Well Control Considerations - Offshore Applications of Underbalanced Drilling Technology
- Don M. Hannegan (Weatherford Drilling and Intervention Services) | Glen Wanzer (University of Oklahoma Blowout Preventer School)
- Document ID
- Society of Petroleum Engineers
- SPE/IADC Drilling Conference, 19-21 February, Amsterdam, Netherlands
- Publication Date
- Document Type
- Conference Paper
- 2003. SPE/IADC Drilling Conference
- 3.1.6 Gas Lift, 4.2 Pipelines, Flowlines and Risers, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.7.5 Well Control, 3 Production and Well Operations, 4.1.5 Processing Equipment, 1.7.6 Wellbore Pressure Management, 4.6 Natural Gas, 5.4.2 Gas Injection Methods, 2.1.7 Deepwater Completions Design, 1.3.2 Subsea Wellheads, 4.2.4 Risers, 1.10 Drilling Equipment, 5.8.3 Coal Seam Gas, 1.7.1 Underbalanced Drilling, 1.7.2 Managed Pressure Drilling, 1.7 Pressure Management, 4.1.2 Separation and Treating
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This paper focuses upon the well control aspects related to offshore applications of the tools and technology normally associated with underbalanced drilling systems (UBS). A discussion of the history of underbalanced drilling and the evolution of the specialized equipment required to practice the technology with a well established and commendable well control track record will help one recognize the potential benefits of offshore application. Whether onshore or offshore, a key component of UBS is a rotating diverter control head (RCH). As a key tool, the development of RCH's enabled the technology of onshore UBD and led the way towards encouraging the development of numerous other pieces of the UBS "tool chest". RCH's are fulfilling the same enabling role offshore, including leading the way towards numerous non-underbalanced drilling uses. Offshore applications of the tool include "onshore models" atop surface blowout prevention stacks (BOP's). Several "offshore variations" of the tool enable deepwater drilling (subsea BOP) with lightweight fluids, managed pressure drilling, dual gradient deepwater drilling, slim riser deepwater drilling with a surface BOP, and one subsea model facilitates controlling abnormally pressured aquifers and/or achieving zero discharge when riserless drilling top hole sections when establishing a subsea wellhead.
Barriers to achieving a true state of underbalance during an offshore well's drilling program include wellbore instability, dealing with produced hydrocarbons, and in some cases, regulatory restrictions. Offshore applications were the intent in using UBS was to drill ahead under a true state of underbalance now total around 100 wells. All but one has been drilled from rigs a surface BOP's. In deeper waters from floating rigs with subsea BOP's, the trend to drill underbalanced is expected to be more aggressive in the future given the large percentage of all known deepwater resources being economically undrillable otherwise.
In the nearer term, non-underbalanced drilling applications of the specialized equipment and technology associated with underbalanced drilling is much less of a step-change and avoids the aforementioned barriers to true underbalanced drilling offshore.
Therefore this discussion places emphasis upon the non-underbalanced drilling applications of the specialized equipment associated with underbalanced drilling and illustrates the well control considerations.
In the context of this paper, well control implications relate to the potential for surface events as well as underground blowouts.
Background and Onshore History of UBS
Underbalanced drilling (UBD) is defined in its most simple terms as drilling ahead with a fluid that imparts a hydrostatic head less than the pore pressure of the formation being drilled.
For several decades now, many tens of thousands of onshore wells have practiced applications of the tools and technology of UBD. The specialized equipment requirements to practice the technology safely and with minimum negative environmental consequences have evolved to be well defined. Equipment availability has facilitated the evolution of several variations of underbalanced drilling.
Compressible fluids drilling (natural gas or air) began over 30 years ago in the Arkoma Basin of western Arkansas and eastern Oklahoma. Low pressure (500 psi) passive seal-type (stripper rubber) RCH's were developed, served as rotating diverters and encouraged the use of choke manifolds, gas busters, IBOP's, and pilot lit flarestacks when drilling for sweet gas in tight sandstone.
For drilling sour gas and depleted zones/reservoirs in western Canada, closed system underbalanced drilling systems were developed. Active seal-type and redundant barrier design RCH's were developed to assure low pressure sealability with sour gas. The balance of the closed system for UBD came to include multi-phase separation (oil, gas, mud, cuttings), nitrogen generation systems and stable foam drilling fluids.
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