HERIOT-WATT UNIVERSITY INSTITUTE OF PETROLEUM ENGINEERING MSC/DIPLOMA COURSE DEGREE EXAMINATION IN PETROLEUM ENGINEERING DRILLING ENGINEERING
A 1 Draw and label a diagram of the component parts of the circulating system on a land drilling rig. [ 4]
A2 Calculate the tension on the fast line and the dead line and the vertical load on the derrick when the following drillstring is pulled from the well.
Buoyant weight of string 210,000 lbs Weight of travelling Block and hook 8,000 lbs Number of Lines strung between crown and travelling block 8 Efficiency of sheave system 81.4%
Load on Fastline: 210000+8000/8*0.814 = 33477lbs.
Load on Deadline: 210000+8000/8 = 27250lbs.
Load on Derrick: 33477 + 27250 + 210000 + 8000 = 278727lbs
A3 Describe three reasons for using Stabilisers in the drillstring
In vertical holes the functions of stabilisers may be summarised as follows:
A4 Briefly describe the structure and content of the IADC dull grading system.
Eight coloms Column 1 -Cutting Structure Inner Row (f): wear range 0-8 Column 2 -Cutting Structure Outer Row (O): wear range 0-8 Column 3-Cutting Structure Dull Characteristics (D): e.g BT- Broken Teeth Column 4 -Cutting Structure Location (L} : nose, middle, gage or all rows Column 5 -Bearing Condition (B): Effective of failed Column 6 - Gauge (G) : level of wear an outside of bit Column 7-Remarks (O): Other Dull character Column 8-Reason for Pulling (R): e.g. ROP
AS List and discuss the major considerations when selecting/designing a drilling fluid for a particular well.
The primary functions of a drilling fluid are:
The drilling fluid must be selected and or designed so that the physical and chemical properties of the fluid allow these functions to be fulfilled. However, when selecting the fluid, consideration must also be given to:
A6 Draw and label the shear stress vs. Shear rate diagram for a Power law and Bingham Plastic Drilling Fluid. Write the mathematical model for each of these models .
A 7 A typical casing string may be described by the following terms:
9 5/8" 4 7 lb/ft L-80 V AM
Explain the meaning of each of the terms in this description. Use examples of alternatives to hi ghlight the attributes of this particular casing
Casing Size (Outside Diameter-O.D.)
API-threaded used for oilwells
premium; gastight; and metal-to-metal seal.
B 1 The intermediate casing of a development well is to be cemented in place using a two stage cement job.
13 3/8" Setting Depth : 5900 ft 17 1/2" Hole (Calipered to 18") : 5930 ft Previous Shoe Depth (20") : 1500 ft Formation Fluid Density :9 ppg Shoetrack : 60ft Cement stage 1 (5930-4500 ft.) Class ' G' + 0.2% D13R (retarder) : 15.8ppg Yield of Class 'G' + 0.2% D13R : 1.15 ft3/sk Mixwater Requirements : 0.67 ft3/sk Cement stage 2 ( 1500-1 000 ft.) Class 'G' + 8% bentonite+ 0.1% D13R : 13.2 ppg Yield of Class 'G' + 8% bentonite+ 0.1% D13R : 1.89 ft3/ sk Mixwater Requirements : 1.37 ft3/sk
(a) Calculate the following (See Attachment 1 for capacities):
(i) The required number of sacks of cement for the 1st stage and 2nd stage of the job (Allow l 0% excess over caliper in open hole).
(ii) The volume of mixwater required for each stage
(iii) The displacement volume for each stage
(b) List and discuss three properties of cement which would be specified when designing the cementation operation.
Cement Density-Ensure that influx does not occur when cementing or that formation will not fracture when cementing
thickening time-Ensure that there is time for mixing, pumping, displacing and for problems during the operation. Ensure that the cement does not take too long to set -to avoid woe.
Compressive Strength-ensure that the cement sheath is strong enough to create a competent seal and to sustain perforation tunnels if on the production string
(c) Write a program for a two stage cementing operation and describe the ways in which a good cement bond can be achieved
The first stage procedure can be summarised as follows:
I. circulate the casing and annulus clean with mud (one casing volume pumped)
2. pump spacer
3. pump cement
4. release shut-off plug
5. displace with displacing tluid (generally mud) until the shut-of'fplug lands on the tloat collar
6. Pressure test the casing and bleed off and check returns
The normal procedure for the second stage of a two stage operation is as follows:
I. drop opening dart
2. pressure up to shear pins
3. circulate though stage collar whilst the first stage cement is setting
4. pump spacer
5. pump second stage slurry
6. release closing plug
7. displace plug and cement with mud
8. pressure up on plug to close ports in stage collar and pressure test the casing.
9. bleed off and check returns
Move casing (ls1 Stage)
Pump as fast as possible to achieve turbulence in Spacer
B2 Whilst drilling the 12 114" hole section of a vertical well with a mudweight of 11 ppg the driller detects a kick. The well is shut in and the following information is gathered
Surface Readings: Shut in Drillpipe Pressure : 700 psi Shut in Annulus Pressure :900 psi Pit Gain :29 bbls Hole I Drillstring Data : Hole Size : 121/4" Depth of kick : 6500 ft Previous Casing Shoe : 13 3/8", 54.5lb/ft Depth 13 3/8" shoe : 3500 ft. TVD LOT at Previous Shoe : 2975 psi (0.85 psi/ft Equiv. Mudweight) BHA: Bit : 12 114" Drillcollars :500 ft of 9" x 213/ l6" Drill pipe : 5", 19.5 lb/ft
(a) Calculate and discuss the following :
(i) The type of fluid that has entered the well bore ?
