Well Control Practices
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a) Good well planning practices benefit the organization in many ways. First, it is an excellent way of organizing the personnel and contractors in the event of a major control problem. If necessary, effective training is also specified in the control plan .The personnel are trained to be prepared for any emergency at any time. In addition, time and money are saved in the event of control problems. Poor planning is the major cause of well kicks. Mud and casing programs play a major role in well control, and failure to plan for them effectively may result in kicks and consequently cause adverse effects. In addition to specifying personnel and their responsibilities, well control planning practices specify the materials, equipment and services to apply and time of their application. The control plan describes methods to be used for handling gas and oil kicks in high pressure. Planning is also essential in the provision of an additional casing string in the case of a kick.
b) The company control policy help in determining safety factors, such as burst, compression, tension and collapse considerations that are necessary for both the safety plan and well control practices. The policy also defines the tools to be used by the responsible personnel for each and every service. It defines the kind of action to be taken in the event of a kick (e.g. closing the well) to ensure safety. For instance, whether or not to use seamed pipes is a decision that is derived from the company’s policy. Personnel responsibility is essential for controlling the well, since everyone is answerable for an activity and emergency events. If the company's policy dictates that, a manager with no direct responsibility is expected to act on his own initiative. The policy will also dictate the presence, quality and maintenance of BOP. In addition, it governs the criteria for identifying potential problems, which is essential for the minimization of damage. It also provides directions on the active mud system monitoring, such as flow check, mud loss avoidance and actions on occurrences, closure of watertight intensities, and evacuation plan in case of emergency, which are important elements of well control. The policies underscore potential dangers of a blowout in the event of its occurrence. Proper policy is needed to avoid well control problems, as they lead to gas dissolving in the mud system.
c) The downhole stress is a major concern during the killing operations. It is essential in the prevention of the occurrences of ta downhole fracture. The knowledge of a downhole fracture helps optimize the trajectory. Neglecting the effects of downhole stress in killing may lead to swab and surge effects that are costly and time consuming. The swab effects lead to significant losses of mud and well control in the long and short term
d) Well killing methods include oil and gas well control. They are applied immediately after the well has been shut in on a kick. Generally, the killing procedures work under the principle of circulating any form of fluid in a wellbore during a kick, as well as a reasonable Kill Mud Weight (KMW) without letting more fluid in. Well killing procedures are discussed in detail in the next paragraphs.
The wait and weight control method, also known as the balanced method, is the most common method applied in killing procedures. It is applied for controlling an influx taken while drilling or circulating on the bottom, i.e. when the casing shoe is set deep in the well. It is advantageous over the other methods due to being faster and imposing lower pressure and less wear .
The driller’s method is another common method used when the string volume is greater than the open hole volume, thus leading to the influx being inside the casing before heavy mud reaches the open hole. This method immediately removes the dangers of gas expansion, while weighing the mud can take several hours. It involves circulating the influx out and then dislocating the well to kill mud density and balance the shut in the drill pipe pressure.
The circular and weight method, also known as the concurrent method, is applied for killing well pressure when circulation is initiated instantaneously, and mud weight is brought up in steps, or augmentations, normally a point at a time. Used for the first circulation, it is the most complicated and unpredictable method lasting for three hours. It imposes high pressure on annulus, and there is no guarantee of the consistency of mixed mud weight.
The low choke method involves the opening of the choke, holding casing pressure at MACP, and starting pump at a drilling rate, while adding barite at plus or minus sacks of barite per minute. It is applied when shut-in casing pressure is near the MACP on the preliminary shut-in, or rather when shut-in casing pressure is going to surpass the posted MACP and gas at the surface.
The volumetric method is deployed when regular kill procedures are impossible from the bottom of the hole. This could be a result of a drill string being out of the hole and meaningless string pressure. Or if an effective kill circulation method is impossible due to a drill string being washed out or twisted off, or its nozzles plugged.
The lubricate and bleed method is applied when gas is at the surface after using the volumetric method. Mud is pumped into the void space in the wellbore occupied by the gas to displace it.
The reverse circulation, bullheading and dynamic killing method is another killing method. The reverse circulation method is used for workovers not used for drilling. It has the advantage of applying lower casing pressure and smaller cumulative pit gains, as well as being faster compared with convectional killing methods. The bullheading method is used during workovers and completion operations.
e) The fluid flowing from the well caused by a kick is controlled by using blowout preventers. There are various types of BOP stacks, eg. multiple blowout preventers. Understanding which well control actions and methods to employ determines the type of equipment to be used. Selecting appropriate equipment is essential in well control. It is also important to take into consideration such factors as maximum anticipated surface pressure, connection and operating lines, and well depth. Selecting wrong equipment could lead to leakages, high costs, and loss of life, caused by neglect of health, safety and environmental issues. The costs issue will often arise from either replacing misused equipment or overusing tools for rarely performed tasks. The latter will lead to disparities in the operations and could cause even more damage to the well.
