Borehole Televiewer Data Research Articles

Structural Controls on Ochoan Salt Dissolution and Delaware Mountain Group Oil Field Permeability Trends in the Delaware Basin, West Texas and Southeast New Mexico

A Landsat TM image of the Delaware basin, west Texas and southeast New Mexico, reveals geomorphic lineaments and tonal anomalies with preferred northwest-southeast and northeast-southwest orientations. Lineament orientations are the same as the trend of joints and fractures observed in Delaware Mountain exposures and from subsurface borehole break-out and televiewer data. These data suggest that lineament trends are controlled by subsurface joints and fractures. Petrographic data indicate that Delaware Mountain Group porosity/permeability development is controlled in large part by the occurrence of calcite/dolomite cement and chlorite/corrensite clays. The unimodality of grain size, sorting, and framework grain mineralogy, along with the virtual absence of detrital clays, favors a diagenetic control on cementation patterns. These observations coupled with formation water chemistry, and cement carbon-oxygen isotope and fluid inclusion data suggest that the occurrence of Delaware Mountain Group cements is related to diagenetic alteration by waters that have dissolved Ochoan halite and potash salts. Hydrodynamic fluid flow along joint and fracture systems coupled with rock-water interactions are proposed that account for the coincidence of salt dissolution fronts and oil field permeability barriers as well as formation water chemical trends and cement isotopic signatures. Preliminary data suggest fracture systems provide conduits for hydrodynamic fluidmore » flow capable of extensive Ochoan salt dissolution and the transport of reactive solutions to remote horizons both laterally and vertically in the basin.« less

Analysis of macroscopic fractures in the Cajon Pass Scientific Drillhole: Over the interval 1829‐2115 meters

The orientation, distribution and apparent aperture of natural fractures intersecting the Cajon Pass research well were determined through analysis of borehole televiewer (BHTV) data over the interval 1829 to 2115 meters. Large open fractures have shallow inclinations and tend to be aligned striking roughly N15°E. There is no apparent relationship between these fractures and the current stress state, as measured by the analysis of wellbore breakouts and hydraulic fracturing experiments in the Cajon Pass well and as observed in other studies in the region. Temperature anomalies due to fluid flow into the well detected during a long‐term permeability experiment occur at several of these fractures. Compressional, shear and Stoneley guided wave velocities are within the expected range for crystalline rocks and elastic‐wave anomalies are associated with the larger fractures. Stoneley wave coherence is reduced where the fractures are hydraulically conductive.

Stress‐induced borehole elongation: A comparison between the four‐arm dipmeter and the borehole televiewer in the Auburn Geothermal Well

The nature and origin of borehole elongation recorded by the four‐arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in Auburn, New York. A preferred orientation N10°W‐S10°E, ±10° and a less prominant E‐W orientation of borehole elongation, was observed on two runs of the dipmeter. Comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm. Comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures, obtained from hydrofracturing tests and televiewer data show that the N10°W‐S10°E borehole elongations (1) are axisymmetric, (2) are aligned with the minimum horizontal stress Sh, and (3) are not associated with natural fractures intersecting the well. These elongations are interpreted as stress‐induced well bore breakouts. The E‐W elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts. This asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter. This study demonstrates that the dipmeter can be used to determine the orientation of Sh (by mapping breakouts), confirming the results of earlier less detailed studies, and provides a firm basis for mapping regional stress patterns using existing dipmeter data.

In situ stress, natural fracture distribution, and borehole elongation in the Auburn Geothermal Well, Auburn, New York

Hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1.6‐km‐deep well at Auburn, New York. This well, which was drilled at the outer margin of the Appalachian Fold and Thrust Belt in the Appalachian Plateau, penetrates approximately 1540 m of lower Paleozoic sedimentary rocks and terminates 60 m into the Precambrian marble basement. Analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9.9±0.2 MPa at 593 m to 30.6±0.4 MPa at 1482 m. The magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13.8±1.2 MPa to 49.0±2.0 MPa over the same depth range. The magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike‐slip faulting regime that, at some depths, is transitional to normal faulting. As expected from the relative aseismicity of central New York State, however, analysis of the magnitudes of the horizontal principal stresses indicates, at least to a depth of 1.5 km, that frictional failure on favorably oriented preexisting fault planes is unlikely. Orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at Auburn is N83°E±15°, in agreement with other stress field indicators for this region. The borehole televiewer log revealed a considerable number of planar features in the Auburn well, the great majority of which are subhorizontal (dips < 5°) and are thought to be bedding plane washouts or drill bit scour marks. In addition, a smaller number of distinct natural fractures were observed on the borehole televiewer log. Of these, the distinct steeply dipping natural fractures in the lower half of the sedimentary section at Auburn tend to strike approximately east‐west, while those in the upper part of the well and in the Precambrian basement exhibit no strong preferred orientation. The origin of this east‐west striking fracture set is uncertain, as it is parallel both to the contemporary direction of maximum horizontal compression and to a late Paleozoic fracture set that has been mapped to the south of Auburn. In addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the Auburn well. Processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall. As these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression, we interpret them to be the result of stress‐induced spalling of the borehole wall (breakouts).

Well bore breakouts and in situ stress

The detailed cross‐sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data. We show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations. Both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression. This work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ.