Guidelines provide framework for deepwater drilling operations

Lee Hunt
International Association of Drilling Contractors
Houston

Morrison Plaisance
Diamond Offshore
Houston

An industry task force has compiled guidelines based on current knowledge and best practices to help operating and service companies work safer and more efficiently in deep water.

According to committee member Stan Christman of Exxon Upstream Development Co., "From the start, our philosophy was to prevent incidents in the first place rather than react to them. Because of this emphasis, the largest section of the guidelines is devoted to well design and well control planning."

Within a 12-month period that began in April 1997, key members from the industry developed the guidelines that will serve as a foundation for conducting deepwater operations.¹ The Deepwater Well Control Guidelines are subject to annual review and will be revised to reflect future advances in deepwater drilling practices.

As Christman points out, "It is important to note that the guidelines do not eliminate the need for thinking, analysis, and decision making," but instead provide information that can be used to minimize risks and avoid potential problems that can arise in deep water.

Task force organization

The Deepwater Well Control Task Force contains a wide cross-section of industry representatives, including major and independent operators, drilling contractors, members of academia, well-control experts, and equipment manufacturers ( Fig. 1 [315,401 bytes]).

The International Association of Drilling Contractors (IADC) was chosen as the industry association best suited to sponsor this work, assisted by the Offshore Operators Committee (OOC).

To expedite communications, the task force set up a website specifically for retrieving comments and peer review (http://iadc.org/dwwctf.htm). Drafts for each section of the guidelines were made available online, minimizing the number of meetings and ensuring that the latest version of each draft was posted.

In addition to section drafts, the site provides general information about the project, an organization chart, the project schedule, task force minutes, subcommittee meetings, and the means to communicate with the appropriate groups.

Deepwater well control guidelines

The guidelines contain five chapters that are broken down into sections ( Table 1 [24,200 bytes]), providing details on work-flow procedures, equipment specifications, and maintenance and preventive measures.

Well planning

Chapter one provides the criteria and procedures for well design that are necessary to withstand the rigors of deep offshore drilling environments. In this context, a deepwater well is drilled in water depths greater than 1,000 ft (300 m).

• Wellhead and structural string design. The need for conservative design criteria is stressed because of the increasing axial and bending loads encountered in deeper water and the serious consequences associated with failure (Fig. 2 [72,404 bytes]). Major component design criteria and standard industry practices are explained, with example calculations and support documents identified.

Some discretionary procedures are discussed that minimize problems concerning well control, hole stabilization, and the expense of successfully completing a project.

• Shallow water flow (SWF) control. Among the most costly of deepwater failures experienced to date, the consequences of SWF are well documented, including different geological and physical environments that cause the problems arising from their encounter.

Key preplanning steps that mitigate the impact of SWF are presented, including geophysical prediction, accurate pore-pressure and fracture-gradient analysis, correct drilling practices and techniques, and the use of mechanical shut off devices where applicable.

• Drilling fluid considerations. The more important problems addressed are the convergence of pore-pressure and fracture-gradient concerns that deal with fluid losses, lost circulation, ballooning, equivalent circulating densities, storage capacity limitations, minimal liquid and bulk storage capacities, contaminant handling, lost circulation material storage, base drilling fluid choices, and the use of synthetic-based drilling fluds.

In addition, this section addresses operational considerations related to drilling fluids, such as the modeling of flow behavior, desired mud properties, flow detection, tripping speeds, circulation parameters, displacement procedures, and spacers.

• Hydrates. This section discusses the conditions required for formation and dissociation of hydrates and the need for super-cooling to initiate nucleation. Preplanning procedures include the use of inhibited mud systems, appropriate well-control procedures, proper risk analysis, utilization of " worst case" design criteria, and remediation plans.

Two types of hydrate formation problems are discussed. The first problem occurs through the entry of shallow gas into an unsealed annulus in the wellhead housing and blowout preventer (BOP) connector cavity. This occurrence hampers disconnect procedures.