The selection of the equipment to use should not be done in haste. Appropriate analysis and designs are to be made, and if possible, prototypical simulations are to be carried out to figure out what the results could be. Well control problems may lead to adverse effects, and therefore, appropriate equipment should be used to prevent such emergencies as kicks. Failures lead to unexpected formation of fluids or gas rigs. However, equipment can be damaged due to neglect of such factors as corrosiveness and strength
In addition to the above inconveniences, failure to select the right equipment may lead to low production. and eventually lead to the closure of the company. The equipment should, therefore, include kick monitoring, drilling and other well control tools.
f) Accumulator performance tests are done on the surface after installation of the BOP. The tests check for the vulnerability of the BOP stack, as well as compliance of the accumulator with the requirements of closing all the BOP stacks and opening hydraulic valves. Therefore, the checks are needed to ensure efficiency of the blow-out prevention technique and operation of the BOP at the correct pressures.
The HSE considerations
As companies and organizations tend to embark on high production practices, there is a need to focus on the health, safety and environmental issues as well. Emergencies that occur in the wells include fires, destruction of marine and animal life, workers' injury and death, and environmental degradation. These could be due to poor management of staff, facilities and other manageable HSE issues. Every staff member and residents of the surrounding wells should be informed of the HSE issues to prevent their occurrence. The HSE considerations in the oil and gas well sites will be discussed in detail in the next paragraphs.
Health considerations have a primary importance in well control practices. Personal protective equipment can only protect against eventualities but can never prevent an accident from taking place. However, it can help one escape with minor injuries, and this explains its importance. Managers, therefore, have the responsibility of letting the staff know which protective equipment to use and making the equipment accessible at all the times. Managers should also give directions on what to do when accidents occur. There should be a plan that defines each accident and appropriate actions.
Priority should also be given to safety. This mostly applies to cases involving accidents that have already occurred or accidents about to occur. The management should provide fire training programs to equip the staff with appropriate techniques to be used in the event of fire. The fire prevention instructions should be well-understood by individuals. Appropriate warnings and safety signs showing escape routes and actions to be taken should be placed in poorly lit areas. International standards on the use of color in messages may be necessary for designing visual aids. There is also a need to ensure safety during spillages and gas emissions. It is worth pointing out that gas emissions are as dangerous as fires.
There should be protection personnel to inform the staff and help with protection practices, such as fire fighting, handling oil spillages and gas rigs.
Lastly, consideration should be given to the environmental issues, such as the effects of well operations on the surrounding atmosphere, water and soil. Other matters of concern include wasteful materials, chemicals, energy and transport.
As far as wasteful materials are concerned, there should be a given amount of disposable waste. This means that reusable materials should be recycled. Wasteful materials should be dumped on the allocated sites and appropriate actions taken regarding safeguarding the dump sites to avoid detrimental effects on the environment. Oil spillages and gas emissions can cause suffocation and fires and result in the deaths of animals, plants, marine and human life.
The HSE provides that the chemicals used in the productive activities are to pose minimal danger to the environment. The companies should be able to account for every emission resulting from production activities and use of raw materials. To deal effectively with such matters, most companies have HSE staff which is responsible for policy implementation and enforcement.
Energy issues concern both production emissions and energy generating technologies. Appropriate technologies should be deployed to avoid misuse of environmental factors. The method used should also have a minimum effect on the environment. Energy-saving policies, such as dim light on a bright day and when premises are empty, should also be put in place.
Transport issues involve the movement of products, staff, and raw materials to their destinations. The transport used should avoid overloading and spilling, which may cause asphyxia, or even fires. Faulty vehicles and transport systems, including pipelines,, should be diagnosed and maintained appropriately.
