2nd EAGE/Aqua Foundation Indian Near Surface Geophysics Conference & Exhibition

Underwater Multichannel Analysis of Surface Waves (U-MASW) is an extension of conventional MASW technique that is used on land surface. The method has received many applications in subsurface investigations of water-bottom sediments, which is essential in design of off-shore structures, laying of underwater cables, etc. However, the source type and setup for data acquisition in this method is largely different from the conventional techniques. One of the important available studies on source mechanism presents the energy variation with respect to frequency and depth. Water-solid interface gives rise to different kinds of wave generation. The paper deals with how these waves differ from one another and where they originate. Additionally, propagation and pressure variation of Scholte waves with respect to time and frequency is presented. In short, here the source characteristics and Scholte wave characteristics are shown and some points are suggested where more investigations are needed.

Electrical Resistivity Tomography (ERT) in integration with the borehole investigation provides a more effective approach to investigate the subsurface. The correlation between ERT and borehole investigation is inadequate which prevents the conversion of electrical resistivity into the engineering properties of soil and vice versa. The present study aims at developing a correlation between borehole investigation and ERT of a site in India. Borehole investigations are conducted by drilling seven boreholes at specific points to obtain the SPT- Nꞌ values and assess the engineering properties of the soil at the site in India. The resistivity profile of subsurface layers has been obtained through five ERT profiles. Results show that only one borehole exhibits a good correlation between Nꞌ (corrected SPT values) with resistivity among all the boreholes. However, two borehole shows a good correlation between Nꞌ and transverse resistivity among all the boreholes. The study recommends the use of more numbers ERT profiles and boreholes to improve the proposed correlation. The study highlights the usefulness of geophysical testing and the requirement for further research on it.

To understand the physical and chemical processes (like metamorphism, migmatization, mineralization, and deformity) occurring in rock structures at high temperatures and pressure, the shear zone is one of the tectonic deformational aspects to consider. Eastern Ghats Mobile Belt (EGMB) is one of those regions that accommodated several types of deformities (such as lineaments, folds, faults, and shear zones). The objective of the present study is to identify these types of structural deformities near the Mahanadi River. Magnetotelluric (MT) is an appropriate geophysical method to delineate these types of structural features. For this purpose, nine MT soundings have been recorded across the Mahanadi Shear Zone (MSZ) and Angul-Dhenkanal Shear Zone (ADSZ). The profile covering all these nine MT soundings is oriented almost N-S.

A two-dimensional resistivity model is generated using nine MT soundings. In the model, the shallow subsurface is imaged as the high electrical resistivity across the profile line while the deeper zones show the conductive signature. The resistive shallower region represents the presence of highly metamorphosed rocks. While the well-connected conductive regions with varying depths confirmed the two dipping shear zones which meet at the deeper level.

This abstract provides a summary of the “Mega Merge Touggourt” project, which is using tomography refraction static to enhance deep information in the Algerian region of Touggourt. The purpose of the project was to obtain detailed subsurface knowledge to improve the geological structures and characteristics of the area.

The Touggourt region is situated in Algeria’s Ouargla Province, in the country’s southeast. Geological terms, the Sahara Desert, which currently holds a huge portion of North Africa, is where the Touggourt region is located. It is a region of interest to oil and gas companies due to the presence of sedimentary basins and geological structures such as the saliferous furrow which presents a more complete Palaeozoic and a thickening of the evaporitic deposits, during this short period it received more than 1500 m of sediments compared to the surroundings of the furrow. There have been seismic surveys and exploration projects in the area to evaluate the potential for hydrocarbons.

However, the complex subsurface geology poses challenges in obtaining detailed information about the deep geological features.

In this study, we employed the tomography refraction static method to overcome these challenges and enhance deep information in the Touggourt region.

The results of the Mega Merge Touggourt project demonstrated the effectiveness of tomography refraction static in providing high-resolution images of subsurface structures. The method enabled us to detect and characterize steeply-dipping structures, improving our understanding of the region’s geological architecture.

Furthermore, the improved knowledge of the deep geological properties of Touggourt can contribute to more accurate environmental assessments, enabling the development of sustainable practices and effective conservation measures.

In conclusion, the Mega Merge Touggourt project successfully utilized the tomography refraction static method to enhance deep information in the Touggourt region of Algeria. The results provide valuable insights into the geological structures and properties, benefiting industries such as resource exploration, geotechnical engineering, and environmental assessments in the region.

The main objective of this study is to assess the potential groundwater zones by employing the electrical resistivity tomography technique. The field data collection was conducted using the Syscal pro switch-72 instrument. Dipole-Dipole, Schlumberger and Wenner-Schlumberger array configurations were utilized during the data acquisition process. Subsequently, the obtained field data was processed using the RES2DINV software, generating inverse model resistivity profiles. The generated profiles have a maximum depth of 36.9m, providing valuable information on the subsurface structures. Moreover, the expansion of the electrodes along the profiles reached a maximum distance of 175m. The resulting profiles provide valuable insights into the variations in lithology at different depths, including clay, boulder, sand, and clayed sand layers. These variations were cross-verified with the lithologs data obtained from borehole records. Additionally, the profiles indicate the possible presence of fracture depths, which serve as indicative markers for potential groundwater zones.