The second can occur within the well bore or BOP cavity while circulating out a gas kick. In this case, the hydrates hinder the control of BOP functions and access to the well bore.

• Drill stem testing. At one time forbidden on floating rigs in many company policies, flowing well tests are now planned and executed in water depths greater than 5,000 ft. The testing of well productivity is necessary because of the high-rate completions usually required to justify deepwater development.

The same dynamic forces that occur in other routine floating operations must be accounted for and typically require reducing allowable operating windows such as emergency disconnect time, watch circles, and acceptable weather conditions.

Other considerations are addressed, such as number of emergency shut-down points, BOP sealing elements, pressure testing of equipment, flaring vs. barging oil, and hydrate inhibition.

• Deepwater regulatory guidelines. This is a summary of regulations pertaining to deepwater operations and includes special considerations and concerns for these operations along with a complete overview of the permitting process.

Issues include new and unusual technologies, oil spill contingency planning, chemosynthetic communities and live bottom areas, air and water quality, endangered and threatened species, and lease abandonment and decommissioning operations.

A discussion of how the current regulations evolved with specific industry involvement shows the need for continuous development of the regulatory framework in order to manage risk effectively. A review of all regulatory agencies involved and identifying their responsibilities and jurisdictional areas is included for reference.

Well control procedures

Chapter 2 covers eight topics and provides procedures for preventing and handling kicks and blowouts in relation to equipment requirements and risk management ( Fig. 3 [53,031 bytes]).

• Kick prevention/detection. This section discusses the inability to use a riser margin and overbalance maintenance in the event of a riser failure. It also addresses the issue of adequate hole cleaning in long risers to prevent excessive equivalent circulating density.
• Shut-in. This section reviews the decision about which BOP to use for close-in and circulation. Other issues include the impact of varying drill-pipe lengths and tool joint spaceout in the BOP stack, cold mud viscosity/gels that mask shut-in casing pressure, and the potential for influx passing through the BOP stack prior to kick detection and shut-in.
• Circulating to kill. This topic discusses the need to adjust choke pressure correctly for choke and kill (C&K) line friction when establishing circulation.

Specifics include how to measure C&K line friction, the selection of circulation rate, ways to use the second C&K line, choosing between the "Driller's" and "Wait and Weight" method, lost return and blowout prevention, and recognizing that narrower mud weight/formation integrity margins may increase potential for lost returns or even underground flow.

• BOP cleanout (trapped gas). This section addresses how the location of C&K outlets affects procedures to remove BOP gas accumulations and how removal techniques that reduce the BOP pressure may create significant inverted pressure difference that may exceed the design basis of the BOP.
• Gas in riser-diverter. Issues in this section include the potential for larger riser volumes and diverter loading in addition to diverter monitoring and handling methods.
• Hydrate prevention and removal. This section addresses the procedural aspects of hydrate formation, including the decreasing ability to fully inhibit water-based muds and the potential for hydrates to form in the wellhead connector operating mechanism.
• Well control prior to BOP installation-shallow water flow. This topic emphasizes the features and impact of these pressurized, unconsolidated formations.
• Plug and abandonment. This section addresses gas under pressure that may exist below casing hanger seal assemblies.

Equipment

Deepwater well control equipment must meet two basic criteria:

1. It must be designed for issues related to the water depth
2. If installed on a dynamically positioned rig, it must deal with the emergency-disconnect needs of that type of vessel. The key considerations for deepwater operations are as follows.

BOP arrangement. This section addresses the number and placement of rams and annulars in consideration of hang off, well control operations, and stack clean out blind shear rams and casing shear rams and bending loads, load ring bearings, location of lower marine riser package split, BOP elastomers, failsafe valves, bolt strength, and BOP pressure ratings.

• Choke manifolds. The use of specialty surface well-control equipment is addressed including the minitrip tank for the choke manifold and low-pressure range gauges for accuracy in formation integrity tests.
• Deepwater risers. Riser management is important to deal with the very large riser mass and tensions required for deepwater operations. The potential for unplanned disconnects and drive-offs further complicates riser management.

