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Cementation jobs.

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Cementation jobs

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Cementation jobs.

  1. 1. CEMENTATION JOBS  ASSIGNMENT SABA SAIF 01-161102-065 BS-GEOPHYSICS-7
  2. 2. Table of Contents INTRODUCTION ................................................................................................... 2 OBJECTIVE: .......................................................................................................... 2 CEMENTING: ........................................................................................................ 3 HOW DOES CEMENTING WORK? .................................................................... 4 PREPARING THE CEMENT: .............................................................................................................. 5 CEMENTING THE WELL: .................................................................................................................. 6 PRIMARY CEMENTING: ..................................................................................... 7 PRIMARY CEMENTING TECHNIQUES: .............................................................................................. 8 API & ISO CLASSIFICATION SYSTEM: ........................................................... 8 SINGLE STAGE CEMENTING: ........................................................................... 8 ZONAL ISOLATION: ............................................................................................ 9 STAGE CEMENTING: .......................................................................................... 9 CEMENT ADDITIVES: ....................................................................................... 11 ACCELERATORS ............................................................................................................................ 11 RETARDERS: ................................................................................................................................. 12 FLUID LOSS ADDITIVES:................................................................................................................. 12 DISPERSANTS: .............................................................................................................................. 12 EXTENDERS: ................................................................................................................................. 13 HEAVY WEIGHT ADDITIVES: .......................................................................................................... 13 CONCLUSIONS: .................................................................................................. 13 REFERENCES:..................................................................................................... 14 1
  3. 3. CEMENTATION JOBS INTRODUCTION: Cementing is performed by circulating a cement slurry through the inside of the casing and out into the annulus through the casing shoe at the bottom of the casing string. In order to precisely place the cement slurry at a required interval on the outside of the casing, a plug is pumped with a displacement fluid behind the cement slurry column, which "bumps" in the casing shoe and prevents further flow of fluid through the shoe. This bump can be seen at surface as a pressure spike at the cement pump. To prevent the cement from flowing back into the inside of the casing, a float collar above the casing shoe acts as a check valve and prevents fluid from flowing up through the shoe from the annulus. Cement fills and seals the annulus between the casing string and the drilled hole. It has three general purposes:  Zone isolation and segregation,  Corrosion control, and  Formation stability and pipe strength improvement. Cement forms an extremely nearly impermeable seal from slurry. The properties of the slurry and its behavior depend components and the additives cement slurry. strong, a thin cement on the in the Figure: 1 Cementing Plugs OBJECTIVE: Cementing is one of the most critical steps in well completion. Well cementing technology is the application of many scientific and engineering disciplines. The objective of my assignment is to understand the concept of cementation and to learn about the various cementing techniques being used by the E & P companies. 2
