SLOTO, Ronald A., U.S. Geological Survey, 111 Great Valley Parkway, Malvern, PA 19355, rasloto@usgs.gov
ABSTRACT
Borehole geophysical methods and measurement of vertical borehole flow are a valuable part of ground-water investigations in the Stockton Formation. Rocks of the Stockton form a complex, heterogeneous, multiaquifer system consisting of a series of gently dipping sandstone and siltstone units with different hydraulic properties. Caliper logs were used to help correlate lithology and identify fractures and possible water-bearing openings. Correlation of caliper logs with single-point-resistance, fluid-resistance, and fluid-temperature logs was used to identify water-producing and water-receiving fractures. Natural-gamma logs were used to differentiate between sandstone and siltstone units and to correlate lithostratigraphy between boreholes. The direction and rate of vertical borehole-fluid flow under nonpumping conditions were measured by injecting a slug of high-conductance fluid at a specific depth in the borehole and monitoring the movement of the slug with the fluid-resistivity tool (brine-tracing method) or by use of a heat-pulse flowmeter. Determination of the potential for borehole flow was based on field evaluation of geophysical logs. In a 9-square-mile area underlain by the Stockton Formation in the Hatboro-Warminster area, the direction and rate of borehole-fluid movement was determined in 83 boreholes by the brine-tracing method and in 10 boreholes using a heat-pulse flowmeter. Fluid movement was measurable in 65 of the 93 boreholes (70 percent) at rates up to 17 gallons per minute. Downwardflow was measured in 36 boreholes, and upward flow was measured in 23 boreholes, not including those boreholes in which two directions of flow were measured. Both upward and downward vertical flow were measured in six boreholes. The direction of fluid movement within boreholes is affected by local pumping of ground water, proximity to recharge and discharge areas, lithology, and geologic structure. At one site, aquifer-isolation (packer) tests were conducted for 27 intervals in 6 boreholes. Three of the five isolated intervals with specific capacities greater than 1 gallon per minute per foot were identified by geophysical logging and flow measurements as water-receiving zones, and one was identified as a water-producing zone.
Citation:
Sloto, Ronald A., 1997,
Use of Borehole Geophysical Methods to Define Ground-Water-Flow Systems
in the Stockton Formation, Newark Basin, Pennsylvania: (abs.), GSA Abstracts
with Programs, Northeast Section, vol. 29, no. 1, p. 81.
Keywords: borehole geophysics, Newark Basin, borehole flow, Stockton Formation, Mesozoic
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