Presentation on theme: "Well Design PE 413 Surface Equipments and Placement Techniques"— Presentation transcript:
1Well Design PE 413 Surface Equipments and Placement Techniques
2Surface Cementing Equiments Jet MixerDry cement must be mixed with the proper amount of water to ensure that slurry and set-cement properties are as designed.The jet mixer induces a partial vacuum at the venturi throat, drawing in the dry cement. High stream turbulence then provides thorough mixing
4Surface Cementing Equiments Batch MixerBatch mixing and/or blending is achieved through use of propellers, paddle mixers, pneumatic mixing, and rotation of the cement tank
5Surface Cementing Equiments Pump Skid TruckThe typical slurry-pumping unit is truck-mounted, and contains diesel engines and displacement tanks that are accurately graduated so that water or mud volumes can be controlled to place the slurry downhole properly.
7Downhole Cementing Equipments Basic EquipmentsA predetermined volume of slurry is pumped into the casing between two wiper plugs.The bottom plug ruptures when it seatsThe top plug is displaced with mud or completion fluid.Flow stops and pressure builds when the top plug lands.Check valves in the float shoe to prevent backflow of the heavier column of slurry
8Downhole Cementing Equipments Guide/Float Shoes and Collars In most cases, except in certain shallow wells, a round-nosed shoe is run on the bottom joint to guide the casing past borehole irregularities encountered while the string is run.
9Downhole Cementing Equipments Guide/Float Shoes and Collars Float equipment reduces derrick stress by increased casing buoyancy. Float equipment consists of casing shoes and collars which contain check valves to prevent wellbore fluids from entering. As the casing is lowered, the hook load is reduced by the weight of fluid displaced. The casing is filled from the surface to prevent casing collapse.Float collar
10Downhole Cementing Equipments Wiper PlugsWiper plugs are used to separate cement from preceding or following fluids. The bottom plug removes mud from the wall of the casing, and prevents this mud from accumulating beneath the top plug.
12Downhole Cementing Equipments Casing CentralizersCasing centralizers are used to:Improve displacement efficiencyPrevent differential pressure stickingKeep casing out of key seats
13Downhole Cementing Equipments Wipers and ScratchersWipers and scratchers are used primarily to remove borehole mud cake. They also aid in breaking up gelled mud. Both rotating and reciprocating styles are available.
14Primary Cementing Techniques ConductorThe conductor is usually the first and shortest casing string. Its purpose is to protect shallow sands from being contaminated by drilling fluids, and help prevent wash-outs which can easily occur near the surface because of loose, unconsolidated formations. The depth is normally less than 300 ft. It can be used for the attachment of a blowout preventer.
15Primary Cementing Techniques IntroductionThe objective of a primary cement job is to place the cement slurry in the annulus behind the casing. In most cases this can be done in a single operation, by pumping cement down the casing, through the casing shoe and up into the annulus. However, in longer casing strings and in particular where the formations are weak and may not be able to support the hydrostatic pressure generated by a very long colom of cement slurry, the cement job may be carried out in two stages.
16Primary Cementing Techniques IntroductionThe first stage is completed in the manner described above, with the exception that the cement slurry does not fill the entire annulus, but reaches only a pre- determined height above the shoe. The second stage is carried out by including a special tool in the casing string which can be opened, allowing cement to be pumped from the casing and into the annulus. This tool is called a multi stage cementing tool and is placed in the casing string at the point at which the bottom of the second stage is required.
17Primary Cementing Techniques ConductorRecommended cements for use with conductor casing are:Accelerated neatReady-mix concreteThixotropic cementLCM additivesWhen cementing down casing, plugs may not be used; cement is simply placedThe cement must have a compressive strength high enough to support the wellhead load; therefore, high-compressive-strength cements are best.
18Primary Cementing Techniques Surface CasingSurface casing is usually the second string of pipe set in the well.Shallow surface casing is cemented in the same manner as conductor casing.For deeper strings of surface casing, a lightweight lead cement is used, followed by heavier-weight completion cement to strengthen the bottom of the surface casing around the shoe. This creates a strong seal with the pipe and formation for solid support of the casing.
19Primary Cementing Techniques Surface CasingRecommended cement types include:Accelerated cementsLCM additivesHigh-strength cements, which are often used on deep-well surface casing to support future stringsThe following is a brief summary of surface-casing cementing practices:Both bottom and top plugs should be used to prevent mud contamination.Centralizers should be used.
