Changes

==Bypassed pays==

==Bypassed pays==

Because the borehole gravity meter is the only tool that can measure bulk density away from the borehole, it is ideal to use for finding bypassed pay zones. In [[:file:applying-gravity-in-petroleum-exploration_fig15-15.png|Figure 4]], Case #1 shows a model of laterally homogenous geology and no density anomalies. Case #2 shows a region of lower density, possibly signifying the presence of missed hydrocarbons [[length::60 m]] from the well. The density difference detects the distant density contrast as a broad, anomalous low with its minimum centered at the correct depth. Such a zone may be within range of a borehole sidetrack. In Case #3 the low-density missed pay zone is within [[length::15 m]] of the well, and a strong density difference exists. Such pay zones may be in the range of a possible [[well completion]] after hydrofracturing the reservoir. In Case #4 the missed pay is about [[length::1 m]] from the well, and the density difference is very pronounced. Such pay zones are within the range of normal [[well completions]] but would still be undetected by any other logging method.

Because the borehole gravity meter is the only tool that can measure bulk density away from the borehole, it is ideal to use for finding bypassed pay zones. In [[:file:applying-gravity-in-petroleum-exploration_fig15-15.png|Figure 4]], Case #1 shows a model of laterally homogenous geology and no density anomalies. Case #2 shows a region of lower density, possibly signifying the presence of missed hydrocarbons [[length::60 m]] from the well. The density difference detects the distant density contrast as a broad, anomalous low with its minimum centered at the correct depth. Such a zone may be within range of a borehole sidetrack. In Case #3 the low-density missed pay zone is within [[length::15 m]] of the well, and a strong density difference exists. Such pay zones may be in the range of a possible [[well completion]] after hydrofracturing the reservoir. In Case #4 the missed pay is about [[length::1 m]] from the well, and the density difference is very pronounced. Such pay zones are within the range of normal [[well completions]] but would still be undetected by any other logging method.

These examples show that borehole gravity can indicate the presence of bypassed pay zones 1–60 m from the well. Once the well is cased, no other logging tool can do this. This is why the borehole gravity tool is currently the best technology available to search for bypassed hydrocarbons in existing wells.

These examples show that borehole gravity can indicate the presence of bypassed pay zones 1–60 m from the well. Once the well is cased, no other logging tool can do this. This is why the borehole gravity tool is currently the best technology available to search for bypassed hydrocarbons in existing wells.

==Combining BHGM with tomography==

==Combining BHGM with tomography==

[[file:applying-gravity-in-petroleum-exploration_fig15-16.jpg|left|thumb|{{figure number|5}}After .<ref name=ch15r7>Lines, L., R., Tan, H., Treitel, S., 1991, Velocity and density imaging between boreholes: CSEG Recorder, vol. 16, no. 6, p. 9–14. A unique case study that integrates borehole gravity with the processing and interpretation of cross-well tomography.</ref> Copyright: CSEG Recorder.]]

[[file:applying-gravity-in-petroleum-exploration_fig15-17.png|thumb|{{figure number|6}}After .<ref name=ch15r12>van Popta, J., Heywood, J., M., T., Adams, S., J., Bostock, D., R., 1990, Use of borehole gravimetry for reservoir characterisation and fluid saturation monitoring: Expanded Abstracts, SPE Europec 90 conference, p. 151–160. Use of time-lapsed borehole gravity logging to monitor fluid movement away from the borehole.</ref> Copyright: SPE.]]

Between-well imaging jointly uses borehole gravity with seismic tomography. Because of the unique distant resolution capabilities of borehole gravity, these data provide a useful integrating tool at the seismic wavelet scale. In the Gulf of Mexico example shown in [[:file:applying-gravity-in-petroleum-exploration_fig15-16.jpg|Figure 5]], Amoco used its borehole gravity log to help interpret a detailed cross-borehole seismic tomography image. The two wells were located less than [[length::250 ft]] apart. Two faults, Fl and F2, are seen in both data sets, and excellent correlations are made of various sands labeled M5, M6, M8, M9, M10, and M10A. Note that the well on the left encountered more pay sands than the well on right. Also note that the M6 sand is missing in the well on the left. The between-well structural and stratigraphic changes in only [[length::250 ft]] can be understood by combining the interpretations of the two comparable distant imaging tools: borehole gravity and seismic tomography.

Between-well imaging jointly uses borehole gravity with seismic tomography. Because of the unique distant resolution capabilities of borehole gravity, these data provide a useful integrating tool at the seismic wavelet scale. In the Gulf of Mexico example shown in [[:file:applying-gravity-in-petroleum-exploration_fig15-16.jpg|Figure 5]], Amoco used its borehole gravity log to help interpret a detailed cross-borehole seismic tomography image. The two wells were located less than [[length::250 ft]] apart. Two faults, Fl and F2, are seen in both data sets, and excellent correlations are made of various sands labeled M5, M6, M8, M9, M10, and M10A. Note that the well on the left encountered more pay sands than the well on right. Also note that the M6 sand is missing in the well on the left. The between-well structural and stratigraphic changes in only [[length::250 ft]] can be understood by combining the interpretations of the two comparable distant imaging tools: borehole gravity and seismic tomography.

==Monitoring gas production==

==Monitoring gas production==