Fractured‐Aquifer Hydrogeology from Geophysical Logs; The Passaic Formation, New Jersey

Abstract

The Passaic Formation consists of gradational sequences of mudstone, siltstone, and sandstone, and is a principal aquifer in central New Jersey. Ground-water flow is primarily controlled by fractures interspersed throughout these sedimentary rocks and characterizing these fractures in terms of type, orientation, spatial distribution, frequency, and transmissivity is fundamental towards understanding local fluid-transport processes. To obtain this information, a comprehensive suite of geophysical logs was collected in 10 wells roughly 46 m in depth and located within a .05 km 2 area in Hopewell Township, New Jersey. A seemingly complex, heterogeneous network of fractures identified with an acoustic televiewer was statistically reduced to two principal subsets corresponding to two distinct fracture types: (1) bedding-plane partings and (2) high-angle fractures. Bedding-plane partings are the most numerous and have an average strike of N84° Wand dip of 20° N. The high-angle fractures are oriented subparallel to these features, with an average strike of N79° E and dip of 71 0 S, making the two fracture types roughly orthogonal. Their intersections form linear features that also retain this approximately east-west strike. Inspection of fluid temperature and conductance logs in conjunction with flowmeter measurements obtained during pumping allows the transmissive fractures to be distinguished from the general fracture population. These results show that, within the resolution capabilities ofthe logging tools, approximately 51 (or 18 percent) of the 280 total fractures are water producing. The bedding-plane partings exhibit transmissivities that average roughly 5 m 2 /day and that generally diminish in magnitude and frequency with depth. The high-angle fractures have average transmissivities that are about half those of the bedding-plane partings and show no apparent dependence upon depth. The geophysical logging results allow us to infer a distinct hydrogeologic structure within this aquifer that is defined by fracture type and orientation. Fluid flow near the surface is controlled primarily by the highly transmissive, subhorizontal bedding-plane partings. As depth increases, the high-angle fractures apparently become more dominant hydrologically.

Effects of crustal stresses on fluid transport in fractured rock: case studies from northeastern and southwestern USA

“…Additional information regarding these tools and their principles of operation may be found in Hearst et al (2000). The logs were analyzed to delineate lithologic units, to identify individual fracture planes and determine their spatial distribution, to recognize fracture types associated with particular units, and to distinguish permeable fractures from the general fracture population and quantify their transmissivities (Morin et al 1997(Morin et al , 2000.…”

“…4;Priest and Hudson 1976;Bai and Pollard 2000). Transmissivities associated with these fractures are not particularly sensitive to changes in vertical loading over the relatively shallow depths observed in well logging (Morin et al 1997).…”

“…3 Transmissivities of the two fracture types and of their intersections as a function of depth at the New Jersey site. Beddingplane partings (circles), high-angle fractures (squares), and intersections of both (triangles) are identified (from Morin et al 1997) tions before applying compression normal to the joint. The model presented here considers the closure of mated fractures; mated fractures are those in which the two halves of the rock sample on either side of the fracture are left in the original relative positions before applying compression normal to the joint.…”

“…Field studies designed to investigate the hydrology of the Newark Basin through the analysis of geophysical logs have been undertaken at sites in New Jersey (Morin et al 1997) and in Pennsylvania (Morin et al 2000; Fig. 1).…”

Geologia estrutural de detalhe para elaboração de modelo conceitual de circulação de água subterrânea: estudo de caso em Jurubatuba, SP

“…Paillet & Ollila, 1994;Paillet, 1995;Stumm, 2001;Johnson et al, 2002, Johnson & Williams, 2003e Pino, 2012 e sedimentares (e.g. Morin et al, 1997Morin et al, , 2000Williams & Paillet, 2002 (Priest, 1993). Além disso, comparando a distribuição e a orientação das fraturas identificadas nos dados de perfilagens e de afloramentos, é possível estimar a distribuição do sistema de fraturas em escala de menor detalhe (Paillet & Ollila, 1994 (1993), este método é ideal para a caracterização do sistema de fraturas e de outras propriedades geométricas de grande escala, devido ao rigor estatístico e à relativa simplicidade do processo de amostragem.…”