Addressing the issue of claim term definiteness, the U.S. Court of Appeals for the Federal Circuit affirmed the district court’s decision that the claims of the patent-in-issue were invalid for failing to meet the requirements of 35 U.S.C. § 112 ¶ 2. Halliburton Energy Services, Inc. v. M-I LLC , Case No. 07-1149 (Fed. Cir., Jan. 25, 2008) (Michel, J.).

The plaintiff, Halliburton Energy Services, was the assignee of U.S. Patent No. 6,887,832 (the ’832 patent), which relates to drilling fluids used in oil fields. The district court granted summary judgment in favor of the defendant, M-I LLC, holding claims of the ’832 patent invalid as indefinite based on the use of the term “fragile gel.” Halliburton conceded that the claimed drilling fluids were limited to “fragile gels,” and offered a three-part construction of the term. A “fragile gel” easily transitions between liquid and gel state upon introduction or removal of force, is capable of suspending drill cuttings and contains little or no organophilic clay or lignite. The Federal Circuit addressed this three-part construction and the ruling of indefiniteness of “fragile gel.”

The Court found the third part of the Halliburton’s construction, regarding clay and lignite, improper since the specification clearly stated that this was “preferable.” The first and second parts of Halliburton’s construction came directly from the specification; however, the Court argued that simply because an articulated definition can be found in the specification does not mean the construction meets the definiteness requirement. The Court rejected Halliburton’s argument that an evaluation of definiteness cannot include whether the patent expressly or clearly differentiates itself from specific prior art. The specification of the ’832 patent stated that Figure 3 distinguished the fluids of the invention from prior art fluids, and therefore, the Court found that a person of ordinary of skill would have looked to the figure to determine the bounds of the claims. Halliburton’s admission that one type of prior art fluid disclosed the same features as the fluid of the present invention was “fatal” to its claim, since no limit was placed on what was invented beyond the prior art. With regard to second part, Halliburton argued that the definition “is capable of” meant “adequate for the circumstances.” The Court found that a skilled artisan would not be able to determine what was within the scope of the claims since a wide variety of factors could affect adequacy.

In conclusion, the Court noted that both the first and second part of Halliburton’s construction of “fragile gel” were purely functional definitions (i.e., “defined by what it does rather than what it is”). The Court found that when a claim limitation is defined purely in functional terms, the task of determining whether the limitation is sufficiently definite is highly dependent on context and invited patent drafters to resolve ambiguities in functional limitations by using quantitative metrics rather than qualitative features.