20Primary Cementing Techniques Intermediate CasingThe intermediate casing is the first string of pipe set after the surface casing. Intermediate casing strings extend from the surface to a formation able to hold the mud weights expected at greater depth.Unlike the conductor and surface casings, additives such as friction reducers, fluid-loss additives, and retarders are required for intermediate slurries. Where the annulus is small, friction reducers lower pump pressures and reduce the chance of losing fluids in a lost-circulation zone.
21Primary Cementing Techniques Intermediate CasingThe following is a brief summary of intermediate-casing cementing practices:Both bottom and top plugs should be used to minimize contamination of the cement.Scratchers, centralizers, and flushes can be important in the successful completion of an intermediate-casing cementing job.This casing string can be cemented in a single-stage primary cement job, but a multistage job is often performed because such a tall annular column of cement slurry would exert a hydrostatic pressure greater than the formation pressure.
22Primary Cementing Techniques Production CasingThe production casing is the last full string of pipe set in the well, and extends to the surface.The production casing is normally run and cemented through a zone to be produced, and then perforated to allow communication with the formation. Sometimes it is set just above the zone, and an openhohle completion is performed. The production casing is normally the last casing set in the well. It may be subjected to maximum well pressures and temperatures, and must be designed to withstand such conditions.
23Primary Cementing Techniques Production CasingRecommended types of cement areFiller cements with high-strength tail-inLow-water-ratio cements (for all potential pay zones)Densified cements (for high competency and pressure control)Fluid-loss control additives
24Primary Cementing Techniques Production CasingRecommended types of cement areFiller cements with high-strength tail-inLow-water-ratio cements (for all potential pay zones)Densified cements (for high competency and pressure control)Fluid-loss control additives
25Single Stage Cementing Operation Cementing TechniquesSingle Stage Cementing OperationThe single stage primary cementing operation is the most common type of cementing operation that is conducted when drilling a well.In the case of the single stage operation, the casing with all of the required cementing accessories such as the float collar, centralisers etc. is run in the hole until the shoe is just a few feet off the bottom of the hole and the casing head is connected to the top of the casing. It is essential that the cement plugs are correctly placed in the cement head. The casing is then circulated clean before the cementing operation begins
27Single Stage Cementing Operation Cementing TechniquesSingle Stage Cementing OperationThe first cement plug (wiper plug) is pumped down ahead of the cement to wipe the inside of the casing clean.The spacer is then pumped into the casing. The spacer is followed by the cement slurry.This is followed by the second plug (shutoff plug). When the wiper plug reaches the float collar its rubber diaphragm is ruptured, allowing the cement slurry to flow through the plug, around the shoe, and up into the annulus. At this stage the spacer is providing a barrier to mixing of the cement and mud.When the solid, shut-off plug reaches the float collar it lands on the wiper plug and stops the displacement process..
28Multi-Stage Cementing Operation Cementing TechniquesMulti-Stage Cementing OperationWhen a long intermediate string of casing is to be cemented it is sometimes necessary to split the cement sheath in the annulus into two, with one sheath extending from the casing shoe to some point above potentially troublesome formations at the bottom of the hole, and the second sheath covering shallower troublesome formations. The placement of these cement sheaths is known as a multi-stage cementing operation
29Multi-Stage Cementing Operation Cementing TechniquesMulti-Stage Cementing OperationThe reasons for using a multi-stage operation are to reduce:Long pumping timesHigh pump pressuresExcessive hydrostatic pressure on weak formations due to the relatively high density of cement slurries.Cost due to the long distance between pay zones (reduce the high quality volume of cement required for the production zones)
31Multi-Stage Cementing Operation Cementing TechniquesMulti-Stage Cementing OperationFirst stage:The procedure for the first stage of the operation is similar to the single stage operation, except that a wiper plug is not used and only a liquid spacer is pumped ahead of the cement slurry. The conventional shut-off plug is replaced by a plug with flexible blades. This type of shut-off plug is used because it has to pass through the stage cementing collar which will be discussed below.
