Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1999-12-23
2002-01-15
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S133000
Reexamination Certificate
active
06339048
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF INVENTION
The invention hereof relates to improved drilling fluids also known in the oil service industry as drilling muds, and, in particular, to oil and invert oil based emulsion types of drilling fluids in which water is dispersed in an oil-based medium. Such drilling fluid compositions when prepared at a mud plant are often called mud plant formulations.
Mud plant formulations contain special materials to enhance drilling fluids properties such as rheology, therefore providing a drilling fluid that is homogeneous and stable and which prevents the weighting material used from settling out during transportation and storage. Once the drilling fluid is used and circulated through the bore-hole it becomes known as a field mud, indicating the mud contains bore-hole cuttings and other contaminants. Additives used to enhance specific properties of the mud plant formulation should not adversely affect mud performance while in the bore-hole. However, these materials in a preferred manner also provide on-going beneficial properties and enhanced mud performance during circulation through the bore hole.
The invention is particularly directed to providing novel fluids with enhanced rheological and anti-settling properties; anti-settling is the ability of the fluids 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 weighting materials and bore-hole cuttings. These properties are particularly valuable when non-vertical directional drilling is undertaken.
The present invention particularly relates to drilling fluid compositions or systems containing a described liquid additive that also reduces or eliminates settling of the weighting material during storage and transportation to the rig and during the drilling operation. The present invention more particularly involves a drilling fluid containing an improved additive which additive is in a pourable, liquid form at ambient temperatures and which does not need a solvent to achieve its liquid state. Such an additive, when incorporated under low shear mixing typically encountered in the mud plant into a drilling fluid, provides improved suspension of weighting agents and other additives both during storage, during transport to the rig and during use in the bore hole.
Surprisingly the additive, described below at length, works in a most preferred embodiment in a synergestic and harmonious manner with organoclays in the fluid, to provide a system which effectively works at both low shear and ambient temperature and at high shear and elevated temperatures.
BACKGROUND OF THE INVENTION
Drilling Fluid Compositions
United States oil industry rotary bit discovery drilling operations use “drilling muds” or drilling fluids. These muds are pumped under pressure down through a long string of drill pipe, then through the center of the drilling bit at the hole bottom, then back up through the annulus between the outside of the string of drill pipe and up the borehole wall to the surface. Oil-based drilling fluids, the liquid carriers of the mud, are often comprised of oils (diesel, poly alpha olefins or mineral, propylene glycol, methyl glycoside, and modified esters and ethers) and invert emulsions of oil in which water is dispersed in an oil-based medium.
Drilling muds provide a number of interrelated functions to satisfy the requirements of the oil industry for a commercial drilling fluid. These functions may be grouped as follows:
(1) The fluid must suspend and transport solid particles to the surface for screening out and disposal.
(2) It must transport a clay or other substance capable of adhering to and coating the uncased borehole surface, both (a) to exclude unwanted fluids which may be encountered, such as brines, thereby preventing them from mixing with and degrading the rheological profile of the drilling mud, as well as (b) to prevent the loss of downhole pressure from fluid loss should the borehole traverse an interval of porous formation material.
(3) It must keep suspended an additive weighting agent (to increase specific gravity of the mud), generally barytes (a barium sulfate ore, ground to a fine particular size), so that the entire column of drilling fluid is not interrupted upon encountering pressurized pockets of combustible gas, which otherwise would tend to reduce downhole pressure, as well as creating a “blowout” in which the fluid and even the drill stem are violently ejected from the well, with resulting catastrophic damages, particularly from fires.
(4) It must constantly lubricate the drill bit so as to promote drilling efficiency and retard bit wear.
The interrelatedness of these 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, the barytes or other weighing materials, and substances particles such as gellants, dissolved gases, and salts created when other fluid constituents become “spent” under the high temperatures encountered in deeper wells, and sometimes fuse in agglomerative particles. Every substance added to achieve a desirable property, such as improved lubrication or pressure control, potentially results in the ultimate creation of a waste to be removed.
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 times when the drill stem is inactive, or is being removed or re-inserted for some purpose. In particular, cuttings must be held in suspension in the event of shut-downs in drilling.
The Anti-settling Properties of Drilling Fluid Compositions
An ideal drilling fluid is a thixotropic system. That is, (1) it will exhibit low viscosity when sheared, such as during agitation or circulation (as by pumping or otherwise) but, (2) when the shearing action is halted, the fluid must set or gel to hold the cuttings in place, and it must become gelled relatively rapidly, reaching a sufficient gel strength before suspended materials fall any significant distance and (3) this behavior should be almost totally reversible. In addition, even when it is 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. Moreover, upon long-term interruption of circulation, such as when drilling fluid has been ejected from the borehole into a quiescent holding vessel or pond, the gel structure should be such as to allow the cuttings and other unwanted particulates over time to settle out from the liquid fraction.
A principal problem facing “mud chemistry” scientists and technicians is the production of drilling fluids, with the necessary thixotropic properties discussed above, which at the same time must possess critically important anti-settling properties. Drilling compositions have over the years involved the attention of both scientists and artisans, with scores of various improvements made and patented. The compositions of these various fluids may be considered a “black art” to many—in reality such fluids and their additives involve highly complex chemical, physical and rheological analysis using advanced scientific apparatus and intricate mathematical calculations and modeling.
“Anti-settling” involves considerations of assurance of suspension and control of widely-varying matter including weighting materials during transportation of the fluid to the drilling site. It ideally entails the necessity of a measure of control when shear rate and force is high, low, or non-existent, and requires control of syneresis and deposition of such particles over wide ranges of a) temperature (from 0° to as high as 300° 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).
A search has been going on for m
McNally Keith
Santhanam Mahalingam
Cronin Michael J.
Elementis Specialties, Inc.
Tucker Philip
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