3D Inversion Research Articles

3D inversion of vertical gravity gradient with multiple graphics processing units based on matrix compression

Among single-component inversions, vertical gravity gradient data have been proven to be sufficient to obtain reasonable density distribution. However, the increasing numbers of observations and model parameters inevitably produce a large-scale sensitivity matrix, causing problems such as large memory occupation and slow computations in the inversion. Aiming at solving these long-standing problems, we have introduced a matrix compression technique to reduce memory occupation and constructed a hybrid parallel algorithm for accelerating focusing inversion. We develop the source codes and the design pattern for the proposed algorithm using C language with open multiprocessing and compute unified device architecture for further improving algorithm feasibility and reusability. A graphical user interface and visualization tools also are developed using Python. In the tests with synthetic data produced by numerical simulation and real data from Vinton Dome, it is verified that the inversion can produce an accurate result of density values and object location. The performance analysis is conducted using different scales of data. The speedup increases with the increasing number of graphics processing units (GPUs) and model parameters, proving that the proposed parallel algorithm is scalable. We compare this algorithm with others without matrix compression to demonstrate how the compressed sensitivity matrix storing and accessing method influences inversion performance. More specifically, for an inversion with 100 × 100 × 20 cells, the average speed is approximately 6 s per iteration, with a maximum speedup of 36.94. Our algorithm has a short running time and high multiple-GPU parallel efficiency. Hence, the hybrid parallel algorithm is more powerful at implementing large-scale data calculations and could be used for solving computing problems in mass data inversions.

Structural setting of the Ischia resurgent caldera (southern Tyrrhenian Sea, Italy) by integrated 3D gravity inversion and geological models

Abstract The structural setting of the Ischia resurgent caldera and its magmatic system has been investigated by a joint interpretation of a 3D inversion of previously collected gravimetric data and all the available geological, geophysical and petrological data. Starting from the available Bouguer gravity map of the Neapolitan volcanic area and a previous 2.5D modelling, a selection of on land and offshore gravity data has been used to perform a 3D inversion, adapting and merging the basic ideas of two already tested methods, used to detect isolated bodies and layered discontinuities respectively. The base of the map is a set of gravity values, covering the whole Neapolitan volcanic area and the Gulf of Naples, which results from the union of 862 offshore and about 2000 on land extant gravity data, made uniform and re-analysed. The final model proposed here allows us to outline a very detailed and well-constrained structural setting of the crustal sector beneath Ischia. In particular, the 3D gravity inversion allowed us to outline a body with negative density contrast under Mt Epomeo, interpreted as the resurgent block, and to describe the magmatic system underneath it as a complex system of intrusions, rather than a uniformly distributed laccolithic body.

Analysis of singular values in a 3D joint inversion problem of MMT and MCSEM data

Abstract Single value decomposition (SVD) is a mathematical method of decomposing a matrix into three other matrices that have very important properties of the original matrix. One of these matrices provides us with the singular values of the original matrix. By analysing these singular values, we can determine whether an inverse problem has an ambiguous solution or whether the solution is stable. With this analysis we can also check whether the estimated solution gives an exact fit to the data, find out which combinations of parameters can be determined by observations and which cannot, and more. In this work, SVD was applied to assess the feasibility of a joint 3D inversion of marine magnetotelluric method (MMT) and marine controlled source electromagnetic method (MCSEM) data, as these methods should theoretically provide complementary information. The singular values were generated from the Hessian matrix of each method and from the joint implementation, and we compared them by considering the null space of each method. The analysis of the singular values proved to be an important step before the iterative inversion process, indicating the feasibility of the inversion without spending much time. However, we still need to spend the time to calculate the Jacobian and Hessian matrices.

3D Geophysical Predictive Modeling by Spectral Feature Subset Selection in Mineral Exploration

Several technical challenges are related to data collection, inverse modeling, model fusion, and integrated interpretations in the exploration of geophysics. A fundamental problem in integrated geophysical interpretation is the proper geological understanding of multiple inverted physical property images. Tackling this problem requires high-dimensional techniques for extracting geological information from modeled physical property images. In this study, we developed a 3D statistical tool to extract geological features from inverted physical property models based on a synergy between independent component analysis and continuous wavelet transform. An automated interpretation of multiple 3D geophysical images is also presented through a hybrid spectral feature subset selection (SFSS) algorithm based on a generalized supervised neural network algorithm to rebuild limited geological targets from 3D geophysical images. Our self-proposed algorithm is tested on an Au/Ag epithermal system in British Columbia (Canada), where layered volcano-sedimentary sequences, particularly felsic volcanic rocks, are associated with mineralization. Geophysical images of the epithermal system were obtained from 3D cooperative inversion of aeromagnetic, direct current resistivity, and induced polarization data sets. The recovered cooperative susceptibilities allowed locating a magnetite destructive zone associated with porphyritic intrusions and felsic volcanoes (Au host rocks). The practical implementation of the SFSS algorithm in the study area shows that the proposed spectral learning scheme can efficiently learn the lithotypes and Au grade patterns and makes predictions based on 3D physical property inputs. The SFSS also minimizes the number of extracted spectral features and tries to pick the best representative features for each target learning case. This approach allows interpreters to understand the relevant and irrelevant spectral features in addition to the 3D predictive models. Compared to conventional 3D interpolation methods, the 3D lithology and Au grade models recovered with SFSS add predictive value to the geological understanding of the deposit in places without access to prior geological and borehole information.

