Applying NMR spin-echo logging to Shaly Sand Formation evaluation: Case studies of Rocky Mountain region gas wells
Journal Article
·
· AAPG Bulletin
OSTI ID:86662
- NUMAR Corp., Arvada, CO (United States)
- NUMAR Corp., Houston, TX (United States); and others
Conventional wireline logs often fail to provide a reliable evaluation of reservoir quality and producibility in shaly mud formations, particularly in the shaly gas sand reservoirs of the Rocky Mountains which are characterized by low porosity (i.e., <15 pu), low permeability (0.1 to 1 md), very fine grain size, and high irreducible water saturations. A new-generation nuclear magnetic resonance (NMR) logging tool, the Magnetic Resonance Imaging Log (MRIL{reg_sign}), enhances log interpretation in such situations by providing lithology-insensitive measurements of effective porosity and the volume fractions of free (i.e., mobile) and capillary-bound (immobile) fluid volumes. This paper presents three examples from Rocky Mountain region wells in which MRIL data were crucial for resolving ambiguous or otherwise misleading interpretations from conventional nuclear porosity and resistivity log data alone. In two wells in the Frontier Group, WY, conventional log responses are nearly identical - the nuclear logs show gas effect while deep resistivity is nearly constant at {approximately}10 ohmm and shows little contrast with readings in nearby shales - but only one well produces gas at commercial rates. In the producing well, the MRIL shows the Frontier internal has significant (6 to 8 pu) free-fluid volume while in the other well FFI averages {approximately}1 pu, consistent with production. In addition, permeabilities computed from MRIL porosity and free/bound fluid volume ratio show excellent agreement with core data and reveal that the permeability-thickness of this thick, low resistivity zone is comparable to that of an overlying thin, but prolific, gas-producing sand.
- OSTI ID:
- 86662
- Report Number(s):
- CONF-9507131--
- Journal Information:
- AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 6 Vol. 79; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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OSTI ID:6861734