The main functions of the offshore rotary drilling rig are as follows:
- Penetrating operations. The drill bit breaks down rock at the bottom-hole by the rotation under the weight. The rotating force of the rotary table is transmitted through the drill string to the bit. Some portion of the weight of drill collars is applied to the bit as the bit weight to push the bit against the rock.
- Hoisting operations. The drill string with the bit is lowered and lifted by the hoisting system, eg. Drawworks. The casing is also handled by the hoisting system.
- Conditioning and circulating the drilling fluids by the circulation system, eg. the mud pumps providing the high pressure mud to the well bore and return of the mud is being processed, filtered and clean through the shakers. The drill cuttings are contained into containers and shipped back to shore.
- Preventing the formation fluids from entering into the wellbore and controlling them to prevent collapse of the well. More serious consequence, after the collapse of well, will be kicks and subsequently well blowout. The highly potential gas contained in the mud return will likely causes ignition of the gas on board and creating serious fire during the blowout.
The drilling fluids, conventionally known as muds, have lots of important functions in the offshore rig drilling. Main functions are as follows:
- Removal of cuttings from the bottom of the hole to the surface. Cuttings are separated from the mud at the shale shaker. The cuttings and samples of the mud may be further analyzed to study geological properties of the rocks penetrated, and to find out the indication of oil and gas in the formations.
- Controlling hydraulic pressure in the hole by adjusting the density of the mud to prevent collapse of the wall of the borehole, and to contain formation fluids in the formations.
- Cooling and lubricating the bit and the drill stem.
In the conventional system of the offshore drilling, the rotary table rotates the drill stem, but the down-hole mud motor and the top drive device are applied to rotate the bit in the directional and horizontal well drilling, or to improve operations in the vertical well drilling. The technical advancement of the measurement-while-drilling tools (MWD) and the logging-while-drilling tools (LWD) has contributed to the almost real-time acquisition of the down-hole information. Owing to these tools it has become easy to drill directional and horizontal wells.
Terminology :-
Casing: Steel pipe lowered into a hole drilled and bonded to formation by cement to keep the well safe.
Christmas tree: An assembly of valves installed at the top of a well to control the flow of oil and gas after the well has been completion.
Drill stem: A drilling assembly of tubulars, to rotate a bit at the bottom of the hole from the surface, which comprises of the kelly,the drill pipe, and drill collars.
Riser: Any pipe with the fluid flow upward in it. In offshore drilling a marine riser system is used to establish a connection between the rig and the seabed. In offshore petroleum production, production riser systems extend from the seabed to the deck of the production platform.
Well completion: A series of work to make a well ready for production after it has been drilled and tested. Although there are wide variations, it typically involves installing the production (deepest) casing, perforating the casing and installing tubing and the Christmas tree. A subsea completion or subsea-completed well is a well that sits entirely, that is, up to its Christmas tree, on the seabed.
Floaters in deep water normally use dynamic positioning system to keep the position above the well, and make use of a guideline-less drilling system. Drilling from a floater also means vertical floater movement (heave) due to sea waves. Introduction of a heave compensation system reduces the relative movement between the drill string and the sea floor. This heave system improves the drillbit performance and reduces wear between the drill string and the well. Most of the time the drill string is free to move relative to the well. That may however not be the case during well testing and landing of the BOP, meaning that the system is vulnerable to heave compensation failures.
Drilling can start when the bit located at the bottom of the drill string reaches the seabed or the bottom of the hole. Drilling requires weight on bit (WOB), bit rotation and mud circulated through the drill string and out through nozzles in the bit. The mud controls the bit temperature, provides bottom hole cleaning and transports cuttings to surface through the annulus. The driller and mud logger must have full volum control of the mud (volume going in and volume coming out of the well) for early detection of kick or lost circulation.
Running the subsea BOP and marine riser consist of :-
The upper part of the subsea BOP is called the lower marine riser package (LMRP) and contains (from the top):
Flex joint
Annular preventer
Hydraulic connector
The lower part of the subsea BOP is called the BOP stack and contains (from the top):
Annular preventer
Blind shear ram
Pipe rams
Wellhead connector
The BOP stack also have a more kill and choke line 'outlets' controlled by choke and kill valves.
Choke and kill valves
Typical diagram of a subsea BOP system :-
The LRMP also includes two redundant subsea control pods (one is back-up) with hydraulic pilot valves which are connected to a common power fluid supply at the floater. The hydraulic pilot valves are activated by a signal from the floater (hydraulically or electrically) to open and close and thus open and close the LMRP and BOP valves. The pods are normally retrievable. Subsea accumulators are located on the LMRP and the BOP and applied to reduce the closing time for the valves. The hydraulic oil return from the valves are normally vented to the sea.
The subsea BOP's are also frequently equipped with back-up control systems like:
Acoustic system
Auto disconnect system
Autoshear system
Deadman system
Emergency disconnect system (EDS)
ROV intervention system
The back-up control system is is typically used when the primary control system has failed during an emergency sistuation. Several scenarios, like accidental riser disconnect, means that the hydrostatic wellhead pressure will drop and that formation the fluid may starts to flow from the reservoir. The flow of formation fluids often starts slowly but increases rapidly. Fast response from the back-up system is therefore highly important. It is also important that the back-up system is independent of the primary system. The auto disconnect, autoshear, deadman and emergency disconnect systems are automatically actuated back-up systems. Note that the auto disconnect, autoshear and deadman need to be armed to be operational. Any back-up system should be reliable and not too complex so that the rig crew does not fear using the system.
The LMRP is connected on the top of the subsea BOP at the cellar deck, which is the lower deck on the drilling rig. The LRMP/BOP stack assembly is functional tested and skidded on rail-beams to the well center of the cellar deck where there is a large hole in the deck called the moon pool. The LMRP is connected to the marine riser coming down from the rotary table in the drill floor above. The LMRP/BOP stack assembly and the marine riser are then run through the moon pool, the splash zone, further through the sea, landed and hydraulically latched on the wellhead by the wellhead connector. The BOP is then overpull- and pressure tested.
A floater will always move up and down and sideways due to waves and sea currents. The floater will thus also move up and down and sideways relative to the marine riser, since the marine riser is fixed to the wellhead at the seabed. After being tested, the marine riser is disconnected from the topdrive and from now on kept in tension and heave compensated through a dedicated riser heave and tension system. The marine riser will have an upper assembly which is fixed to the floater, consisting of (from the top):
Diverter
Flex joint
Male part of the slip joint
This upper assembly will move with the rig and relative to the rest of the riser. The slip joint is a telescopic joint that allows movement up and down while maintaining a hydraulic seal. The flex joint allows sideways movements. There is also a flex joint on the riser bottom just above the BOP. The diverter has an annular preventer that can be used to control returning fluids that have escaped the BOP and entered the riser. E.g., it may be difficult to detect gas escaping the BOP when drilling in deep waters with a high hydrostatic pressure at the BOP, since the expansion of gas is restricted. The gas may however expand in the riser due to reduced pressure. This will be detected by increased mud return at the surface. This gas will be stopped by the annular preventer and diverted to flare. A simple illustration of the floater after the marine riser is in place is given in figure 1.
One of the annular preventers is closed if a kick is detected. The well must be killed by circulating heavy mud into the well. To make this possible there is a kill and choke line from the BOP and up to the platform. These lines are connected outside the riser. Kill mud is circulated into the well through the drillpipe if possible and the return through the choke line with 'outlet' below the annular preventer. If not, kill mud has to be pumped into the well through the kill line. The return is directed to the choke and kill manifold. The gas may be separated in the poorboy degasser or burned without separation. The diverter on the top of the riser may also be used in a kick situation.
Once an oil/gas well is being drilled and commercially viable quantities of oil/gas are present for extraction, the well must be 'completed' to allow for the flow of petroleum out of the formation and up to the surface. This process includes strengthening the well hole with casing, evaluating the pressure and temperature of the formation and installing proper equipment to ensure an efficient flow of oil/gas out of the well.
Condensate wells are wells that contain natural gas, as well as a liquid condensate. This condensate is a liquid hydrocarbon mixture that is often separated from the natural gas either at the wellhead, or during the processing of the natural gas. It is important to remember that natural gas, being lighter than air, will naturally rise to the surface of a well. Because of this, in many natural gas and condensate wells, lifting equipment and well treatment are not necessary.
Completing a well consists of a number of steps: installing the well casing, completing the well, installing the wellhead, and installing lifting equipment or treating the formation should that be required.
