produced water treatment

Download Produced Water Treatment

If you can't read please download the document

Post on 24-Sep-2015

35 views

Category:

Documents

7 download

Embed Size (px)

TRANSCRIPT

  • POLPetroleum Open Learning

    OPITO

    THE OIL & GAS ACADEMY

    Produced WaterTreatment

    Part of thePetroleum Processing Technology Series

  • Petroleum Open Learning

    Designed, Produced and Published by OPITO Ltd., Petroleum Open Learning, Minerva House, Bruntland Road, Portlethen, Aberdeen AB12 4QL

    Printed by Astute Print & Design, 44-46 Brechin Road, Forfar, Angus DD8 3JX www.astute.uk.com

    OPITO 1993 (rev.2002) ISBN 1 872041 85 X

    All rights reserved. No part of this publication may be reproduced, stored in a retrieval or information storage system, transmitted in any form or by any means, mechanical, photocopying, recording or otherwise without the prior permission in writing of the publishers.

  • Petroleum Open Learning

    Visual Cues training targets for you to

    achieve by the end of the unit

    test yourself questions to see how much you understand

    check yourself answers to let you see if you have been thinking along the right lines

    activities for you to apply your new knowledge

    summaries for you to recap on the major steps in your progress

    Produced Water Treatment(Part of the Petroleum Processing Technology Series)

    Petroleum Open Learning

    Contents Page* Training Targets 4

    * Introduction 5

    * Section 1 - The Problems Associated with Produced Water 6 TheMechanicsofWaterProduction CorrosionProblems ScaleProblems TransportationProblems DisposalProblems

    * Section 2 - The Basics of Produced Water Treatment 15 PrimarySeparation GravitySeparation Coalescence ShortDistanceGravitySeparation GasFlotation CentrifugalForceSeparation ChemicalTreatment

    1

  • Petroleum Open Learning

  • Petroleum Open Learning

    Visual Cues training targets for you to

    achieve by the end of the unit

    test yourself questions to see how much you understand

    check yourself answers to let you see if you have been thinking along the right lines

    activities for you to apply your new knowledge

    summaries for you to recap on the major steps in your progress

    Produced Water Treatment(Part of the Petroleum Processing Technology Series)

    Petroleum Open Learning

    Contents (contd) Page

    * Section 3 - Produced Water Cleaning Equipment 23 APISeparators PlateInterceptors(orSeparators) Oil/WaterFiltersCoalescers GasFlotationUnits Hydrocyclones UseofChemicalAdditives

    * Section 4 - A Typical Produced Water System 36 TiltingPlateSeparators TheFlotationUnit ChemicalDosingPackage ProducedWaterCaisson

    * Test Yourself - Answers 47

    3

  • Petroleum Open Learning

    Training Targets

    When you have completed this unit on Produced Water Treatment you will be able to :

    List the sources of produced water

    Describe the mechanics of water production

    Explain what problems can arise from the production of water

    Explain the basic principles which govern the separation of oil from produced water

    Describe the construction and operation of 5 types of oily water clean up facility

    Explain the requirement for chemical injection in a produced water treatment system

    Describe the flow of water and separated oil through a typical produced water treatment facility

    Tick the box when you have met each target.

    4

  • Petroleum Open Learning

    In the vast majority of oil fields, water productionbecomes a problem as the field gets older. Towardsthe end of their useful lives some oil wells may beproducing 95% of their total liquid as water. Thisproduced water may be extremely salty and likely tobe of little value to the operator. It is removed fromthe oil stream during primary separation and byother facilities, and has then to be disposed of.However, we are talking of a great deal of water insome cases. How do we dispose of it, and where dowe put it?

    Offshore, the obvious place would be into the sea.Dumping this produced water directly fromseparators into the sea, would however, soon havethe operator in trouble with the authorities. Evenafter initial separation the water still contains oil insmall amounts. Serious environmental pollutionwould build up if oil contaminated water were to bedumped directly to the sea.

    Onshore, disposal wells may have to be drilled, intowhich the produced water can be injected fordisposal. This also may have its problems. Oil inthe water, or fine solids, could plug the injectionwells in a very short time.

