Geomechanical Properties of Marcellus Shale Core Samples within a Sequence Stratigraphic Framework

Open Access
Author:
Call, Travis T
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 29, 2012
Committee Members:
  • James Terry Engelder, Thesis Advisor
  • Dr Rudy Slingerland, Thesis Advisor
  • Chris J Marone, Thesis Advisor
Keywords:
  • geomechanical properties
  • fracture toughness
  • tensile strength
  • elastic modulus
  • Brinell hardness
  • Marcellus shale
Abstract:
This study uses a sequence stratigraphic model for the Marcellus shale to correlate approximately coeval deposits across 6 core wells from the Appalachian Basin. I performed a series of geomechanical tests on core samples from the correlated intervals to determine the variation of fracture toughness, tensile strength, and elastic modulus across the basin. Four-point bend tests of single-edge notched beam (SENB) and rectangular beam specimens generally conform to the American Society for Testing and Materials (ASTM) standards for fracture toughness and flexural (tensile) strength tests of ceramic materials. I obtained elastic modulus values from the stress-strain curves generated by the tensile strength experiments. I indented select rectangular beam specimens with a 2mm Tungsten carbide ball indenter and analyzed them with an optical profilometer to calculate the Brinell hardness number (BHN). In addition to the Marcellus shale, I tested other lithologies from the Middle Devonian section (i.e., sandstone and limestone) to determine the effect of rock type on geomechanical properties. Lastly, I used X-ray diffraction (XRD) and total organic carbon (TOC) analyses to examine the influence of mineralogy and organic content on the geomechanical properties. Quartz-rich sandstones of the Mahantango Formation have the highest fracture toughness while clay and organic-rich black shales of the Marcellus Fm. have the lowest fracture toughness. A carbonate concretion from the Unions Springs mbr. of the Marcellus Fm. shows the greatest BHN of the intervals tested. I loaded samples with two different bedding plane orientations and black shales commonly display increased fracture toughness for the divider geometry. Although the calculated fracture toughness for Marcellus members generally agrees with petrophysically derived values used for hydraulic fracture modeling, results of this study indicate that the experimental fracture toughness of the Tully and Onondaga limestones is significantly higher than those used for modeling purposes. I observed considerable variation in geomechanical properties on a parasequence scale throughout the Union Springs mbr. of the Marcellus Fm., as well as a second-order brittle-ductile couplet. Finally, the calculated BHN values for the Marcellus shale are much higher than those encountered in the literature, likely due to the size of the ball indenter and applied load used in this study.