WELL CONTROL

The 1999 LSU/MMS Well Control Workshop: An overview

A summary of technical presentations on underbalanced operations and ongoing / future well control-related research and equipment development by LSU and industry

John Rogers Smith, Louisiana State University, Baton Rouge, Louisiana

ouisiana State University (LSU) and the Minerals Management Service (MMS), in cooperation with the International Association of Drilling Contractors (IADC), hosted an open workshop on well control March 24 and 25, 1999, in Baton Rouge, Louisiana. More than 140 professionals, representing operators, service companies, consulting companies, regulatory agencies, industry organizations and universities participated.

As described in this article, the workshop was held to present and foster discussion of three subject areas. Underbalanced operations, especially for potential offshore applications, were discussed extensively on the first day. Ongoing research at LSU to improve technologies for well control and wellbore integrity was described on the second day. The final topic was the need for future research on well control and related safety and environmental concerns, especially for ultra-deepwater operations.

Underbalanced Operations

The first day of the workshop was a Regional Operations Technology Assessment Committee (MMS) Workshop on underbalanced drilling / completion. Don Howard of the MMS introduced the subject, noting that no underbalanced operations have been formally proposed offshore in the U.S. However, underbalanced operations have begun to be done offshore elsewhere in the world, and operators and industry publications have raised the question about whether it can be done in the U.S. MMS regulations are relatively silent on this issue, but operators must endeavor to "maintain well control at all times" and "minimize the potential for the well to flow or kick" prior to production. One intent of this workshop was to begin the dialogue between industry and MMS on the potential to conduct underbalanced operations on the U.S. outer continental shelf.

Defining operations, advantages / limitations. The first four presentations were intended to provide a broad perspective of underbalanced operations, their current applications and future possibilities. Ted Bourgoyne, LSU, reviewed the applications and limitations of, and also the well control considerations in, underbalanced operations. Rick Stone, Signa Engineering, described underbalanced drilling (UBD) techniques and how those techniques are being used to create new operating methods for other applications. John McClennan, TerraTek, provided a similar review of current and prospective underbalanced completion / well-servicing operations.

Common advantages of UBD / completion are (see also Fig. 1):

• Increased well productivity due to less pore / fracture plugging
• Productivity determined during drilling
• Faster penetration rates
• Ability to drill concurrently with losses or flows
• Minimized mud losses due to lost circulation, and
• Minimized differential sticking problems.

Current limitations of UBD / completion are:

• Formations must be competent to provide wellbore stability when underbalanced.
• Maximum flowrates must be predicted and surface equipment sized to handle these rates.
• Surface pressures must not exceed the capability of rotating seal equipment.
• Pressure control is complicated for operations such as connections, trips and cementing.

The specific technologies used for these operations vary substantially depending on the application. Nevertheless, by definition, wellbore pressure must be less than formation pressure. Given that any permeable zone will flow under these circumstances, a seal is required at the surface, which is generally provided by a rotating head or rotating BOP. Drilling fluid density in the annulus must be controlled to maintain the underbalance, but such fluids may be anything from a gas to a weighted mud, depending on formation pressure. Aerated liquids are frequently used, with the vapor phase resulting from either produced formation fluids or from a gas compressed and injected from the surface.

Use of the technologies developed for UBD, completions and well servicing is rapidly increasing. About one-fourth of all rigs in the U.S. are equipped with some kind of rotating seal at the surface. Applications have spread beyond horizontal drilling in low-productivity reservoirs. These technologies also support a variety of new drilling applications, such as near-balanced drilling, drilling underbalanced through long impermeable intervals, drilling with surface pressure to maintain an overbalance when drilling with low-density fluids, and controlling a well with a variable gradient pressure profile in the annulus.

Actual UBD applications. Three presentations were made on actual applications of underbalanced drilling. The first was by Brian Tarr, Mobil, who described UBD used to re-enter existing wells and drill horizontal sidetracks to replace the original completions in a severely depleted, high-productivity gas reservoir in Arun field, Indonesia. Although the operations were not offshore, they were remote. UBD was necessary to avoid severe lost returns, differential sticking and formation damage.

Major challenges that were overcome in Arun included understanding downhole hydraulics to maintain a controlled underbalance, selecting a stable, compatible drilling fluid, building a suitable surface separation system, establishing safe operational procedures, and then providing practical training for this unusual operation. The subject well was successfully drilled with full returns. The 1,000-ft horizontal section was completed and delivered double the expected gas production rate.

