Sonic log

We need the porosity. R is given by R in the lower sand. We also need R. Ultrasonic Caliper and Sonic Log while Drilling... 

The data acquisition rate is generally set so that the sample spacing of the sonic log (the distance between two acquired data points) ranges from 6 in. to 1 ft based on the anticipated drilling rate of penetration (ROP). 

Figure 4-292. Comparison of a wireline sonic iog with an LWD sonic log. (Courtesy SPWLA [116]. ...

The -sonic log can also be used to detect overpressured zones. The sonic measurements until recently were available only on wireline. Now, MWD sonic tools have been developed adding one more parameter for overpressure detection while drilling. Two equations relating the formation porosity to the transit time are used ... 

Figure 4-333. Example of sonic log data collected in the shale formations of a well in Jefferson County, Texas. (Courtesy SPE [101]. ...

Sonic log a well log based on the time required for sound to travel through rock,... 

Two methods have been developed for estimating seal embrittlement in shales. One method requires calculation of the overconsolidation ratio, which is essentially a measure of uplift, and in the other, the unconfined compressive strength is estimated from sonic log data. Both methods produce results which may be used to assess the relative risk of dilatant behaviour. 

An alternative method to quantify the brittleness of a seal rock uses the unconfined compressive strength derived from sonic logs. This method uses the brittleness index, BRl= UCSIUCSf c, where t/CS c is the unconfined compressive strength of a normally consolidated rock. UCS can be measured directly or is estimated from logs based on empirical correlations using the equation... 

The entire flow chart for pressure prediction using seismic velocity (without well control) is shown in Fig. 5. With a sonic log from a well, a similar proce-... 

Fig. 12. A comparison of the seismic interval velocity at the well location (pre-drill model) with those obtained from sonic log (post-drill). The sonic log has been filtered to mimic the seismic bandwidth.

The predicted pore pressures from seismic are compared with those predicted from sonic log in Fig. 14. The curve marked lithostatic is the overburden pressure obtained from integrating the seismically... 

Fig. 14. A plot of predicted fluid pressures versus depth derived from seismic velocity and calibrated sonic log. Pressure data from RFT measurements are also shown for comparison. The lithostatic or overburden curve was also generated using seismic velocity.

Fig. 8. Continuously cored interval with high recovery (100%) of the Namorado Sandstone composed of numerous individual turbidite layers. Observe that density, neutron and sonic logs clearly show decreasing porosity values below the oil-water interface. Arrows indicate the strongly cemented sandstones. Note also that type II calcite commonly occurs in the oil zone, whereas type III dominantly appears below the oil-water contact.

Density, neutron and sonic logs show a distinct shift below the oil-water interface identifying reduced porosity because the frequency of calcite-cemented beds is greater below than above the interface. We also note that type II calcite occurs mostly above the oil-water contact, whereas type III calcite appears below this limit (Fig. 8). Abreu et al. (1992) suggested that the interval below the water-oil interface was continuously cemented by calcite after oil had filled the crest structure. 

Core samples and cuttings were collected from the Angel and Gidgealpa Fields following on-site correlation of the lithologies against gamma-ray and sonic log responses (Table 2). 

Fig. 17. Wireline log characteristics, smoothed acoustic impedance curve and 3D seismic response over the Upper Angel Formation at Angel-2. Note that the major dolomite-cemented zones (black bars) are identifiable on the basis of neutron, density, resistivity and sonic log profiles. The zones appear as discrete layers at this location, with a cumulative thickness of 164 m, and are not fully cemented but contain some residual porosity. The dolomite-cemented zones occur both above and below the gas-water contact (GWC). The smoothed acoustic impedance curve shows that the zones produce a visible seismic response which is mappable. For an example of a line through the 3D seismic volume see Ryan-Grigor Schulz-Rojahn (1995 their Fig. 10a,b).

Another factor which has exacerbated the problem is that in some foundations, e.g. drilled shafts (or bored piles) and caisson, part of the constmction process, take place out of sight below ground. Furthermore, for all pile foundations, the pile shafts below ground are not visible or accessible after completion. Such lack of visibility hamper quahty control although special measures, such as sonic logging, may be adopted to alleviate the problem. 

Spruit R, van Tol F, Broere W, Slob E, Niederleithinger E (2014) Detection of anomalies in diaphragm walls with crosshole sonic logging Can. Geotech J 51 369-380... 

McNally (1987) studied the correlation between the uniaxial compression strength (142 samples) and the compressional wave slowness (measured with a sonic log) of fine to medium-grained sandstone. There is— for this geological situation—a good correlation (Fig. 7.19) that is probably controlled by... 

Sonic logs. The sonic log provides in situ measurement of the speed of sound in the formation over the scale of the sonde. It can only be used in open, uncased holes. The measurement is useful in seismic processing, it can be used to infer porosity but not that accurately and can be used to identify the rock type since the sound speed is a definite characteristic of each type of rock. Further detail can be found in [45, 138]. 

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