«Paper #2-11 SUBSEA DRILLING, WELL OPERATIONS AND COMPLETIONS Prepared by the Offshore Operations Subgroup of the Operations & Environment Task Group ...»
Working Document of the NPC North American Resource Development Study
Made Available September 15, 2011
SUBSEA DRILLING, WELL
OPERATIONS AND COMPLETIONS
Prepared by the Offshore Operations Subgroup
Operations & Environment Task Group
On September 15, 2011, The National Petroleum Council (NPC) in approving its report,
Prudent Development: Realizing the Potential of North America’s Abundant Natural Gas and Oil Resources, also approved the making available of certain materials used in the study process, including detailed, specific subject matter papers prepared or used by the study’s Task Groups and/or Subgroups. These Topic and White Papers were working documents that were part of the analyses that led to development of the summary results presented in the report’s Executive Summary and Chapters.
These Topic and White Papers represent the views and conclusions of the authors.
The National Petroleum Council has not endorsed or approved the statements and conclusions contained in these documents, but approved the publication of these materials as part of the study process.
The NPC believes that these papers will be of interest to the readers of the report and will help them better understand the results. These materials are being made available in the interest of transparency.
The attached paper is one of 57 such working documents used in the study analyses.
Also included is a roster of the Subgroup that developed or submitted this paper.
Appendix C of the final NPC report provides a complete list of the 57 Topic and White Papers and an
for each. The full papers can be viewed and downloaded from the report section of the NPC website (www.npc.org).
Subsea Drilling, Well Operations and Completions Page 1 of 45 Working Document of the NPC North American Resource Development Study Made Available September 15, 2011 Offshore Operations Subgroup Chair Kent Satterlee III Manager, Regulatory Policy – Shell Exploration & Offshore, Upstream Americas Production Company Assistant Chair David L. Smith, Jr. Chief Global Technical Advisor Halliburton Company Members Jennifer J. Barringer Health, Safety and Environment ConocoPhillips Manager, Upstream BD Support & New Ventures Brad J. Blythe Oceanographer, Bureau of U.S. Department of the Ocean Energy Management, Interior Regulation and Enforcement Louis P. Brzuzy Marine Science and Regulatory Shell Exploration and Policy, Upstream Americas Productio
Table of Contents EXECUTIVE SUMMARY
B. Well Completions and Subsea Completions
TYPES OF OFFSHORE STRUCTURES AND DRILLING UNITS
A. Common Types of Drilling Rigs
B. Offshore Drilling and Production Platforms
C. Subsea Completions
BASIC WELL CONSTRUCTION
A. Sequence of Well Construction Operations
B. Circulation System
C. Formation Logging
D. Riserless Drilling
DRILLING WASTE MANAGEMENT
A. Drilling Fluids and Cuttings
C. Air Emissions
D. Solid Waste
E. Source Reduction, Recycling and Re-Use
BENEFITS AND OPPORTUNITIES WITH SUB-SEA COMPLETIONS
A. Environmental and Economic Benefits
B. Barriers and Opportunities
C. Long-Term Vision (Year 2050)
A. Appendix 1: Glossary
B. Appendix 2: World population of oil and gas wells by vertical depth and lateral length.... 45
EXECUTIVE SUMMARYAs drilling extended further offshore into deeper water, offshore drilling rigs became larger and more complex with workers who are more highly skilled. Both the equipment and personnel must deal with well-construction conditions that are greatly challenging. The combination of deepwater overburden on the wellhead and formation conditions in the deep subsurface place both high-pressure (seafloor and formation) and high-temperature (formation) stresses on materials and equipment. In addition, the relative isolation from shore-based resources necessitates work methods that are largely self-reliant.
There are two basic categories of offshore drilling rigs: those that can be moved from place to place, allowing for drilling in multiple locations, and those rigs that are temporarily or permanently placed on a fixed-location platform. The type of rig used for a specific project is chosen based on geographic location, water depth and access to supporting resources. But in all cases, drilling and completion are the two main phases of the well-construction operations.
Drilling involves all aspects of creating the borehole whereas completion deals with finishing the well into a system that produces hydrocarbons in a controlled, operational manner. A subsea completion denotes the assembly of equipment that controls and connects individual producing wells into a system that directs the hydrocarbons to a processing or storage facility.
Most drilling and completion challenges have been met and overcome on a case-by-case basis although collective knowledge, and general industry improvements, have progressed rapidly since the late 1990s. Many of the more difficult hurdles involve changing regulatory requirements that add uncertainty to project planning and cost estimations. Important
considerations for the future of offshore drilling and completion work include:
• Significant efforts, and considerable progress, have been made in formulating and handling drilling fluids to be more environmentally compatible. Because of the need to optimize drilling techniques during different phases of deep well construction, the chemistry of drilling fluids is expected to be an ongoing variable that will require collaboration between technologists and environmental regulators.
• Disposal of drilling-related wastes currently is done by a variety of permitted processes that are chosen to meet the needs of individual well-construction projects where volumes of wastes, water depths and distance from shore all factor into waste-disposal choices.
Ongoing collaboration between technologists and environmental regulators also will be essential with regard to sustainable solutions for waste issues.
• Subsea completions for gathering hydrocarbons from subsea wells have demonstrated both environmental and economic benefits for offshore oil and gas projects. Barriers and opportunities for expanded use of subsea completions involve both technological and regulatory issues. Advanced technologies are needed to assure long-lived and serviceable subsea equipment (especially downhole). Reasonable regulations also are needed to assure that the best available technologies and practices are considered in rulemaking that affects subsea operations.
