ALMOND, Judge.
This is an appeal from the decision of the Board of Appeals affirming the prior art rejections of claims 1, 3, 4, 6,13, 15, 23, and 24 of appellants’ application serial No. 106,473, filed May 1, 1961, for “Improvements in Method of Fracturing Underground Formations and Propping Agent Therefor.” No claim has been allowed.
Appellants’ invention relates to a method of hydraulically fracturing subsurface formations penetrated by well bores to increase the production of fluids therefrom and to a propping agent to be placed in the fracture to hold it open. Such methods are designed to improve production from the well by either creating new flow channels or enlarging existing ones. To accomplish hydraulic breakdown of the producing sections, a thickened fluid having a propping agent consisting of finely divided particles of material suspended therein is injected into the well bore under pressure high enough to overcome the tensile strength of the formation to be fractured. After fracturing occurs, the propping agent carried by the fluid is deposited in the fracture to hold it open. Propping agents such as sand or ground nutshells have been used in this art prior to appellants’ invention.
In the invention here claimed, the propping agent used is ground nutshells or granular hard plant seeds such as peach seeds, the particular novelty asserted being in the selection of such materials to provide a particle size in the range of 4 to 40 mesh screen and having [485]*485an average Krumbein roundness and sphericity in the range of 0.8 to 0.9.
Appellants’ specification defines the terms “Krumbein roundness and spher-icity” as follows:
The term “sphericity” * * * is equal to the ratio of the nominal diameter of a particle to the maximum intercept of the particle. The nominal diameter of the particle is the diameter of a sphere having the same volume as the particle. The maximum intercept of the particle is the diameter of a sphere circumscribing the particle. The roundness of a particle is the ratio of the average radius of corners and edges of the particle to the radius of the maximum inscribed circle. * * *
It is immediately apparent from inspection of the above definitions that the maximum roundness and sphericity value of 1.0 is attained when the particle has the shape of a perfect sphere.
Claims 1, 3, 4, 6 and 23 are drawn to appellants’ propping agent and claims 13, 15, and 24 are directed to a method of fracturing a subterranean formation and propping the fracture open using the propping agent. Claims 1 and 13 are .illustrative and read as follows:
1. An agent for propping open a fracture in a subsurface formation comprising particles of a hard material selected from the group consisting of nutshells and seeds of fruits, said material having a high compressive .strength and the character of deforming without shattering when subjected to compressive load, said particles having an average sphericity and roundness between 0.8 and 0.9 and a size such that said particles pass a No. 4 screen and are retained on a No. 40 screen of the U. S. Sieve Series.
13. A method of fracturing a subterranean formation and propping the fracture open to increase the flow of fluids into a well penetrating said formation comprising pumping a liquid containing a fluid loss reducing additive down the well and applying pressure to said liquid adequate to create a fracture extending from the well into the formation, displacing a liquid containing a fluid loss reducing additive and 0.2 to 0.5 pound of propping agent per gallon of liquid into the fracture adapted to deposit said propping agent in a partial monolayer in said fracture, said propping agent comprising a hard material selected from the group consisting of nutshells and seeds of fruits, said materials having a high compressive strength and the character of deforming without shattering when subjected to compressive load, the particles of said propping agent having a size in the range of 4 to 40 mesh and being further characterized by an average Krumbein roundness and sphericity in the range of about 0.8 to 0.9, and thereafter releasing the pressure on the well.
The references relied upon to support the rejections are:
Clark et al. (Clark) 2,838,116 June 10, 1958
Scott etal. (Scott) 2,943,680 July 5, 1960
McGuire et al. (McGuire) 2,950,247 August 23, 1960
Morse 2,962,095 November 29, 1960
[486]*486The examiner rejected product claims 1, 3, 4, 6, and 23 as unpatentable over Scott and all appealed claims as unpat-entable over Morse in view of Clark with further reference to McGuire under 35 U.S.C. § 103. We do not find it necessary to consider the former ground of rejection since we hold that the latter ground is worthy of affirmance.
