DEFINATION
A drilling break (FAST BREAK) is a sudden increase in the drill bit's rate of penetration. This
may result simply from a formation change, but sometimes indicates that the bit has penetrated a
high-pressure zone and thus warns of the possibility of a kick.
A flow check is a method of determining whether a kick has occurred. The mud pumps are
stopped for a short period to see whether mud continues to flow out of the hole. If it does, a kick
may be occurring, with the formation fluids entering the well bore and displacing mud from the
annulus at the surface. The flow check may be performed by visually inspecting the annulus
through the rotary table, or by directing the mud returns to the trip tank and observing the mud
level.
Reaming is performed to open an under-gauge hole to its original full-gauge size.
Circulating is the process of pumping drilling fluid out of the mud pits, down the drill string, up
the annulus and back to the mud pits, and is a continual process while drilling.
Hook load (HKL) this is the load on the hook (summation of the strings: BHA and bit).
Weight on bit ( WOB) it s calculated from the hook load and its decrease on it (if HKL is 200
tones then become 150 tones due to formation resistance so WOB is 50 tones).
Stand pipe pressure (SPP) pressure of the pumped fluid inside the pipes and hoses.
Casing pressure (annular pressure) the pressure of the pumped cement into casing.
Rotary speed The speed of rotation of the string
Rotary torque The resistance of the formation to the drilling and rotation of string
Pump speed The speeds of pumping of mud inside the pipes (related to SPM or efficiency of
pump)
Slow pump rate Test on each pump to notice the pressure exerted by each one in order to use
specific SPM for each pump to kill the well in case of kick.
Blind drilling drilling of hole without any return of cutting or fluid so they drill with seawater in
order to reduce the costs.
Free point indicator The point at which they can make cut for the sticky string; firstly they try
to make jarring to free this point.
Tw ist off Cut of the drill string from any weak point predicted by sharp drop in SPP and sharp
drop in HKLD.
Over pull (pick up) & Drag when tripping out, additional resistance must be overcome in order
to lift the pipe. This additional hook load is termed over pull. When tripping in, a portion of the
string weight will be supported by the tight spot, so that the measured hook load will decrease.
This is known as drag.
Equivalent circulated density (ECD) this is mud wt in the dynamic state.
Nippling up BOP It s the setting up & installing of the BOP for new open hole, which followed
by the BOP test to see what is the maximum allowable pressure on the annulus.
On slips It s done when the floor man makes anew connection.
The wash out in pipes
A-Vertical: when WOB increasing, the crack increases and the pressure will continue drops
B-Horizontal: that on decreasing the WOB, the pressures will increase.
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Barite: barium sulfate BaSO4; a mineral used to increase the weight of drilling mud. Its specific
gravity is 4.2 (it is 4.2 times heavier than water).
Caving: collapse of the walls of the well bore, also called sloughing.
Degasser: the equipment used to remove unwanted gas from a liquid, especially from a drilling
fluid.
De- sander: a centrifugal device for removing sand from drilling fluid to prevent abrasion of
the pumps. It may be operated mechanically or by a fast-moving stream of fluid inside a special
cone-shaped vessel, in which case it is sometimes called a hydrocyclone.
De- silter: a centrifugal device for removing very fine particles, or silt, from drilling fluid to keep
the amount of solids in the fluid to the lowest possible point. Usually, the lower the solids content
of mud, the faster the rate of penetration.
Whip stock: a long, steel casing that uses an inclined plane to cause the bit to deflect from
the original borehole at a slight angle. Whip stocks are sometimes used in controlled directional
drilling, to straighten crooked boreholes, and to sidetrack to avoid UN retrieved fish.
Azimuth In the azimuth system, directions are expressed as a clockwise angle from 0° to
359.99°, with North being 0°.
Doglegs a sharp bend in the well bore.
Key seats an under-gauge channel or groove cut in the side of the borehole that results from the
pipe rotating on a dogleg.
Ledges an irregularity caused by penetrating alternating hard and soft formations,
Where the soft formation is washed out and changes the hole diameter.
Coring is an operation performed to cut and retrieve a cylindrical rock sample.
Strapping the pipe refers to manually measuring each stand of drill pipe as it is pulled from the
hole. Strapping is performed to confirm the pipe tally and actual hole depth.
Rabbiting the pipe refers to cleaning debris from the inside of the drill pipe by dropping a rabbit
(usually wooden) down the vertical length of the pipe. Rabbiting is performed more often when
using expensive down hole tools such as motors and (MWD) instruments.
Repeat formation testing ( RFT) or wire line formation testing, is a quick and inexpensive
way to sample formation fluids and measure hydrostatic and flow pressure at specific depths.
Repeat formation testing provides the information required to predict formation productivity and to
plan more sophisticated formation tests, such as drill stem tests. Repeat formation tests can be run
in open holes or cased holes (through perforated production liners), and multiple tests can be
performed during one trip in the hole.
Drill stem testing is conducted to record formation pressures and flow rates over large
intervals of interest, and to gather formation fluid samples in order to determine the potential
productivity of a reservoir formation.
