1 of 41

Drilling (Exploration)
Module 4a

2 of 41

Drilling
Agenda
Seismic survey Well construction Onshore drilling Blow out preventer/Christmas tree Drilling fluids Drill bit/cutting Offshore drilling

3 of 41

Seismic surveys

	Earth’s crust has many layers with different thickness and densities Part of the energy/shock wave, sent from surface by explosives, is reflected by each layer and part it travels through 2D 3D 4D!

4 of 41

Visualization of 3D seismic interpretation

5 of 41

Types of traps present

6 of 41

Seismic surveys (offshore)

Air guns, hung from seismic survey vessel, blasts compressed air below the surface of the water. Sound reflections are received by acoustic receivers attached to streamers.

7 of 41

Types of wells

Exploration well Appraisal or delineation well Development (producing) well Injection or disposal well

8 of 41

Well construction
A quick run-through

9 of 41

Cellar and conductor

10 of 41

Moving in & rig up

	The derrick itself is supported by a strong base called a substructure. The substructure is tall enough to accommodate the well and associated drilling equipment, such as blow-out preventers (BOPs).

11 of 41

Conductor and BOP installation
BOP: blow out preventor

Adapter flange is welded to the conductor pipe

⁽¹⁾

(3)

(1)

(2)

(3)

12 of 41

Wellbore diagram

13 of 41

Drilling/producing equipment

The BOP is used during drilling to monitor and control the flow and pressure of oil/gas. It prevents damage to the rig and crew in the event of a blowout. Three types of valves (rams) are used:

BOP used only during drilling

The Xmas Tree replaces the BOP during production

14 of 41

Rotary drilling rig
Main components of the drilling rig
	Mud system Derrick or Mast Hoisting system Rotary system

15 of 41

Hoisting system/derrick

16 of 41

Travelling block

17 of 41

Hoisting system

Air winch

Hook

18 of 41

Elevators and slips

19 of 41

Inserting slips

20 of 41

Working with tongs

Tongs are used to tighten a joint to the drilling string

Mousehole used to store a drill pipe (a joint) to be added to the drilling string

21 of 41

Pipe connection and tripping

	Round trip: process of pulling out of hole and disconnecting pipe stands; usually to replace a dull or damaged drill bit. Then connecting pipes with a new bit and running them in the hole (RIH). A typical round trip of 30,000 ft (9,230 m) takes about 32 hours and depends on the condition of the wellbore.

22 of 41

Rotary system

23 of 41

Drill bits
Bit types
Roller cone bits Milled Tooth Tungsten Carbide Insert Polycrystalline Diamond Compact (PDC) Natural Diamond Impregnated Diamond

24 of 41

Mud system

25 of 41

Mud shakers

Mud shakers remove solids (drill cuttings) from mud, which influences the service life of bits, pumps, and other mechanical equipment.

26 of 41

Functions of drilling fluid

Cleans the bottom of the hole of cuttings. Lifts cuttings up the annulus and out of the hole and prevents them dropping back when circulation has stopped. Cools the bit, which heats up due to friction during the cutting process. Provides lubrication. Supports the borehole wall, stopping it from caving in or washing out. Prevents the well from flowing, hence allowing drilling to proceed safely. Minimizes pressure gains (surges) and losses (swabbing) during circulation and when running and pulling the drill pipe. Used as a medium for hydraulic telemetry. Tolerates salt and entrapped solids without degradation of its properties. Protects the formation from chemical or physical damage. Acts as a displacing medium for placing cement in the hole at the right place.

