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The DIANAUT program provided the first opportunity to directly measure vertical fluid flow in ocean boreholes by means of a high resolution thermal flowmeter. Measurements of volumetric flow rate were obtained in DSDP (Deep Sea Drilling Project) Holes 395A and 534A. These results identified a total flow of 2300 L/hr of seawater entering Hole 395A from the seafloor that diminished to about 550 L/hr at a depth of 251 meters below seafloor (mbsf), indicating that approximately 3/4 of the original downward flow had exited the borehole and entered the open formation across the upper 140 m of basement. This information allows the upper oceanic crust at this site to be delimitated into three hydrologic units, with basalt permeabilities of 3.0 × 10−14 m2 near the sediment/basement interface decreasing sharply as a function of depth to values much less than 10−16 m2 below 440 mbsf. It is estimated that approximately 108 L of seawater have entered this well since it was drilled in 1975. Quantitative flow measurements in Hole 534A were inconclusive because of technical problems with the flowmeter packer. Nevertheless, results showed that borehole fluid was moving upward and out into the open ocean at a rate on the order of a few hundred liters per hour, roughly one order of magnitude less than that determined for Hole 395A and moving in the opposite direction. There is good correlation between these field measurements and the attendant temperature logs from each well, and the results provide strong evidence of important mass-transport processes associated with the diverse submarine hydrologic systems in the upper oceanic crust.

Heat-flow values determined from the DIANAUT program provide insight into the geothermal state of three DSDP holes situated on the western flank of the Mid-Atlantic Ridge. Very low values (20 mW/m2 max.) observed in 3.5-m.y.-old crust at Hole 333A decrease with depth and indicate persistent basement cooling due to cold water circulation in the porous level of the upper oceanic crust. Cold ocean bottomwater continues to invade the upper level of fractured 7.3-m.y.-old basement at Hole 395A, but temperature v. time records show large-scale temperature fluctuations, probably associated with borehole convection, at 500 mbsf and stable temperatures, probably indicating a slow return to thermal equilibrium, at 600 mbsf. The 154-m.y.-old crust at Hole 534A exhibits a relatively steady thermal state with a heat flow close to theoretical values for a conductively cooling plate; small variations in the thermal gradient recorded in this well probably represent very slow and subtle movement of borehole fluids. The close comparison of these latest results with those obtained several years previously, demonstrates the presence of relatively stable thermal regimes.

The French wireline re-entry expedition known as DIANAUT culminated in the successful completion of a series of downhole measurements in three Deep Sea Drilling Project (DSDP) holes in the north-central Atlantic Ocean. Among these measurements was a borehole televiewer (BHTV) log obtained in Hole 395A from bottom of casing at 112 meters below seafloor (mbsf) to a depth of 605 mbsf. In contrast with a BHTV survey previously conducted in this well during DSDP Leg 78B in 1981, televiewer data were not degraded by random cable oscillations due to ship heave and the quality of this log is excellent. These latest data were digitized and processed in terms of acoustic travel time and amplitude to compute hole size and shape, evaluate the structural integrity of the surrounding rock, and characterize intersecting fractures. The acoustic caliper and reflectivity logs correlate well with the lithologic column, particularly at the boundaries between major units which often are marked by breccias. Fractures in the lower part of the hole appear to be effectively sealed, in contrast with the open fractures identified in the upper sections. This supports a systematic pattern derived from complementary geophysical logs of increasing density, electrical resistivity, and elastic-wave velocity, and decreasing in situ permeability as a function of depth. Fractures intersecting the well exhibit a wide range of orientations marked by some clustering of dip azimuths approximately east-west. The presence of moderately dipping fractures striking subparallel to the ridge axis is consistent with both ridge-parallel topographic elongations observed in this area and with azimuthal seismic anisotropy reported elsewhere, suggesting that fractures such as those identified from the BHTV record contribute to these effects.

Borehole televiewer (BHTV) and 4-arm caliper (dipmeter) logs were obtained in the Toa Baja well (drilled to a depth of 2704 m into sediments of the North Coast Tertiary Basin, Puerto Rico) from 704 to 2676 m depth. The only observations suggesting that stress-induced wellbore failure (breakouts) had occurred were small intermittent features at a depth of approximately 2600 m with azimuths of 70° and 250° and the fact that, during drilling, wellbore stability became a problem near total depth. An increase in mud weight to 10 Lb/gal required to stabilize the deteriorating wellbore was accompanied by loss of drilling fluid into the formation, suggesting that hydraulic fracturing or the reopening of pre-existing near vertical fractures had occurred. A series of vertical fractures at a variety of azimuths (averaging N3l°W) was detected by the BHTV. The loss of circulation due to an increase in mud weight, combined with the absence of well-developed breakouts, enables us to estimate stress magnitudes near the well for reasonable values of rock strength: S1=Sv; S3=Shmin ≈ 0.5v; SHmax ≈ (0.55–0.63)Sv, and an associated incipient normal faulting stress regime. This stress regime is consistent with focal mechanisms determined for earthquakes with epicenters near the drillsite.

Oval images etched into the wall of a deep borehole were detected in DSDP (Deep Sea Drilling Project) Hole 504B, eastern equatorial Pacific Ocean, from analysis of an acoustic televiewer log. Initial speculation as to the origin of these remarkable features considered the intersection of pillow basalts with the wellbore. However, a systematic inspection of these ovals has identified intriguing consistencies in appearance that cannot be explained satisfactorily by a random, coincidental distribution of pillow lavas. As an alternative hypothesis, Mohr-Coulomb failure criterion is used to account for the generation and orientation of similarly curved, stress-induced fractures. Consequently, these oval features can be interpreted as fractures and related directly to stress conditions in the oceanic crust at this site. The azimuth of the oval center corresponds to the orientation of maximum horizontal principal stress (S{sub H}), and the oval width, which spans approximately 180{degree} of the borehole, is aligned with the azimuth of minimum horizontal principal stress (S{sub h}). The oval height is controlled by the fracture angle and thus is a function of the coefficient of internal friction of the rock.