  4. 4. CEMENTING: After the casing string is run, the next task is cementing the casing in place. An oil-well cementing service company is usually called in for this job although, as when casing is run, the rig crew is available to lend assistance. Cementing service companies stock various types of cement and have special transport equipment to handle this material in bulk. Bulk-cement storage and handling equipment is moved out to the rig, making it possible to mix large quantities of cement at the site. The cementing crew mixes the dry cement Figure: 2 Well Cementing with water, using a device called a jetmixing hopper. The dry cement is gradually added to the hopper, and a jet of water thoroughly mixes with the cement to make a slurry (very thin water cement). Special pumps pick up the cement slurry and send it up to a valve called a cementing head (also called a plug container) mounted on the topmost joint of casing that is hanging in the mast or derrick a little above the rig floor. Just before the cement slurry arrives, a rubber plug (called the bottom plug) is released from the cementing head and precedes the slurry down the inside of the casing. The bottom plug stops or "seats" in the float collar, but continued pressure from the cement pumps open a passageway through the bottom plug. Thus, the cement slurry passes through the bottom plug and continues on down the casing. The slurry then flows out through the opening in the guide shoe and starts up the annular space between the outside of the casing and wall of the hole. Pumping continues and the cement slurry fills the annular space. A top plug, which is similar to the bottom plug except that it is solid, is released as the last of the cement slurry enters the casing. The top plug follows the remaining slurry down the casing as a displacement fluid (usually salt water or drilling mud) is pumped in behind the top plug. Meanwhile, most of the cement slurry flows out of the casing and into the annular space. By the time the top plug seats on or "bumps" the bottom plug in the float collar, which signals the cementing pump operator to shut down the pumps, the cement is only in the casing below the Figure: 3 Cementing Plugs 3
  5. 5. float collar and in the annular space. Most of the casing is full of displacement fluid. After the cement is run, a waiting time is allotted to allow the slurry to harden. This period of time is referred to as waiting on cement or simply WOC. After the cement hardens, tests may be run to ensure a good cement job, for cement is very important. Cement supports the casing, so the cement should completely surround the casing; this is where centralizers on the casing help. If the casing is centered in the hole, a cement sheath should completely envelop the casing. Also, cement seals off formations to prevent fluids from one formation migrating up or down the hole and polluting the fluids in another formation. For example, cement can protect a freshwater formation (that perhaps a nearby town is using as its drinking water supply) from saltwater contamination. Further, cement protects the casing from the corrosive effects that formation fluids (as salt water) may have on it. HOW DOES CEMENTING WORK? Part of the process of preparing a well for further drilling, production or abandonment, cementing a well is the procedure of developing and pumping cement into place in a wellbore. Figure: 4 Onshore Cementing Operations and Equipment Used for a number of different reasons, cementing protects and seals the wellbore. Most commonly, cementing is used to permanently shut off water penetration into the well. Part of the completion process of a prospective production well, cementing can be used to seal the annulus after a casing string has been run in a wellbore. 4
  6. 6. Additionally, cementing is used to seal a lost circulation zone, or an area where there is a reduction or absence of flow within the well. In directional drilling, cementing is used to plug an existing well, in order to run a directional well from that point. Also, cementing is used to plug a well to abandon it. Cementing is performed when the cement slurry is deployed into the well via pumps, displacing the drilling fluids still located within the well, and replacing them with cement. The cement slurry flows to the bottom of the wellbore through the casing, which will eventually be the pipe through which the hydrocarbons flow to the surface. From there it fills in the space between the casing and the actual wellbore, and hardens. This creates a seal so that outside materials cannot enter the well flow, as well as permanently positions the casing in place. PREPARING THE CEMENT: In preparing a well for cementing, it is important to establish the amount of cement required for the job. Measuring the diameter of the borehole along its depth, using a caliper log, does this. Utilizing both mechanical and sonic means, multifinger caliper logs measure the diameter of the well at numerous locations simultaneously in order to accommodate for irregularities in the wellbore diameter and determine the volume of the open hole. Additionally, the required physical properties of the cement are essential before commencing cementing operations. The proper set cement is also determined, including the density and viscosity of the material, before actually pumping the cement into the hole. Special mixers, including hydraulic jet mixers, re-circulating mixers or batch mixers, are used to combine dry cement with water to create the wet cement, also known as slurry. The cement used in