introduction to coiled tubing unit final touch

Introduction of Coiled Tubing Unit & Its Applications

Introduction to Coiled Tubing Unit & Its Applications

While the hunt for the oil and its economical availability goes on, the oil industries are indulged in an everlasting quest for the more efficient and cost effective works for the exploration and production jobs to acquire the hydrocarbons with the least expenses. The industry has under gone many development and revolution that has given this business a new height and fame in every possible way including the usage of fossil fuel and natural gas in newly arrived industries and for the growth of recently introduced technologies that has not only eased the capabilities of different working sectors but also helped many underdeveloped or even undeveloped countries to make their statement on an international level.

Apart from many revolutions in the world’s most renowned work field, the coiled tubing has been making its name more and more far and wide ever since it was first used in the late 1960s and not only it has groomed itself for its working and design but also this technology has added many other extra and overtime jobs under its name and still it is making its name as a cheap solution for many drilling and production oriented problems and looks a healthy competitor to snatch the job of conventional works with its modern working and equipment’s. Not only this unit has under gone many developments but also has many of the conventional and unconventional workings that have been performed by it. Coiled tubing (CT) has become an important tool regarding to the different well operations due to its ever increasing usage in many well operations, reduction in the cost and improving reliability, the technology got higher acceptance all around.

A Brief History

Early coiled tubing (CT) technology can be traced to project PLUTO (Pipe Lines under the Ocean) which was a top-secret effort to install pipelines across the English Channel during World War II.

In June 1944, Allied engineers deployed several pipelines across the English Channel to provide fuel for forces. The lines had 40-ft [12-m] joints of 3-in. inside diameter (ID) and 0.212-in. thick steel pipe welded together to form 4,000-ft [1,220-m] sections.

End-to-end welding technique was used to join these long pipes and was spooled onto 40-ft diameter floating drums that were towed behind cable-laying vessels. 23 pipelines ranging in

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length from 30 to 70 miles [48 to 113 km] were successfully deployed that made the stage set for the usage of coiled tubing in the near future on oil and gas wells.

Modern CT injector head’s elements were made because by an innovative idea taken from Bowen Tools Co. when they deployed radio antennae on to the ocean surface using submarines submerged as deep as 600 ft. [183 m] in the early 1960s. The antennae were stored on a spool beneath the injector for easy extension and retrieval.

Afterwards, the first CT unit was built by Bowen Tools and the California Oil Company in 1962, that included an injector rated for surface loads up to 30,000 lbm [13,608 kg] that ran a continuous string of 1.315-in. outside diameter (OD). The unit’s 9-ft [2.7-m] diameter storage reel included a hub with a rotating fluid swivel to allow continuous pumping down the coiled tubing and it was used for sand wash out, sub-surface valve retrieval and for lifting of the fluids from the well.

But due to the low yield-strength steels with end-to-end or butt welds, the tubing could not withstand repeated bending cycles and high tensile loads. As a result, the weld failed and the equipment broken down that caused operators to lose confidence in this technology.

Bowen Tools, Brown Oil Tools, Uni-Flex, Inc., Hydra Rig Inc. and Otis Engineering, continued making improvements in CT equipment and injector heads in the 1970s.

In 1980, Southwestern Pipe introduced 70,000-psi (70-kpsi) [483-MPa] high-strength, low-alloy (HSLA) steel coiled tubing with 11⁄2-in. and 13⁄4-in. OD

In 1983, Quality Tubing Inc. began using 3,000-ft [914-m] sheets of Japanese steel that reduced the joints up to 50% and also bias welding was introduced to take over the butt welds. Bias welding involves cutting flat steel strips diagonally to enhance tubing life by spreading the heat-affected weld zone spirally around the tube.

In 1990, the first string of 2-in. coiled tubing was milled for a permanent well completion.

Today, coiled tubing is manufactured from steel with high yield strengths of 90, 100, 110 and 120 kpsi [620, 689, 758 and 827 MPa] with corrosion resistant alloys.

Higher strength steel, larger diameters and the need to reduce costs were key factors behind the CT revolution.

History of Coiled Tubing Drilling

Coiled Tubing Drilling has a history dating back almost 100 years but the first official coiled tubing drilling rigs were developed in 1964 by the Cullen Research Institute. The first commercial system was developed in 1976 by the Canadian company, Flex tube. CTD as we know it today really started to develop in the early 1990’s and in the third quarter of 1991 the

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first serious attempt was made to drill horizontally with coil. This was done by Oryx Energy in combination with a CT company and 3 directional service companies. Throughout the 1990’s CTD became commonplace in Canada and has since been used around the world with particular growth in the United States, Alaska and Saudi Arabia.

Core Components of Coiled Tubing Unit

The core components of the coiled tubing unit are as follow: Injector head Coiled tubing reel Power Pack Control Cabin Pressure Control Equipment

Now by the assistance of the highly qualified and skilled professional’s job on the well will have been accomplished by the integration of these components successfully.

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Injector Head

Injector heads components are driven by the two sets of uninterrupted chain attached in series of short gripper block and dependent on the size of tubing being used for performing the job. The load of the coiled tubing reel is detained by the friction of this gripper block. These endless chain are moved by the help of hydraulic motors which allowing the run in or out of the wellbore. Injector head is large working equipment and also consist of the very basic components which include the following:

Drive chains Gooseneck or guide arch Weight indicator Chain tensioners Hydraulic motors

Drive ChainThe chains consist of links, gripper blocks and roller bearings (conventional chain).

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Control CabinCoiled tubing reelInjector head

Figure 1.1: Coiled Tubing Unit of OGDCL


Gooseneck or Guide Arch

The gooseneck, or guide arch, work as a guide for the tubing, bending it through the angle as the tubing leaves the reel, to the vertical position as it enters the top of the injector-head chains. Profiled rollers support the tubing as it is bent over the gooseneck arc.

Weight Indicator

The weight indicator stipulates the tension applied on the tubing hanging from the injector head chains.

Chain Tensioners

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Figure 1.33: Gooseneck or Guide Arch


As the coiled tubing is run deeper into a well, the injector chain experienced increasing load on it, therefore requiring an enlarged force to the gripper blocks to sustain enough traction. This is accomplished by consuming the applied hydraulic pressure in the inside chain tensioner system.

Hydraulic MotorHydraulic motor deliver the power to move the tubing in and out of the well during performing the job.

Coiled Tubing ReelThe tubing is mounted on the coiled tubing reel and the transport, storage of tubing is take place by this reel and the safe and smooth transport of the tubing from the reel to the injector head is take place by the aid of the CT reel.Parts of the CT reel are as follow:

Reel drum Reel drive system Levelwind assembly Reel swivel and manifold

Reel DrumThousands feet of reel is wounded on the reel drum. It basically carries the entire reel at the required location.The capacity of any reel of the required size of tubing is calculated by the given formulae:L= (A+C) (A) (B) (K)WhereL = tubing capacity (ft),A = tubing stack height (in.),B = width between flanges (in.),C = reel drum core diameter (in.), andK = K value for different tubing sizes.

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Reel Drum

Figure1.31: Coiled Tubing Unit of OGDCL


Reel Drive System and Level-Wind

In usual practice reel use a chain drive connection of the hydraulic motor straddling on the support frame to a big sprocket on the side of the drum. The motor use to drive the reel also helpful in providing dynamic braking during slack off to sustain tension on the CT between the drum and guide arch. When it is programmed to make CT static the reel brake locks the reel in the very exact position, but should be avoid during use in dynamic braking. During pull out of hole the reel drive motor have to apply more torque to the drum than necessary to pace the injector head pull out speed. To keep the CT reel stretched and stiffens the wraps on the drum this all provided by the superfluous of torque.

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Figure1.54: Fully-loaded CT Reel


Power Pack and Control Cabin

For efficiently working of the coiled tubing unit the uninterrupted supply of power is provided by the power pack which provide the hydraulic energy for controlling all the functions of the coiled tubing unit. Mostly the power pack is fuelled by diesel engine.

Main components of power pack are as below: Engine Pumps Pressure control valves Hydraulic reserves Filter and strainers Heat exchangers Hydraulic fluid

Engine

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Figure1.65: Typical CT Reel Level-wind and Mechanical Depth Counter


The engine is the main power supply unit for the accomplishment of all jobs. It is either truck mounted engine or separate engine may be used for power supply purpose.

