Method for determination of the in situ compressive strength of formations penetrated by a well borehole

Abstract

A formation test tool is set forth in the present disclosure and has a snorkel on one side and upper and lower diametrically opposite back-up pistons on the opposite side. The back-up pistons are constructed with a back-up plate on the end of the back-up piston encircling and centered around a formation punch. The formation punch has a small diameter and specified length so that, during operation, the punch contacts the sidewall of the well borehole, and pressure is increased thereafter to force the punch into the formation until fracture failure occurs evidenced by a change in hydraulic pressure and a lurching movement of the back-up piston as the punch penetrates the formation. By knowing the diameter of the punch and by observing the hydraulic pressure necessary to obtain failure of the formation at the point of contact with the punch, data can be obtained which is indicative of the compressive strength of the formation.

Dependencies are inferred from the claim text.