Kyle Bethel, Expro Americas, presented a case history of the first UBD offshore the Netherlands. The objective was a partially depleted, low-permeability gas reservoir. This well also required special equipment and training. A surface separation system was devised, with an operating pressure equal to full wellhead pressure. This well was terminated with only a 128-ft horizontal borehole due to a casing problem, but it still achieved a production rate nearly equal to an offset with a 2,000-ft horizontal section that was drilled overbalanced, then stimulated with a massive frac job.

Edson Nakagawa, Petrobras, described UBD operations being planned offshore Brazil (see accompanying article). The goal is to use aerated drilling fluids for floating drilling to continue development of 10 partially depleted fields in the Campos basin. Water depths in these fields range from 250 to 2,600 m. Multiple new systems are being developed by a joint industry project to conduct these operations, including a four-phase separation system, a riser-top rotating head, new aerated drilling fluids and a wireline-transmission MWD tool. The first field test is planned this year with a semisubmersible in 454-m water.

New tools, techniques. Many important tools and techniques are being developed as a result of the increasing use of UBD. A rotating head mounted below the slip joint on a riser has been proposed for more than 15 years. Don Hannegan, Williams Tool, showed how they have developed a rotating head, called RiserCap, to give an equivalent capability for use in the Petrobras project, Fig. 2. It will be connected to the drilling choke and surface separation system with 4-in. hoses after installation on top of a closed riser slip joint. The actual head was displayed during the workshop at an open house at LSU’s Petroleum Engineering Research and Technology Transfer Laboratory.

Darryl Bourgoyne, BEI, and Ian Calder, ABB Vetco Gray, introduced two new systems that are evolving from underbalanced drilling technology. The Williams Tool Co. system is called a Virtual Riser, and the ABB system is described as a Shallow Water Flow Diverter. Both would use a seafloor rotating control head and a choke to impose a controlled backpressure on the annulus at the seafloor while drilling a subsea well without a riser. The back-pressure is used to overbalance shallow, slightly overpressured water or gas formations while drilling with returns to the seafloor, Fig. 3 and Fig. 4.

Currently, these zones are either: allowed to flow during drilling, force casing to be set early, or they must be drilled with a weighted mud that is continuously lost at the seafloor. Drilling with flow can result in seafloor subsidence or cratering, and using mud to drill without returns is very expensive. Both of the new systems are intended to keep overpressured zones killed until after running casing and isolating the zones with cement. This would allow the zones to be drilled safely while extending the interval drilled, with returns to the seafloor, to achieve an appropriate casing point for the casing string supporting the high-pressure wellhead.

Two additional presentations were made relative to underbalanced operations. Bob Davis, Signa Engineering, explained the importance of analyzing accumulator and ram closure performance during BOP tests. Don Hannegan, Williams Tool, and Steve Kropla, IADC, described the ongoing development of a new WellCAP training program for UBD.

Well Control Research

MMS and LSU have conducted a continual program of research to improve well control technology for offshore operations since 1979. Ted Bourgoyne started the second day’s presentations with an overview of the current five-year program focused on underground blowouts. A number of specific tasks are essentially complete and have been described in previous workshops. These include fracture resistance of shallow sediments, automated detection of underground blowouts, and requirements for dynamic kills of underground blowouts. The overall program will be completed this year.

Sustained casing pressure is defined as the presence of pressure that builds back up after bleeding a tubing-casing or casing-casing annulus. It exists on more than 11,000 annuli in 8,000+ wells in the Gulf of Mexico. The overall problem and the beginnings of R&D to diagnose / remediate these problems were featured in the 1997 / 1998 workshops. LSU’s recent efforts have been focused on prevention / remediation aspects of the problem as it occurs in casing-casing annuli, Fig. 5. The extent of the sustained casing pressure problem implies that these and other efforts to diagnose, control, and permanently isolate these problems will need to continue beyond the current program.

Casing displacement system. Frank Ditka, ABB Vetco Gray, gave an update on a system that has been developed to insert a flexible hose through the casing annulus valve on a wellhead. The advantage is the ability to displace annulus fluids with a denser fluid from the tip of the hose back to surface. To date, this system has been used in three wells. Significant reductions in casing pressure have been achieved in two of the wells. A more advanced system is being developed, with more than 20 additional wells identified for treatment.

Somei Nishikawa, LSU, described his research on remediation of sustained casing pressure using injection and downward settling of dense liquids in a casing annulus. He has tested several dense liquids for potential injection into less-dense annular liquids using a full-size, clear test cell. Dense, immiscible liquids were most effective. The dense brines commonly used in the field for this purpose tend to flocculate water-based drilling muds and prevent settling. This is a likely explanation for why brine injection has been unsuccessful in some field tests.