Hydraulic PumpThe hydraulic pumps are driven by the engine. Engine draws oil from the reservoir and powers it to flow to the several components of the CTU. Pumps in power packs can contrast because of the demand of the customer choice. Two types of positive displacement hydraulic pumps are used in a CTU power pack:

Vane pumps Piston pumps.

Vane pumpsVane pumps are the old pump of CTU power pack. Vane pumps are inexpensive than piston pumps and very reliable. They are fewer complexes to hydraulic oil contamination and run at a lesser temperature.

Piston pumpPiston pumps are newer models of hydraulic pumps for power pack and more efficient. These pumps can generate higher pulling forces. A Denison P16 is an example of a piston pump used in CTU power packs. Piston pumps are, more profound to hydraulic oil contamination and more expensive than vane pumps.

Pressure Control Valves

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Figure1.76: Vane pumps

Figure1.87: Piston Pump


These valves have installed to maintain the pressure in optimum working limits during performing of any job. It also has a relive valve for regulating the pressure. Its purpose is to bounds the pressure in a system to a fixed extreme by diverting some or all of the flow to the hydraulic fluid reservoir.

Now for the running of the CT operation in a proficient manner a control cabin is required which contain all the necessary control instruments which guide the angle of gooseneck, the speed of ruin in or out of the CT reel in the wellbore, the flow rate of the injected fluid through the reel, control of the BOP’s, and so much other minute operations related to the whole coiled tubing working operations. The control cabin is fixed on the separate skid or may be on the truck permanently attached.

Pressure Control EquipmentThe last and the most deciding component of the coiled tubing unit is the pressure control equipment, because for safe, reliable and efficient working of the job the influx of unwanted fluid during the job is only managed and controlled by the use of BOP’s. The basic components associated with the pressure control equipment are:StripperQuad and Combi BOPsQuad and Combi BOPs comprise the following components:

Blind rams Shear rams Pipe rams Equalizing valves Top and bottom connection Side port and pressure port

StripperThe stripper (stuffing box) between the BOP and the injector head delivers the major effective seal between pressurized wellbore fluids and the surface environment, during run in or out of hole with a surface pressure. To provide the necessary stiffness or the seal is accomplished by revitalizing the stripper packer which forcefully pushes the inserts to seal against the tubing. To achieve this strengthened force either applied hydraulically and is operated from the operator control cab.

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Quad and Combi BOPsMostly the BOPs are using with the CT assembly having working pressure of 10000-psi and are also H2S resistant. These are operated from the control cabin mostly hydraulically using the BOP hydraulic circuit and accumulator. For the operation of the BOP a reserve of the hydraulically energy is provide by the accumulator.

Blind RamsWhen there is no tool or the CT reel or tubing inside of the well then to isolate the pressure from below “Blind rams” are designed to work in such circumstances. The design of blind rams integrates a tight seal arrangement which is being helpful by using the well pressure to assist in

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Figure1.98: CT Side Door Stripper


closing of the rams once they have been initiated. Since the rams provide complete separation, when it is desire to open the rams a pressure equalization system is required to facilitate the pressure above and below to be balanced.

Shear RamsIn very extreme situation when there is no alternate to loss the part of tubing inside the well Shear rams are the only solution to operate. This may happen under any uncertain conditions, and the importance in shearing the tubing is ordinarily to preserve the safety of the well. After losing the part of tubing in the well the tubing at the surface is wound back to reel and to retrieve the tubing from the well fishing technique have to adopt. In Combi BOP configurations, the blind ram and shear ram operate as combined in one ram set.

Slip RamsSlip rams are fixed with toughened steel inserts which are formed to the profile of the tubing. When sealed, they hold the CT and are skilled of assistant the weight of the tubing in the well, or force acting to push the tubing from the wellbore. Slip rams are usually closed in combination with the pipe or shear rams

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Figure1.109: Stewart and Stevenson Quad BOP


Applications of Coiled Tubing Unit

The approach we have used in this thesis is first precisely explain the abundant worldwide accepted applications of the coiled tubing unit and then provide reader a profound knowledge of the applications practiced especially by coiled tubing unit of “Oil & Gas Development Company Pakistan “on their oil & gas fields. In oil and gas industry before the invent of coiled tubing unit many application perform by conventional method which required extraneous labor and much wastage of time but after the innovation in oil & gas industry many new equipment’s introduced by the manufacturer which steadily bring a revolution in this customary industry where it is a myths that professionals associated with the oil industry were reluctant to adopt the new equipment’s and methods but the coiled tubing unit confound all the myths associated with this industry.

