Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1998-04-28
2001-02-13
Warden, Jill (Department: 1743)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S138000, C166S270000
Reexamination Certificate
active
06187719
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved oil based well bore fluids known in the oil service industry as drilling fluids, and, in particular, to oil based invert emulsion types of drilling fluids in which water is dispersed in an oil-based medium. The invention is particularly directed to providing enhanced viscosity and anti-settling properties to such fluids over the wide temperature ranges found in more recent drilling operations; that is, the ability of the fluids to possess the proper viscosity profile, and to retain in suspension in their structure and to convey along with the fluid, a variety of types of solid particles, the most important of which are bore-hole cuttings. These properties are particularly valuable when non-vertical directional and deep water drilling is undertaken.
2. Description of the Prior Art
The oil industry has used “drilling muds” or drilling fluids since the beginning of United States oil well drilling operations in Pennsylvania, Texas and Oklahoma. These drilling fluids are pumped under pressure down through the string of drill pipe already in the ground, then through the center of the drilling bit, and then return up through the space between the outside of the drill pipes and the borehole wall finally being brought back up to the surface. Drilling base fluids, the liquid carriers of the system, are often comprised of oils (diesel, mineral and poly(alpha-olefin)), propylene glycol, methyl glucoside, modified esters and ethers, water, and emulsions of oil and water of varying proportions.
A drilling fluid must accomplish a number of interrelated functions for it to satisfy the minimum requirements for a commercial drilling fluid. These functions can be grouped as follows:
(1) The fluid must constantly lubricate the drill bit so as to promote drilling efficiency and retard bit wear,
(2) The fluid must have a proper thickness or viscosity to meet the many different criteria required by the drill owner/operator,
(3) The fluid must provide filtration control,
(4) The fluid must suspend and transport solid particles to the surface for screening out and disposal, and
(5) The fluid must keep suspended solid particles and weighting agents (to increase specific gravity of the mud; generally barytes; a barium sulfate ore, ground to a fine particle size), when drilling is interrupted.
The above functions must be satisfactorily provided throughout the time the fluid is in the entire length of the drill hole. Since the drill hole can be as much as tens of thousands of feet long, varying and extreme temperatures are encountered, which temperature changes effect the fluid's physical properties and performance.
The interrelatedness of the above functions can be seen by the fact that the unwanted materials to be removed at the surface can include not only “cuttings” from the material through which the bit is passing, but also pieces of the drill bit itself, barytes or other weighing materials, and substances such as gellants, dissolved gases, and salts created when other fluid constituents become “spent” under the high temperatures encountered in the bottom of deep wells. Sometimes various constituents fuse into agglomerated particles using present additives if low temperatures are encountered in the “trip” back to the surface.
Finally, it should be noted that a drilling fluid must perform its various functions not only when the drill bit is actively encountering the bottom of the borehole, but also at all times and at all locations in the drill stem. In particular, cuttings must be held in suspension through their long journey back to the surface through regions of quite different and varying temperatures compared to that found in the hole at depth.
A drilling fluid is typically a thixotropic system; that is, (1) it exhibits low viscosity when sheared, such as on agitation or circulation (as by pumping or otherwise) but, (2) when such shearing action is halted, the fluid thickens to hold cuttings in place; the fluid must become thick relatively rapidly, reaching a sufficient gel strength before suspended materials fall any significant distance—and (3) this behavior must be totally reversible at all temperatures encountered. In addition, even when a free-flowing liquid, the fluid must retain a sufficiently high viscosity to carry all unwanted particulate matter from the bottom of the hole to the surface. To maintain these functions under the widely varying temperatures encountered in deep water drilling has proved extremely difficult with the use of commercial rheological drilling fluid additives presently available on the market.
One of the principal problems facing “mud chemistry” scientists is the production of thickening agents, thixotropes and drilling fluids having satisfactory dispersibility, with the necessary subsidiary thixotropic properties discussed above, while at the same time possessing critically important antisettling properties over a wide range of temperatures. While the compositions of these various fluids is considered a “black art” to many, in reality, fluids and their additives involve highly complex chemical, physical and rheological analysis using state-of-the-art scientific apparatus and intricate mathematical calculations and modeling.
A different measure of control during drilling occurs because of wide ranges of a) encountered temperature (from as low as below 5° C. to as high as 200° C.), b) time durations, c) pressures (from only a few bars to those exerted by a column of fluid that can extend for thousands of feet) and d) drilling directions (from vertical to horizontal).
Accordingly, a search has been going on for many years for an improved additive for modifying and controlling the suspension properties of drilling fluids that would be efficient, easily handled, and readily dispersible in a broad range of drilling muds, and be usable under a broad range of temperature and pressure conditions.
Drilling Mud Circulation
As was noted above, drilling fluid is pumped under pressure down through the string of drill pipe, through the center of the drilling bit, then through the annulus between the outside of the drill stem and the borehole wall, back up to the surface. This circulation constantly removes cuttings from the instantaneous bottom of the hole, and lifts them the entire distance from this bottom to the surface for disposal. Such a distance today can be in the thousands or tens of thousands of feet and involve quite remarkable changes of temperature.
Further, it is desirable for the drilling fluid to possess less dynamic anti-settling properties when being circulated down the drill pipe and out the bit, and to have higher viscosity and anti-settling properties while rising through the annulus. Unless the fluid removes cuttings from beneath the bit before the next bit tooth arrives, the cuttings will be reground into a finer particle size, and made more difficult to remove by screening and also materially slow down the rate, since the same material is being reground over and over again. The presence of unremoved cuttings in the fluid will decrease drilling penetration rates, with resultant increase in the overall costs of drilling the well.
Once in the annulus, the cuttings which are generally denser than the drilling mud itself, tend to settle downward under the influence of gravity. The upward velocity of the drilling fluid in the annulus must be higher than the settling rate, so as to bring the cuttings to the top of the hole. All of the above properties must largely be independent of temperature.
Off Shore Deep Water Drilling and Temperature Sensitivity
In modern times, hydrocarbon drilling for exploratory and production wells has increasingly been done from platforms located in water settings, often called off-shore drilling. Such fresh and salt water drilling employ floating barges and rigs fixed in some fashion to the submerged surface of the earth.
Economic and technical advances have recently pushed these drilling operations into deeper waters. Although adva
Chiavoni Araxi
Cody Charles
Dino David
Magauran Edward
Cronin Michael J.
Cross Latoya J.
Rheox Inc.
Warden Jill
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