A single- shot survey recording provides a single record of the drift angle, or inclination, and
(compass) direction of the hole.
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A gyroscopic survey is used to record single or multi-shot surveys in cased holes. The
gyroscope's pointer is set towards a known direction and all hole directions are referenced from
this known direction.
Kick off point this is point at which the wellbore is first taken away from the vertical. It can be
achieved through various techniques such as the use of jetting, whipstocks, motors and bent subs.
Swabbing & Surge
1-Swabbing
Bottom Hole Pressure temporary reduction results from the upward movement of pipe in the hole.
If the drill pipe is pulled too fast during tripping (Swabbing), formation fluid will be
Pulled into the well bore.
Swabbing is caused by the piston action of the bit when it is pulled upward Swabbing
pressure make BHP decrease.
2-Surge
Bottom Hole Pressure temporary increase results from the downward movement of pipe
in the hole.
The opposite of swabbing, Surge pressure makes BHP increase.
If it is high enough, surge will result in formation split fracture. Loss of circulation
Spot & Sweep & Slug
Spot: it is a high mud left on bottom, in order to POOH with dry pipes as possible.
Sweep: it is high viscosity mud to clean hole from cuttings in order to clean only.
Slug: it is high mud weight used to clean the string from cutting during the tripping.
Drilling processes
Rotary drilling Sliding drilling
run with BHA rotary assemblies run with BHA motor assemblies
with surface and equal bit RPM with only bit RPM, no surface RPM
with TRQ reading without TRQ reading
with normal SPP values with higher value of SPP
Types of losses
1- Surface losses: it's the losses of mud due to surface equipments like (desander, desilter, mud
cleaner and centrifuge.) 2- Hole fills: its mud needed to fill the hole
3- Down hole losses: its mud lost in the formation due to fracturing or higher mud weight
Pick up point & Slack of point & Rotary weight
Pick up point = weight of drill string
Slack of point = weight of drill string resistance of mud (no RPM)
Rotary weight = weight of drill string (with RPM)
There are several different types of pressure test:
FIT Formation Integrity Test This is a pressure test to a predetermined pressure, which is
designed to be below the probable fracture pressure.
LOT Leak Off Test This test done after each casing and the beginning of new open hole, this
occurs by drilling of 5ft nearly to know what is the allowable pressure on the formation through
pumping high pressure mud to reach before break the formation. (Cement pump)
Formation Breakdown This is a test that fractures the formation and injects fluid.
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Killing Procedures
1. Wait and Weight Method. The well is shut-in, the surface mud is weighted and the kill weight
mud is pumped in one cycle.
2-The Driller Method.
1. The influx is pumped out first,
2. The well is shut-in until the mud is weighted,
3. The kill weight mud is then pumped.
3- The Concurrent Method Pumping is begun immediately and the mud weight is raised while
circulating the kick out. It needs several cycles of circulation
Funnel Viscosity
Is a routine field measurement of the viscosity of drilling fluid are made with a marsh funnel. This
measures a timed rate of flow in seconds per quart under specific gravity free fall. The values
obtained are called apparent viscosity.
Plastic viscosity:
Is that part of flow resistance in a mud caused primarily by the friction between the suspended
particles and by the viscosity of the continuous liquid phase.
For practical purposes plastic viscosity depends on the concentration of solids present and the size
and shape of these solid particles.
Yield point:
is a measurement under flowing conditions of the forces in the mud which cause gel structure to
develop when the mud is at rest. These forces exist between the solid particles, and are the result
of positive and negative electrical charges located on or near the surface of each particle. When
the mud is at rest, the solid particles tend to arrange themselves in such a manner that these
attractive and repulsive forces are best satisfies.
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Pump or Standpipe Pressure
Standpipe pressure = Total System Pressure Loss = Surface Pressure loss+
Drill string Pressure loss + Annulus Pressure loss + Bit Pressure loss
The measured standpipe pressure is dependant on a number of parameters: -
1- Density of the mud: - The higher the density, the higher the pressure
2- Mud viscosity: - The higher the viscosity, the higher the pressure
3- Flow rate: - The faster the flow rate and annular velocity of the mud, the higher the pressure
4- Depth: - Pressure will increase with depth since annular and drill string sections are increasing,
therefore increasing frictional pressure losses
5- Pipe and hole diameters: - The smaller the diameters, the larger the pressure
6- Bit nozzles or TFA: - The smaller the nozzles or flow area of the bit, the larger the pressure
7- Efficiency of pumps and surface equipment - any leaks will cause a drop in standpipe pressure
Changes in standpipe pressure may be caused by the following conditions: -
1- Loss of circulation: - If mud is being lost to a permeable or fractured formation, there will be a
reduction in pressure.
2- Gas cut mud: - If a large quantity of gas is held in the mud and not removed at surface, there
will be a reduction in pressure as a function of the reduced mud density.
3- Influx of formation fluid: - In the event of a kick, an initial increase in pump pressure may be
seen. This will be followed by a gradual decrease as the influx feeds in and rises in the annulus.
This is a function of the influx (in particular, a gas influx) reducing the mud weight and hydrostatic
pressure in the annulus.
