PNG 301
Introduction to Petroleum and Natural Gas Engineering

8.5: Key Learnings

  • There are six stages in the life cycle of a producing oil or gas field
    • Exploration Stage
    • Appraisal/Delineation Stage
    • Development Stage
    • Plateau Stage
    • Decline Stage
    • Abandonment Stage
      During the Exploration Stage, wells are drilled with the objective of proving the existence or non-existence of oil or gas at locations deemed promising by geophysicists and exploration geologists. During the Appraisal/Delineation Stage, wells are drilled with the objective of gaining information about the reservoir. The appraisal wells and delineation wells may or may not be suspended for future use as development wells. During the Development Stage, production and injection wells are drilled as part of the original development plan designed by the engineers and geologists that make up the Asset Team for the reservoir. During the Plateau Stage, production and injection wells are drilled with the objective of keeping the surface facilities producing at 100 percent capacity. During the Decline Stage, infill production wells and pattern realignment wells are drilled to attempt to arrest the natural decline of the reservoir. Finally, during the Abandonment Stage, all wells are abandoned.
  • Drilling engineers take the lead role in developing well proposals and rig schedules during all stages of the field development
  • Drilling engineers take the lead role in any activity requiring a drilling rig. They are active members of any Asset Team during all phases of the life cycle of an oil or gas field. The drilling engineers reform all activities designing the well. They perform all calculations relating to the well design including: drilling fluid specifications, casing design (grades and depth), cement calculations, and drill string design
  • Drilling engineers take an active role in coordinating all rig activities including: liaising with the drilling contractor, supply companies, government agencies, internal HSE (Health, Safety, and Environment Groups) and any other groups required for safe and efficient rig operations.
  • Many companies and their personnel are involved in drilling oil and gas wells. These include:
    • Drilling contractor company
    • Operating company
    • Service companies
  • Cable tool rigs had their origins in the percussive drilling techniques used by ancient Chinese and Persian civilizations and are of historic importance because Colonel Edwin Drake used a cable tool rig to drill for oil in Titusville, PA in 1859. This event is considered to be the beginning of the modern oil and gas industry.
  • Rotatory rigs are used almost exclusively in the oil and gas industry today. The two most common rotary drilling rigs are:
    • Conventional rotary table rig
    • Top-drive rig
  • The conventional rotary table rig applies torque to the drill string and drill bit through a series of mechanical devices that sit on the rig floor. These are:
    • Kelly
    • Kelly bushing
    • Master bushing
    • Rotary table (or turn table)
  • The rotary table is the device that is connected to the main power system of the rig (usually through a chain and gear system). The rotary table imparts the rotation (torque) to the master bushing, kelly bushing, kelly, drill string, and drill bit).
  • The drill string is made up of 30-foot joints of drill pipe. These joints are connected as doubles (two joints) or triples (three joints) and racked and stored onto the side of the derrick as stands of drill pipe depending on the specifications of the rig.
  • On a conventional rotary table rig, drill pipe is added to the drill string, one joint at a time. The next joint of drill pipe to be added to the drill string is temporarily stored in the mousehole on the rig floor.
  • A top-drive rig applies torque to the drill string and drill bit with a motor mounted on the traveling block of the derrick.
  • On a top-drive rig, a single joint, a double, or a triple of drill pipe can be added to the drill string during a connection. When multiple joints are connected, a significant reduction in the time required to connect drill pipe is achieved. This creates a more efficient drilling process.
  • In this lesson, we also discussed three Mobile Offshore Drilling Units (or MODUs) used for offshore drilling:
    • Jack-Up rigs
    • Semi-Submersible rigs
    • Drill ships
  • A jack-up drilling rig is a rig with three or more (typically three) retractable legs that can be used to jack the rig up above the wave action of the water surface. Jack-up rigs are towed (or self-propelled) to the well’s surface location. Jack-up rigs can be used in water depths of up to 400 ft of water; can be used to drill wells to a Total Depth (TD) of 30,000 – 35,000 ft; and can be used to drill exploration, appraisal, delineation, or development wells.
  • A semi-submersible drilling rig is a rig with multiple pontoons that are used to keep the rig floating while drilling. A semi-submersible rig uses a system of thrusters for dynamic positioning of the rig while drilling and is considered the most stable drilling rig for offshore drilling. Semi-submersible rigs can be used to drill wells in water depths up to 9,500 ft and are capable of drilling wells to a TD of 30,000 – 35,000 ft.
  • A drill ship is a sea-going ship that is specifically modified to perform deep water drilling operations. Drill ships are used for deep water drilling in regions with little onshore logistical support. They can typically store large quantities of supplies which allows for their use in drilling exploration wells in more remote regions. In addition, drill ships can be used to drill appraisal, delineation, and development wells in oil or gas fields beneath deep water surface locations.
  • In addition to the Mobile Offshore Drilling Units, we saw that offshore drilling can be performed off of large Production, Drilling, and Quarters Platforms.