INTRODUCTIONA. Drilling One of the remarkable accomplishments of the petroleum industry has been the development of technology that allows for drilling wells offshore to access additional energy resources. The basic offshore wellbore construction process is not significantly different than the rotary drilling process used for land based drilling. The main differences are the type drilling rig and modified methods used to carry out the operations in a more complex situation.
For offshore drilling a mechanically stable offshore platform or floating vessel from which to drill must be provided. These range from permanent offshore fixed or floating platforms to temporary bottom-supported or floating drilling vessels.
Drilling offshore began near the turn of the 20th century when shallow water fixed platforms were used to access offshore reservoirs. But offshore drilling and production did not really develop to be widely viable until after 1947 when the first offshore well was drilled at a location completely out of site of land. Since then, offshore production, particularly in the US Gulf of Mexico, has resulted in the discovery and delivery of a significant contribution to the total US energy production, with about 35% of crude oil production in the US coming from offshore developments.
Offshore drilling has considerably higher costs than for land-based drilling, depending on water depth and well complexity, which requires a larger volume of hydrocarbon reservoirs that can be economically justified.
Despite an increase in complexity, improvements in drilling technology have allowed more complex well patterns to be drilled to a greater depth such that additional hydrocarbon resources can be developed at a greater distance from the drilling or production structure, allowing more energy to be produced with less environmental impact. Some of these improved capabilities include complex directional and horizontal drilling, ultra-HTHP drilling (for high-temperature, high-pressure environments), and extreme extended-reach drilling (Appendix 2).
Technical developments which have enabled the industry to achieve those significant
improvements in capabilities include:
• Addition of embedded operation-while-drilling functions that include measurement, logging pressure management, reaming, casing installation.
• Low-viscosity non-aqueous drilling fluids (clay-free, flat-rheology and micronized barite systems).
• Improved software modeling (wellbore stability, hydraulics, torque and drag, etc.).
• Improved hole-cleaning practices.
It is anticipated that those and additional improved drilling technologies will continue to be developed to allow continued improved drilling performance which ultimately results in a reduced environmental impact.
B. Well Completions and Subsea Completions “Completion” is used in offshore oil and gas activities in two different contexts. A well completion involves a set of actions taken to convert an individual borehole into an operational system for controlled recovery of underground hydrocarbon resources. Those actions include installation of the final well casings that isolate fluid migrations along the borehole length while also establishing perforated sections where needed to capture the hydrocarbons from the geologic reservoir into the production casing.
A subsea completion refers to a system of pipes, connections and valves that reside on the ocean bottom and serve to gather hydrocarbons produced from individually completed wells and direct those hydrocarbons to a storage and offloading facility that might be either offshore or onshore.
Ronalds (2002) reviewed the many factors involved in selecting drilling and production approaches for offshore oil and gas projects, including the increasing attraction to subsea completions for deepwater projects.
TYPES OF OFFSHORE STRUCTURES AND DRILLING UNITSA. Common Types of Drilling Rigs As drilling extended further offshore into deeper water, offshore drilling rigs have become larger and more complex with workers who are more highly skilled. International oil companies do not normally own fleets of drilling rigs; instead they contract or lease them from a drilling contractor. The drilling contractor provides the drilling rig and people to supervise, operate and maintain the equipment.
There are two basic categories of offshore drilling rigs (Fig. 1): those that can be moved from place to place, allowing for drilling in multiple locations, and those rigs that are temporarily or permanently placed on a fixed-location platform (platform rigs).
Figure 1. Common types of drilling rigs (BOEMRE, 2010c).
Platform Rigs. Platform rigs are complete drilling rigs that are assembled on a production platform and may be temporary or permanent installations. Some production platforms are built with a drilling rig that is used for the initial development and completion then may be “cold stacked” for a period of time until it is again needed to drill or workover a well.
Mobile Offshore Drilling Unit (MODU). MODUs (Fig. 2) are drilling rigs that are used exclusively to drill offshore and that float either while drilling or when being moved from location to another. They fall into two general types: bottom-supported and floating drilling rigs.
Bottom-supported drilling rigs are barges or jack-ups. Floating drill rigs include submersible and semi-submersible units and drill ships.
Figure 2. Varieties of mobile offshore drilling units (MODUs).
Drill Barge (TODCO via NETL, 2011), JackUp Rig (Transocean, 2011), Semi-submersible Rig (Eni, 2008), Drill Ship (BP p.l.c., 2011).
Drilling Barges. A drilling barge consists of a barge with a complete drilling rig and ancillary equipment constructed on it. Drilling barges are suitable for calm shallow waters (mostly inland applications) and are not able to withstand the water movement experienced in deeper, open water situations. When a drilling barge is moved from one location to another, the barge floats on the water and is pulled by tugs. When a drilling barge is stationed on the drill site, the barge can be anchored in the floating mode or in some way supported on the bottom. The bottom-support barges may be submerged to rest on the bottom or they may be raised on posts or jacked-up on legs above the water. The most common drilling barges are inland water barge drilling rigs that are used to drill wells in lakes, rivers, canals, swamps, marshes, shallow inland bays, and areas where the water covering the drill site in not too deep.
Submersible Rigs. Submersible drilling rigs are similar to barge rigs but suitable for open ocean waters of relative shallow depth. The drilling structure is supported by large submerged pontoons that are flooded and rest on the seafloor when drilling. After the well is completed, the water is pumped out of the tanks to restore buoyancy and the vessel is towed to the next location.