Installing well casing is an important part of the drilling and completion process. Well casing consists of a series of metal tubes installed in drilled hole. Casing strengthens the sides of the well hole, ensures that no oil or natural gas seeps out of the well hole as it is brought to the surface. A good deal of planning is necessary to ensure that the proper casing for each well is installed. The type of casing used depends on the subsurface characteristics of the well, including the diameter of the well and the pressures and temperatures experienced throughout the well. The diameter of the well hole depends on the size of the drill bit used. In most wells, the diameter of the well hole decreases the deeper it is drilled, leading to a type of conical shape that must be taken into account when installing casing.
There are five different types of well casing. They include:
-Conductor Casing
-Surface Casing
-Intermediate Casing
-Liner String
-Production Casing
-Conductor Casing
Conductor casing is installed first, usually prior to the arrival of the drilling rig. The hole for conductor casing is often drilled with a small auger drill, mounted on the back of a truck. Conductor casing is usually no more than 20 to 50 feet long. It is installed to prevent the top of the well from caving in and to help in the process of circulating the drilling fluid up from the bottom of the well. Onshore, this casing is usually 16 to 20 inches in diameter, while offshore casing usually measures 30 to 42 inches. The conductor casing is cemented into place before drilling begins.
Surface casing is the next type of casing to be installed. It can be anywhere from a few hundred to 2,000 feet long, and is smaller in diameter than the conductor casing. When installed, the surface casing fits inside the top of the conductor casing. The primary purpose of surface casing is to protect fresh water deposits near the surface of the well from being contaminated by leaking hydrocarbons or salt water from deeper underground. It also serves as a conduit for drilling mud returning to the surface, and helps protect the drill hole from being damaged during drilling. Surface casing, like conductor casing, is cemented into place.
Intermediate casing is usually the longest section of casing found in a well. The primary purpose of intermediate casing is to minimize the hazards that come along with subsurface formations that may affect the well. These include abnormal underground pressure zones, underground shale, and formations that might otherwise contaminate the well, such as underground salt-water deposits. In many instances, even though there may be no evidence of an unusual underground formation, intermediate casing is run as insurance against the possibility of such a formation affecting the well.
Liner strings are sometimes used instead of intermediate casing. Liner strings are commonly run from the bottom of another type of casing to the open well area. However, liner strings are usually attached to the previous casing with 'hangers', instead of being cemented into place.
Production casing, alternatively called the 'oil string' or 'long string,’ is installed last and is the deepest section of casing in a well. This is the casing that provides a conduit from the surface of the well to the petroleum-producing formation. The size of the production casing depends on a number of considerations, including the lifting equipment to be used, the number of completions required, and the possibility of deepening the well at a later time.
Installing Well Casing
Well casing is a very important part of the completed well. In addition to strengthening the well hole, it provides a conduit to allow hydrocarbons to be extracted without intermingling with other fluids and formations found underground. It is also instrumental in preventing blowouts, allowing the formation to be 'sealed' from the top should dangerous pressure levels be reached.
Well completion commonly refers to the process of finishing a well so that it is ready to produce oil or natural gas. In essence, completion consists of deciding on the characteristics of the intake portion of the well in the targeted hydrocarbon formation. There are a number of types of completions, including:
It is the philosophy that during the drilling, - testing, completion water injection and workover of an oil or gas well, any work undertaken should be executed in such a manner that:
1. Loss of human life and injury to crewmembers shall be avoided
2. Pollution of the surrounding environment shall be avoided
3. Loss of rig and damage to equipment shall be avoided.
If all of the aforementioned conditions are fulfilled then the economic and ecological result shall be successful. It is also the philosophy :
1. That detection and controlling a kick takes a team effort from all members of the rig crew. Each member must be completely familiar with his duties so that any well control operation can proceed smoothly and efficiently
2. To maintain all well control equipment in first class condition and ready for use whenever required
3. To ensure that all personnel directly involved in well control situation shall be educated to a standard that ensures complete understanding of any situation that may arise.