Generally the basic applications of coiled tubing unit are as follow:

Work over and completion application Drilling applications Pipeline applications Permanent installation

Work over and completion application:CT is usually used as worthwhile solution for frequent work over applications. A fundamental benefit of CT in this application is the capability to uninterruptedly circulate through the CT while using CT pressure control equipment to treat a live well. This prevents potential formation damage associated with well killing operations. The ability to circulate with CT also enables the use of flow-activated of hydraulic tools. Further basic features of CT for work over applications contain the in-built stiffness of the CT string. In addition, CT permits much faster trip times as compared to jointed pipe operations.

Mostly adopted CT Work over Applications

Mechanical Application Pumping Applications Setting a plug or packer Removing sand or fill from a wellbore Fishing Fracturing/acidizing a formation Perforating Unloading a well with nitrogen Logging Gravel packing Scale removal (mechanical) Cutting tubular with fluid Cutting tubular (mechanical) Pumping slurry plugs Sliding sleeve operation Zone isolation (to control flow profiles Running a completion Scale removal (hydraulic) Straddles for zonal isolation Removal of wax, hydrocarbon, or

hydrate plug Drilling

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Drilling Applications:The drilling through the CT reel is latest challenge but the highly skilled professionals get through this challenge and drilled many formations by it. Initially a question mark was put either the drilling through CT would be possible or beneficial or not but now it experienced and the answer is “Yes”. Drilling by CT have many advantages over the conventional drilling method in definite applications but it also has a number of limitations that a driller engineer must be aware before compelling the decision of drilling through CT. CT does have distinctive proficiencies that make it excel in true underbalanced drilling, although overbalanced drilling also take place with CT, but the specialization of CT is underbalanced drilling.

Pipeline applications:CT can be used as an effective tool for several pipeline applications, including:

Transportation of inspection tools Removing organic deposits and hydrate plugs Removing sand or fill Placing a patch or liner to repair minor leaks Setting temporary plugs

Permanent installation:Regardless of many applications of CT as a unit some applications of CT are little bit unique because of their conventional methodology of job performing such as the entire permanent installation of the CT reel in the wellbore for production or injection of fluid. The further applications include flow lines, velocity strings, and control lines.The largest market for composite CT is for flow line and pipeline installations. Velocity strings are the final resting place for many used CT strings. And, control lines are the largest market for small diameter CRA tubing.

Main objective is of our thesis are the the applications of the coiled tubing unit mostly executed under the supervision of Pakistan largest exploration & Production stake holder formerly called “Oil & Gas Development Company Limited Pakistan, OGDCL” on their fieldsThis thesis focuses on the work over and completion applications accomplished by the coiled tubing unit of OGDCL on their fields.

Our determination of selecting this topic is to make a comparative study and explore the distinctive applications of the coiled tubing unit practiced worldwide and practiced in Pakistan especially by the OGDCL on their fields and also discover the number of applications mostly performed by the CT unit of OGDCL on their fields.

Our thesis emphasis on getting answers of the following basic questions regarding the execution of the jobs of coiled tubing unit.

In work over and completion category numerous jobs were performed word wide by this coiled tubing unit, in Pakistan under the supervision of OGDCl which jobs commonly performed by them.

What is the reason of performing a job on a well? What results will be expected after the completion of job

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What procedure adopted for the entire job performance What will be the working efficiency, limitations, of the unit?

In drilling applications: In Pakistan where the drilling is mostly take place by conventional method but in Canada and in some states of USA expended innovation occur in the field of drilling also, and now coiled tubing unit also used for drilling a well. We’ll focus to find out whether in Pakistan any attempt was made by this coiled tubing unit for drilling purposes. If yes then what are the parameters which must be fulfilled before taking initiative of drilling a well by this unit. Design of entire BHA for drilling, WOB for drilling, characteristics of the drilling fluid used, maximum depth that can be drilled by CT reel, compatible formation for drilling by CT

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introduction to coiled tubing unit final touch

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