Second EAGE International Conference on Engineering Geophysics

Applied Geophysics to Engineering, Geotechnics and Environment is generally synonymous of shallow target, but, at the same time, it demands a detailed reconstruction of the subsurface. The question is:”Is the Airborne EM ready to accept this challenge ?”. Our answer is positive, based on experiences of some case studies, dealing with landslides, shallow geological investigation and so on. Indeed the applications of AEM to geotechnical issues are very few: Beard and Lutro [1] showed the case of an airborne prospect, by using not only EM, but also magnetic, radiometric and VLF data, for the planning of a railroad in Norway; Pfaffhuber et al. [2] used the AEM for the study of rock slides and tunnelling hazards in Norway again; several are the application of the method for environmental purposes, such as potential hazards at coal-waste impoundments [3] or waste site characterization [4, 5, 6, 7]. Other rare applications are focused on the supply of sands and gravels for engineering purposes [8], while the detection of lithologic distributions in alluvial aquifer, due to hydrogeological purposes, is more frequent [9, 10,11].

Karst voids were encountered during a stadium construction in Mosul city, NE Iraq. Drilling in the site showed the presence of cavities and zone of weak rocks in some boreholes. However, the boreholes show only a limited picture of the subsurface beneath the borehole only, while drilling in all the site is expensive and time consuming. Surface geophysical methods can successfully be applied to detecting and mapping cavities, fractures and other karst features. These methods provide in-situ measurements of the subsurface non-invasively and can therefore provide a dramatic increase in spatial and temporal coverage. A 2D resistivity imaging has been one of the most effective methods in this regard in that it often can provide a detailed picture of underground conditions without digging, and it lacks many of the limitations of other geophysical tools. The method was successfully applied in the proposed site of the Mosul Stadium Project, which gave very clear pictures of the cavities and weak rock zones in the subsurface.

The different resistivity techniques are being extensively used in environmental and civil engineering to investigate the subsurface conditions. However, the application of the known ground resistivity techniques is subjected to the space availability in the investigated areas. Therefore, in order to avoid the space restriction, geophysicists use the borehole tomography in two or more wells. This approach requires more time and adds cost to survey execution. In this work, the use of the L-Shape resistivity array is being proposed as borehole to surface resistivity measurement technique. The procedure is to put the potential electrodes in the well and to keep the current electrodes on the surface and to conducted the measurements with different spacing in a radial manner around the borehole.

The case studies presented here illustrate the usefulness of geophysical surveys to aid more expensive conventional drilling programs. In all case studies, the use of a mobile, high-speed time-domain electromagnetic system is demonstrated. The geophysical data was acquired at several project locations in the United States and the United Arab Emirates.

An alternative to Water Balance Method (WBM) for estimating the quantity of leachate at landfill sites is presented in this paper. The WBM emphasis is on generating rate, while this geophysical approach estimates the in-situ quantity of leachate. The 3D inverted sections were generated using RES2DINV and RES3DINV programs. The resistivity variation in the inverted pseudo-sections clearly delineated the contaminant leachate plume (ρ < 5 Ωm), which facilitated its volume computation. The effective porosity values of clay (0.15) and sand/gravel (0.28) deduced from lithology logs were used in calculating the imaged sections of the leachate. Electrical conductivity values of 1782 µS/cm and 4521 µS/cm were determined for uncontaminated and contaminated zones respectively. A total leachate volume of 2.21 x 102 m3 was estimated beneath the 1600 m2 surveyed area.

Since they have been developed in the last few decades geophysical techniques have rarely been applied on archaeology in the United Arab Emirates. This article presents a Ground Penetrating Radar (GPR) survey of an Early Islamic site in Al Ain (8-10th centuries AD), which has been tentatively identified as ancient ‘Tawam’, the old name of Al Ain. The previous archaeological investigations at the site (1999-2000), without applying geophysical surveys at the site, will be briefed whilst the results of the GPR surveys (2011-2013) and sub-sequent test-excavations are provided. Ariel photos of 1968 shows the area of the site covered with sand dunes which seems to have been bulldozed and leveled off shortly afterwards.

