Borehole Logging Data Research Articles

Delineation of saltwater intrusion zones using the time domain electromagnetic method: the Nabeul–Hammamet coastal aquifer case study (NE Tunisia)

AbstractThe time domain electromagnetic method (TDEM) is applied to monitor, to delineate and to map the saltwater intrusion zones in the Mediterranean Plio‐Quaternary aquifer. Forty‐two TDEM soundings were carried out in the coastal plain of Nabeul–Hammamet region (NE Tunisia). TDEM resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater–seawater transition zone. The geoelectric sections showing the vertical configuration of seawater intrusion, with the brackish‐salty‐saturated zones, have a resistivity ranging from ~0.1 to 5 Ω⋅m and are detected at a depth lower than 1.5 m. The salinized zones are located at Nabeul (Sidi Moussa, Sidi El Mahrsi, Al Gasba and Mrazgua) and at Hammamet (Touristic zone of Hammamet north and south, Baraket Essahel) and reached a distance of 4 km from the coastline, indicating a severe state for the aquifer in these zones. These TDEM results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells. Moreover, in the northeastern part, the presence of a saltwater front located far from the coast and along the NW–SE major surface fault can be explained by two hypothesis: (i) this fault seems to provide a conduit for seawater to move readily towards the water wells and (ii) the clay and gypsum infiltration of marine Messinian deposits through the fault plane leads to low resistivities. Finally, it comes out from this study that TDEM survey has successfully depicted salinized zones of this coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd.

Groundwater flow and geological model estimated from the borehole log data in the Setagaya and Suginami district, Tokyo, Japan

Groundwater flow and geological model estimated from the borehole log data in the Setagaya and Suginami district, Tokyo, Japan

Lithological Study and Mapping of Barind Tract Using Borehole Log Data with GIS: In the Context of Tanore Upazila

In this paper the lithological study and mapping of Barind Tract is done by using irrigation boreholes log data in the context of an upazila under Barind Tract in northwest Bangladesh. Northwestern part of Bangladesh is severely drought prone area with lowest yearly rainfall in the country. Before groundwater irrigation only one crop was cultivated in this area in rainy season. After spreading of groundwater irrigation agriculture is flourished here, but groundwater level is severely going down, which is making this area risky for several adverse effect like land subsidence, biodiversity loss etc. Lithology is one of the important factors that affect the recharging of groundwater aquifer of any area. This research mainly based on secondary data. Irrigation boreholes log data are collected from Barind Multipurpose Development Authority (BMDA), a local authority under the Ministry of Agriculture of Bangladesh government provide irrigation in Barind Tract. A GPS survey is conducted to locate the boreholes in the study area. From the study highest thickness of clay layer found 90 ft and lowest 20 ft, and thickness gradually increase from eastern to western side. Aquifer is located between 20 - 90 ft depth from the surface and direction of aquifer is western to eastern side. Agriculture of study area is totally dependent on groundwater irrigation. Thick layer of clay impede recharging of groundwater table. Due to thick layer of sticky and plastic clay land subsidence risk is low, but it act as aquitard which impede groundwater recharging and increase surface runoff.

Utilization of borehole log data as basic data of country land

Utilization of borehole log data as basic data of country land

Application of conditional simulation of heterogeneous rock properties to seismic scattering and attenuation analysis in gas hydrate reservoirs