Given that a common cause of pressure on casing-casing annuli is fluid migration through imperfect cement jobs, LSU has also been researching potential causes of cement failures. Desheng Zhou, LSU, presented his research concerning the potential for cement-to-formation bond failure causing sustained casing pressure. He concluded that the contact stress between the set cement and open-hole formations was controlled by wellbore pressure while the cement is setting. He also concluded that low contact stresses would allow excessive wellbore pressures to cause separation between cement and formation at a lower pressure than required for formation fracture.

Gursat Altun, LSU, described his related work on interpreting leak-off tests. A common problem in shallow leak-off tests is non-linear behavior due to fluid loss to permeable formations and / or through channels in the cement. This work has focused on separating the effects of fluid compressibility, leaks and formation fracture to correctly determine the cause of non-linear behavior and whether remedial cementing is required.

Well control for horizontal drilling has increased significantly in importance as larger numbers of horizontal wells — especially wells in higher-pressure and higher-productivity environments — are being drilled. Dimitris Nikitopoulos, LSU, discussed research into the behavior of gas kicks and flows into wells with inclinations above 90°.

This work is still in progress, but it has shown that it is possible for gas to flow counter-current to mud flow and collect in high spots in the horizontal section. Gas and mud flowrates, well inclination and mud viscosity control this tendency. The collection of large volumes of gas in the horizontal section is a likely explanation for large kicks causing rapid increases in surface pressure in some horizontal gas wells drilled in Louisiana. These phenomena are just beginning to be explored quantitatively and will need more extensive experimental research to provide reliable guidelines for field operations.

Ted Bourgoyne reviewed work performed at LSU to improve the functionality of drillstring safety valves. Brian Tarr, Mobil, provided complementary information on work by API and GRI. Apparently, most manufacturers believe that the market will not pay the increased cost for valves with more effective sealing mechanisms and more practical torque requirements for closing under pressure.

This author gave an update on work at LSU to develop training modules for prevention / remediation of underground blowouts. Recent work has focused on simulator exercises and a programmed learning module. The simulator exercises recreate specific critical situations in actual case histories so that trainees can make, implement and observe results of their own decisions. The programmed learning module is being built to provide a mechanism for individual training based on a case history that has been used for effective group learning exercises.

Future Research Opportunities

The workshop concluded with sessions focused on needs / opportunities for research to improve future operations. John Shaughnessy, BP-Amoco, described current and emerging challenges for effective well control in ultra-deepwater operations. He highlighted the need for special training to pass on lessons learned by experience to new personnel manning the ten-fold increase in rigs capable of working in deep water. He also emphasized the need to look for new problem areas related to: large swings in well temperature from producing to shut-in, equipment fatigue and intervention techniques. Better pore / fracture pressure interpretations and new technology, such as dual-density or riserless drilling, will also be important to the economic viability of deepwater development.

Representatives from LSU’s Coastal Marine Institute and petroleum, mechanical, industrial and chemical engineering departments introduced additional areas of interest for offshore oil and gas operations. These included the detection, "fate," effect and cleanup of deepwater blowouts and leaks, human factors and safety concerns for offshore operations, materials research for deepwater structures, dual-density riser systems for deepwater drilling and opportunities to reduce time requirements for — and improve interpretation of — BOP test results.

Paul Martin, Technology Assessment and Research Chieffor MMS, gave the final presentation. He explained strategies being used by MMS to meet new regulatory challenges resulting from both maturing shelf production and unknowns relating to ultra-deepwater operations. Of particular importance to the workshop audience were: 1) movement away from the well-control focus to cover a broader range of topics, and 2) the intent to participate in joint-industry projects to leverage limited research funds.

The workshop concluded with a wide-ranging discussion of topics addressed over the two days. LSU appreciates the broad-based participation in this workshop and the opportunity to both facilitate and participate in the delivery of practical technologies for use by industry and regulators alike. It will endeavor to engage both industry and regulatory participation in future research and technology transfer to continue its legacy of supporting the progress and long-term viability of the upstream oil industry.

Additional details on most of the presentations described herein can be found in the workshop proceedings. Copies can be provided on request by contacting John Rogers Smith or Jeanette Wooden at LSU, Tel. 1 225 388 5215. Note: By cooperative agreement, the information in this article will also be published in the June 1999 issue of The Brief.

The author

John Rogers Smith, an assistant professor in the Craft and Hawkins Department of Petroleum Engineering at Louisiana State University, holds a BS in electrical engineering from the University of Texas, and MS and PhD degrees in petroleum engineering from LSU. He worked for Amoco Production Co. for 23 years in drilling, production, facilities and research. His primary interests are rock / drilling mechanics, well control, well design and completions. He is a life member of SPE, a member of AADE, ASME and ARMA, and a registered professional engineer.

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Copyright © 1999 Gulf Publishing Company