«Paper #2-11 SUBSEA DRILLING, WELL OPERATIONS AND COMPLETIONS Prepared by the Offshore Operations Subgroup of the Operations & Environment Task Group ...»
Since the formations penetrated in subsea wells are typically thicker or more dispersed compared with formations penetrated by onshore wells, barriers to successfully completing subsea wells include bigger gravel-pack job volumes, more wear on downhole components, and various surface issues related to fluid and gravel storage prior to pumping the job. Pumping up to 1.2 million pounds of gravel at rates up to 60 barrels per minute are not uncommon. Performing all the gravel placement operations without multiple trips is an obvious advantage to some completion types (Burger et al., 2010).
Production issues for multiple-zone, sand-control completions include water invasion (sometimes in a wormhole fashion) (Wibawa et al., 2008) and stability of the gravel pack over time. Water or other unwanted fluid invasion is sometimes addressed by inflow control devices and the use of fiber optics to monitor inflow is possible (Berthold, 1997). Intelligent well completions also offer downhole monitoring and control of flows (Mathiesen et al., 2006).
After the lower completion is successfully installed and gravel packed, an isolation or barrier valve is closed to protect the formation from damaging effects of overbalanced fluid while the upper completion is run. The time and method required to open the isolation valve in conjunction with other monitoring or well control products is typically a focus of improvements in well operations.
The upper completion typically consists of a lower production packer, tubing, and a subsurface safety valve (SSSV). The operations of the packer and SSSV have been the focus of new technology to overcome the barriers of time and consistency of operation as subsea completions move into ever deeper water. Hydrostatic set packers (Maldonado et al., 2006), pressure-pulse set packers (Simonds et al., 2000) and electric-operated safety valves (Bouquier et al., 2007) are all examples of how technology has developed to address the issues. Electric operations remove the issue of pressure loss down hydraulic control lines in deepwater operations. Other improvements focus on fewer moving parts to achieve higher reliability or isolating moving parts from tubing pressure (LeBoeuf et al., 2008).
Subsea completed wells require technology to address both the produced fluid as well as maintain and manage the hydrocarbons still in the reservoir to obtain the ultimate recovery of the resources. The produced fluids, in combination with the surroundings and/or the changing environment inside the production tubulars, create conditions where asphaltenes and hydrates may form. Those by-products of production are typically managed by chemical injection. The specific challenge of subsea completions is the storage and injection system of the injected chemicals considering the depths, temperatures, and location of the subsea completion relative to the control system.
The produced fluid itself may also attack the production tubulars and form scale or corrosion inside the tubulars. Metallurgical controls on the selection of the production tubulars with knowledge of the producing environment and the stress state of the items is required to adequately plan and manage corrosion and its by-products. Depending on the production rate, the produced fluid may also contain particulates from the reservoir that are large enough, hard enough, numerous enough, and traveling at sufficient velocity to erode the production tubulars or subsea completion equipment. Technology for remote monitoring of production includes both fluid composition and rate as well as equipment wall thickness in critical sections to allow the prediction of remaining life of the equipment. Again, the depths, temperatures, and location of the subsea completion relative to the control system are factors that must be considered in the overall completion plan.
The reservoir containing the hydrocarbons must also be maintained to insure efficient overall recovery of the hydrocarbons. Reservoir management may include pressure maintenance by means of injection of gas or other fluids and possibly a field completion plan using a driving fluid such as gas (Kelly and Strauss, 2009) to recover the maximum amount of hydrocarbons.
Environmental Issues. The barriers and opportunities for subsea completions relative to environmental aspects fall into two categories. The first opportunity is reduction of overall resources needed to develop the hydrocarbon production. Considering the size and mass of steel required to construct an offshore platform, the development of a series of wells using subsea
completions make the latter attractive. Similarly, the economic abandonment point for well production can be optimized with subsea completions considering that they obviate the considerable maintenance requirements and decommissioning costs of topsides structures. Those advantages are not without impact as a topsides structure offer stable platforms that can facilitate well interventions to perform wellbore maintenance such as sealing off unwanted production or permanently abandoning production. The effort required to perform well intervention on a subsea completion by bringing in a support vessel, removing production equipment, etc., is frequently cost-prohibitive relative to simple abandonment. Advances in well intervention without the use support vessels are required to overcome those constraints.
The second category of environmental effects is that on the potential for reduction of spills, leaks, and other releases of hydrocarbons during well construction and production. The subsea completion by its nature is a well-controlled activity as the equipment must be designed to operate under water (at sometimes significant pressures) which, in itself, requires sealed connections to prevent water ingress and therefore prevents hydrocarbon egress. Equipment operating at atmospheric pressure in air may not have such design requirements. Similarly, subsea processing of produced fluids with subsequent re-injection on unwanted fluids for pressure maintenance may be an area where the potential for spills, leaks, and other releases of hydrocarbons are minimized.
C. Long-Term Vision (Year 2050)
The long-term outlook and vision for subsea completions is bright. Continuous advances in materials, sensing capabilities (Berthold, 1997), and control systems (Mathiesen et al., 2006) will allow more economic recovery of resources. Additionally, well and field architecture developments, including multilateral wells and extended-reach drilling, offer even more potential. Adding to those advances are possibilities for complete field development, production and control including subsea processing (Baker and Lucas-Clements, 1990), re-injection, and potential waterflooding all controlled without intervention (Dick, 2005), and matching a predefined model of field drainage.