Abstract We present a conditional simulation algorithm to parameterize three-dimensional heterogeneities and construct heterogeneous petrophysical reservoir models. The models match the data at borehole locations, simulate heterogeneities at the same resolution as borehole logging data elsewhere in the model space, and simultaneously honor the correlations among multiple rock properties. The model provides a heterogeneous environment in which a variety of geophysical experiments can be simulated. This includes the estimation of petrophysical properties and the study of geophysical response to the heterogeneities. As an example, we model the elastic properties of a gas hydrate accumulation located at Mallik, Northwest Territories, Canada. The modeled properties include compressional and shear-wave velocities that primarily depend on the saturation of hydrate in the pore space of the subsurface lithologies. We introduce the conditional heterogeneous petrophysical models into a finite difference modeling program to study seismic scattering and attenuation due to multi-scale heterogeneity. Similarities between resonance scattering analysis of synthetic and field Vertical Seismic Profile data reveal heterogeneity with a horizontal-scale of approximately 50 m in the shallow part of the gas hydrate interval. A cross-borehole numerical experiment demonstrates that apparent seismic energy loss can occur in a pure elastic medium without any intrinsic attenuation of hydrate-bearing sediments. This apparent attenuation is largely attributed to attenuative leaky mode propagation of seismic waves through large-scale gas hydrate occurrence as well as scattering from patchy distribution of gas hydrate.

Ground Water Estimation and Water Table Detection with Ground Penetrating Radar

A shallow subsurface survey was conducted along a 20 m long profile on a test site with the aim of mapping and assessing ground water resource of the area. The profile was scanned with ground penetrating radar using common offset geometric configuration. Velocity information obtained from the processed radar image were used to estimate and mapped the spatial distribution of the ground water within the shallow depth based on Topp’s empirical relation between the water content and the dielectric constant of the soil medium. Due to the absence of scattering objects within the deeper high water content region, borehole log data were used to correlate the radar reflection signatures with the observed stratigraphic sequences. Layer picking was used to delineate the water table which correlates well with the log data. Significant lateral variation in both the shallow water content and the level of water table were observed with the water table found to be within a depth range of 0.5 to 1.4 m. These were attributed to the nature of the soil identified as till with variable grain size distribution. The soil is therefore, considered to have great variation in hydraulic conductivity which implies significant variability in water retention capacity. Region of maximum water content within the shallow level was found to coincide with the region of higher level of the water table. The study therefore, appraised the effectiveness of GPR as a tool for precision agricultural practice and environmental studies.

Reply to comment on ‘Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration’ by G.K. Hodlur and Ratnakar Dhakate, Geophysical Prospecting doi:10.1111/j.1365–2478.2009.00831.x

We are thankful to Dr P.C. Chandra for his comments and for the interest he has shown in our article. To begin with, the doubt concerning equivalence and suppression are explained. By following the principle of equivalence, certainly at a single site of investigation, various subsurface geophysical models can give the same sounding curves. However, while deciding the final model, the model that fits with the subsurface geological conditions in the field around or at the site of investigation is to be given importance. Hence, in any study area few parametric soundings are carried out near existing borewells whose lithologs are available, in order to assess the resistivities and thicknesses of the subsurface geological formations. This knowledge is used as calibration to interpret the vertical electrical soundings carried out around the parametric soundings. When compared with the parametric sounding, the interpreted results of the soundings located around the region of parametric sounding should generally show a similar subsurface geophysical structure, namely in the number of subsurface layers and patterns of resistivity changes of the interpreted geoelectric layers. Variations in resistivities and thicknesses of different geoelectric layers will have to occur as the vertical electric soundings (VES) are located at different sites and hence the subsurface geometry, degree of compaction and saturation of the geoelectric layer changes in space. However, the trends should match satisfactorily. Such an exercise facilitates in choosing the right interpretation from the various subsurface models created by interpretation of any sounding curve. This is the method to tackle the problems of principle of equivalence. For example, in this article at the Ramanu-

Migration-based location of seismicity recorded with an array installed in the main hole of the San Andreas Fault Observatory at Depth (SAFOD)

SUMMARY We present the principles of a recently developed event location procedure and its application to seismicity recorded in the main borehole of the San Andreas Fault Observatory at Depth (SAFOD). The basic idea of the location approach is the backpropagation of the recorded wavefield along rays using a Gaussian-beam-type weighting factor. In the case of a sufficient number of receivers, the intersection of these rays results in a distinct maximum at the corresponding hypocentre location. We have applied this technique to data recorded with an 80-level three-component (3C) receiver array in the SAFOD main hole and we have located a number of events in the vicinity of the fault system. A modification of the location algorithm also allowed the precise location of one of the so-called target events, which are the subject of recent drilling activities as well as ongoing research at SAFOD. We summarize the principles of the location method and the performed processing steps, provide estimates of the uncertainties for the target event location and test the robustness of the location using six different 3-D velocity models. Furthermore, we discuss the event locations in comparison with borehole logging data and coincident seismic reflection images and we also show identified events with highly correlated waveforms.

Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods

The resolution of the freshwater and saline water aquifers in a coastal terrain (Mahanadi Basin, India) is updated. We analysed electrical borehole log data at four sites and compared the water resistivity regime of the freshwater and saline water zones obtained from electrical borehole logging, with the resistivity regime obtained by interpreting vertical electrical sounding (VES) data. The multilayer VES data interpretation is modified to a simple model, containing only the freshwater zone and the saline water zone. The composite geophysical parameters of the freshwater and saline water zones, in particular the resistivity and longitudinal unit conductance regime, are identified. The resolution obtained from the composite geophysical data analyses is very clear and convincing. The composite longitudinal unit conductance regime of the saline water zones is very high compared to that of the freshwater zones. This makes the identification of the two aquifers easy and increases its reliability. A technique which enables analysis of composite geophysical data of freshwater and saline water zones at VES sites in the vicinity of the borehole log sites is proposed. The significance of longitudinal unit conductance in resolving the freshwater and saline water aquifers is illustrated graphically. The proposed technique is validated by correlating the longitudinal unit conductance and resistivity with the total dissolved solids. The efficiency of the technique is validated by carrying out discriminant function analysis. Citation Hodlur, G. K., Dhakate, R., Sirisha, T. & Panaskar, D. B. (2010) Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods. Hydrol. Sci. J. 55(3), 414–434.

Comments on ‘Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration’ by G.K. Hodlur and Ratnakar Dhakate, Geophysical Prospecting doi:10.1111/j.1365‐2478.2009.00831.x

Comments on ‘Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration’ by G.K. Hodlur and Ratnakar Dhakate, <i>Geophysical Prospecting</i> doi:10.1111/j.1365‐2478.2009.00831.x

Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration

ABSTRACTWe have correlated the longitudinal unit conductance CL obtained from interpreted vertical electrical sounding data with the formation resistivity Rt and the formation resistivity factor F, obtained by carrying out electrical borehole logging. Interpreted geophysical data of eleven soundings and two electrical borehole log records are used for the analysis. The geophysical data used were acquired in a sedimentary basin. The study area is called Lower Maner Basin located in the province of Andhra Pradesh, India. Vertical electrical soundings were carried out using a Schlumberger configuration with half current electrode separation varying from 600–1000 m. For logging the two boreholes, a Widco logger‐model 3200 PLS was used. True formation resistivity Rt was calculated from a resistivity log. Formation resistivity factor F was also calculated at various depths using Rt values. An appreciable inverse relation exists between the correlated parameters. The borehole resistivity Rt and the formation resistivity factor F decrease with the increase in the longitudinal unit conductance CL. We have shown the use of such a relation in computing borehole resistivity Rt and formation resistivity factor F at sites that posses only vertical electrical sounding data, with a fair degree of accuracy. Validation of the correlation is satisfactory. Scope for updating the correlation is discussed. Significance and applications of the relation for exploration of groundwater, namely to update the vertical electrical sounding data interpretation by translating the vertical electrical sounding data into electrical borehole log parameters, to facilitate correlations studies and to estimate the porosity (φ), permeability (K) and water saturation Sw of water bearing zones are discussed.