(ii) The mudweight required to kill the well.
(iii) The volume of kill mud that would be required to reach the end of stage 1 of the well killing operation (assuming that the One Circulation kill method is used).
(b) Briefly explain how and why the well bore pressure is monitored and controlled throughout the well killing operation (assuming that the 'one circulation method' is to be used).
Phase I (displacing drillstring to heavier mud)
Phase ll l(time taken for all the influx to be removed from the annulus)
Phase IV (stage between all the influx being expelled and heavy mud reaching surface)
(c) Briefly explain why the 'one circulation method' is considered to be safer than the drillers method for killing a well
The One Circ method is considered safer than the Drillers method because:
(d) List and briefly describe three of the warning signs that a driller should see if a gas influx had occurred downhole.
The primary indicators of a kick are as follows:
The most common secondary indicators that an influx has occurred are:
B3. The 9 5/8" production casing string of a well is to be designed for burst and collapse on the basis of the following data.
Setting Depth of9 5/8" Casing : 8320 ft Top of Production Packer :7500 ft Normal Formation Fluid Density :9 ppg Expected gas gradient : 0.115 psi/ft Depth of Production Interval (TYD) : 7750-8220 ft Maximum expected pressure at top of Production interval :4650 psi Packer fluid density :9 ppg Design Factors (burst) : 1.1 (collapse) : 1.1
Casing Available (See Attachment 2 for specifications of this casing):
9 5/8" 47 lb/ft P-110 YAM
9 5/8" 53.5 lb/ft P-110 YAM
Note : Only one weight and grade of casing is to be used in the string
(a) Design the casing for Burst and Collapse loads (do not consider the tensile loads). Discuss critically the scenario s considered when determining the loading conditions used in the above design process. [ 1 1]
(b) List and describe four (4) of the tensile loads which would be considered when designing the casing for tension.
Dry weight of Casing
The suspension of a string of casing in a vertical or deviated well will result in an axial load.
Buoyant Force on Casing
When submerged in a liquid the casing will be subjected to a compressive axial load. This is generally termed the buoyant force
When designing a casing string in a deviated well the bending stresses must be considered. In sections of the hole where there are severe dog-legs (sharp bends) the bending stresses should be checked. The most critical sections are where dog-leg severity exceeds lOoper 100'.
Plug Bumping Pressure
The casing will experience an axial load when the cement plug bumps during the cementation operation.
Overpull when casing stuck
If the casing becomes stuck when being run in hole it may be necessary to apply an overpull' on the casing to get it free.
Effects of Changes in Temperature
When the well has started to produce the casing will be subjected to an increase in temperature and will therefore expand. Since the casing is restrained at surface in the wellhead and at depth by the hardened cement it will experience a compressive( buckling} load.
Overpull to Overcome Buckling Forces
When the well has started to produce the casing will be subjected to compressive (buckling} loads due to the inc rease in temperature and therefore expansion of the casing. Attempts are often made t o compensate for these buckling loads by applying an overpull to t he casing when t he cement i n the annulus has hardened. This tensile load (t he overpull) is ' locked into' the string by using the slip type hanger
Axial Force Due to Ballooning (During Pressure Testing)
If the casing is subjected to a pressure test it will tend to 'balloon'. Since the casing is restrained at surface in the wellhead and at depth by the hardened cement, this ballooning will result in an axial load on the casing.
Effect of Shock Loading
Whenever the casing is accelerated or decelerated, being run in hole, it will experience a shock loading. This acceleration and deceleration occurs when setting or unsetting the casing slips or at the end of the stroke when the casing is being reciprocated during cementing operations.
(c) List and discuss the operations involved in running casing, from the point at which it arrives on the rig, to the point at which the cementing operation is about to commence.
Casing Running Procedures
B4. It has been decided to drill a deviated well to a target at 8700 ft. TVD. The well is to be kicked off just below the 13 3/8" casing at 2000 ft. The well is to have a build and hold profile. The details of the well profile are as follows
KOP : 2000ft Target Depth (TVD) : 8700ft Horizontal Departure of Target :3700 ft Buildup Rate : 2011 OOft
a) Calculate the Following :
(i) The drift angle of the well.
(ii) The along hole depth at the end of the build up section.
(iii) The along hole depth at the target
(b) List and discuss the advantages and disadvantages of the various types of surveying systems that could be used to survey this well whilst drilling.
Magnetic Single Shot (MSS)
Gyro single Shot
(c) List and discuss two types of tool or techniques that could be used to alter the direction of this well if it were found to be deviating from the designed course.
Bent Sub and Mud motor
Conventional Steerable Drilling System
(d) List and discuss the issues which must be considered when designing the tangent section of a deviated well
Tangent (or Drift) Angle
This section of the well is termed the tangent section because it forms a tangent to the arc formed by the build up section of the well. The tangent angle will generally be between 10 and 60 degrees since it is difficult to control the trajectory of the well at angles below 10 degrees and it is difficult to run wireline tools into wells at angles of greater than 60 degrees. It is also difficult to remove the cuttings from the well and high torque and drag can be experienced on the drillstring