    So the water which is produced with, and separatedfrom, the oil in an oilfield must be cleaned prior todisposal. This is what this unit is all about. In the

    unit, we will be looking at the produced waterhandling system of an oil production facility. Beforewe examine a typical system, however, I think weshould look at where the water comes from and theproblems it poses in a little more detail. So, I havesplit the unit into four sections as follows:

    In Section 1 we will look at the sources of produced water and the problems which may be encountered if we fail to treat it.

    Section 2 will cover the basic principles involved in the treatment and clean-up of produced water.

    In Section 3 we will examine the construction and operation of produced water clean-up equipment.

    Finally, in Section 4, I will take you through a typical produced water handling facility which may be found on an offshore production platform.

    Although produced water treatment applies to bothonshore and offshore locations, I will beconcentrating on the offshore situation in this unit.However, most of what I have to say would apply toboth.

    Produced Water Treatment Introduction

    5

  • Petroleum Open Learning

    Water is present in some form, in most oil reservoirsbefore any production takes place.

    There are however, many different types ofreservoir. In one very common one, the oilaccumulates above large volumes of water, which isusually salty. This water is what remains of ancientseas from an earlier period of Earths history.

    This body of water is called an aquifer, and thereservoir is known as a water drive reservoir.

    In addition, a considerable amount of water may alsobe found as small droplets distributed throughout theoil (and gas) in a reservoir. For reservoirengineering purposes this water is called connatewater or interstitial water. We will just call itformation water.

    During production, further injection water may be pumped into the reservoir to assist in pressure maintenance.

    Any of these types of water may eventually find theirway into the oil wells and be produced to the surfacealong with the oil. It is all then called producedwater.

    Before we look at the problems which can be causedby this produced water, let us first consider how thewater gets into the producing wells,

    The Mechanics of Water ProductionLook at Figure 1 which shows a cross section through a typical water drive reservoir.

    Produced Water Treatment Section 1 - The Problems Associated with Produced Water

    6

  • Petroleum Open Learning

    PERMEABILITYPermeability is a measure of the ability of a fluid to flow through the rock from one pore to another. In order for it to be able to do this, the pores must be interconnected.

    Permeability is measured in darcys- named after a French engineer who studied the flow of liquids through filters. He found that the flow increased in proportion to the pressure increase. However he also discovered that the flow was affected by the thickness, or viscosity, of the fluid.

    Generally there is a wide spread of permeability in reservoir rocks.

    So, the rock properties of porosity and permeabilityallow the oil to flow towards the producing wells. Butwhat causes the oil to flow through the reservoir?

    Lets look at that now.

    You are probably aware that fluids always flow fromareas of high pressure to areas of low pressure:

    The oil producing wells create areas of low pressure in the surrounding reservoir rock as the well is opened at the surface and oil flows into the well

    The aquifer is usually at a relatively high pressure. In addition, the injection of water into the aquifer is intended to maintain the reservoir pressure

    You can see that the oil lies above the aquifer and thewell is taking oil which is not contaminated with water.The point at which the oil and water touch each other is called the oil water contact.

    The oil is able to flow through the reservoir rocktowards the well because the rock is porous andpermeable. These are probably the two most important properties of reservoir rocks.

    POROSITYPorostiy is the property of the rock which enables it to hold fluids within itself. The oil, gas and water are contained in tiny holes in the rock called pores.

    Sandstone is a common reservoir rock. It is made up of grains of sand which are cemented together at the points where they touch. Between the sand grains are void spaces - the pores.

    The ratio of the volume of the pores to total rock volume expressed as a percentage is the rocks porosity.

    This means that, if you have a sandstone reservoir with a porosity of 25%, for every 4m3 of reservoir rock, 1m3 consists of holes and 3m3 solid sand grains.

    Another common reservoir rock is limestone. This is a rather brittle rock which contains lots of tiny cracks and fissures. These tiny cracks give the limestone its porosity.

    The high pressure water in the aquifer,therefore, will tend to displace the oiltowards the low pressure areassurrounding each well bore.

    Figure 2 on the next page, shows thesituation with just one producing welland one water injection well.

    7

  • Petroleum Open Learning

Recommended

View more >