Morse teaches the general principle that fractures formed and extended by hydraulic methods “are normally filled or held open by depositing therein a solid granular medium which has a substantial compressive strength and is highly permeable to fluid flow.” With regard to the materials, sizes, and shapes of his propping agents, Morse discloses:
As examples of such organic materials may be mentioned ground hard fruit stones, nutshells * * * preferably formed or ground to approximately uniform sizes * * * a screen size behveen about 8 and about 40-mesh being preferred. The more nearly uniform in size the particles are within this range the greater is the permeability of the fracture that is filled with them. It is also highly desirable that the shape of the particles be rounded so as to be cylindrical or spherical, and when manufactured particles are employed such shapes can be easily provided. [Emphasis ours.]
Thus, Morse teaches the use of the same materials employed by appellants as propping agents, and a “preferred” size range of 8 to 40 mesh, which is only slightly narrower than appellants' claimed range of 4 to 40 mesh, with the same preferred upper limit on particle size. Although Morse does not teach in terms of numerical values for roundness and sphericity, it is clear from the definitions quoted above from appellants’ specification that the “spherical” particles said to be “highly desirable” possess the maximum Krumbein roundness and sphericity of 1.0. Appellants acknowledge in their brief that “the effective teaching of Morse is that spherical propping agents; that is, propping agents having a roundness and sphericity of 1.0 are preferred.”
McGuire teaches the use as propping agents of large particle size materials of “generally spherical” shape. Such particles, like those of Morse, would have a roundness and sphericity of 1.0. McGuire also discloses the preferred practice of depositing the propping agent particles in the fracture as a monolayer. The patent also speaks of the disadvantages inherent in the use of sand as a propping agent and the desirability of using other materials of appropriate size and “generally spherical” shape and having higher compressive strength than sand.
Clark discloses the use of a propping agent, typically sand, in the amount of 0.5 to 10 pounds per gallon of fracturing liquid. With regard to the shape of his propping agent particles, Clark states:
A well rounded sand, typically a sand having a
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ALMOND, Judge.
This is an appeal from the decision of the Board of Appeals affirming the prior art rejections of claims 1, 3, 4, 6,13, 15, 23, and 24 of appellants’ application serial No. 106,473, filed May 1, 1961, for “Improvements in Method of Fracturing Underground Formations and Propping Agent Therefor.” No claim has been allowed.
Appellants’ invention relates to a method of hydraulically fracturing subsurface formations penetrated by well bores to increase the production of fluids therefrom and to a propping agent to be placed in the fracture to hold it open. Such methods are designed to improve production from the well by either creating new flow channels or enlarging existing ones. To accomplish hydraulic breakdown of the producing sections, a thickened fluid having a propping agent consisting of finely divided particles of material suspended therein is injected into the well bore under pressure high enough to overcome the tensile strength of the formation to be fractured. After fracturing occurs, the propping agent carried by the fluid is deposited in the fracture to hold it open. Propping agents such as sand or ground nutshells have been used in this art prior to appellants’ invention.
In the invention here claimed, the propping agent used is ground nutshells or granular hard plant seeds such as peach seeds, the particular novelty asserted being in the selection of such materials to provide a particle size in the range of 4 to 40 mesh screen and having [485]*485an average Krumbein roundness and sphericity in the range of 0.8 to 0.9.
Appellants’ specification defines the terms “Krumbein roundness and spher-icity” as follows:
The term “sphericity” * * * is equal to the ratio of the nominal diameter of a particle to the maximum intercept of the particle. The nominal diameter of the particle is the diameter of a sphere having the same volume as the particle. The maximum intercept of the particle is the diameter of a sphere circumscribing the particle. The roundness of a particle is the ratio of the average radius of corners and edges of the particle to the radius of the maximum inscribed circle. * * *
It is immediately apparent from inspection of the above definitions that the maximum roundness and sphericity value of 1.0 is attained when the particle has the shape of a perfect sphere.
Claims 1, 3, 4, 6 and 23 are drawn to appellants’ propping agent and claims 13, 15, and 24 are directed to a method of fracturing a subterranean formation and propping the fracture open using the propping agent. Claims 1 and 13 are .illustrative and read as follows:
1. An agent for propping open a fracture in a subsurface formation comprising particles of a hard material selected from the group consisting of nutshells and seeds of fruits, said material having a high compressive .strength and the character of deforming without shattering when subjected to compressive load, said particles having an average sphericity and roundness between 0.8 and 0.9 and a size such that said particles pass a No. 4 screen and are retained on a No. 40 screen of the U. S. Sieve Series.