FINDINGSA review of technologies currently applied in offshore environments to drill and complete subsea wells for hydrocarbon production confirms that many opportunities exist to improve methodologies in ways that can be more economically beneficial and more environmentally sustainable. The combination of deepwater overburden on the wellhead and formation conditions in the deep subsurface place both high-pressure (seafloor and formation) and hightemperature (formation) stresses on materials and equipment that require ongoing research to assure reliability of operations.
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 facing the drilling and completion phases of future offshore oil and gas operations involve changing regulatory requirements that add uncertainty to project planning and cost estimations.
Air emissions, liquid wastes and solid wastes generated by offshore drilling activities are managed in accordance with established permitting processes. Offshore technology developments include techniques for reducing all types of waste.
Specific findings include:
• Significant efforts, and considerable progress, have been made in formulating and handling drilling fluids to be more environmentally friendly. 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.
REFERENCESAlvarado, A. (1998). Regulatory Issues and Deepwater Production. Minerals Management Service, US Department of the Interior. 19 p.
https://www.mms.gov/homepg/whatsnew/speeches/alex.pdf ASME (2010). Boiler and Pressure Vessel Code – 2010 Edition, II. Materials, American Society of Mechanical Engineers. http://www.asme.org/kb/standards/publications/bpvcresources/boiler-and-pressure-vessel-code---2010-edition/ii--materials Baker, A.C. and Lucas-Clements, D.C. (1990). Application of Subsea Separation and Pumping to Marginal and Deepwater Field Developments (20698-MS). SPE Annual Technical Conference and Exhibition, New Orleans, LA, September 23-26, 1990, 7 p.
http://www.onepetro.org/mslib/app/Preview.do?paperNumber=00020698&societyCode= SPE Bernier, R., Garland, E., Glickman, A., Jones, F., Mairs, H., Melton, R., Ray, J., Smith, J., Thomas, D., and Campbell, J. (May). Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations. (Report No.
342). International Association of Oil & Gas Producers, May 2003, 114 p.
http://www.ogp.org.uk/pubs/342.pdf Bernt T. (2004). Subsea Facilities (16553-MS). Offshore Technology Conference, May 3-6, 2004, Houston, Texas, 10 p.
http://www.onepetro.org/mslib/servlet/onepetropreview?id=OTC-16553-MS&soc=OTC Berthold, J.W. (1997). Overview of Fiber Optic Sensor Technology and Potential for Future
Subsea Applications (UTI 97-137). Underwater Technology International Conference:
Remote Intervention, Aberdeen, UK, April 8-10, 1997, 16 p.
http://www.onepetro.org/mslib/servlet/onepetropreview?id=SUT-UTI-97soc=SUT&speAppNameCookie=ONEPETRO BOEMRE (2010a) Information Requirements for Exploration Plans, Development and Production Plans, and Development Operations Coordination Documents on the OCS (NTL No. 2010-N06). U.S. Department of the Interior, June 18, 2010, 4 p.
http://www.gomr.boemre.gov/homepg/regulate/regs/ntls/2010NTLs/10-n06.pdf BOEMRE (2010b) Report on the progress of the Joint Industry Task Forces. Bureau of Ocean Energy Management, Regulation and Enforcement, US Department of Interior, September 7, 2010, 26 p.
http://www.boemre.gov/forums/documents/Final_BOEM_Houston_Sept_7.pdf BOEMRE (2010c). Technology Assessment & Research (TA&R) Project Categories, Offshore Structures, US Department of Interior, December 6, 2010.
Bouquier, L., Signoret, J. P., and Lopez, R. (2007). First Application of the All-Electric Subsea Production System – Implementation of a New Technology (18819-MS). Offshore Technology Conference, Houston, TX, April 30-May 3, 2007, 5 p.
http://www.onepetro.org/mslib/app/Preview.do?paperNumber=OTC-18819MS&societyCode=OTC BP p.l.c. (2011) Jack Ryan Drill Ship. BP p.l.c.
http://www.bp.com/popuppreviewthreecol.do?categoryId=121&contentId=7012268 Bradley, A. A., Brimmer, A.R., Pettus, R. (2006). K2 Subsea Trees and Controls: 15k; 5" Bore;
70 Tons-The Challenges (18302-MS) Offshore Technology Conference, Houston, TX, May 1-4, 2006, 11 p. http://www.onepetro.org/mslib/servlet/onepetropreview?id=OTCMS&soc=OTC Burger, R., Grigsby, T., Ross, C., Sevadjian, E., and Techentien, B. (2010). Single-Trip Multiple-Zone Completion Technology Has Come of Age and Meets the Challenging Completion Needs of the Gulf of Mexico's Deepwater Lower Tertiary Play (128323-MS).
SPE International Symposium and Exhibition on Formation Damage Control, February 10-12, 2010, 20 p. http://www.onepetro.org/mslib/servlet/onepetropreview?id=SPEMS&soc=SPE Cadigan, M. and Payton, K. (2005). Baselining and Reducing Air Emissions from an Offshore Drilling Contractor’s Perspective (94432-MS). SPE/EPA/DOE Exploration and Production Environmental Conference, Galveston TX, March 2005. 3 p.
Code of Federal Regulations (2011a). Code of Federal Regulations, 30CFR250, Title 30:
Mineral Resources, Part 250 – Oil and Gas and Sulphur Operations in the Outer Continental Shelf. US Government Printing Office.