Fracture spacing in slant/horizontal cores, Mesa Verde Formation, CO: Comparison with outcrop and vertical-core data
- Sandia National Labs., Albuquerque, NM (United States)
Core from the U.S. Department of Energy's Slant Hole Completion Test well (SHCT-1) shows an irregular but remarkably close fracture spacing in flat-lying reservoirs of the Mesaverde Formation in northwestern Colorado. Core was taken from 30 ft thick lenticular sandstones where the wellbore is inclined 60{degree} to vertical (266 ft of core), and from a 60 ft thick marine blanket sandstone where the wellbore is near-horizontal (115 ft of core), at the vertical depths of about 7100 and 7850 ft, respectively. In both zones, fractures cut across the core at a near-orthogonal angle to the core axis, with true lateral spacing averaging about 3 ft/fracture. Fracture spacing is not proportional to bed thickness. Fractures occur in swarms of up to five fractures each, and swarms are somewhat more regularly spaced at 8-10 ft, although individual fracture spacing ranges from less than an inch to 17 ft. Only one fracture was present in the same zones in 175 ft of 4 in. diameter core taken in nearby vertical wells. Outcrops of the same facies, however, show irregular spacings that average on the order of 1.5 ft (lenticular sandstones) and 3 ft (blanket sandstones). Extrapolation of outcrop fracture data, or of fracture data from vertical wellbores, to engineering models of subsurface fracture spacing should be undertaken cautiously. However, subsurface fractures in flat-lying reservoirs can be more closely spaced than is commonly acknowledged.
- OSTI ID:
- 7024941
- Report Number(s):
- CONF-910403-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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