Patent ID: 8056408
Filing Date: 2011-11-15
Classification: E21B

Abstract:
1. A method of determining whether non-hydrocarbon gas exists in a formation surrounding an earth borehole being drilled with a drill bit at the end of a drill string, using drilling fluid that flows downward through the drill string, exits through the drill bit, and returns toward the earth's surface in the annulus between the drill string and the periphery of the borehole, comprising the steps of: obtaining, downhole near the drill bit, a pre-bit sample of the mud in the drill string as it approaches the drill bit; obtaining, downhole near the drill bit, a post-bit sample of the mud in the annulus, entrained with drilled earth formation, after its egression from the drill bit; implementing pre-bit measurements on the pre-bit sample; implementing post-bit measurements on the post-bit sample; and determining from the pre-bit measurements and the post-bit measurements whether non-hydrocarbon gas exists in the formation; wherein at least one of the step of implementing pre-bit measurements on the pre-bit sample and the step of implementing post-bit measurements on the post-bit sample comprises separating solid components and at least a portion of fluid components of the sample and further wherein the step of separating solid components and at least a portion of fluid components of the sample includes heating the sample to obtain a vapor, and analyzing the vapor or expanding a volume of the sample.