Geophysical logs

This material will give the first picture of the aquifer and will be the basis for complementary site investigations. These may include test drillings, geophysical logs and pumping tests with water chemistry in order to fully understand the aquifer conditions. 

Down-hole geophysical logs (resistivity measurements by means of down-hole electrodes, reflectance at frequencies between 50 and 150MHz and natural y-ray logging)... 

Geophysical logging Records and profiles the rock formations surrounding the well... 

Salisbury M. H., Donnelly T. W., and Francheteau J. (1979) Geophysical Logging in Deep Sea drilling project hole 417D. Initial Rep. Deep Sea Drill. Proj. 51-53(1), 705-713. 

We have drilled two 4000-ft-deep exploratory holes at a site about 30 miles east of Garlsbad and 40 miles southwest of Hobbs. Hydrological tests have been made, and geophysical logs of both holes were taken. Gores were recovered for mineralogical studies and physical properties measurements. Additional investigations under way in New Mexico include a local microseismic study, and appraisals of the oil and potash potentials of the area of interest. 

Folger, P F., E, Poiiii R, R. B. Wanty, D. Frishman, and W. Day. 1996. Controls on ---Rn variations in a fractured crystalline rock aquifer evaluated using aquifer te.sts and geophysical logging. Ground Water 34(2) 250-61. 

The study area comprises 28,000km in southeastern Alberta (Fig. 1). Rocks of interest to this study range in age from Tertiary to Carboniferous. The stratigraphic sequence, however, does contain older Paleozoic and Precambrian rocks at depth. With the exception of certain carbonate rocks in the Upper Paleozoic, the dominant lithology is shale with occasional sandstone units and minor coal. Some of the sandstone units contain substantial quantities of oil and gas. As a result of continued exploration for and development of these resources, a tremendous quantity of conventional lithologic log, geophysiced log, core and drill-stem test data is available for this area. 

Figure 3. Stratigraphic section and borehole geophysical logs for test hole DH3.

Though geophysical logging of the borehole is desirable in many situations, the additional expense and equipment necessary may be prohibitive. For the smaller, more shallow wells used in small-scale ground-water studies this is not necessary. 

Dutton Flanders examined the diagenesis and reservoir quality of the East Ford Field, Texas, which is undergoing a carbon dioxide flood. The compartmentalization of the arkosic sandstone reservoir is chiefly controlled by authi-genic calcite layers associated with the tops and bottoms of turbidite sandstone units. Gases produced from zones below low permeability calcite cemented sandstone intervals in new infill wells have high carbon dioxide contents. These, together with geophysical log interpretations, indicate that the calcite-cemented zones are laterally continuous and act as vertical barriers in the reservoir. 

It is difficult to determine the lateral extent of calcite-cemented layers observed in geophysical logs or core. Thin zones of calcite-cemented sandstone are commonly assumed to be concretions that extend no more than a few metres laterally, thus having little effect on production. Engineering production data from East Ford field provide evidence that some calcite layers extend hundreds of metres laterally and form... 

Geological data observations cover many different aspects such as observations of lithology, fracturing, alteration, mineralisation, tectonic indications, and hydraulic indications from flow etc. The tools for observing these characteristics are both by direct visual inspection and using indirect tools, such as various types of geophysical logging tools, packer tests, down-hole cameras, radar and seismics. 

Collect data through monitoring drill cuttings and cavings shape and quantity, geophysical logging data, and simple well-site tests. 

Table 2. Oil yields of wells showing similar characteristics of their geophysical logs...

In addition to the visible gas hydrates recovered in cores, several lines of indirect evidence for gas hydrate occurrences were derived. Downhole geophysical logging shows that the gas... 

The geophysical logging of some of these boreholes using the natural ganuna and density probes also allowed to detect the presence of karstic caves. Two of these borehole, SI and S2, whose location is shown in Figure 18, are described below. 

Geophysical logs are run to acquire data about the formation or fluid penetrated by the borehole. Each log provides a continuous record of a measured value at a specific depth in the boring, and is therefore useful for interpolating stratigraphy between sample intervals. Most downhole geophysical logs are... 

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