Drilling Engineering Module Introduction to New Examination Format.

Introduction The structure of the examination has been slightly changed but the overall aims of the assessment have not changed. The same range and depth of knowledge understanding and application and are examined. The questions in Section A are now more clear and this should help all students to understand better what is being asked for. Specific Changes: There are four major changes to the Drilling Engineering examination paper. They are:

The first section of the paper (Section A) is now worth 31% of the total marks rather than 40% previously.

In the previous format the student was allowed to choose 5 from 8 questions and each question was worth 8 marks. The student must now answer all questions in Section A of the paper.

The questions in Section A of the paper test the acquisition of knowledge and only simple applications of knowledge such as calculations related to hoisting capacity or Leak-off tests.

The second section of the paper (Section B) is now worth 69% of the marks but the questions are the same as before. This section tests the application (calculations) and deeper understanding of knowledge as before. The student still has a choice of three from four questions in Section B.

The example section A (with solutions) given in the attached has been compiled from the sample examination and solution in the current Drilling Manual to demonstrate that although the questions in this new Section A are more clear, they are asking for almost the same information as previously.

Course Code - 28-137 Class/Examination Code - 289DE3

HERIOT-WATT UNIVERSITY

DEPARTMENT OF PETROLEUM ENGINEERING

MSC/DIPLOMA COURSE DEGREE EXAMINATION IN PETROLEUM ENGINEERING

DRILLING ENGINEERING

JANUARY, 2006 hrs - hrs

SECTION A

Answer ALL Questions in SECTION A TOTAL MARK of THIRTY ONE MARKS

SECTION B

Answer any THREE QUESTIONS from B1 to B4

Each question carries TWENTY THREE MARKS

Section A A1. Describe three features of a roller cone drillbit used for a soft claystone. (3) A2. Describe the three most common methods for assessing the performance of a drillbit when it has completed its run? (3) A3. What are two main criteria used to quantify the mudweight for a well? (2) A4. What are two other (in addition to the above) reasons for keeping the mudweight in a well as low as possible. (2) A5. Describe three of the principle indicators that an influx had occurred whilst drilling ahead (3) A6. What are two advantages and two disadvantages of oil based mud as opposed to water based mud? (4) A7. What are two of the main properties of a drilling mud and what are the laboratory equipment used to test the mud for these properties. (3) A8. Briefly describe three components of subsea equipment which are run between the wellhead and rig when drilling a subsea well. (3) A9. What are three differences between a surface and subsea wellhead. (3) A10. Describe two downhole components of an MWD system. (2) A11. What are three reasons for using an MWD tool (3)

SOLUTIONS - SECTION A A1. Bit for Soft formations:

Long widely spaced teeth for deep penetration and good cleaning of cuttings from between teeth.

Small journal bearings to allow large cones and teeth High offset to give scraping action in soft formations

A2. Performance Criteria: ROP - ft drilled per hour Length run number of ft drilled Cost/ft: Cost/ft = Bit cost + Rig Rate(Trip time + Drilling time)/Interval Drilled Cost/ft includes both ROP and length of run therefore the best option A3. The minimum mudweight is selected so that it exerts 200psi above the pore pressure - to avoid influx. It may also be chosen to avoid borehole stability problems The maximum mudweight in any hole section is based on the fracture pressure of the formations to be drilled. A4. Minimise overbalance to avoid:

Chip hold down effect differential sticking formation damage in reservoir

A5. (List any three of the following) Flow Rate Increase - If flowrate from a well increases without changing the pump rate this is a sign that formation fluids are feeding into the wellbore. Pit Volume Increase - A rise in the level of mud in the active pits is a sign that some mud has been displaced from the annulus by an influx of formation fluids. . Flowing Well with Pumps Shut Off - When the rig pumps are not operating there should be no returns. If the pumps are shut down and the well continues to flow it must be due to a kick.

Improper Hole Fill-Up During Trips - If well does not require the correct volume of mud to fill up when pulling out pipe then the drillpipe volume has already been replaced by formation fluids Changes in Pump Pressure - The lower viscosity of an influx will cause a gradual drop in frictional pressure drop in the annulus and therefore pump pressure. Gas Cut Mud - Any significant rise above background gas level may occur due to aninflux due to negative pressure differential. Drilling Break - If drilling parameters have not been changed the increased penetration rate may be attributed to reduced overbalance (increase in pore pressure). A6. OBM (List any two of each of the following) Advantages - Shale Drilling - Inhibition of clays - Lubrication of drillstring in extended reach wells (reduce torque and drag) - Produces Gauge hole for cementing in shales - Creates a Thin Mud Cake preventing differential sticking of pipe - Minimises Formation/Reservoir damage Disadvantages - High Cost - Environmentally sensitive - Complex formulation - Poor Temp. Stability - Kick detection is difficult in gas reservoirs - Special logging tools are required - Rheological control difficult - Require Rig Modifications to prevent Leaks A7. (List any two of the following) Mud density A sample of mud is weighed in a mud balance. The density can be read directly off the graduated scale at the left-hand side of the rider. Viscosity Two common methods are used on the rig to measure viscosity: Marsh funnel: This is a very quick test which only gives an indication of viscosity and not an absolute result. The funnel is of standard dimensions (12" long, 6" diameter at the top, 2" long tube at the bottom, 3 /16" diameter). However the funnel viscosity can only be used for checking radical changes in mud viscosity. Further tests must be carried out before any treatment can be recommended.

Rotational viscometer : This device gives a more meaningful measure of viscosity. A sample of mud is sheared at a constant rate between a rotating outer sleeve and an inner bob. The test is conducted at a range of different speeds, 600 rpm, 300 rpm, 100 rpm etc. (laboratory models can operate at 6 different speeds). Gel Strength The gel strength can be measured using the viscometer. After the mud has remained static for some time (10 secs) the rotor is set at a low speed (3 rpm) and the deflection noted. This is reported as the initial or 10 second gel. The same procedure is repeated after the mud remains static for 10 minutes, to determine the 10 minute gel. A8. BOP stack - Hydraulic connector, BOP Rams (Pipe and shear) and Ann. preventer LMRP - Hydraulic connector, Ann. preventer and uniflex joint Riser Joints and telescopic joint (to accommodate the vertical movement or heave of the rig) A9. The major differences between the subsea wellhead and suface systems are:

Component/Function Subsea Surface BOP casing supported annulus access annulus seal

on seabed on seabed only between tubing and prod. casing, all at seabed

at surface at surface all annuli all at surface

A10. (Two of the Following)

Power system Batteries/Turbine Measuring device Directional tools (inclin. or azimuth)/petrophysical (GR or

Resistivity)/Drilling Mechanics (WOB/Torque/Annulus Pressure) Transmitter positive pulse/negative pulse/mud siren system

A11. (Three of the following) MWD tools are very useful for real time identification of the formations which have just been drilled. If not available can only determine position geologically by circ. bottoms up to retrieve cuttings. This is very time consuming. The tool is therefore widely used for:

Core point selection Casing point selection (when precise placement required) Formation correlation when geosteering - to stay in the reservoir

They are used to replace wireline logging operations saving time and money. They are most widely used to provide real time information on bit trajectory (Directional Control) providing more frequent surveys and saving time and money over the conventional survey techniques.

Each question carries TWENTY THREE MARKS