Achmad Malik_gas Compresi Untuk Gas Lift

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OPERATOR & TECHNICIAN TRAINING PROGRAM TOTAL E & P INDONESIE By : ACHMAD MALIK IBRAHIM

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tentang gas compression

Transcript of Achmad Malik_gas Compresi Untuk Gas Lift

OPERATOR & TECHNICIAN

TRAINING PROGRAMTOTAL E & P INDONESIE

By :ACHMAD MALIK IBRAHIMPUSAT PENDIDIKAN DAN PELATIHAN MINYAK DAN GAS BUMIPUSDIKLAT MIGAS CEPU

JL. SOROGO No. 1 CEPU 58315 KAB.BLORA JAWA TENGAH

TROMOL POS 1. TELEPON (2096)421888 FAKSIMILE (0296) 421891

http://www.pusdiklatmigas.com e-mail : [email protected] APPROVALTopic

: Gas Compression for Gas Lift InjectionBy

: Achmad Malik Ibrahim

Name of Training: Operator Technician Traning Program 2 PT. Total E&P

IndonesieThis Paper Approved in Maret 2013 at PUSDIKLAT MIGAS CEPU,

Approved by,Preceptor,

English Corrector,Course Leader,

PREFACE

All praises are just for Allah SWT for blessing me and for giving me inspiration to finish thus paper on time. This paper is one of the requirements to pass Operator Technician Training Program TOTAL E & P INDONESIE which is held in PUSDIKLAT MIGAS CEPU from October, 2sc 2012 until March, 14th 2013.

The title that discussed in this paper is GAS COMPRESSION FOR GAS LIFT INJECTION. In the progress of making this paper, of course I cannot do it without help and motivation from all people around me. On this occasion, I would like to extend my thanks and high appreciation to :1. The Management of TOTAL E & P INDONESIE

2. The Management of PUSDIKLAT MIGAS CEPU

3. Mr. Purnomo Sidi as the Course Leader4. Mr. Totok

5. All of instructors and staff in PUSDIKLAT MIGAS CEPU

6. My family who always support me

7. All of people who have helped to finish this paper

All corrections, suggestions and criticisms to me will be highly appreciated for the improvement of this paper.Cepu, 20 February 2013

Writer,

Achmad Malik Ibrahim

ABSTRACT

Gas lift is the method of artificial lift that uses an external source of high preassure gas supplementing formation gas to lift the well fluids. The primary consideration in the selection of a gas-lift system to lift the fluid, a grounp of wells, or an entire field is the availability and compression cost of gas.

There are two types of gas lift methods which are widely used they are continous flow gas lift and intermittent gas lift. Most wells are gas lifted by continuous flow, which means the gas is injected continuously into the production conduit at a maximum depth on the basis of the variable injection gas pressure. In the other way, diffrent with continuous flow gas lift, an intermittent gas lift requires high instantancous gas volume to displace liquid slugs to the surface. The intermittent gas lift operation is used, if sufficient drawdown in the Bottom Hole Pressure (BHP) is not possible by continuous flow.

The type of installation is influenced principally by whether the wells is to be placed on continuous or intermittent flow. In determining the initial type of installation, judgment should be based on future well performance, including BHP decline and Productivity index (PI) decrease. Type of gas installation usually used are open installation, semi closed instalation, and closed iinstallation.

The application of gas lift is particularly for lifting the fluid where high pressure gas is available. Gas compressors may have been installed for gas injection, or high pressure gas well may be nearby. This paper will describe more about gas lift principle and gas compretion CONTENTSLIST OF FIGURESI. INTRODUCTION1.1 BackgroundWell is produced using its own drive mechanism to lift hydrocarbon fluid from productive zones. Such a well is usually called natural flow well. Pressure difference is the basic principle. When a well no longer flow naturally, as a result of decline in natural reservoir energy, it becomes necessary to supplement that reduced or lost energy artificially. This is done by installing an artificial lift system to restore or imporve production rate. One of any production methods is gas lift system.Gas lift system is an artificial lift method that uses energy from the gas (high pressure gas), which is inserted in annulus and the gas enters the tubing string through many gas lift valve to rovide lifting energy. There are two types of gas lift methods which are widely used, continuous flow gas and intermittent gas lift. Basically, this method lifts the hydrocarbon fluid by lowering system density, so that high drawdown pressure can be gained. This is reached by mixing gas to fluid.

