Fossil Fuel Drilling Engineering and Production Technology Study Notes

Overview and Historical Context of Oil Well Drilling

• Definition of Oil Well Drilling: This is the systematic process of creating excavations or holes in the earth's surface to facilitate the extraction of oil.

• Early History:

  • China (347 BC): The earliest recorded oil wells were drilled using bamboo poles acting as modern drillpipes to reach and extract oil.

  • Canada (1857): Became the first nation to produce oil in commercial quantities, achieving a rate of $37\,\text{barrels per day}$.

  • USA (1859): Colonel Drake drilled the first well in the United States, reaching a depth of approximately $69\,\text{feet}$.

Purposes of Well Drilling

Oil and gas wells are drilled to satisfy specific functional objectives, including:

• Geothermal Power: To generate steam required for electricity production.

• Hydrocarbon Production: For the commercial extraction of oil and gas.

• Injection Wells: Used for gas or water injection to maintain reservoir pressure and support gas conservation efforts.

• Fresh Water Production: To access and produce potable drinking water.

• Information Gathering: To conduct subsurface evaluations through data collection.

Drilling Well Classifications and Engineering Roles

Wells are classified based on their defined purpose during the lifecycle of a field:

• Wildcat Well: A small exploratory well drilled in a location not previously known to be an oil field. Its goals are to gather geological information, determine the potential for hydrocarbon deposits, and identify specific drilling targets.

• Appraisal Well: Drilled after a wildcat well identifies the presence of hydrocarbons. The objective is to establish the size and extent of the deposit and determine the most efficient development strategy.

• Development Well: Drilled within a proven producing field. The intention is to maximize economic production and the overall recovery of known reserves.

Roles of Drilling Engineers: Drilling engineers are responsible for facilitating efficient earth penetration and managing cementing operations. Their duties include:

• Planning the well architecture prior to drilling.

• Monitoring active drilling operations.

• Reviewing drilling results to recommend future improvements.

• Preparing comprehensive drilling reports.

Drilling Rig Personnel and Crew

The personnel operating a drilling rig are organized into specific roles based on expertise:

• Roustabout: Represents any unskilled manual laborer working on the rig site.

• Roughneck: A floor hand responsible for making or breaking the connections of the drill pipe as it is "tripped" (moved) in or out of the hole.

• Motorman: Responsible for the maintenance and operation of the engines and other rig machinery.

• Derrickman: Positions himself on the derrick approximately $25\,\text{m}$ above the rig floor to guide the top portion of the drill pipe during operations.

• Tool Pusher: An experienced individual responsible for ensuring the rig has sufficient materials, spare parts, and skilled personnel.

• Driller: A supervisor in charge of the efficient operation of the rig site. The driller operates machinery from a centralized control room.

Classification of Drilling Rigs

Drilling rigs are steel structures housing the equipment necessary to drill a well. They are primarily classified by their location and design:

Onshore Rigs:

• Primarily land-based and capable of drilling to depths exceeding $30,000\,\text{ft}$.

• Examples include Portable Masts, Conventional Land Rigs, and Coiled-tubing Rigs.

Offshore Rigs:

• Swamp Barge: A fixed-bottom rig for water depths between $2\,\text{m}$ and $7\,\text{m}$. The hull is filled with water to rest on the river or seabed.

• Jack-Up Rig: The most common offshore exploration rig worldwide. These are used in shallow water with depths less than $120\,\text{m}$. They feature legs that can be jacked down to the seafloor to lift the hull above the water.

• Semi-submersible: A floating rig featuring columns and pontoons. It is flooded to submerge to a predetermined depth for stability. It can drill in water up to $3000\,\text{m}$ deep.

• Drillship: A vessel-shaped floating rig used in depths exceeding $3500\,\text{m}$. Stability is maintained via anchors or Dynamic Positioning Systems (DPS).

Other Offshore Platform Options:

• Deep-water jacket.

• Gravity-base structure.

• Compliant tower.

• Tension-leg platform (TLP).

• Spar designs (Classic spar and Truss spar).

Drilling Rig Systems and Components

A drilling rig consists of several integrated systems:

• Rotary System: Provides rotational motion to the drillstring. Components include the Top Drive or the Rotary table & kelly.

• Hoisting System: Used for raising and lowering the drillstring, casing, and associated equipment. The primary structure is the Derrick.

• Power System: Provides the "prime mover" or raw power for operations via diesel engines, steam engines, or spark ignition engines. Power is transmitted through AC, DC, or mechanical drives. Key components include the Drawworks, Mud Pumps, Electric Generators, and Control Switch Houses.

• Circulating System: Circulates drilling mud from the surface down the hole and back. Components include:

  • Mud Pump: Circulates the drilling fluid.

  • Shale Shaker: Removes drilled cuttings.

  • Desander: Removes granular waste.

