Boring or penetrating the earth – Boring a submerged formation
Reexamination Certificate
1999-04-19
2001-11-13
Tsay, Frank S. (Department: 3672)
Boring or penetrating the earth
Boring a submerged formation
C175S006000
Reexamination Certificate
active
06315061
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to abrine-based drilling fluid and methods for storing such fluids on drilling vessels, and more specifically to storing brine-based drilling fluids in drilling vessel ballast tanks.
BACKGROUND OF THE INVENTION
For may years petroleum companies concentrated on developing oil and gas fields on land. But the world's appetite for energy sources, coupled with diminishing returns from land drilling, has driven petroleum companies to develop offshore reserves.
Sub-sea geologic sediments and structures are often similar and in some cases superior to geologic conditions that have proven highly productive on land. In fact, offshore reserves have been estimated at 21% of the world's proven reserves, with estimates that 40% to 50% of all future resources will come from offshore reserves.
A need exists for a method to store sufficient quantities of drilling fluids on a drilling vessel to reduce the dependency of a drilling operation on supplies brought in by work boats, thereby ensuring uninterrupted drilling in the event of inclement weather.
A further need exists for drilling fluid compositions suitable for storage on a drilling vessel.
Drilling offshore wells in deep water, greater than 1000 feet in depth, creates its own set of problems. When drilling on the edge of the continental shelf, quite frequently pressured shallow depth sands, of apparently artesian flow, are encountered. The depth of these sands and the pressures that they exhibit create a unique well design situation.
The unique well design is the result of being unable to hydrostatically control the shallow water flows (SWF) by the conventional method of returning the drilling fluid to the drilling rig. The hydrostatic head generated by returning the fluid to the rig exceeds the fracture gradients of the rock above the SWF. Therefore, the well is designed in a manner that a fluid of the proper density returns only to the sea floor, riserless drilling.
In a riserless drilling situation, large volumes of drilling fluid are required due to the fact that the fluid is not returned to the rig and reused. Depending upon the depth of SWF, volumes from 10,000 to over 30,000 bbls of drilling fluid could be required. The surface mixing equipment of existing rigs is insufficient to store or prepare the large volumes of fluids required to drill riserless. To date, riserless drilling operations have been dependent upon work boats and barges to store and transport the required fluids that were prepared at land based facilities. Often, bad weather has interrupted the supply of work boats and therefore the supply of drilling fluid, causing the termination of drilling operations.
SUMMARY OF THE INVENTION
The invention contemplates a system for storing, mixing and pumping drilling fluids on drilling vessels such as deep water rigs.
In accordance with one aspect of the invention, a process for storing drilling fluids on a drilling vessel is provided including preparing a drilling fluid suitable for ballast tank storage, transporting the drilling fluid to a drilling vessel, pumping the drilling fluid into at least one ballast tank compartment of the drilling vessel, and trimming the drilling vessel during the addition of the drilling fluid.
In accordance with another aspect of the invention, a drilling fluid is prepared, transported to a drilling vessel, pumped into a ballast tank compartment of the drilling vessel for storage until the drilling operation begins, removed from the ballast tank compartment, mixed with solid particulate matter and pumped into the wellbore during drilling.
The stored drilling fluid will be designed (1) to contain no undissolved solids, (2) to be rheologically stable, (3) to be biostatic, (4) to be capable of suspending particulate matter that is added in the drilling operation, and (5) to provide density through dissolved solids.
The foregoing has outlined, rather broadly, aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the system for storing, mixing and pumping drilling fluids on a drilling vessel will be described hereinafter which forms the subject of the claims of the invention. It should be appreciated by those skilled in the art that the concept and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other processes or compositions for carrying out the same purpose of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for storing drilling fluids in ballast tanks of drilling vessels and drilling fluid formulations suitable for ballast tank storage.
As petroleum companies have turned to developing offshore oil and gas reserves, they have been faced with a number of problems. For example, a number of offshore wells have been lost due to shallow water flows.
The use of weighted drilling fluids during the drilling of offshore wells would be helpful in controlling shallow water flows. A drilling fluid is a liquid circulated through the wellbore during rotary drilling operations. In addition to its function of bringing cuttings to the surface, drilling fluid cools and lubricates the bit and drill stem, protects against blowouts by holding back subsurface pressures, and deposits a mud cake on the wall of the borehole to prevent loss of fluids to the formation. Drilling fluids are formulated to maintain the hydrostatic pressure within the wellbore necessary to prevent shallow water flows into the wellbore.
Drilling fluids are used throughout the drilling process. A drilling operation requires a large quantity of drilling fluid (10,000 to 30,000 barrels) to complete the operation. Such large quantities of drilling fluid present a problem for offshore drilling operations, since the drilling fluid is typically supplied by work boats or barges bringing the drilling fluid from land out to the drilling vessel. However, bad weather can interrupt the supply of work boats and therefor the supply of drilling fluid to the drilling vessel.
Whenever the supply of drilling fluid is terminated, the drilling must cease until the drilling fluid supply is once again available. Interrupted drilling operations require a larger overall quantity of drilling fluid, than uninterrupted drilling operations and such interruptions can put the well at risk of shallow water flows. The present invention addresses this problem by storing sufficient drilling fluid on the drilling vessel to reduce the dependency of a drilling operation on supplies brought in by work boats, thereby ensuring uninterrupted drilling in the event of inclement weather.
A number of drilling vessels (such as floating mini-tension leg platforms like the SeaStar™, floating production systems with semi-submersible drilling and production equipment, tension leg platforms, and SPAR™ platforms, and drillships) are designed with ballast tanks that are filled with fluid to provide platform stability. The ballast tanks are typically filled with sea water and the water level raised or lowered as necessary to trim the platform.
One embodiment of the present invention utilizes ballast tanks of drilling vessels to store large quantities of drilling fluids in order to reduce the dependency of drilling vessels on the supply of work boats during the drilling operation. Drilling fluid formulations are based on an analysis of geologic information gathered about or at the drilling site. Thus drilling fluids with the desired characteristics can be prepared for storage in the ballast compartment of a drilling vessel.
Once the drilling fluid is prepared, a period of predicted good weather is selected, preferably a period of at least two days of predicted good weather is selected. The drilling fluid is loaded on work boats a
Boatman Charles
Estes Brent
Morales Leonard
Halliburton Energy Service,s Inc.
Roddy Craig W.
Tripp Karen B.
Tsay Frank S.
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