Drilling and Well Engineering Assignment
The completed assignment is due on Friday, 3rd November 2017 at or before 12:00 noon. This assignment accounts for 40% of the total marks available for the GL5035course. Each question carries equal marks.
- Given the following information on Well “VB - 1”:
- Mud line (ML) – 1650m TVDSS
- Type of well – Vertical
- TD at 5,100m TVDSS
- Location of well – UTM Zone 49N, WGS84 Datum
- Prospect characterisation – Miocene and Oligocene Sandstones and Carbonates
- Seabed temperature is +/- 30C
- Distance to supply base 170 nautical miles
- Anticipated spud date August 2018
- Select the type of drilling rig you would prefer to use to drill Well “VB - 1”. Fully explain the reasons for your choice, taking metocean, environmental, drilling and economic considerations into account. (8 marks)
- With the help of suitable diagrams, briefly describe two options for installing the conductor casing. (6 marks)
- Bottom hole temperatures in the lower sections of the well are expected to exceed 1100 C. Reactive mudstones and shales are also prognosed in the lower sections intercalated with reservoir quality rock. What mud system would you choose to drill these sections? Explain the reasons for your choice.
- The graph below shows predicted pore and fracture pressures (inclusive of safety margins) for the commitment well 220/02a – 22 which is to be drilled by a jackup rig. The water depth at the location is 50m and the rig’s rotary table (RT) elevation is 35m AMSL. Average sea temperatures are 80C. The reservoir section consists of alternating sandstone and shale sequences between 2,375m and 2,875m TVDSS. The reservoir is overlain by 50m of anhydrite. The planned TD is 3,000m TVDSS in 8.1/2” hole. A 20” conductor/riser has been set at 230m TVDSS. The reservoir fluids are methane gas, H2S and 2% BS&W. The H2S partial pressure is 0.08 psi.
The pressure containment casing strings available are:
7”, 32 ppf, P110 with VamTop connections
9.5/8”, 47 lb/ft, L80 with Vam Top connections
9.5/8”, 53.5 ppf, L80 with VamTop connections
9.5/8”, 47 ppf, P110 with VamTop connections
13.3/8”, 72 ppf, L80 with Vam Top connections
13.3/8”, 68 ppf, K55 with Vam Top connections
- i. Draw a casing schematic showing where you would select the preliminary casing points. Clearly identify on the schematic the casing sizes and shoe depths and whether the casing would be run as a full string or as a liner. (10 marks)
Note: Due allowances will be made for errors of graphical interpolation.
- ii. What is the maximum mud weight that could be used while drilling the reservoir sections of the well? Assume the annular pressure loss (APL) is 400 psi when drilling these sections. (5 marks)
- iii. Calculate the maximum gas to wellhead pressure. Assume a gas gradient of 0.1 psi/ft from base reservoir. The wellhead is 10m below RT. Show your calculations. (5 marks)
Universal Transverse Mercator’s (UTM) Coordinate System