32Multi-Stage Cementing Operation Cementing TechniquesMulti-Stage Cementing OperationSecond stageThe second stage of the operation involves the use of a special tool known as a stage collar, which is made up into the casing string at a pre-determined position. The ports in the stage collar are initially sealed off by the inner sleeve. This sleeve is held in place by retaining pins. After the first stage is complete a special freefall plug is released form surface which lands in the inner sleeve of the stage collar. When a pressure of psi is applied to the casing above the freefall plug, the retaining pins on the inner sleeve are sheared and the sleeve moves down, uncovering the ports in the outer mandrel. Circulation is established through the stage collar before the second stage slurry is pumped.
33Multi-Stage Cementing Operation Cementing TechniquesMulti-Stage Cementing OperationStage collar installed in the casing for multi-stage cementing operation
34Cementing Techniques Liner Cementing Liners are run on drillpipe and therefore the conventional cementing techniques cannot be used for cementing a liner. Special equipment must be used for cementing these liners.As with a full string of casing the liner has a float collar and shoe installed. In addition there is a landing collar, positioned about two joints above the float collar. A wiper plug is held on the end of the tailpipe of the running string by shear pins.The liner is run on drillpipe and the hanger is set at the correct point inside the previous casing string. Before the cementing operation begins the liner setting tool is backed off to ensure that it can be recovered at the end of the cement job.
36Cementing Techniques Liner Cementing The cementing procedure is as follows:Pump spacer ahead of cement slurryPump slurryRelease pump down plugDisplace cement down the running string and out of the liner into the annulusContinue pumping until the pump down plug lands on the wiper plug.
37Cementing Techniques Liner Cementing Apply pressure to the pump down plug and shear out the pins on the wiper plug. This releases the wiper plugBoth plugs move down the liner until they latch onto landing collarPump the plugs with 1000 psi pressureBleed off pressure and check for back flow
39Cementing Techniques Squeeze Cementing Squeeze cementing is the process by which hydraulic pressure is used to force cement slurry through holes in the casing and into the annulus and/or the formation. Squeeze cement jobs are often used to carry out remedial operations during a workover on the well. The main applications of squeeze cementing are:To seal off gas or water producing zones, and thus maximise oil production from the completion intervalTo repair casing failures by squeezing cement through leaking joints or corrosion hole
40Cementing Techniques Squeeze Cementing To seal off lost circulation zonesTo carry out remedial work on a poor primary cement job (to fill up the annulus)To prevent vertical reservoir fluid migration into producing zonesTo prevent fluids escaping from abandoned zones.
42Evaluation of Cement Jobs A primary cement job can be considered a failure if the cement does not isolate undesirable zones. This will occur if:The cement does not fill the annulus to the required height between the casing and the borehole.The cement does not provide a good seal between the casing and borehole and fluids leak through the cement sheath to surface.The cement does not provide a good seal at the casing shoe and a poor leak off test is achieved
43Evaluation of Cement Jobs A primary cement job can be considered a failure if the cement does not isolate undesirable zones. This will occur if:The cement does not fill the annulus to the required height between the casing and the borehole.The cement does not provide a good seal between the casing and borehole and fluids leak through the cement sheath to surface.The cement does not provide a good seal at the casing shoe and a poor leak off test is achievedWhen any such failures occur some remedial work must be carried out. A number of methods can be used to assess the effectiveness of the cement job. These include:
44Evaluation of Cement Jobs Temperature Survey(a) Temperature surveys:This involves running a thermometer inside the casing just after the cement job. The thermometer responds to the heat generated by the cement hydration, and so can be used to detect the top of the cement column in the annulus.
45Evaluation of Cement Jobs Radioactive Surveys(b) Radioactive surveysRadioactive tracers can be added to the cement slurry before it is pumped (Carnolite is commonly used). A logging tool is then run when the cement job is complete. This tool detects the top of the cement in the annulus, by identifying where the radioactivity decreases to the background natural radioactivity of the formation.
46Evaluation of Cement Jobs Cement Bond Logs(a) Cement bond logs (CBL)The cement bond logging tools have become the standard method of evaluating cement jobs since they not only detect the top of cement, but also indicate how good the cement bond is.The CBL tool is basically a sonic tool which is run on wireline. The distance between transmitter and receiver is about 3 ft.Since the speed of sound is greater in casing than in the formation or mud the first signals which are received at the receiver are those which travelled through the casing. If the amplitude (E1) is large (strong signal) this indicates that the pipe is free (poor bond).