Patent ID: 7458257

Claim:
A method for determining a property of formations 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 said property of the formations from said post-bit measurements and said pre-bit measurements; wherein said steps of implementing pre-bit measurements on the pre-bit sample and implementing post-bit measurements on the post-bit sample are performed downhole; and wherein said step of determining said property of the formations from said post-bit measurements and said pre-bit measurements comprises determining said property from ratios of said post-bit measurements and said pre-bit measurements.