27 of 41

Types of drilling fluid

	Water base mud (WBM) Oil base mud (OBM) Synthetic oil mud, which has less toxic fumes than oil Foam Three key factors drive decisions about the type of drilling fluid selected for a specific well: Cost Technical performance Environmental impact

28 of 41

Drilling fluids

Bentonite Provides gel strength (viscosity) to help carry the drill cuttings and manage sloughing shale. Bentonite becomes gel under static conditions, which keeps the cuttings suspended. Caustic soda Keeps mud pH between 8.5 to 9.0. Low value pH or acid mud reduces the mud’s ability to gel. Caustic soda is added to the drill mud to keep its pH in the desired range. Barite Barite chemical composition is BaSO4 (barium sulfate). It has a high gravity of 4.50 g/cm3 and is used as weighting material in the drill mud. The API specification for mud is 4.2 g/cm3. Viscosity enhancers Polymers (xanthan gum, guar gum, glycol), increases mud viscosity Reduce water loss Good lubricant

29 of 41

Type of drilling rigs (off-shore)

30 of 41

Offshore rig day rates

31 of 41

Semi-submersible drilling rig

	Anchoring or dynamic positioning system to keep rig at location

32 of 41

Drill ships

Drill ships are seagoing vessels that drill in waters as deep as 12,000 feet. Drilling equipment is installed on deck, with the derrick normally placed in the middle of the ship. Wells are drilled through an opening (called a "moon pool") that extends to the water's surface below the derrick. Because of their cargo-carrying capacity and exceptional mobility, drill ships are especially useful for drilling exploratory wells. Although they are less stable than semi-submersibles in rough water, they can be relocated quickly. They maintain their position through mooring or dynamic positioning systems.

33 of 41

Drilling procedures (offshore)

The conductor with a guide are run on the drill string to allow the conductor to penetrate the sea floor.

Drilling starts, sea water circulates, and cuttings are displaced to the sea floor.

Casing is run through the conductor and cemented & drill pipe is pulled back.

BOP is run on the riser & connected to the wellhead, which is located on the casing pipe.

34 of 41

Drilling procedures (offshore)

Drilling begins using mud instead of sea water.

The riser system connects the vessel to sea floor to circulate mud and bring cuttings up to the drillship.

Cuttings are removed from the mud, which is recycled.

35 of 41

What is different about offshore drilling?

Drilling principles/techniques for offshore are like on-shore drilling; however, safety/environment concerns are more significant. The flexible pipe, called the riser, connects the rig to the BOP and is used to run the drill pipe and circulate mud. Risers are kept in tension to protect it from buckling. Due to constant up/down movements of a rig, a special riser connects the rig to the wellhead, which uses a “ball and slip” connection. Also “heave compensation” is used, which keeps a constant tension on the riser whilst the rig goes up and down. The BOP is installed on the seabed, not on the platform; in case of emergency, the BOP is shut-in and the riser is disconnected to move the rig if necessary.

36 of 41

Riser system for a floating drilling rig

	A ball joint angle > 4 degrees indicates that something is wrong! Riser tension should be < 1/3 of breaking strength Proper design and inspection of these risers

37 of 41

What is different about offshore drilling?

Remotely Operated Vehicle (ROV) performs repair or installation of subsurface facilities. Today, more production operations occur subsea by separating water from oil and re-injecting it rather than pumping it up to a platform. Shallower environments are challenged by seabed gouging by drifting ice features (means of protecting offshore installations against ice action includes burial in the seabed). Deeper water is very cold, resulting in potential forming of gas hydrate. Supplies and waste are transported by ship, and the supply deliveries must be carefully planned because storage space on the platform is limited.

38 of 41

Remotely Operated Vehicle (ROV)

ROVs are unoccupied, highly maneuverable, and operated by a crew aboard a vessel. They are linked to the ship by a neutrally buoyant tether. When working in rough conditions or in deeper water, a load-carrying umbilical cable is used along with a tether management system (TMS). This performs repairs and installation of facilities by the seabed.

Mine Neutralization Vehicle

The ROV is operating a torque tool (wrench) on a valve on the subsea structure

39 of 41

Transportation offshore of produced fluids

Produced fluids from offshore fields can be transported by several methods, including: Under-ocean pipelines Floating Production Storage and Offloading vessel (FPSO) Floating Liquified Natural Gas (FLNG)

40 of 41

Safety in offshore environment

	Offshore environment is far riskier than onshore because of: Sea storms and high waves Staff evacuation in case of emergencies Completion operations and potential leaks Icebergs

41 of 41

Thank you
UNEP-Norway Partnership
United Nations Avenue, Gigiri PO Box 30552 – 00100 GPO Nairobi, Kenya	www.unep.org