Borehole gravity: uses, advantages, and disadvantages
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| Exploring for Oil and Gas Traps | |
| |
| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Predicting the occurrence of oil and gas traps |
| Chapter | Applying gravity in petroleum exploration |
| Author | David A. Chapin, Mark E. Ander |
| Link | Web page |
| Store | AAPG Store |
Borehole gravity uses
Borehole gravity is especially effective for the following exploration and production purposes:
Exploration purposes
- Locating nearby salt structures
- Locating distance to nearby structures (e.g., reefs) for step-outs and sidetracks
- Better synthetic seismograms
Production purposes
- Measuring bulk density when radioactive tools are too risky
- Logging cased holes for lithologic changes
- Calculating overburden for hydrofracture jobs
- Monitoring injection fluids
- Monitoring reservoirs during fluid withdrawal
- Exploring for bypassed, behind-casing gas zones
- Evaluating reservoir porosity, especially in carbonate reservoirs where other tools are not as reliable
Borehole gravity advantages
The following characteristics give borehole gravity surveys advantages in certain situations:
- Directly measures bulk density
- Is a deep imaging tool
- Is effective in both cased and uncased wells
- Is unaffected by washouts, hole rugosity, or mud invasion effects
- Can help determine seismic wavelet scale density
- Is a passive measurement, e.g., does not have active radioactive sources
Borehole gravity disadvantages
The following characteristics give borehole gravity surveys disadvantages in certain situations:
- Direction away from the well to distant source cannot be determined without other information
- Engineering limitations of the tool restricts use to certain candidate wells (hole size, low deviation, slow reading)
- Only a few tools presently available for use
- Expensive to operate
Theory
Density effects caused by downhole geology can be detected by very sensitive instrumentation and by knowing precisely where the sensor is located in the borehole. For petroleum exploration, gravity typically is measured in microgals (μGal). Typical exploration anomalies are on the order of
See also
- Applying borehole gravity methods
- The borehole gravity tool
- Examples of borehole gravity applications
External links
| find literature about Borehole gravity: uses, advantages, and disadvantages |
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