The stress field at Soultz-sous-Forêts from focal mechanisms of induced seismic events: Cases of the wells GPK2 and GPK3

The stress field at the EGS geothermal site of Soultz-sous-Forêts has been the subject of many studies, because it largely controls the response of the reservoir to fluid injection. The analysis of borehole logging data, especially breakouts and drilling-induced tension fractures, in the four geothermal wells define an average SHmax orientation ranging between 170° and 180° down to 5 km depth. It also reveals strong heterogeneities in several depth intervals. In this paper, the inversion of double-couple source mechanisms of seismic events induced during GPK2 and GPK3 stimulation tests is performed to retrieve the orientation and shape factor of the stress tensor, using the Slickenside Analysis Package of Michael (1984, 1987a, 1987b). The results indicate a well-determined orientation of Shmin in GPK2 and in GPK3; in GPK3 Shmin is clockwise rotated by about 10°. The stress tensor defines an uniaxial extension. The results from both methods, analysis of borehole logging data and inversion of focal mechanisms, are only slightly different; the discrepancy may be due to the larger reservoir volume covered by the focal mechanisms, which can include strong stress heterogeneities.

Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California

We refined the three‐dimensional (3‐D) Vp, Vs and Vp/Vs models around the San Andreas Fault Observatory at Depth (SAFOD) site using a new double‐difference (DD) seismic tomography code (tomoDDPS) that simultaneously solves for earthquake locations and all three velocity models using both absolute and differential P, S, and S‐P times. This new method is able to provide a more robust Vp/Vs model than that from the original DD tomography code (tomoDD), obtained simply by dividing Vp by Vs. For the new inversion, waveform cross‐correlation times for earthquakes from 2001 to 2002 were also used, in addition to arrival times from earthquakes and explosions in the region. The Vp values extracted from the model along the SAFOD trajectory match well with the borehole log data, providing in situ confirmation of our results. Similar to previous tomographic studies, the 3‐D structure around Parkfield is dominated by the velocity contrast across the San Andreas Fault (SAF). In both the Vp and Vs models, there is a clear low‐velocity zone as deep as 7 km along the SAF trace, compatible with the findings from fault zone guided waves. There is a high Vp/Vs anomaly zone on the southwest side of the SAF trace that is about 1–2 km wide and extends as deep as 4 km, which is interpreted to be due to fluids and fractures in the package of sedimentary rocks abutting the Salinian basement rock to the southwest. The relocated earthquakes align beneath the northeast edge of this high Vp/Vs zone. We carried out a 2‐D correlation analysis for an existing resistivity model and the corresponding profiles through our model, yielding a classification that distinguishes several major lithologies.

Generalized reciprocal method applied in processing seismic refraction data from the basement terrain of Zaria, Northwest Nigeria

A geophysical investigation was carried out at Shika, near Zaria, using seismic refraction method; with the aim of analyzing the data obtained using the generalized reciprocal method (GRM). The technique is for delineating undulating refractors at any depth from in-line seismic refraction data consisting of forward and reverse travel-times. An in-line geometric spread with optimum geophone distance of 25m was used. The result obtained showed that the optimum XY spacing, the upward and downward traveling segments of the rays to each geophone emerged from near the same point on the refractor. This method proved to be particularly well-suited for situations involving large lateral velocity variations and highly irregular refractor surfaces. By using computer processing techniques and advanced interpretational features of GRM, it has been possible to derive a picture of the subsurface layering from the refraction results even in geologically complex environments. However, average velocities of 1356 m/s, 2309 m/s to 2543 m/s and 4065m/s were obtained for the Overburden, weathered Basement and Basement respectively. The borehole log data correlated perfectly with the depth sections as far as the thickness and lithology of the strata from the surface to the basement, is concerned. Subsurface features such as loose ground and low velocity zones were identified and mapped correctly. Finally, it was evident from the processed data that this technique is best suitable for investigating and mapping these geologic features which are of great significance in engineering and geotechnical studies.

