Patent Application
20130037325
1. Field of the Invention
This invention relates to the drilling of boreholes in subterranean formations.
2. Description of the Prior Art
The drilling of boreholes for use in forming oil wells, natural gas wells, exploration drilling rigs, and the like, is commonly performed with the aid of a drilling fluid, commonly referred to as “drilling mud.” The drilling fluid typically serves as a lubricant and coolant for the drill bit or drill string, and also as a carrier fluid to remove cuttings from the borehole as the borehole is being formed. To serve these functions, the drilling fluid is circulated through the drill pipe or string that supports the bit as the pipe or string is rotating. The drilling fluid is often pumped downward through the string to cross the drill bit at the lower end of the string. The fluid then returns to the surface by traveling up the annular space between the drill string and the sides of the hole being drilled. The composition of the fluid will be chosen to meet the requirements of the particular drilling operation, including the composition, density, porosity, and fluid content of the formation in which the borehole is being formed as well as the function(s) that the drilling fluid is intended to serve. Oil-based fluids, fresh-water aqueous fluids, salt-water aqueous fluids, and polymer-based fluids have all been used.
A problem that is often encountered with the use of a drilling fluid is loss of the fluid to the surrounding formation. Such loss will result in a loss of the cooling and lubricating functions, as well as a loss of hydrostatic pressure at the bottom of the borehole, which can lead to the influx of fluids from the formation into the borehole. Among the reasons for the loss of drilling fluid are formations that are not sufficiently dense to withstand the hydrostatic pressure that must be applied to the drilling fluid, fissures in the formations, and the porosity of the formations. The problem is typically mitigated by the use of additives to the drilling fluid that are known as lost circulation materials, i.e., materials designed to reduce or eliminate the loss in circulation of the drilling fluid by closing the gaps or pores or the foundation at the borehole walls.
The worksites where borehole drilling is performed are typically at remote locations, however, and the transport of equipment and supplies, including drilling fluid and lost circulation material, is an integral part of the cost of the borehole. Any means of reducing the consumption of supplies at the worksite, therefore, is a benefit.
It has now been discovered that the packaging material for drilling fluid can be used as lost circulation material, by shredding the packaging material to a size that is comparable to the particle sizes of lost circulation materials of the prior art. The shredding can be done at the worksite by first removing the drilling fluid from its packaging and then running the empty packaging material through a shredder. The result can be a reduction, and in some cases an elimination, of the cost of the lost circulation material, or of the transport of the lost circulation material, as well as an elimination of the need for disposal or recycling of the packaging material in which the drilling fluid was supplied. The shredded packaging material can serve either by itself as the entire lost circulation material or it can be used to supplement lost circulation materials of conventional composition and from conventional sources. In addition, if conventional lost circulation material is purchased from an outside source or shipped to the worksite, or both, the packaging in which this lost circulation material was shipped can itself be shredded and used as further lost circulation material.
Drilling fluid is typically a liquid or a slurry, and is most often packaged in containers of paper, plastic, or wood, or combinations such as plastic-lined paper or plastic-lined wood. The containers are typically in the form of barrels or tubs. Shredding of the empty containers can be achieved by conventional shredding equipment, such as shredders, both wet and dry, grinding mills, roller mills, and hammer mills. The optimal equipment will vary with the material to be shredded. Shredding can be done to a size that compares with the sizes of conventional lost circulation materials, and the optimum sizes will vary with the nature of the drilling fluid, and the condition and composition of the formation. In most cases, particle sizes of about 0.25 inch (0.6 cm) or less, or from about 0.01 (0.025 cm) inch to about 0.25 inch (0.6 cm), will suffice, although in certain cases it may be beneficial to use smaller sizes, such as from about 0.01 (0.025 cm) inch to about 0.1 inch (0.25 cm). The amount of the shredded material used relative to the amount of drilling fluid will also be the same as that used with conventional lost circulation materials. In most cases, the desired results will be obtained with from about 10 kg to about 150 kg per square meter of drilling fluid, and in certain cases, from about 20 kg to about 50 kg per square meter of drilling fluid.
In the claims appended hereto, the term “a” or “an” is intended to mean “one or more.” The term “comprise” and variations thereof such as “comprises” and “comprising,” when preceding the recitation of a step or an element, are intended to mean that the addition of further steps or elements is optional and not excluded. All patents, patent applications, and other published reference materials cited in this specification are hereby incorporated herein by reference in their entirety. Any discrepancy between any reference material cited herein or any prior art in general and an explicit teaching of this specification is intended to be resolved in favor of the teaching in this specification. This includes any discrepancy between an art-understood definition of a word or phrase and a definition explicitly provided in this specification of the same word or phrase.