Question No. Two
a) Equipment Properties
This is an effective tool for releasing a stuck drill pipe. It derives its energy from the applied forced by either tension or compression. This energy is stored in the drill string into which the drilling jar swiftly releases the energy when tripped. The main features of the jar include hydrostatical balance; hence it is not affected by hydrostatic pressure and is fully sealed for a long service life. It also maximizes at the bottom time, thus there is no wait time for the jar to bleed when applying pressure. It is not affected by torque and may be used in high friction or directional holes, a feature known as linear latch. Fewer body connections reduce potential connection failures. The jar has a safety nut to minimize potential finishing jobs by preventing parts from being left in the hole in case of accidental breaks. The backup jarring feature enables the tool to continue functioning in the event of a hydraulic delay. Finally, the separate spline, latch and hydraulic chambers prevent contamination of fluid in the hydraulic chamber. In addition to these features, the jar is less restricted to placement in the BHA, and the hydraulic delay timing remains relatively constant, even after prolonged jarring.
A reamer is a multi-fluted tool. Its cutting action takes place only on the conical flutes at the front of the reamer. Made of high-speed steel for optimum strength, a reamer has a simple design. Its flutes cut a raw material in a hole to be reamed, and their cutting edge and face are similar to most cutting tools. Because a reamer requires no safety clamps, it can be used in elevated temperatures. There is a starting taper for guiding a reamer; and the flutes’ design allows it to maintain continuous cutting action even during more difficult jobs.
Stabilizers are designed to stabilize the drilling string. Their features include a one-piece mandrel design, which is simple and strong; long fishing and bottom neck to provide plenty of tong space and room for rectus; 17 1/2 and smaller sleeves; annular flow area is maximized to guarantee adequate circulation; they are hard-faced with crushed tungsten carbide. This feature is purposed to minimize wearing and keep rebuild costs down. The integral blades are used to centralize the bottom hole assembly during drilling operations. They prevent the differential sticking of the drill string by stabilizing the BHA and keeping drill collars and drill pipes away from the borehole wall. This action reduces vibration, drill pipe whirl and wellbore tortuousity.
The Shock Sub
The shock sub is the most useful tool when drilling broken formations, hard rock and/or hard and soft streaks. It is designed for maximum protection, reliability and durability. There are two kinds of shock subs, namely the mechanical and hydraulic. Shock subs help prolong drill string life and reduce its fatigue through elimination of drill bounce. Their main features include optimized spring rate and better absorption over dynamic range. They also reduce bit bounce and prolong bit life, ensure improved penetration rates, and help achieve neutral effect on the BHA directional attitude. Shock subs reduce premature failures of bottom-hole assembly that result from shock and vibration loads. They also ensure that smooth drilling force is delivered to the drill even in the most inconvenient conditions.
Vibration dampeners work by converting kinetic energy of the moving parts into thermal energy, thereby reducing hard stops and large oscillation amplitudes. They are able to symmetrically distribute force in both tension and compression directions. Such models ensure dampening even if the movements are reversed. The integration piston forces the tension and compression directions and can be set independently from each other. Therefore, the construction elements can be installed in any orientation depending on the type. All the above make vibration dampeners perform their primary function of absorbing string vibration.
b) Basic Components of the Coiled Tubing Used in Underbalanced Drilling
The use of the coiled tubing in underbalanced drilling ensures limited lost circulation, air drilling in competent crystalline rocks, depleted reservoirs and impairment prevention during drilling. The components of the coiled tubing will be discussed in detail in the next paragraphs.
The coiled tubing string transmits drilling fluids and torque to the drill bit and enables other well interventions. The Coiled Tubing (CT) injector head provides the power and traction required for running and retrieving the CT string into and out of the wellbore. The CT reel has the principal function of safely storing and protecting the CT string. This helps avoid excessive damage to the string through bending or any other mechanical damage. It includes swivel assembly that permits fluid to be pumped through the tubing string, as the reel drum rotates.
The CT power pack provides hydraulic power to operate the CT unit, as well as primary and secondary pressure systems. Moreover, it includes an accumulator facility to tolerate limited operations of pressure control apparatus caused by engine shutdown. The check valves are attached to the CT connector at the end of the CT string. Their role is to prevent the flow of wellbore fluids into the CT. The CT cleanouts are used to clean debris and/or other forms of boreholes. This is mostly done with a wash nozzle, a connector, and a double check valve. The existence of the chock line and kill line in the CT ensures that killing can be done. The hydraulic-controlled remote valve on the chock line is essential for well control. It is shut when a kick is encountered. The CT connector allows for the connection of the bottom hole assembly to the end of the CT. It also helps transfer torque and tensile to the bottom hole assembly. The goose neck is used as a medium for high-pressure drilling fluids.
In addition to the above, the crane and substructure are needed for lifting, moving and placing of other equipment. They also provide stability to the wellhead. The annulus in the CT also stops the excess drilling from accumulating in the annulus cuts, thus preventing the possibility of pipe sticking.
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