Patent ID: 7861801

Claim:
A method of obtaining a whole core from a region of interest of a subterranean formation using resistivity measurements ahead of a drill bit obtained while drilling a well, the method comprising: a) selecting an initial drilling mud, drill bit, drill string, and apparatus for determining resistivity in front of the drill bit; b) drilling toward a region of interest at target azimuth and dip angles using the selected drilling mud, drill bit, drill string, and resistivity apparatus; c) gathering resistivity data ahead of the bit during drilling and prior to penetrating the region of interest in a target subterranean formation using the drill bit and a drilling mud, the drill string progressing at the target dip and azimuth angles toward the region of interest; d) identifying a top of the region of interest in the formation using a method selected from i) gathering resistivity data ahead of the bit during drilling the well prior to penetrating a target subterranean formation and identifying an approaching resistivity character indicative of the top of the region; and ii) gathering resistivity data ahead of the bit during drilling the well prior to penetrating a target subterranean formation and comparing the resistivity data obtained from the well to resistivity measurements from one or more offset wells; e) running the drill string out of the well, removing the drill bit from the drill string, installing a core bit on the drill string, and running the drill string back into the well; f) adjusting the density, specific gravity, weight, viscosity, water content, oil content, composition, pH, flow rate, solids content, mud properties, solids particle size distribution, resistivity, conductivity, or any combination of any of these, of the drilling mud to minimize damage to the whole core from improperly conditioned mud used during coring; and g) coring into the region of interest using the core bit, obtaining a whole core.