the well cementing process is Portland cement, and it is calibrated with additives to form one of eight different API classes of cement. Each is employed for various situations. Additives can include accelerators, which shorten the setting time required for the cement, as well as retarders, which do the opposite and make the cement setting time longer. In order to decrease or increase the density of the cement, lightweight and heavyweight additives are added. Additives can be added to transform the compressive Figure: 5 Cementing Techniques strength of the cement, as well as flow properties and dehydration rates. Extenders can be used to expand the cement in an effort to reduce the cost of cementing, and antifoam additives can be added to prevent foaming within the well. In order to plug lost circulation zones, bridging materials are added, as well. 5
  7. 7. CEMENTING THE WELL: After casing, or steel pipe, is run into the well, an L-shaped cementing head is fixed to the top of the wellhead to receive the slurry from the pumps. Two wiper plugs, or cementing plugs, that sweep the inside of the casing and prevent mixing: the bottom plug and the top plug. Keeping the drilling fluids from mixing with the cement slurry, the bottom plug is introduced into the well, and cement slurry is pumped into the well behind it. The bottom plug is then caught just above the bottom of the wellbore by the float collar, which functions as a one-way valve allowing the cement slurry to enter the well. Then the pressure on the cement being pumped into the well is increased until a diaphragm is broken within the bottom plug, permitting the slurry to flow through it and up the outside of the casing string. Figure: 6 Bottom and Top Plugs After the proper volume of cement is pumped into the well, a top plug is pumped into the casing pushing the remaining slurry through the bottom plug. Once the top plug reaches the bottom plug, the pumps are turned off, and the cement is allowed to set. The amount of time it takes cement to harden is called thickening time or pumpability time. For setting wells at deep depths, under high temperature or pressure, as well as in corrosive environments, special cements can be employed. 6
  8. 8. PRIMARY CEMENTING: Primary cementing is the first cementing operation performed after the casing has been run in the hole. This is accomplished by pumping cement slurry down inside casing and displaced it out into the annular space between the casing and the borehole. The cement is then allowed to set before drilling is resumed or the well is completed. The main functions of primary cementation are:  To bond and support the casing.  To isolate the drinking water zone  To keep the well safe for drilling oil & gas zones  Protecting the casing from corrosion.  To restrict fluid movements between formations.  Protecting the casing from shock loads during drilling deeper.  Sealing-off problematic zones.  Last and the most important is Complete and durable zonal isolation for oil and gas production. Figure: 7 Primary Cementation 7
  9. 9. PRIMARY CEMENTING TECHNIQUES: Numbers of techniques are used for primary cementing. Following are the three most commonly used techniques:  Single stage cementation  Multi stage cementation  Liner cementation API & ISO CLASSIFICATION SYSTEM: The requirements for well cements (WC) are more rigorous than construction cements (CC) .WC must perform over a wide range of temp and pressures and are exposed to subterranean conditions that CC do not encounter. Oil well cements are compositions variable concentrations of C3S2, C2S, C3A and C4AF. There are 8 classes of API-ISO Portland cement designated A-H CLASS-A-ordinary Portland Cement. CLASS-B-medium (MSR) to high (HSR) sulphate resistance Portland Cement. CLASS-C- Portland Cement wit high early strength in O, MSR & HSR property. CLASS-D/E/F-known as retarded cements by reducing fast hydrated phases (C3S and C3A) with increase in particle size-rarely used. CLASS-G/H- for use as basic Oil well Cement developed in response improved technology in slurry acc /returd by chem means. SINGLE STAGE CEMENTING: Single stage cementing is most commonly used for primary cementing, where there is no complication or lost circulation and where cement rise in the annulus can be attained in one stage. The single stage primary cementing is normally accomplished by pumping one batch of cement down the casing between two rubber plugs. The bottom plug is placed in the casing, followed by cement slurry. When the batch of cement has been pumped into the casing, a top plug is released the top plug is pumped down until it lands on the top of float collar. Thus completing the cement job. 8