A partial list of items in this section includes cuttings removal from the riser, tracking of riser joint service for inspection and maintenance, angle indicators for extreme current and environmental conditions, and comprehensive riser analysis.

• Deepwater diverting. This topic covers diversion at the ocean floor for riserless drilling and surface diverter systems that handle gas from the marine riser.
• Riser gas. This section discusses the dangers of free gas in the riser and diverter system designs.
• Deepwater control systems. This topic includes a detailed discussion of hydraulic vs. multiplex closing times, fluid volumes required for operations, working pressures for systems, and back-up systems.
• Preventive maintenance. This section discusses general recommendations related to maintenance, including minimal time between stack running on DP operations.
• Riser recoil. This topic covers hazards related to riser recoil, including extremely high top tensions. Other topics include unplanned disconnect and riser-recoil control systems.
• Subsea remotely operated vehicle (ROV) intervention. This section addresses equipment modifications for deepwater operations and BOP override functions.

Emergency response

Emergency response for deepwater operations is more complex and less developed than practices customary for traditional operations. However, conventional measures of source control such as relief wells and dynamic kill methods differ little in deep water compared to shallow water situations.

Committee member Curtis Weddle of BP-Amoco plc said, "These measures may even be more effective due to the high hydrostatic back-pressure from the sea water."

• Introduction to emergency response. This section covers the four main objectives of emergency response efforts

1. Protection of the health and safety of people
2. Protection of the environment
3. Protection of the physical plant (for source control)
4. Protection of the mineral resource.

This section also reviews the purpose, value, and features of a proper emergency-response drill.

• Emergency-response plans. This section contains recommendations for blowout contingency planning and organization, the necessary command and control structure, and the establishment of a blowout task force.
• Vertical intervention, rig positioning and surveying for relief wells, and dynamic kill considerations. These three sections describe potential means of vertical intervention for source control as well as the key success factors for relief wells and the dynamic kill of a blowout. Factors influencing vertical intervention are covered, as well as vertical intervention tools, and global positioning systems.
• Spill control. The final section presents information on known spill behavior and the best available means for spill containment and recovery.

Training

The final chapter provides information concerning personnel training procedures and is broken down into three sections.

• Overview. This section provides a comprehensive list of deepwater well control training topics derived from the preceding chapters.

These issues are categorized and cross-referenced to the materials assembled in the guidelines for easy access and include 18 informational categories along with 88 referenced topics. The list is not meant to be an exhaustive listing of topical issues for a well control curriculum, but rather provide guidelines that specifically address deepwater concerns.

• Curriculum considerations and simulator requirements. Technologies that support training are examined in this section.

A deepwater well control simulator assessment was made based on current industry simulation hardware, software, and procedural offerings. Hardware enhancements are identified along with software and procedural issues that would improve the effectiveness of simulators in deepwater training.

• Training guidelines. This section offers recommendations that can assist with hands-on training and assessment, including equipment configuration and operating procedures.

Continuation

The Task Force Steering Committee has also taken on the job of identifying areas for studies and research, either under way or proposed, that would further improve deepwater well control. In addition, all members of the Steering Committee, along with the five subcommittee chairpersons, have agreed to serve as a revision committee.

In this role, the members review comments and suggestions received by the IADC concerning improvements to the guidelines. They will also track technical developments in deepwater well control to ensure the document remains current while incorporating advances in deepwater well control technology as they are established.

Instructions on how users can submit comments to IADC and participate in future updates are contained in the guidelines. The IADC Deepwater Well Control Guidelines are available through the IADC at 281-578-7171 or .

Reference

1. Christman, S., Kelly, A., Plaisance, M., Kropla. S., Metcalf, J., Robinson, E., and Weddle, C., "An Overview of the IADC Deepwater Well Control Guidelines," SPE/IADC paper 52761. To be presented at the SPE/IADC Drilling Conference, Amsterdam, March 9-11, 1999.

The Authors