AN EXPERIMENTAL STUDY OF OPEN-HOLE HYDRAULIC FRACTURING AS A STRESS MEASUREMENT METHOD WITH PARTICULAR EMPHASIS ON FIELD TESTS

OPEN-HOLE HYDRAULIC FRACTURING SHOWS GREAT POTENTIAL FOR IN-SITU STRESS MEASUREMENT. SPECIAL EQUIPMENT SUITABLE FOR FRACTURING IN 2-1/4 INCH DIAMETER BOREHOLES WAS DEVELOPED. THE BOTTOM HOLE PRESSURE WAS RECORDED WITH THE AID OF A PRESSURE TRANSDUCER AND THE FRACTURE ORIENTATION DETERMINED BY MEANS OF AN IMPRESSION PACKER. TESTS WERE CARRIED OUT CLOSE TO THE SURFACE IN A QUARRY AS WELL AS IN THREE UNDERGROUND LOCATIONS. THE ROCK IN WHICH THE TESTS WERE PERFORMED HAD NEGLIGIBLE PERMEABILITY WHEN TESTED IN THE STANDARD MANNER. AT EACH LOCATION SEVERAL BOREHOLES 2-1/4 INCHES IN DIAMETER AND UP TO 60 FEET LONG WERE DRILLED. WHEREVER POSSIBLE, THE HOLES WERE ORIENTED IN MUTUALLY PERPENDICULAR DIRECTIONS. FAR-FIELD STRESSES WERE CALCULATED FROM THE BREAKDOWN PRESSURE OBTAINED IN THE FRACTURING TESTS AND THE RUPTURE STRENGTH IF THE ROCK, TAKING INTO ACCOUNT THE SEPARATELY DETERMINED INFLUENCE OF THE UNDERGROUND EXCAVATIONS. RESULTS ARE IN GOOD AGREEMENT WITH LABORATORY EXPERIMENTS DESCRIBED IN THE LITERATURE. IN PARTICULAR, RADIAL FRACTURES FOUND TO ENSUE PERPENDICULAR TO THE LEAST COMPRESSIVE STRESS WHEREVER IT WAS POSSIBLE TO DETERMINE THE DIRECTION OF THE LATTER WITHOUT ANY DOUBT. IN THE REMAINING CASES IT APPEARED TO BE AT LEAST PROBABLE THAT THE FRACTURES WERE ORIENTED ACCORDINGLY. THE TECHNIQUE SHOWED A REMARKABLE SENSITIVITY TOWARD RAPID CHANGES IN THE STRESS FIELD OF THE KIND EXPERIENCED AROUND MINE OPENINGS, FOR EXAMPLE. THE BREAKDOWN PRESSURE RESULTS SUGGEST THAT THE STATE OF STRESS IN THE ROCK IS ONE OF THE MAJOR FACTORS IN THE INITIATION OF HYDRAULIC FRACTURES. HYDRAULIC FRACTURING APPEARS TO BE SUITABLE, THEREFORE, TO SERVE AS A USEFUL METHOD TO DETERMINE IN-SITU STRESSES IN MAGNITUDE, AS WELL AS IN DIRECTION, IN ROCKS OF NEGLIGIBLE PERMEABILITY. LABORATORY TESTS WERE ALSO CONDUCTED, TO STUDY SIZE EFFECTS AND PROPAGATION OF FRACTURES. /AUTHOR/

  • Supplemental Notes:
    • Tech Rept MRD-3-70, 204 PP, FIGS, TABS, 55 REF, 6 APP
  • Corporate Authors:

    Army Department /US

    /Chief of Engineers Office
    ,   United States 
  • Authors:
    • Von, SCHONFELDT H
  • Publication Date: 1970-11

Subject/Index Terms

Filing Info

  • Accession Number: 00235870
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Apr 1 1971 12:00AM