1.2 Objectives

Besides to fulfilling requirement for finishing the Operator & Technician Training Program (OTP) TOTAL E & P INDONESIE in Pusdiklat Migas Cepu, I write this papre to get better understanding of gas lift, including its principle, equipment andthe operation.1.3 Scope

This paper will discuss about Gas Compresion for Gas Lift Injection.

II. BASIC GAS LIFT

2.1Basic Concept

Gas lift method is one of production methods employedon production well when natural flow no longer exists. There are many reasons why natural flowing on longer in production state, including drop of reservoir pressure. Basically gas lift method works by injecting gas through operation valve to create a homogenous mixture betwen fluid and gas above injection point. Injection gas will lower the density of the combined fluid. The lower density decreases the hydrostatic pressure of the fluids in the tubing, enabling them to be lift to the surface.

Gas lift offers many advantages. Some of theses advantages are :

1. Low lift cots2. Low installation and maintenenance costs

3. Simplicity of operation

4. Excellent flexibility in injection / production rate

5. Ability to deplete a reservoit

6. Execellent gas handing (obvious applicability, for gassy wells)

7. Execellent sand and solid handling

2.2Methods of Gas Lift

As already mentioned, there are two types of gas lift methods, continuous flow gas lift and intermittent flow gas lift. Chose method will determine how and where were going to place injection valve. In continuous flow gas lift, although here are many valve involved, only ine valve will be operated. There other valves are used in unloading process. In reverse in intermittent flow gas lift there can be many valves operating together. Beside on number of valve and where to place them, the methods have differences on the way inject gas to the production well. In continuous flow, gas injected continuously. In intermittent flow gas lift, gas injection is done periodically.

2.2.1Continuous Flow Gas Lift

In continuous flow gas lift, the gas is injected into the liquid stream for the purpose of reducing the density of the vertical liquid colum sufficiently to allow the formation pressure to lift it to the surface. On this type of gas lift, gas injected continuously. Only one valves operates at a time, called operational valve. But it is possible to place additional valve of this type. It is done to anticipate if after somtimes the main operating valve cant lift the hydrocarbon fluid. The cause cuold be drops of bottom hole pressure or the of water in production. Valve placed above the main operating valve are used in uploading process.

The advantages of continuous flow gas lift are:

1. It takes full advantage of the energy available in the reservoir

2. It is high volume method

3. Equipment can be centralized

4. It can handle sand or trash best

5. Valve may be wire-line.

Continnuous flow gas lift is often installed on wells with high Productivity Index (PI) and high bottom hole pressure (relatively depend on well depth)

2.2.2 Intermittent Gas Lift

On well having low PI and low BHP (Bottom Hole Pressure), periodical gas injection is more efficent than the continuous one. This method allows formation fluid to accumulate in tubing before lifted to the surface by injected gas. This method also uses gas than continuous flow gas lift. As gas is injected periodically, intermittent flow gas lift has additional equipment compared with continuous one. It is a time cycle controller. This equipment is used to control injection period to obtain optimum production rate. As the continuous installation, intermittent flow gas lift has operation valve and unloading valve.

Somtimes, intermittent lift may be accomplished without using a surface intermittent. This type of installation requires a valve that is somewaht more fluid sensitive than normal and uses a built-in speread. Use of this type of valve can present problems when wells must be lifted into long flow lines against surface chokes or under other conditions where the sensitivity of the valve will become a disadvantage. However, there are other instances in which a valve of this type is an advantage, e.g. in some rotary compressor system.

Intermittent lift may also be accomplished by the multi point injection of gas through more than one gas lift valve. The installation must be designed so the lowest gas lift valve open just as the bottom of the slug passes each valve. Normally, this type of list is used with fluid-operated valves which, by design, require a smaller port size to assure clouser of the valve.