The present work illustrates the inversion results of the Time domain Induced Polarization (TDIP) data by showing how the parameters are affecting the form of the IP response curve. The subsurface is a resistive network that relaxes according to the Cole-Cole model. The resistivity (ρ), chargeability (m), relaxation time (τ), and frequency exponent (c) factors in this model explain the shape of the IP curve. Initially, modeling is done to see the dependence of each parameter on the IP phenomenon. Accordingly, a 1D forward modeling code for time domain IP has been developed, followed by a non-linear inversion using a heat bath algorithm. In this scenario, the equations used for modeling are non-linear, and the Cole-Cole parameters are its independent variables. The code is developed in MATLAB and validated on synthetic data, thereafter on field data, which was measured in the lower deltaic region of West Bengal. Then, contours have been plotted for each Cole-Cole parameter to see their variation in the subsurface, it is found that the results are in synchronization with the geology of the field area.

Bhavnagar city located on the eastern part of the Saurashtra region has experienced an earthquake sequence which started on 9 August 2000. The city has received 132 earthquakes of M (magnitude) 0.5–3.8 from 9 August 2000 to 15 December 2000 and were restricted to south-eastern part of the Bhavnagar district. Two main events of M 3.6 and M 3.8 that occurred on 10 August 2000 and 12 September 2000 led the earthquake swarm activity. Magnetotelluric (MT) study has been carried out in the earthquake epicentre region along the NW-SE profile to investigate the crustal structure and its correlation with the seismicity. The MT data is analysed for dimensionality, directionality and a 2-D inversion is performed. Two conductive zones are observed in the 2-D model, which are inferred as fracture/faults. A listric fault is observed in the central part of the profile inferred as a Sihor fault and may be the possible cause for the seismicity in the area. Another North dipping fault is observed in the North-Western part of the profile named as Chamaradi fault. A highly resistive body is observed in the central part of the profile, inferred as a subvolcanic complex (a basaltic magma and granitic crustal contaminants). The majority of the earthquakes are concentrated at shallow depths (less than 6km). The cause of the seismicity near the conductive zones is due to the variation in the temperature and the pressure, which give rise to accumulation of local stresses and resulting in the earthquake swarm activity.

The long-term safety of geologic carbon storage can be monitored using a variety of geophysical approaches. Monitoring CO2 migration in a geologic carbon storage site is generally carried out using the seismic method. In the present study, a seismic inversion based on simulated annealing is used to monitor CO2 migration, providing more detailed information. Seismic modeling can be used to image and monitor the fluid flow effects and leak detection in the reservoir. The Gassman fluid substitution was carried out to calculate the volume of the CO2 plume for the post-injection case. A 2D seismic model was generated to simulate the CO2 injection scenario. In the present study, synthetic data was used to check the reliability of the algorithm used in the case of the global optimization inversion technique. After performing the inversion analysis, a decrease in the impedance values is observed at the injection site. The inverted section shows very clear CO2 information which cannot be estimated from the interpretation of seismic data alone.

Pore pressure (Pp) is a crucial factor for the analysis of geomechanical properties of reservoirs and hydrocarbon field development. Prior information on pore pressure is needed for safe drilling operations and is a fundamental input for well design and mud weight estimation for wellbore stability. However, the pore pressure trend prediction in complex geological provinces is challenging, particularly at the oceanic slope setting, where the sedimentation rate is relatively high and Pp can be driven by various complex geo-processes To overcome these difficulties, here an advanced machine learning tool is implemented with empirical methods. The empirical method for Pp prediction is comprised of data pre-processing and model establishment stage. Eaton’s’ method has been used for Pp calculation of the well U1517A located at the Tuaheni Landslide complex of the Hikurangi Subduction zone of IODP expedition 372A. Sonic travel time, bulk density, gamma ray, caliper, temperature, neutron porosity, and nmr porosity are extracted from well log data for the theoretical framework construction. The normal compaction trend (NCT) curve analysis is used to check the optimum fitting of the low permeable zone data. The statistical analysis is done using the histogram analysis and Pearson correlation coefficient matrix with Pp data series to identify potential input combinations for ML-based predictive model development. The dataset is prepared and divided into two parts: Training and Testing. The Pp data and well log of borehole U1517A are pre-processed to scale in between [−1, +1] to fit into the input range of the non-linear activation/transfer function of the random forest regression model. The Random Forest Regression (RFR) algorithm is built and compared to the model performance to predict the Pp and identify the overpressure zone in the Hikurangi Tuaheni Zone of IODP Expedition 372.

Tunneling is a risky job due to unforeseen geological conditions. Geological characterization during the tunnel excavation phase is commonly done using probe drills from the tunnel face. Although useful information provided by this technique is one dimensional and represents only a small fraction of the volume being excavated. Therefore, hazardous areas such as fault and shear zones, cavities, etc., may not be detected on time and the excavation may enter these areas resulting in large collapses, water inrush and other severe events. Hence, the risk of decreasing safety and increasing costs is always latent in this type of projects. In addition, probe drills are cost and time demanding. In mechanized tunneling using Tunnel Boring Machines, the presence of the excavator itself reduces the area available for applying other type of exploration techniques. Moreover, due to cost of this machines, there is a noticeable time pressure for keeping the production cycle, i.e. the entire excavation process, constantly running as much as possible. Not by chance, daily, monthly, and annual advance rate records are reported frequently from projects all around the globe.

Tunnel reflection seismic has been applied for various decades in all type of tunneling tasks in hard rock. Advantages of the seismic method are its penetration depth, spatial coverage (2D or 3D) and spatial resolution. One technology, the Tunnel Seismic Prediction method (TSP) has established as a reliable tool for geological prediction while tunneling. The most recent generation comprises a wireless system which can be set fully independently using a local WiFi network. Seismic sensors and required devices are synchronized together allowing an easy and fast data recording. With this novel system, a unique pneumatic impact hammer, also wireless, can be employed as the seismic source. The impact hammer fulfills all requirements for being used in mechanized tunneling environments. In this paper, the integration of this system is presented and results coming from a tunnel project are discussed.