13. A method of fracturing a subterranean formation and propping the fracture open to increase the flow of fluids into a well penetrating said formation comprising pumping a liquid containing a fluid loss reducing additive down the well and applying pressure to said liquid adequate to create a fracture extending from the well into the formation, displacing a liquid containing a fluid loss reducing additive and 0.2 to 0.5 pound of propping agent per gallon of liquid into the fracture adapted to deposit said propping agent in a partial monolayer in said fracture, said propping agent comprising a hard material selected from the group consisting of nutshells and seeds of fruits, said materials having a high compressive strength and the character of deforming without shattering when subjected to compressive load, the particles of said propping agent having a size in the range of 4 to 40 mesh and being further characterized by an average Krumbein roundness and sphericity in the range of about 0.8 to 0.9, and thereafter releasing the pressure on the well.
The references relied upon to support the rejections are:
Clark et al. (Clark) 2,838,116 June 10, 1958
Scott etal. (Scott) 2,943,680 July 5, 1960
McGuire et al. (McGuire) 2,950,247 August 23, 1960
Morse 2,962,095 November 29, 1960
[486]*486The examiner rejected product claims 1, 3, 4, 6, and 23 as unpatentable over Scott and all appealed claims as unpat-entable over Morse in view of Clark with further reference to McGuire under 35 U.S.C. § 103. We do not find it necessary to consider the former ground of rejection since we hold that the latter ground is worthy of affirmance.
Morse teaches the general principle that fractures formed and extended by hydraulic methods “are normally filled or held open by depositing therein a solid granular medium which has a substantial compressive strength and is highly permeable to fluid flow.” With regard to the materials, sizes, and shapes of his propping agents, Morse discloses:
As examples of such organic materials may be mentioned ground hard fruit stones, nutshells * * * preferably formed or ground to approximately uniform sizes * * * a screen size behveen about 8 and about 40-mesh being preferred. The more nearly uniform in size the particles are within this range the greater is the permeability of the fracture that is filled with them. It is also highly desirable that the shape of the particles be rounded so as to be cylindrical or spherical, and when manufactured particles are employed such shapes can be easily provided. [Emphasis ours.]
Thus, Morse teaches the use of the same materials employed by appellants as propping agents, and a “preferred” size range of 8 to 40 mesh, which is only slightly narrower than appellants' claimed range of 4 to 40 mesh, with the same preferred upper limit on particle size. Although Morse does not teach in terms of numerical values for roundness and sphericity, it is clear from the definitions quoted above from appellants’ specification that the “spherical” particles said to be “highly desirable” possess the maximum Krumbein roundness and sphericity of 1.0. Appellants acknowledge in their brief that “the effective teaching of Morse is that spherical propping agents; that is, propping agents having a roundness and sphericity of 1.0 are preferred.”
McGuire teaches the use as propping agents of large particle size materials of “generally spherical” shape. Such particles, like those of Morse, would have a roundness and sphericity of 1.0. McGuire also discloses the preferred practice of depositing the propping agent particles in the fracture as a monolayer. The patent also speaks of the disadvantages inherent in the use of sand as a propping agent and the desirability of using other materials of appropriate size and “generally spherical” shape and having higher compressive strength than sand.
Clark discloses the use of a propping agent, typically sand, in the amount of 0.5 to 10 pounds per gallon of fracturing liquid. With regard to the shape of his propping agent particles, Clark states:
A well rounded sand, typically a sand having a Krumbein roundness of at least 0.7, is preferred. Roundness in this range or lack of angularity appears to decrease the tendency to bridging of the sand or “sanding out” in the fracture whereby the sand is filtered out of the fracturing liquid and deposited in or adjacent to the well. The size of propping agent also is important * * *. [Emphasis ours.]
