US Patent 8141419 In-situ formation strength testing

Estimating formation properties includes a member coupled to a carrier, the member having a distal end that engages a borehole wall location, the distal end having a curved surface having a radius of curvature in at least one dimension about equal to or greater than a borehole radius. A drive device extends the first extendable member with a force sufficient to determine formation strength, and at least one measurement device providing an output signal indicative of the formation property. Articulating couplings may be used to change an angle of extension of the extendable member.