III. Gas lift equipment3.1Surface Equipment

That was meant by equipment on the surface to be all equipment that was needed for the process of the injection of gas into the well that was located in the surface. These equipments covered:3.1.1Well Head and Gas Lift Christmas Tree

Well head not was the special implement in the operation of gas lift, but was used in the method of spitting on nature. This implement functioned as the place make dependent casing and tubing as well as was the place of the mount christmas tree. Whereas Christmas tree personally had a function of arranging the rate of the production and maintaining the pressure reservoir. Lift gas of X-mastree was used for wells of lift gas that in and the production of his daily was big enough.

3.1.2Compressor Station

Gas lift volume and pressure are two extremely important consideration which play a role in gas lift system design and these related to gas lift string design and compressor selection. Gas lift volume is the total gas lift requirement for the field or group of wells determind by adding individual well requirements. Gas lift pressure is a critical design parameter in gas lift system design. It has a major impact on completion design (number of valves), well performance (injection depth), system operating pressure (compressor discharge), and obiviously equipment specification all of which will have a significant impact on costs.

Compressor are selected on the basis of the necessary suction and discharge pressure, the required gas delivery rate, mechine duty, and cost. Discharge pressure should be selected 100-200 psi higher than the operating injection pressure used in the field to provide the necessary safety and to cover frictional pressure drops occurring inthe gas line of the distribution system. Compressor capacity is determind by the gas lift systems total daily gas injection reguirement.

3.1.3Distribution Station

In distributing injection gas from kompressor to the well was gotten by several method sorts, that is:a. The direct distribution injectionIn this system gas from kompressor was distributed directly to the production well. This system had the weakness that is when the requirement for gas to respectively the well not be the same so as the injection was inefficient.b. The distribution station with the induk pipeThis system was more economical because long the pipe could be shortened. But because of the well that one was connected with the other well then if one of the wells was done by the injection of gas, the other well could be affected.c. Station distribution with station distributionThis station was very effective so as often was used. Gas was sent from the central station kompressor to the distribution station afterwards was divided to wells by using the pipe.

3.1.4Gathering System

The Gathering system includes the separator, all pipes, storages, scrubber, and flowmeter. Gas that has been separator from separator passing the flowmeter to measure the flow rate of gas and then enters low pressure storage. Then, gas enters the scrubber to prevent any liquids that might be entrained in the gas before the gas is pressurized by compressor. A proprerly disign gathering system ensure that the compressor is supplied with a sufficient amount of gas. If all the wells are continuous flow, system desifn is simple since there is an uninterrupted flow of gas to the separator providing ideal operation conditions for the compressor station. Intermittent wells, however, do not provide a constant supply of gas into the gathering system because they produce in cycle. In order to provide a constant flow of gas at the proper pressure to the compressors suction, the gathering system must have the right amount of gas storage capacity. The gas storage capacity of gathering system is properly designed if the gas volume stored in the system covers the deliverability of the compressor puls the gas used for fuel and losses.

3.1.5Equipment Control

The efficient gas lifting of any well or group of well can only be ensured if gas lift is properil distributed to each well i.e gas at the proper pressure and the right volumetric rate is injectied to the wells.Those devices situated at the wellhead and taking care of this requirement constitute the surface gas injection control of the given well. Surface injection control, in general, invloves the control of the surface injection pressure (measured at the casing head) as well as of the surface gas injection rate, and for intermittent wells, the duration and frequencey of gas injection per day. The different requirements in timing, injection rates, and injection pressure of different wells (continuous and intetmittent) necessitate the use of different surface control device. Surface injection control on the other hand, can be manual semiautomatic, or fully automatic, but since all versions utilize the same general principles, manual control will be described in the following.

For any surface control to be efficient, continuous measurement of pressures and gas surface control to be efficient,continuous measurement of pressures and gas flow rate are required. This can be ensured by installing on the well head a two-pen pressure recorder simultaneously recording casing head and tubingpressures, and meter run to measure injection rates.