  10. 10. ZONAL ISOLATION:  Complete and durable zonal isolation is the foremost goal of the cement job  During the life of a producing oil or gas well, quality of the cement job has a direct impact on the economic longevity of the well.  From starting of production to abandon the well, slurry design and placement technique will effect the well productivity, both physically & economically  If allowed to set undisturbed Portland cement system with 16-ppg density usually exhibit very matrix permeability.  During the production phase cement is subject to various severe conditions that effect the longevity of the matrix permeability-termed called cracking /Debonding is caused by thermal & pressure fluctuations- subsequently cement integrity is lost resulting secondary cement job for isolation repair. Figure: 8 Zonal Isolation STAGE CEMENTING: Stage cementing consist of placement of cement slurry first around the lower portion of a casing string using conventional primary cementing technique and then 9
  11. 11. cementing the successive upper stages through ports in the stage collar. Most stage cementing is in two stages, although additional stages are possible. Cementation is required to be done in two or more stages because of the following reasons:  Down hole formation unable to support hydrostatic pressure exerted by a long column of cement.  Cement not required between widely separated intervals.  When the volumes of cement cannot be handled with the limited cementing equipment.  To cement deep wells with high bottom hole temp, where cement slurries of different thickening time for different stages can be used.  For cementing of high-pressure gas zones and water producing horizons. Figure: 9 Stage Cementing 10
  12. 12. Figure: 10 Showing two-stage cementing of a casing string The sequence of operation for two-stage cementation is shown in the figure above. After first stage cementing has been performed in a conventional manner, an opening bomb is dropped to land in the lower seat of the stage collar. By pressuring up (1200 to 1500 psi). The retaining pins are sheared, the sleeve moves down and the ports are opened. The well is then circulated to clear the ports and condition the mud. For cementing the second stage, spacers and slurries are mixed as in any single stage job. The closing plug is dropped after the slurry pumping and is displaced till it seat on the upper sleeve in stage collar. After the plug has seated, a minimum of 1200-1500 psi above the second stage displacing pressure is required to close the collar ports. And thus completing the two stage cementing job. CEMENT ADDITIVES: ACCELERATORS  Accelerating a slurry means shortening the Thickening Time or reducing the time required to gain Compressive Strength or both.  In general an in-organic material will act as an accelerator. 11
  13. 13. Examples: Calcium Chloride, Sodium Chloride, Sea water, potassium Chloride, Sodium Silicate, Gypsum etc. RETARDERS:  A material that allows sufficient time for slurry placement by delaying the set of the cement is called a retarder.  In general, any organic material will retard the setting time of cement slurry. Examples: Calcium Lignosulfonates, Calcium sodium Lignosulfonates, Organic acids etc. FLUID LOSS ADDITIVES:  Reduces the rate at which filtrate is lost to a permeable formation.  Works by viscosifying the mix water or by plugging the pore throat in the filtrate cake with long polymer chains. Examples:  Organic polymers (Cellulose)  Organic polymers (Dispersants)  CMHEC. DISPERSANTS:  Also called friction reducers, these materials make cement slurries easier to mix and pump.  Act on surface charges of the cement grains.  Secondary retardation  Enhances fluid loss control. Examples:  Polynapthalene sulfonate (PNS),  Non-lignosulfonate. 12
  14. 14. EXTENDERS:  Additives that reduce slurry density and increase slurry yield are called extenders.  Cement may be lightened to protect the weak formations or slurry yield may be increased to reduce the cost. Examples: Water, Bentonite, Pozzolan, Gilsonite etc. HEAVY WEIGHT ADDITIVES: These are required to counter high formation pressures. Common high-density materials are: a) Hematite b) Ilmenite c) Barytes CONCLUSIONS: Cement forms an extremely strong, nearly impermeable seal from thin slurry. The property of the cement slurry and its behavior depends on the components and the additives in the cement slurry. Casing has been cemented in wells for more than 100 years. Cementing best practices have been known for more than 60 years. Best practices have to be used by everyone to protect the environment and community and to obtain maximum value from your. 13
  15. 15. REFERENCES:  Smith, D. K.: Cementing, SPE Monograph, 1987  Davies, D. R., Hartog, J. J., Cobbett, J. S.: "Foamed Cement- A Cement with Many Applications," SPE 9598, Middle East Oil Tech, Conf. Manama, Bahrain, March 9-12, 1981.  http://www.usoilandgas.net/cementing.htm  http://gekengineering.com/Downloads/Free_Downloads/Cementing_ Chapter_3.pdf  http://en.wikipedia.org/wiki/Cementation_(geology)  http://www.rigzone.com/training/insight.asp?insight_id=317&c_id=1  http://petrofed.winwinhosting.net/upload/30May-01June11/10.pdf 14

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