Regional fracture network permeability using outcrop scale measurements

Estimating the hydraulic properties of fractured aquifers is challenging due to the complexity of structural discontinuities that can generally be measured at a small scale, either in core or in outcrop, but influence groundwater flow over a range of scales. This modeling study uses fracture scanline data obtained from surface bedrock exposures to derive estimates of permeability that can be used to represent the fractured rock matrix within regional scale flow models. The model is developed using PETREL, which traditionally benefits from high resolution data sets obtained during oil and gas exploration, including for example seismic data, and borehole logging data (both lithological and geophysical). The technique consists of interpreting scanline fracture data, and using these data to generate representative Discrete Fracture Network (DFN) models for each field set. The DFN models are then upscaled to provide an effective hydraulic conductivity tensor that represents the fractured rock matrix. For each field site, the upscaled hydraulic conductivities are compared with estimates derived from pumping tests to validate the model. A hydraulic conductivity field is generated for the study region that captures the spatial variability of fracture networks in pseudo-three dimensions from scanline data. Hydraulic conductivities estimated using this approach compare well with those estimated from pumping test data. The study results suggest that such an approach may be feasible for taking small scale fracture data and upscaling these to represent the aquifer matrix hydraulic properties needed for regional groundwater modeling.

Seismic modeling of multidimensional heterogeneity scales of Mallik gas hydrate reservoirs, Northwest Territories of Canada

In hydrate‐bearing sediments, the velocity and attenuation of compressional and shear waves depend primarily on the spatial distribution of hydrates in the pore space of the subsurface lithologies. Recent characterizations of gas hydrate accumulations based on seismic velocity and attenuation generally assume homogeneous sedimentary layers and neglect effects from large‐ and small‐scale heterogeneities of hydrate‐bearing sediments. We present an algorithm, based on stochastic medium theory, to construct heterogeneous multivariable models that mimic heterogeneities of hydrate‐bearing sediments at the level of detail provided by borehole logging data. Using this algorithm, we model some key petrophysical properties of gas hydrates within heterogeneous sediments near the Mallik well site, Northwest Territories, Canada. The modeled density, and P and S wave velocities used in combination with a modified Biot‐Gassmann theory provide a first‐order estimate of the in situ volume of gas hydrate near the Mallik 5L‐38 borehole. Our results suggest a range of 528 to 768 × 106 m3/km2 of natural gas trapped within hydrates, nearly an order of magnitude lower than earlier estimates which did not include effects of small‐scale heterogeneities. Further, the petrophysical models are combined with a 3‐D finite difference modeling algorithm to study seismic attenuation due to scattering and leaky mode propagation. Simulations of a near‐offset vertical seismic profile and cross‐borehole numerical surveys demonstrate that attenuation of seismic energy may not be directly related to the intrinsic attenuation of hydrate‐bearing sediments but, instead, may be largely attributed to scattering from small‐scale heterogeneities and highly attenuate leaky mode propagation of seismic waves through larger‐scale heterogeneities in sediments.

Blocking geophysical borehole log data using the continuous wavelet transform

The interpretation of geophysical log data is frequently difficult due to the noisy downhole environment. Blocking algorithms attempt to smooth the log data while leaving the boundaries between different geological units sharp. This paper introduces a method for the determination of the boundaries based on the zero contour of the continuous wavelet transform (CWT) of the data. The amount of blocking can be controlled by the choice of the scale of the wavelet used. The method is compared with results from the median filter and with discrete wavelet transform (DWT) blocking methods, and is here applied to log data from Australia. The application of the new CWT method overcomes the rounding and shifting of boundaries inherent in median filtering, and provides greater flexibility by overcoming the power of two limitations in the DWT log blocking.

Karst systems analyzed using borehole logs — Devonian carbonates of the Świętokrzyskie (Holy Cross) Mountains, central Poland

