Changes

[[file:borehole-gravity_fig1.png|thumb|300px|{{figure number|1}}An example of a BHGM log. The sharp difference In density between 6330 and 6370 ft is caused by porosity not detected by the gamma-gamma [[density log]]. The broader difference anomaly observed over the length of the logged interval is explained by the structural influence of the reef complex.]]

[[file:borehole-gravity_fig1.png|thumb|300px|{{figure number|1}}An example of a BHGM log. The sharp difference In density between 6330 and 6370 ft is caused by porosity not detected by the gamma-gamma [[density log]]. The broader difference anomaly observed over the length of the logged interval is explained by the structural influence of the reef complex.]]

The borehole gravity meter (BHGM) can be described simply as a deep-investigating density logging tool. Applications range beyond this simple description to include detection of oil- and gas-filled [[porosity]] and detection and definition of remote structures, such as salt domes, faults, and reefs.

The borehole [[gravity]] meter (BHGM) can be described simply as a deep-investigating density logging tool. Applications range beyond this simple description to include detection of oil- and gas-filled [[porosity]] and detection and definition of remote structures, such as salt domes, faults, and reefs.

One of the great advantages of the BHGM is that it is the only logging method that can directly measure density at a significant distance away from a well. It is also the only logging method that can reliably obtain density through well casing.<ref name=Chapin, David A. and Mark A. Ander>Chapin, D. A. and M. A. Ander, 1999, [http://archives.datapages.com/data/specpubs/beaumont/ch15/ch15.htm Applying borehole gravity methods], in Exploring Oil and Gas Traps: [http://store.aapg.org/detail.aspx?id=545 AAPG Treatise of Petroleum Geology 3], p. 15-15,</ref> It is practically unaffected by near-borehole influences, which are the scourge of nuclear tools: casing, poor cement bonding, rugosity, washouts, and fluid invasion. Another advantage is the fundamental simplicity of the relationships among gravity, mass, rock volume, and density. Complex geology can be easily modeled so that the response of a range of hypothetical models can be studied and understood before undertaking a survey.

One of the great advantages of the BHGM is that it is the only logging method that can directly measure density at a significant distance away from a well. It is also the only logging method that can reliably obtain density through well casing.<ref name=Chapin, David A. and Mark A. Ander>Chapin, D. A. and M. A. Ander, 1999, [http://archives.datapages.com/data/specpubs/beaumont/ch15/ch15.htm Applying borehole gravity methods], in Exploring Oil and Gas Traps: [http://store.aapg.org/detail.aspx?id=545 AAPG Treatise of Petroleum Geology 3], p. 15-15,</ref> It is practically unaffected by near-borehole influences, which are the scourge of nuclear tools: casing, poor cement bonding, rugosity, washouts, and fluid invasion. Another advantage is the fundamental simplicity of the relationships among gravity, mass, rock volume, and density. Complex geology can be easily modeled so that the response of a range of hypothetical models can be studied and understood before undertaking a survey.