Since no upper limit is expressly stated for “this range” which is “preferred” by Clark, the range could be interpreted as either a definite or indefinite one. If the range is considered in its broadest, but definite sense, it extends from the lower limit of 0.7 to the maximum upper limit of 1.0, the Krumbein roundness and sphericity of a perfect sphere, particles of which shape are preferred by Morse and McGuire. In that event, appellants’ claimed range of 0.8 to 0.9 embraces the only two values in the preferred definite range which are not clearly anticipated by the prior art, which dis[487]*487closes the two extremes of this narrow range, i. e. particles “having a Krum-bein roundness of at least 0.7” (Clark) and “spherical” (Morse) or “generally spherical” (McGuire) particles, which by definition possess roundness and spher-icity of 1.0.
Alternatively, “this range” which Clark discloses to be “preferred” may be interpreted in a narrower, indefinite manner to include 0.7, certainly the next adjacent higher value, 0.8, and possibly the next higher value, 0:9, which' the Solicitor in his brief asserts to be “the next value after 0.7 on the Krumbein visual indicator scale.”
We think Clark’s disclosure that “Krumbein roundness of at least 0.7, is preferred” would clearly suggest to any person skilled in the art that a Krum-bein roundness slightly greater than 0.7 would be even more preferred than 0.7 itself. The next two values greater than 0.7 are both embraced by appellants’ claimed range of 0.8 to 0.9.
The Huitt affidavit of record shows that those skilled in the art know that sand having a roundness as low as 0.5 can be used as a propping agent. However, it is generally true that a preferred range is narrower in scope than the broadest operable range, and the fact that the operable roundness range for sand is 0.5 to 1.0 does not in any way detract from Clark’s effective teaching that “this range” which he “preferred” is either 0.7 to the maximum value of 1.0 or 0.7 to slightly greater than 0.7, e. g. 0.8 or 0.9. Regardless of whether Clark’s preferred range is interpreted to have the definite upper limit of 1.0 or an indefinite upper limit such as 0.9, we agree with the examiner’s position, also quoted with approval by the board, that:
* * * to select a particular roundness and sphericity range within this [narrow] range suggested by the prior art which produces optimum results would be within the purview of one skilled in the art, and to so use particles having such a roundness and sphericity would not patentably distinguish over the art under 35 USC 103. * * *
In their brief appellants acknowledge the “suggestion by Clark et al of using sand having a roundness higher than 0.7 resulting from the use of the term ‘at least 0.7,’ ” but urge that the affidavits of record “show extensive research over several years before the appellants made their invention, commercial success, and acknowledgment by the industry of appellants’ contribution.” We have considered appellants’ proofs of these relevant “secondary considerations,” Graham v. John Deere Co., 383 U.S. 1, 17-18, 86 S.Ct. 684, 15 L.Ed.2d 545, but under the particular circumstances of this case these factors do not persuade us that the claimed subject matter is nonobvious under 35 U.S.C. § 103, just as the Supreme Court was not persuaded by proof of similar factors in a companion case heard and decided concurrently with Graham, namely Calmar Inc. v. Cook Chemical Co., 383 U.S. at 35-36, 86 S.Ct. 684. We think it is also worthy of mention here that three of the four prior art patents relied on by the Patent Office issued in the latter half of 1960, less than one year before appellants’ filing date of May 1, 1961. Thus, we are not faced with a situation where the information disclosed by these patents was made available to the public long prior to the date of appellants’ invention. See Calmar, Inc. v. Cook Chemical Co., supra.
In summary, we are in full accord with the following analysis by the examiner of the fact situation in this case:
* * * the Morse and Clark et al references definitely point the way to the use of rounded and spherical shaped nutshell propping agents and broadly suggest a [narrow] range with respect to roundness and sphericity of .7 to 1.0 which encompasses the presently claimed range. It is the Examiner’s position that the use of particles having a roundness and sphericity [488]*488within this range (e. g. .8-.9) which represents the best compromise between reduced tendency to screen out on the one hand and good fluid flow capacity on the other would be well within the purview of one skilled in the art with the teachings in the references before him.
It is frequently true, in general life as well as in the field of invention, that optimum results are achieved by pursuing the path of moderation and avoiding the extremes of suggested ranges. This is precisely the case here, where appellants have discovered that “the best compromise” lies at the midpoint, 0.8 to 0.9, of the relatively narrow range, 0.7 to 1.0, which is clearly suggested by the prior art. We consider this discovery to be one which, “as a whole,” is obvious under 35 U.S.C. § 103. Therefore, the decision of the board is affirmed.
Affirmed.