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A Study To Determine Necessity of Pilot Holes When Drilling Shallow Gas Zones Using Top Hole Dual Gradient Drilling TechnologyKing, Lauren 16 January 2010 (has links)
When drilling offshore, shallow gas hazards are a major concern because of their
potential to cause a major blowout. This is a special concern when drilling in shallower
water, where the gas influx reaches the rig sooner. A common practice used to avoid the
potential dangers of shallow gas is to drill a pilot hole through the shallow gas zone with
the hope that the smaller diameter hole will prevent such a large influx. The use of dual-gradient
top hole drilling technology would allow for a larger hole to be drilled and the
possible gas influx to be killed dynamically, which I have simulated with the use of a
top hole dual-gradient simulator.
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An evaluation of subsea pump technologies that can be used to achieve dual gradient drillingOluwadairo, Tolulope 15 May 2009 (has links)
Dual Gradient Drilling is an exciting technology which promises to solve the current
technical hurdles and economic risks of Deepwater Drilling. Several techniques for Dual
Gradient Drilling have been proposed to the industry. One such method involves
installing a subsea booster pump at the seafloor with the aim of returning the drilling
fluid back to the rig. The pump will manage annular pressures in the wellbore as
circulation rates and mud weights vary and will permit early detection of wellbore
influxes. Any such pump chosen to achieve this objective will be subjected to very high
differential pressures and will be faced with the onerous task of lifting very abrasive and
viscous mud slurries from the sea floor back to the drilling rig. This distance in deep
water may be well within the range of about 4, 000 – 12,000 feet depending on the
operating water depth of the rig.
Several pump technologies available to the industry were examined. Piston pumps are
very efficient and can withstand the high differential pressures encountered in the
Mudlift Drilling System. However, their drawbacks are their large size and weight and
high initial capital cost and maintenance costs. Centrifugal pumps on the other hand are relatively smaller than piston and diaphragm pumps and are generally less expensive.
Disc pumps, with their non-impingement design are able to handle solids and fluids with
a high gas volume fraction but, like centrifugal pumps, are generally less efficient than
reciprocating pumps. Diaphragm pumps are capable of maintaining a constant rate
regardless of pressure fluctuations. They can handle very abrasive solids with limited
wear on the pump. They also excel at handling very viscous fluids and they can be
modified to handle up to 95% gas volume fraction. Like piston pumps, they have very
high efficiencies.
The potential of each of these pump technologies to meet the requirements for the
Mudlift Drilling System was examined in this thesis. The benefits and drawbacks of
each of these pump technologies were highlighted and modifications to meet the
demands of the mudlift system evaluated.
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Managed Pressure Drilling Candidate SelectionNauduri, Anantha S. 2009 May 1900 (has links)
Managed Pressure Drilling now at the pinnacle of the 'Oil Well Drilling' evolution tree,
has itself been coined in 2003. It is an umbrella term for a few new drilling techniques
and some preexisting drilling techniques, all of them aiming to solve several drilling
problems, including non-productive time and/or drilling flat time issues. These
techniques, now sub-classifications of Managed Pressure Drilling, are referred to as
'Variations' and 'Methods' of Managed Pressure Drilling.
Although using Managed Pressure Drilling for drilling wells has several benefits, not all
wells that seem a potential candidate for Managed Pressure Drilling, need Managed
Pressure Drilling. The drilling industry has numerous simulators and software models to
perform drilling hydraulics calculations and simulations. Most of them are designed for
conventional well hydraulics, while some can perform Underbalanced Drilling
calculations, and a select few can perform Managed Pressure Drilling calculations. Most of the few available Managed Pressure Drilling models are modified
Underbalanced Drilling versions that fit Managed Pressure Drilling needs. However,
none of them focus on Managed Pressure Drilling and its candidate selection alone.
An 'Managed Pressure Drilling Candidate Selection Model and software' that can act as
a preliminary screen to determine the utility of Managed Pressure Drilling for potential
candidate wells are developed as a part of this research dissertation.
The model and a flow diagram identify the key steps in candidate selection. The
software performs the basic hydraulic calculations and provides useful results in the
form of tables, plots and graphs that would help in making better engineering decisions.
An additional Managed Pressure Drilling worldwide wells database with basic
information on a few Managed Pressure Drilling projects has also been compiled that
can act as a basic guide on the Managed Pressure Drilling variation and project
frequencies and aid in Managed Pressure Drilling candidate selection.
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Economical Impact Of A Dual Gradient Drilling SystemPeker, Merter 01 June 2012 (has links) (PDF)
Dual Gradient Drilling (DGD) system is a promising technology that was developed to overcome the deep water drilling problems occurred due to narrow operating window between pore pressure and fracture pressure.
In conventional drilling practice, single mud weight exists from drilling unit to TVD (True Vertical Depth) which creates big hydrostatic pressure in bottom hole ,moreover, minor changes in mud weight results a big pressure changes proportional to the length of hydrostatic column increase with water depth. On the other hand, DGD allows using two different mud weights to get same bottom hole pressure / low gradient drilling fluid from drilling unit to the sea floor and high gradient drilling fluid form the sea floor to TVD, to decrease the effect of water column on mud hydrostatic pressure in TVD.
In this thesis, a conventionally drilled deepwater well was redesigned considering the DGD system and drilled virtually to determine the changes of cost of services and materials on total operation budget to prove the positive impact of system on total operation cost.
This study not only proved the technical advantages of the DGD system, but also showed economical impact of the system on total drilling cost, by decreasing around 19%.
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