However, for any other Well Control procedures and guidelines to take precedence over the ones shown in the ”Well Control Manual”, the following is a must and can not be deviated:
1. At least two tested Safety Barriers shall be present in drilling and producing wells. If for some reason only one Safety Barrier is present, all activities shall cease until two Safety Barriers are reestablished
2. All Safety Barriers must be tested in accordance with approved procedures, or as specified in the programme prepared for the specific operation
3. Activity Typical Independent Barriers:
• Drilling: A sufficient amount of mud or fluid of adequate density to control the well bore pressure; certified and tested BOP stack dressed with suitable rams; unperforated, cemented and pressure tested casing or liner; tested downhole plug; back pressure valve (BPV)
• Casing: A sufficient amount of mud or fluid of adequate density to control the well bore pressure; certified and tested BOP stack dressed with suitable Casing rams
• Snubbing: BOP stack; back pressure valve in the work string; independent safety shear seal immediately on top of Christmas tree; wireline set plug
• Wireline: Christmas tree valves; wireline BOP; wireline lubricator.
For Jack-Ups Operating under the API Standard
Frequency : - All blow out prevention components that may be exposed to well pressure shall be function and pressure tested as follows:
1. When installed
2. After casing has been run, cemented and BOP nippled-up; but prior to drilling out of the shoe
3. Prior to production testing or completion
4. At any time the integrity of the BOP and casing becomes suspect
5. Function test BOP with low manifold pressure, flush kill - and choke lines each week, unless well operations prevent testing
6. Or at least every 21 days (API RP 53 Third Edition section 17.3.3), unless well operations prevent testing. Well operations that may prevent testing are stuck pipe and kick control. If a period greater than 21 days has elapsed since the previous test the reason for the test postponement must be entered on the drilling report.
Drilling offshore for the 'black gold" or oil in the deepwater is one of the greatest technological breakthroughs in recent decades, and many new techniques have been developed to profit from the abundance of oil underneath the seabed. While offshore shallow water drilling has been around for hundreds of years in one form or the another, the effective extraction of petroleum from beneath the sea floor did not surface until the last forty years and more recent deepwater areas are high on the look out.. The search for oil often turns out to be unproductive, but this practice is vital for the economic future of many nations, some countries drilled for their own domestic consumption and some for export.
In order for any drilling to take place, an offshore drilling rig, ship or semi-submersible must first be deployed. These offshore vessels or MODU ( mobile offshore drilling units ) can be situated in water up to a several hundred meters to thousand meters in water depth. But before any drilling takes place, an oil and gas "trap" must first be located in the ocean, and with the ocean floor being at such great depths, the visibility is often very poor. To locate potential traps, engineers use seismic surveying, and then analyze the data they receive to decide whether or not drilling in the area would have the chance of containing oil and/or gas. The engineers will not know whether their assumptions are true until they penetrate the trap with a drill bit. Due to the fact that the traps can sometimes be a great distance below the ocean, advanced computer technology is required to guide the drill bit to a fixed location. Installed above the drill bit is a navigation device, which sends back information to the controller, also known as logging the well, allowing them to locate the exact location that is presumed to have the oil and to measure and monitor the trap. Inside the drill pipe, there is a steerable motor that can be controlled to adjust the drill and the direction in which it is headed.
Latest MODU designs are to make offshore drilling rigs and vessels much safer to operate in view of the recent accident and spill at the Gulf of Mexico while drilling and BP corporate image has somewhat suffered some setback. Offshore watchdogs, like USCG, etc, are now going to get tougher on violators and some redefining of offshore operation rules are looked at.
To make offshore drilling a little safer, extensive training would be mandatory for all of the worker on the rigs and platforms, which would reduce the number of spills due to human mistake or equipment faliure to operate under emergency situation. Furthermore, the technology in offshore drilling would need to be improved further, with new tools created that would eliminate the amount of pollutants released.
Marine biologists and researchers could perform a detailed study of the marine life in the surrounding area and attempt to design a rig that would be safer to the marine ecosystem and that could also be utilized by the marine life around the proposed area(s). Then they could use this new knowledge to make the existing rigs and platforms more eco-friendly.
Inspections of the rigs and platforms should continue, but the oil drilling companies should not be notified when the inspections will take place.
