Earth boring – well treating – and oil field chemistry – Well treating – Contains inorganic component other than water or clay
Reexamination Certificate
2001-11-09
2004-06-22
Tucker, Philip C. (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
Contains inorganic component other than water or clay
C507S906000, C507S924000, C166S280100, C166S308400, C501S127000, C501S128000, C501S129000, C501S130000, C501S131000, C501S133000
Reexamination Certificate
active
06753299
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to oil and gas well proppants and, more particularly, to sintered proppants made from ingredients which can be uncalcined, partially calcined or fully calcined, a method of making such proppants, and to a method of maintaining a fracture in a subterranean formation in a propped condition by utilizing such proppants.
Oil and natural gas are produced from wells having porous and permeable subterranean formations. The porosity of the formation permits the formation to store oil and gas, and the permeability of the formation permits the oil or gas fluid to move through the formation. Permeability of the formation is essential to permit oil and gas to flow to a location where it can be pumped from the well. Sometimes the permeability of the formation holding the gas or oil is insufficient for economic recovery of oil and gas. In other cases, during operation of the well, the permeability of the formation drops to the extent that further recovery becomes uneconomical. In such cases, it is necessary to fracture the formation and prop the fracture in an open condition by means of a proppant material or propping agent. Such fracturing is usually accomplished by hydraulic pressure, and the proppant material or propping agent is a particulate material, such as sand, glass beads or ceramic pellets, which are carried into the fracture by means of a fluid, such as oil or water.
Spherical pellets of uniform size are believed to be the most effective proppant body shape due to maximized permeability. For this reason, assuming other properties to be equal, spherical or essentially spherical proppant bodies, such as rounded sand grains, metallic shot, glass beads and tabular alumina, are preferred. Examples of prior art proppants and their use are found in U.S. Pat. Nos. 2,950,247, McGuire, et al.; 3,026,938, Huitt, et al.; 3,126,056, Harrell; 3,497,008, Graham, et al.; 3,976,138, Colpoys, et al.; and 4,068,718, Cooke, et al.
There has been an evolution in the development of manmade proppants since the 1970′s. The early manmade proppants were produced from high alumina based feedstocks such as bauxite, a material commonly used to produce high alumina bodies. Bauxite was a popular feedstock because it was readily available, many of the early producers had a good working knowledge of the material in conjunction with prior work in abrasives and refractories, and the cost was consistent with initial demands of the enhanced oil and gas recovery market. The early proppants had the advantage of high strength when compared with the traditional proppant, sand, used in hydraulic fracturing, a basic method of enhanced oil and gas recovery. The high strength of the alumina can be directly related to the high specific gravity and therefore bodies fabricated from these materials have high densities.
The hydraulic fracturing process requires that the proppant be suspended in a fluid and pumped under pressure into the well. To maintain the suspension of the proppant the viscosity of the fracturing fluid must be capable of keeping the proppant suspended. For deep wells, the high specific gravity and associated high viscosity required to adequately fracture a well, may be acceptable when maximum proppant strength is required. Not all oil and gas wells are of sufficient depth to require proppants with high strength. It is especially true of shallow depth wells that have been successfully enhanced by fracturing using sand as the propping agent.
By the late 1970′s it became evident that there was a need for a proppant with lower density, lower cost, and the presumably lower strength. During the next two decades proppants became available with lower specific gravities. The density or specific gravity of these proppants was reduced by replacing the alumina content having a theoretical density of 3.95 grams per cubic centimeter with silica having a theoretical density of 2.5 grams per cubic centimeter. The original bauxite based proppants of the early 1970′s contained >80% alumina (Cooke). Subsequent generations of proppants contained an alumina content of >70% (Fitzgibbons), 40% to 60% (Lunghofer), and later 30% to <40% (Rumpf, Fitzgibbons).
The other major element typically contained in proppants is silica. As mentioned above, the replacement of the alumina with the silica resulted in a proportionate drop in the density of the proppant material and a decrease in strength in most cases. It is believed that the proppant's strength was associated with the crystalline corundum phase, mullite phase, and/or silica-cristobalite phase (Rumpf). Many prior inventors expressed a desire to maintain the silica contained in the raw material and/or sintered proppants in either the amorphous phase or cristobalite phase. In addition, many prior inventors recommended that the quartz phase of silica was to be specifically avoided or limited in proppant compositions. The quartz phase is known to undergo an inversion at 573° C. from &agr; to &bgr; form during which a thermal expansion occurs upon heating and is reversed during cooling. Inversions of this type are often associated with cracking or inducing a stress in a quartz containing body subject to thermal treatment above the inversion temperature of 573° C.
As a result, it is desirable to develop a proppant having a composition with a highly reduced bauxite component. In addition, it is desirable that any such proppant material maintain relatively high permeability as well as high end strength so that it is capable of effective use in shallow as well as deep wells.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a proppant composition capable of being used as an oil and gas well proppant that includes a reduced amount of bauxite and/or alumina.
It is another object of the invention to provide a proppant composition that includes quartz as a material component of the composition.
It is still another object of the invention to provide a method for forming the above composition which can employ either a high intensity mixer or a spray fluidizing bed to form spherical pellets.
It is still a further object of the invention to provide a method for forming the proppant composition which sinters the spherical pellets utilizing a rotary kiln, a box kiln, or a fluidized microwave sintering bed.
The subject of this invention is a proppant using as its raw materials; quartz, shale containing quartz, bauxite, talc, and wollastonite. The resultant proppant made from such raw materials may contain as much as 65% quartz, and has yielded sufficient strength to be used in wells to a pressure of 10,000 pounds per square inch. Also, the resultant proppant has an alumina content of less than 25% by weight, and a silica content of greater than 45% by weight.
The quartz and shale representing >60% of the raw materials are inexpensive and readily available. Quartz is one of the most readily available and least expensive materials in the world. (Ref.
Crystalline Silica Primer
, U.S. Bureau of Mines, Dept. of the Interior, pp 11,12). The use of uncalcined bauxite, including the weight of the crystal water, represents <33% of the raw material required to produce the proppant and is of a low grade and is considered relatively inexpensive. The alumina content of the bauxite is low and contributes <25% and preferably <20% of the total proppant weight. The talc and wollastonite represent <10% of the raw material and are available on the world market to satisfy the desire to utilize low cost materials. The source of the silica may be from sand, clay (in the form of fine particles of hydrous aluminum silicates) and the bauxite.
The raw materials may contain low amounts of surface moisture that need not be removed. The surface moisture need only be remove if it is excessive or if the moisture removal is required by the preferred crushing and grinding method to prevent agglomeration. The raw material must be ground to an acceptable size, however there is no requirement to eliminate
Lunghofer Eugene P.
Wolfe Larry A.
Andrus Sceales Starke & Sawall LLP
Badger Mining Corporation
Tucker Philip C.
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