4- Plugged or washed out nozzles: - Causing an immediate, dramatic increase or decrease.
5- Washout in the drill string: - A hole or crack that results in a gradual decrease. The pressure
decreases more rapidly as the size of the washout increases.
6- Bit or pipe twist off: - This will cause an immediate, dramatic drop due to the large larger flow
area in comparison to the nozzles.
7- Hole packing off: - If the walls of the well bore are closing in on the drill string, restricting
circulation, a pressure increase will result.
8- Mud Condition: - If mud density and/or viscosity is not consistent throughout the system, erratic
pump pressure may be seen. This patchiness may be as a result of poor surface treatment;
variable solids content; remnants of viscous or hi/low density mud pills. Similarly, muds may be
prone to aeration or foaming, causing drops in pump pressure.
9- Down hole tools: Failing or malfunctioning tools such as motors or MWD tools will result in
pressure spikes or erratic pressure. High torque will also cause pressure spikes from such down
hole tools.
10- Increased ROP: - A significant increase in ROP will load the annulus with more cuttings leading
to a pressure increase.
11- Increased WOB: - This is a function of the bit being buried more into the bottom of the hole,
restricting the flow of mud from the bit nozzles.
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GAS SYSTEM
General factors affecting the size of a gas show:
1- Amount of hydrocarbons present in the formation. 2- Type of hydrocarbons present
3- Porosity and permeability of the formation. 4- Mud weight overbalance (or under balance) and
amount of flushing. 5- Mud flow rate. 6- Mud properties, specifically viscosity. 7- Mud temperature.
8- Mud type in use. 9- Hole size. 10- Rate of penetration.
11-Type of bit; affecting size of cuttings and amount of cuttings gas released into the mud.
12- Efficiency of gas trap, sample line and gas detectors.
Factors that control the size of this formation gas shows.
- The ROP (Rate of penetration) controls the concentration of gas in the mud for a given flow rate
and is therefore the primary factor causing a variation of gas readings.
- The P (Differential pressure) and ? (Flow rate) control the degree of flushing.
- The hoe size is G an important factor affects the size of the gas show, the larger the hole size,
the more the cuttings, the more the gases liberated from these cuttings entering the mud.
- The Q (Porosity) affects the gas concentration but as the flow rate is usually constant for a bit
run this is not as important factor as a change in ROP.
- As the Depth increases the gas shows should increase due to the increase of expansion that
occurs
TYPES OF RECORDED GASES
1-Cuttings gas (formation gas)
It is the gas liberated from the drilled cuttings enters the well bore mud.
2- Background gas
This is the gas recorded while drilling through a consistent lithology. Often it will remain constant;
however, in over pressured formations this value may show considerable variation.
3-Trip gas
It is quite common for an increase in the mud gas reading to occur at the first bottom s up
circulation after a trip has been made.
The amount of this gas depends on the following:-
1-Differential Pressure (Mud Weight / Formation Pressure)
2-Pipe Movement Speed
3-Mud Properties; viscosity
4-Annular Size
4- Connection gas
A connection gas may appear at the first bottom s up circulation after a connection has been made.
The reason of this is the reduction of the hydrostatic head when pumps are shut-off loosing the
effect of the E.C.D, along with the upward pipe movement that causes another negative swabbing
pressure.
5- Circulation gas
This is the value of gas seen by a gas detector when circulating under normal conditions, meaning
a clean, balanced borehole with drill pipe in the hole and rotating but with the bit off bottom and
with no vertical movement. Under such conditions some gas will be present in the sample drawn
from the mud stream, but it will represent only contamination or recycled hydrocarbons in the
mud.
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6-Miscellaneous gases
A- Kelly gas
Results from air trapped in the drill string during a connection. It can be easily
identified by the time of its appearance relative to the time of connection and the pump rate to get
this gas down the drill pipe up the annulus.
B- Carbide gas
Is caused by the mud logger putting a specified amount of carbide in a dissolvable
package into the drill pipe at the time a connection is made. This carbide reacts with the mud and
creates acetylene that is a check for the time required to pump cuttings off bottom to the surface;
lag check.
Origins of Gas
Mercer s classification (1974)
1- Liberated Gas 2- Produced Gas 3- Recycled Gas 4- Contamination Gas
1- Liberated Gas
The gas that is mechanically liberated, by the action of the bit, into the drilling fluid as the bit
penetrates the formation
2- Produced Gas
The gas that is produced into the drilling fluid, from a specific zone or formation, as a result of the
formation pressure exceeding the opposing hydrostatic pressure due to the drilling fluid.
3- Recycled Gas
- Any gas, that has not been liberated and removed from the drilling fluid while at surface that is
pumped back down into the well bore
- Appears one complete circulation after the original peak (surface time + downtime + lag time)
4- Contamination Gas
- Any gas that has been artificially introduced into the drilling fluid from any source other than the
drilled formations
- Contamination Causes
- Oil based mud systems
- Addition of petroleum products
- Conditioning and re-use of mud systems
- Contaminated transporters or mud tanks
- Thermal degradation or reaction of mud additives
- Hydrogen from drilling casing plugs/shoes
- Resulting from lag checks
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