- The possibility of further pollution still exists
- The possibility of more offshore rigs being used is increased
- Oil companies would need to clean up their rigs and platforms to pass the inspections
- Some countries would no longer need to import oil, causing the supplying countries to lose money The right for the marine life to live a healthy and safe life still remains at risk
- Environmentalists worries would be put at ease (to an extent) knowing the rigs are safer Oil companies wouldn’t have to worry about being questioned for their actions
For most of us, the fact that a statement is false might constitutes in itself a reason, however weak and easily overridden, not to make the statement. ... people are guided by their beliefs concerning the way things are when either in lying or telling the truth. It guide them as they have tendency to describe to the society correctly or to describe it untruly or half-truth. For such case, making out half-truths might not tend to unfit an individual for telling the truth in the same way that bullshitting tends to. Through extensive indulgence in the latter activity, which involves making assertions without paying attention to anything except what it suits one to say, a person's normal habit of attending to things may become attenuated or lost. Someone who give half-truths and someone who tells the full truth are playing on opposite sides, so to speak, in the same game. Each responds to the facts as he understands them, although the response of the one is guided by the authority of the truth, while the response of the other defies that authority and refuses to meet its demands. The bullshitter ignores these demands altogether. By virtue of this, bullshit is a greater enemy of the truth than lies or half-truth are.
Determine what serves the presenter’s self-interest. Whenever someone is presenting a point of view, you owe it to yourself to consider how their opinion might correlate to their own self-interest. After all, there must be some reason they have to make the argument to you in the first place. And that reason more likely correlates with their own self-interest than with yours.
Question the info or data. We live in a world of pseudo science, skewed sample sets and anonymous experts. Don’t accept anything as an important truth without first examining the source.
Look out for truth qualifying statements. “To tell you the truth” or “Let’s be frank” or “I have to be honest…” are all statements that beg the question – “Are we starting to be honest just now?”
Hear for name dropping. Credibility should always be derived from the strength of the argument, known facts and/or the reputation of the person present. If absent prominent people are the backbone of an argument, you should be suspect.
Identify confusion in response to logical counterpoints. This type of response is meant to undermine your confidence in the soundness of your counter argument without seeking to specifically or factually oppose the point itself. Watch out for confusion when there should be none.
Be careful of the obvious. If a conversation provides you with one obvious thought after another, wait for the end of the train of thoughts as it is typically an illogical conclusion. After getting into a “yes…yes… yes…” rhythm, you may easily accept a well placed random conclusion or mistruth.
When staff in organization started to show signs of not being truthful and behaving in the opposite, it will end up costing the company due to some of the related impact due to personnel being not giving the correct reporting and trying to cover up in fear of being reprimand should their mistake is uncovered, some of the greater impact could lead to following broader senses :-
- Persistent and disruptive strategy changes without correct stakeholders information.
- Constant debate over issues with no real feedback lacking action plan.
- Plans are agreed but some groups follow them while others hide away due to cover ups.
- Product shortfalls due to inaccurate and unreliable reporting.
- Miscommunication between management levels, i.e. middle managers are constantly "BS" by incorrect information, plans, datas.
- Consistent budget misses in either direction due to inconsistent reporting
- Support organizations like planning or production cannot cope with changing demands from technical.
Ways to Know When Someone’s BSing You
Story or context changes. You can ask them the same thing two or three times and get different answers or replies.
They look or pretend dumb but they’re not. It’s disingenuous, not a good sign.
They put up a smart look but they’re not. Not necessarily disingenuous, but also not a good sign.
They try overly hard. That’s got to give you pause.
They look nervous when they shouldn’t be.
They look scared when they shouldn’t be.
They ask the question repeatedly. Give them time to think of an appropriate answer.
There’s something in it for them. Anytime somebody’s trying to sell you something, there’s a good chance you’re being BS.
They’re fanatical. Fanaticism, fundamentalism, call it whatever you want, it’s a one-sided view of an issue that cuts off debate.
It is seen to be quite obvious - pundits, politicians, senior/junior executives, engineers, technicians, labourers, and even journalists - have sunk into habits of "BSing" from which many of them could be rescued. Many who claim to speak from faith have so cherrypicked their scripture sources that their announcements are nothing but bullshit. I do believe that most people whose characters haven't been metastasized by the greed of fame and publicity hold firmly to the conviction that "bsing" is no better than lying. What they are going to have to learn, if the society or organization is to be saved is that hearing what you want to hear and filtering out the rest which may be part of the BS.