The methodological assessment of the quality and the usefulness of borehole logs for karst analysis versus the use of data obtained via direct observation is the first objective of this paper. The second objective of the paper is to present — in the form of a case study — regional analysis of karst in Devonian carbonates of the Świętokrzyskie (Holy Cross) Mountains, south-central Poland. The subjects of the discussion are karst evolution stages, karst horizons, and their relationship to relief development. The analyzed examples (sites) presented herein, where the reliability of borehole data has often been verified by field observations, prove that descriptions of borehole logs can be used for karst analysis. However, borehole log data analysis is subject to many limitations and requires extensive validation. The basic condition that has to be met is the explicitness of the descriptions of karst forms in borehole logs. The number and the length of logs (“macro-records”) as well as the number and the size of karst forms (“micro-records”) are other important factors that affect log interpretation quality. Nevertheless, the principal general advantage of borehole log analysis is the representative nature of the obtained information. The formation of karst horizons independent of the lithology and the stratigraphy of the Kowala Fm in the Świętokrzyskie Mountains but controlled by external morphological factors suggests an isotropic character of this formation. Two general vertical types of karst systems are distinguished in this formation: (1) karst horizons, and (2) extensive karst development without distinct differentiation. The former could have been connected with fluvial base levels whereas the latter represents systems formed within the vadose zone.

Sediment Input into the Heidelberg Basin as determined from Downhole Logs

Abstract. The Upper Rhine Graben, and the Heidelberg Basin in particular, play an important role in the investigation of climate change and tectonic activity during the Tertiary and Quaternary periods. Several research boreholes were recently drilled to acquire data for a new interpretation of the geology of the northern Upper Rhine Graben. This paper investigates in detail the boreholes at Heidelberg, Viernheim and Ludwigshafen-Parkinsel, as well as the shallower boreholes at Pfungstadt, Stadtwerke Viernheim and Hüttenfeld, in terms of their geophysical parameters. The physical properties of the lithologies described in the cores are characterised on the basis of borehole logging data. A hole-to-hole correlation between adjacent boreholes is then conducted, using the characteristic changes in the ‘natural radioactivity’ parameter to acquire information on changes in sediment provenance (Rhine, Neckar, Pfälzerwald and Odenwald). An interpretation applying the statistical method of cluster analysis allows identifi cation of sections with homogenous physical properties from downhole measurements and thus the determination of possible sediment provenance.

地下構造モデルと強震動シミュレーション

The Japan islands are in a complex tectonic setting with various subducting plates, and most of urban areas are located over large-scale sedimentary basins. Since the sediments filling basins amplify ground motions and their velocity structures complicate the propagation of seismic waves, it is important for the prediction of strong ground motion and seismic hazard to determine the three-dimensional (3-D) velocity structures of these urban basins. This importance motivated various organizations to carry out extensive geophysical experiments and geological investigations, and velocity structure models are being constructed all over Japan. We have already proposed a standard procedure for modeling a regional 3-D velocity structure in Japan, simultaneously and sequentially using various kinds of datasets such as the extensive refraction/ reflection experiments, gravity surveys, surface geology, borehole logging data, microtremor surveys, and earthquake ground motion records. We applied the procedure to the Tokyo metropolitan area for constructing a reference 3-D velocity structure model. As this application confirmed the validity of the standard procedure, it is then applied to the central, eastern, and western parts of Japan in 2006 to 2008, to construct the Japan Integrated Velocity Structure Model. The velocity structure and source modelings have been dramatically improved after the 1995 Kobe earthquake with the advance of ground motion simulations based on substantial data of strong motion observation. The quality of broadband ground motion simulations enable us to predict realistic strong ground motions. The National Seismic Hazard Maps released in 2005 as a result of comprehensive research on long-term evaluation of earthquake occurrence and strong ground motion prediction are expected to be proved useful in earthquake disaster mitigation and scientific outreach to the public. It is also quite important for the simulation of long-period ground motion and its seismic hazard to validate the three-dimensional (3-D) velocity structure for the whole Japan islands. Since we are threatened by future earthquakes whose probabilities of occurrence are estimated to be high in long-term evaluation, long-period ground motions from future Tokai, Tonankai, Nankai, and Miyagi-oki earthquakes and their response spectra will be computed by using this Japan Integrated Velocity Structure Model, and combined into the Long-Period Ground Motion Hazard Maps in 2009 and later by the Headquarters for Earthquake Research Promotion. These hazard maps for the megathrust earthquakes may be proved to be touchstones of strong motion seismology.