Installation of that devices, therefore, do not only ensure an efficient surface gas injecttion control (and, consequntly high system efficiency) but also form the bassis analyzing and troubleshooting og the well operation. Type of operation needs quite simple surface control, as follow:

a. Choke control

The simplest way to inject a constant gas rate into the well placed on continuous flow gas lift is to install a fixes / positive choke, or adjustable choke in the injection line at the well head. The choke is sized to pass the required injection gas rate at the designed casing head pressure by installing the proper size of fixed choke or setting the right size on the adjustable choke. Use of an adjustable choke or metering valve is recommended since adjustment of choke sizes is much easier and does not require the interruption of gas flow, which is the case when using a fixed choke.

b. Regulator control

When the pressure of the surface gas lift system, avaliable at the wellhead, fluctuates widely a fixed choke passes fluctuating gas rates into the annulus. Under such conditions, causing a drop in system efficiency or due to an insufficient gas injection rate, the well liquid rate will decrease. The effects of widely various line pressures are usually eliminated by a pressure regulator, which can be connected with the fixed or adjustable choke.

c. Intermitten control

Besides using choke and regulator, the intermittent gas lift uses the ijection control method called intermittent or a time cycle controller. The basicd feature of any intermitter control is that the cyclic operation is ensured by programming opening and closing of the surface injection line. Daily cycle number (as well as the duration of gas injection) can be set on the intermittenter, independently of any other conduction. The intermitter is an adjustable device controlling to operation (opening and closing) of a motor valve installed in the gas ijection line near the wellhead. Intermitter control can be used with any type of operating gas lift valve, and it is the only solution when a balanced valve gas lift is used. It is highly recommended for wells with extremely high or very low daily liquid production rates.

3.2Sub Surface Equipment

3.2.1Gas Lift Valve

Equipment under the surface for the operation of gas lift was valve (the valve) lift gas. Valve-valve this was installed in tubing and functioned to :

a. Vacated the well from the fluid workover or kill fluid to the fluid could reach the optimum point inside tubingb. Arranged the injection current of gas inside tubing, both in the process unloading (the evacuation of the well) and in the process of the appointment of the fluid.Was based on the pressure kind (the pressure casing or the pressure tubing) that was influential towards the operation valve, then valve lift gas could be divided into three groups, that is :

a. Casing Pressure Operating ValveValve this worked because of the pressure casing and usually was mentioned "pressure valve" valve this in the position was closed sensitive (50 100 %) towards the pressure casing and 100 % towards the pressure casing in the situation was open. This meant to be opened valve was needed by the rise in the pressure in casing and to close valve was needed by the existence of the decline in the pressure in casing.b. Fluid Operated ValveValve this worked because of the fluid pressure in tubing. In the position was closed valve this (50 100 %) was sensitive to the pressure in tubing and in the position was open 100 % was sensitive to the pressure in tubing. This was significant valve will be opened if the pressure in tubing rose and valve will close when the pressure in tubing descended.c. Pilot Casing Pressure OperatedPilot valve is required for intermittent gas lift system that needs the large size of port, because the volume of gas injection is more.

d. Thortling Pressure ValveValve this was mentioned with valve that proposional or valve the current continued. In the position was closed valve this be the same as pressure valve, but if in the position was open, valve this was sensitive to the pressure in tubing. This means that to be opened valve was needed by the pressure in casing and to close valve was needed by the decline in the pressure in tubing or casing.3.2.2Side Pocket Mandrel

The gas lift mandrel is a device installed in the tuning string of a gas lift well onto or which into a gas lift valve is fitted. The type of mandrel can be divided into two types:

a. Conventional Mandrel

In conventional gas lift mandrel, the gas lift valve is installed as the tubing is placed in the wel. Thus, to replace or he valve, the tubing string must be pulled out.

b. Side Pocket Mandrel

Several types of retrivable mandrels are avaliable, but the must common is the side pocket mandrel. In the side pocket mandrel, the gas lift valve is installed and removed by wireline.