Changes

==Bypassed pays==

==Bypassed pays==

[[file:applying-gravity-in-petroleum-exploration_fig15-15.png|thumb|{{figure number|4}}<ref name=ch15r1>Beyer, L., A., 1991, [[Borehole gravity]] Surveys: SEG Short Course notes, June, 350 p. Excellent source for general principles of borehole gravity. Very good figures and references.</ref> Copyright: SEG.]]

[[file:applying-gravity-in-petroleum-exploration_fig15-15.png|thumb|{{figure number|4}}(1) Model of laterally homogenous geology and no density anomalies. (2) Region of lower density, possibly signifying the presence of missed hydrocarbons [[length::60 m]] from the well. (3) Low-density missed pay zone within [[length::15 m]] of the well, with a strong density difference. (4) Missed pay about [[length::1 m]] from the well; the density difference is very pronounced. From Bayer;<ref name=ch15r1>Beyer, L., A., 1991, [[Borehole gravity]] Surveys: SEG Short Course notes, June, 350 p. Excellent source for general principles of borehole gravity. Very good figures and references.</ref> Copyright: SEG.]]

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.