  • Desilter: Removes fine particles.

  • Degasser: Removes entrained gases from the mud.

• Well Control & Monitoring System: Uses the Blowout Preventer (BOP) to contain pressure for safety. Monitoring involves real-time devices and the Driller’s Console.

Drillstring and Drill Bit Technology

Drillstring Components:

• Drillpipe: Steel pipe categorized by length ranges: $18-22\,\text{ft}$, $27-30\,\text{ft}$, and $38-45\,\text{ft}$.

• Stabilizer: Short pipe with blades (straight or spiral) to reduce buckling and bending stresses.

• Drill Collar: Thick, heavy steel pipe that provides weight on the drill bit.

• Drill Bit: The cutting tool used to create the cylindrical wellbore.

Drill Bit Classifications:

• Fixed Cutter Bits:

  • Polycrystalline Diamond Compact (PDC): Matrix body bits offer erosion resistance; steel body bits allow for higher Rate of Penetration (ROP) due to better cleaning.

  • Diamond Bits: Includes Natural Diamond, Thermally Stable Polycrystalline (TSP), and Impregnated bits. These perform well in abrasive, heterogeneous formations.

• Rolling Cutter Bits (Roller Cone):

  • Mill Tooth Bits: Steel cutters used to gouge soft formations.

  • Tungsten Carbide Insert (TCI) Bits: Hard inserts used to crush abrasive, hard formations.

• Specialty Bits:

  • Coring Bits: Used to extract rock samples (cores) for analysis.

  • Hybrid Bits: A combination of two different bit types.

The Process and Sequence of Drilling

Drilling follows a specific operational sequence:

1. Drilling Program: Planning Phase.

2. Rig Setup: Physical installation.

3. Make a Hole: Active drilling.

4. Casing Setup: Lining the hole with steel pipe.

5. Cementing: Filling the annulus (gap between hole and casing) with slurry to achieve zonal isolation.

6. Repetition: Repeating steps 3–5 with progressively smaller bits and casing strings.

7. Completion: Upon reaching the pay zone (reservoir), the well is completed with perforation and tubing installation.

Casing Configuration:

• Conductor Casing: Prevents surface soil washout.

• Surface Casing: Protects freshwater aquifers and supports the BOP.

• Intermediate Casing: Protects against abnormal pressure zones.

• Production Casing: Isolates the reservoir from damage and other zones.

Surface Production Facilities

After a well is drilled, surface facilities process the produced fluids (oil, gas, and water):

• Gathering System: Flow lines and manifolds direct fluids to a central location.

• Wellhead: Includes chokes (adjustable or positive) to control production rates and automatic shut-down valves for safety.

• Christmas Tree (Xmas Tree): A collection of valves and gauges atop the wellhead:

  • Lower Master Valve: Emergency shut-in (usually open).

  • Upper Master Valve: Main well control, often actuator-driven.

  • Wing Valves: Controls flow to the production line.

  • Swab Valve: Used for wireline maintenance accessibility.

  • Gauges: Measure Tubing Pressure and Casing Pressure.

• Manifold: Commingles production from multiple wells into common lines.

Process Design and Fluid Dynamics

Design Factors:

• Physical Properties: Vapor pressure, density, molecular weight, viscosity, surface tension, and composition.

• Phase Behavior: Changes in relationships between phases under varying conditions, often predicted using Equation of State (EOS) or Empirical Correlations.

• Fluid Flow: Measured using the Reynolds number ($Re$):

  • Laminar Flow: $Re < 2000$

  • Turbulent Flow: $Re > 4000$

Separation and Storage

Separators:

• Types: Two-phase (gas-liquid), Three-phase (gas-oil-water).

• Geometry:

  • Vertical: Handles surge capacity well, easier to clean solids, but more expensive and requires larger diameters.

  • Horizontal: Better for skid-mounting and foamy crude, larger settling area, less expensive, but more sensitive to liquid level surges.

• Multistage Separation: Conducted at successively lower pressures to increase liquid recovery efficiency.

Storage Facilities:

• Floating Roof Tanks: Used for high vapor pressure products to minimize emissions.

• Fixed Roof Tanks: Used for low vapor pressure liquids like water.

• Non-Conventional Storage: FPSO (Floating Production Storage and Offloading), PFLNG (Petronas Floating LNG), and specialized units like Turritella.

Water Treatment and Metering

Produced Water Treatment:

• Produced water is a waste product unless used for injection. It requires de-oiling, degassing, and contaminant removal before disposal or injection.

Flow Metering:

• Well Testing: Accuracy deviation must be less than $5\%$.

• Custody Transfer: Maximum allowed deviation is $0.5\%$.

Pipelines:

1. Gathering Pipeline: From wellhead to processing.

2. Transmission Pipeline: Long-distance transport.

3. Distribution Pipeline: Final delivery to consumers.