which could not produce directly against the manifold pressure

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Experience has shown that in some sever cases, the combination of the total depth of the well, the

extent of the liquid loading and the inflow characteristics of the well, demand the use of downhole AL

systems or flowing the well at near atmospheric pressure for the initial revival of the well, before the

simpler solution, using SJPs can become effective on its own to maintain stable production. It is for thisreason that initial testing of the wells at pressures below the manifold or pipeline pressure helps to

establish the severity of the liquid loading and the solution which is the most cost effective way to revive

the well.

The challenge of multiphase flow and oil wells

In addition to gas wells which produce some liquids, oil wells may suffer from the same fate of liquid

loading, but in this case the production rate of the liquids could be well in excess of the gas wells.

Production rate of liquids beyond 1% to 2% by volume of the mixture at the operating pressure and

temperature, affects the performance of SJPs, in both oil and gas production applications.

In such cases a HP liquid phase is needed as the motive flow for the SJP. The HP liquid phase can be

from HP wells, HP export oil, and HP water such as injection water.Figures 8A&Bshow the solution where because of lack of HP liquid phase, flow from LP oil wells is

split into the gas and liquid phase, and the separated LP liquid phase is boosted by a single phase liquid

pump.

Figure 7Use of the test separator, combined with SJP and a booster pump to revive LP wells

Figure 8AFlow diagram of the Wellcom system using SJP to boost the pressure of LP gas and a booster pump to boost the pressure

of LP liquids

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The separator needed for separation of gas and liquids in such applications should ideally be compact

and simple to operate, as in many cases the system operates in remote onshore fields or on unmanned

offshore platforms where space is also a premium. The patented Caltec system uses the cyclonic patented

I-SEP separator to separate LP gas and liquid phases. For further information on I-SEP and its range of

applications refer toreference 2

Figure 9shows the photograph of the boosting system with I-SEP mounted on the same skid which

carries the SJP.

Figure 10 shows an alternative patented solution, known by the trade name of the Wellcom Boost

system. This solution is suitable for cases where no HP source, gas or liquid phase, is available. In this

Figure 8BPhotograph of the Wellcom system using compact separator I-SEP/HI-SEP and the liquid booster pump

Figure 9Use of the HP oil well to revive and boost production from a LP oil well

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case a single phase liquid booster pump is used to generate the motive flow and the SJP handles the total

multiphase flow from the selected LP wells. One of the benefits of this system is that it allows the

selection of the booster pump and the delivery pressure of the pump to allow the SJP to generate the

desired reduction in the FWHP of the LP wells.

The selection of each system depends therefore on the conditions of the LP wells, and the availability

of the HP motive gas or liquids.

How to predict the achieved boost in production

The SJP system of any type reduces the FWHP of the LP oil or gas wells. The amount by which the FWHP

of the selected wells is reduced, is dictated by the following main factors;

The pressure and flow rate of the available HP source

The flow rate of LP gas and liquids

The production characteristics of the LP wells

Both flow rates of LP gas and liquids are in turn dictated by the amount of reduction in the FWHP of

the selected LP wells, particularly by the inflow characteristics of the selected LP wells and factors such

as PI (productivity index) of the LP wells.

In practice, the SJP and the producing LP wells adjust their performance so that they meet the

performance of both.Figure 11shows this phenomenon and the point which matches the performance of

both the SJP and the LP well(s).

Figure 10Use of a booster pump and SJP to revive LP oil well (Wellcom Boost system)

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Economics and benefits of the SJP system

Selection and deployment of any boosting system can be only justified if it has a good or acceptable

business case. The field experience related to all field applications of the SJP solutions has shown that the

recovery of the capital invested is achieved within a few weeks to a few months, depending on the

complexity of the system, the materials used and the extent of the interconnecting pipe work involved.

In addition to the economic justification, the SJP solutions have the following benefits which should

be considered when comparing various production boosting options;

The operation of the system is simple and does not require active control or operator

Maintenance requirements are next to none

The system can be easily modified if the operating conditions change

Alternative solutions are costlier and more complex

The system is highly reliable and does not suffer from limited or short mean time before failure

Naturally, all SJP applications require a high pressure source to power the SJP. Lack of the existing HP

source may lead to adopting the solutions which involve the use of a booster pump. The use of the booster

pump adds to the complexity and cost of the system. However, compared to alternative solutions such as

the use of multiphase pumps, or downhole ESPs, the booster pump handling the liquid phase is still a

simpler system with good track records, and its power consumption is much less than the power needed

by multiphase pumps.

Concluding remarks

The need for a production boosting system is inevitable to maintain production, and to maximize recovery

from mature oil and gas fields. The use of the SJP solutions compliments other major EOR (enhanced oil

recovery) or IOR (Improved oil recovery) systems which are essential to ensure that total recovery from

the fields reaches values in excess of 35% of the reserves.

The SJP solutions have an excellent track record and are amongst the lowest risk solutions to maximize

production and recovery from mature fields. For oil and gas producing companies which have not used

the SJP systems, initial field trials can provide them with the confidence which they need to adopt the

system.

References1. Some novel examples of the use of surface jet pumps (SJPs) to enhance production and

processing. Case histories and lessons learned. By; Sacha Sarshar & N. Beg. Caltec Ltd, U.K.

GPA annual conference, May 23-25, 2012, Berlin.

Figure 11Showing how the LP well and SJP performance match

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2. The applications and performance of a novel compact separator in the oil and gas industry. By;

MM (Sacha) Sarshar, Technical Director, Caltec. 2nd GCC-EU Advanced oil and gas Technology

Conference. Abu Dhabi, UAE, May 21-22, 2001

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