Ground penetrating radar (GPR) is a standard tool in archaeological surveying, and offers high-resolution imaging of buried archaeological targets. In this paper, we explore the potential of GPR methods to detect ancient irrigation channels, aflaj (singular: falaj), in Oman’s Hajar Region. These aflaj, dating from the second-half of the 4th millennium BC, are associated with ancient settlements called Hajar Oasis Towns, and provide the most reliable means of water supply in the region. Locating the aflaj with geophysical methods can be difficult since they typically lack a geophysical contrast with their host material. They occasionally have anomalous magnetic properties, allowing them to be detected with magnetometry and thereafter excavated. However, where a magnetic contrast is absent, we trial the application of GPR. During two field seasons, we acquired GPR data (using a 500 MHz Sensors&Software system) around three Hajar Oasis Towns close to the modern towns of Bahla and Bisya, in Oman. For the most part, we acquired pseudo-3D GPR grids sampled at 5x50 cm resolution. As with magnetomtery, it appears that aflaj are only occasionally detectable with GPR. In one survey grid, a falaj is detectable and is shown to extend further north from the current limit of its excavation; however, no aflaj are confirmed elsewhere, and they cannot be detected even when acquired over known falaj positions. Nonetheless, our surveys have revealed new archaeological features of the Hajar Oasis Towns, including buried pits from which ancient pottery fragments were recovered. We suggest that the material filling the ancient aflaj generally lacks sufficient physical contrast with either its overburden or host-rock to be reliably imaged with GPR, but that GPR has other interesting applications in the Hajar Region.

Shale Gas exploration in the UK began in 2010 with five stages of hydraulic fracturing of the Bowland Shale. Hydofracturing in Cuadrilla Preese Hall-1 used 5 couplets of mini- and main-fracs with c. 10,000 bbl per stage, hydraulically isolated from each other during injection. An earthquake of 2.3 ML, a 1.5ML and a series of smaller events occurred from 31st March through May 2011 when work ceased for detailed analysis. Seismicity commenced after stages 2, 4 and 5; the largest occurring 10 hours after stage-2 shut-in. Seismological analysis using observations from seismometers emplaced after the 2.3 event, and regional data detected 55 seismic events from ML-2 to ML2, with 14 between ML 0.2 to M2.3, indicating a low B-value of 0.8 (+/- 0.3) suggesting an unusually small number of weaker events. The timing was highly correlated with injection with the largest events (stages 2 and 4) preceded by weaker events (ML0 and ML1.4) all located near the Preese Hall well, c. 500 meters south of the injection interval. The observed seismicity is almost certainly induced by hydraulic fracturing of the Preese Hall well. Future mitigation based on microseismic monitoring during hydrofracturing should reduce the likelihood of inducing further felt earthquakes.

Many definitions of the capillary number currently used in petroleum science neglect the contact angle or set it equal to zero by assuming strongly water-wet reservoir conditions. Nonetheless mixed-wet and oil-wet reservoirs are more common than water-wet ones. In those studies in which the contact angle or its cosine, respectively, is considered, wettability alterations are often treated independent of the water-oil interfacial tension. However, drastic reductions of the latter, which have been in the focus of studies on surfactant flooding for several years, should not be thought to leave the contact angle unchanged. Also, to the knowledge of the authors, the vertical component of water-oil interfacial tension and its effect on the capillary number have not been discussed in petroleum science by now. This value, described extensively by Kern and Müller (1991), is considered to be of some relevance in the mathematical treatment of microscopic wetting phenomena. Taking the vertical component of the interfacial tension into account, a new expression of the capillary number was derived to explain the connection between contact angle, oil-rock surface tension, water-rock surface tension and water-oil interfacial tension.