Magnetotellurics study of Atambua area, West Timor, Indonesia

Timor Island, located in the eastern Indonesian archipelago, has a complex tectonic evolution causing complex geological structures. Many hypothetical tectonic models are proposed mainly based on regional geological and geophysical data. Available geophysical data to support geological study at a more detailed scale are still very limited. Therefore, this study aimed to map the sub-regional subsurface geology in Atambua, West Timor, and its surroundings by using the magnetotelluric (MT) method. The estimated geo-electrical strike direction from the phase tensor analysis confirmed the regional Southwest - Northeast general structural orientation. The dimensionality analysis also showed the validity for 2D approximation in that direction. The subsurface resistivity models from 2D inversion of the MT data at representative lines perpendicular to the regional structural direction delineate the primary sequences and their boundaries from their resistivities. They are, from top to bottom, Viqueque and Bobonaro sequences, Kolbano sequence, Kekneno sequence, and the basement dominated by rocks with Australian affinity. These main rock formations represent the regional sedimentary depositional fill resulting from the major tectonic events on Timor Island.

3D gravity inversion based on deep learning

Gravity inversion is a typical geophysical inversion method that obtains the underground density distribution by analyzing the gravity anomaly. Normally, it can be divided into geophysics-based and deep learning based inversion. The 3D geophysics-based inversion is a time- and memory-consuming method, so 3D inversion is not routinely implemented in practical data interpretation. Here, we propose a deep learning method to transfer the 3D inversion problem to a multiple layers 2D mapping problem by decomposing the 3D target into four 2D images, including the horizontal location, vertical center, thickness and density distribution. This method is denoted as “decomposition network”. By implementing synthetic experiments with regular and complex models, and comparing with the 3D U-Net inversion, the proposed network has proved can reconstruct underground targets with high accuracy and high efficiency.

ELIMINATION OF THE GROUND SURFACE TOPOGRAPHIC EFFECT IN THE 2D INVERSION RESULTS OF ELECTRICAL RESISTIVITY TOMOGRAPHY DATA

This paper presents the results of a study that was conducted on the development of an alternative topographic effect elimination method at the 2D data inversion. Today, the problem of the ground surface topographic effect is being solved by correcting electrical resistivity tomography data and including topography in the inversion model meshes. In this paper, we studied the effectiveness of eliminating the ground surface topographic effect using inversion methods that form the basis of most 2D and 3D inversion programs. We then developed and tested a ground surface topographic effect elimination method by cor- recting apparent resistivity values for 2D inversion. We used the integral equation method to model apparent resistivity curves. Applying the developed ground surface topographic effect elimination method allowed obtaining more accurate inversion results. Application of the proposed method in geophysical surveys will more accurately exclude the topographic effect at the inversion of the observed data.

Effective 3D-transient electromagnetic inversion using finite-element method with a parallel direct solver

The correct interpretation of time-domain or transient electromagnetic (TEM) data relies on effective inversion techniques. Herein, we have developed an effective 3D-TEM inversion method based on the vector finite-element method. The domain was discretized with unstructured tetrahedra to simulate complex geologic structures. We develop a second-order backward-Euler scheme, rigorously with nonuniform time-step sizes, to approximate the time derivative of the electric field. The waveform was directly simulated and considered in the forward modeling and inversion. In a 3D inversion, the most time-consuming element of the workflow is solving a large system of linear equations. To alleviate this problem, we adopt a parallel direct solver for solving a large system of equations involved in forward modeling and sensitivity calculations. We use the Gauss-Newton approach to solve the inverse problem and formulate the least-squares problem to obtain model updates. We avoided the explicit sensitivity calculation by solving the matrix-vector multiplication between the sensitivity matrix (or its transpose) and vector. The developed inversion algorithm is validated using several realistic synthetic models. Finally, we apply the method to practical TEM data with complex topography for coal mine goaf detection. We thus obtain a detailed 3D resistivity model that revealed the layering structure and some localized anomalies related to the coal mine goaf.

Carapaces of the Dnieper-Donets Basin as a New Exploration Target for significant hydrocarbon deposits

New geological structures — displaced blocks of salt overburden — were identified in the axial part of the Dnieper-Donets basin (DDB) beside one of the largest salt domes due to modern high-precision gravity and magnetic surveys and their joint 3D inversion with seismic and well log data.
 Superposition of gravity lineaments and wells penetrating Middle and Lower Carboniferous below Permian and Upper Carboniferous sediments in proximity to salt allowed proposing halokinetic model of displaced salt overburden, assuming Upper Carboniferoussalt reactivation.
 As an analogy todescribed halokinetic deformationswe consider rafts and carapaces of the US Gulf of Mexicobasin.
 Density of Carboniferous rocks within the displaced blocks evidence a high probability of hydrocarbon saturation. Possible traps include uplifted parts of the displaced blocks, abutting Upper Carboniferous reservoirs, and underlying Carboniferous sequence. Play elements (reservoir type and quality, seals, hydrocarbon generation) are analyzed using analogues from the Dnieper-Donets basin and the Gulf of Mexico basin.
 Hydrocarbon reserves of the displacedblocks within the study area are estimated to exceed Q50 (Р50)=150 million cubic meters of oil equivalent.

The Electromagnetic Prediction of the Open Porosity beyond Boreholes

Abstract —Prediction of the open porosity factor below boreholes and in the interwell space, from electromagnetic sounding and electrical logging data, has been studied. Modeling porosity data are synthesized from laboratory studies on the samples of two boreholes drilled in the Bishkek geodynamic site. The porosity prediction is carried out using specific electrical resistivity data obtained from 1D inversion of magnetotelluric sounding data collected in the vicinities of these wells. A new approach to predict porosity is suggested, based on the constructing of electromagnetic resistivity pseudo-logs at the target location. The comparison of this technique with other options indicates that its application results in substantial improvement of the predicted accuracy (in particular, relative errors of prediction in double depth of the borehole and in the interwell space could be 2 and 8%, respectively). In general, the porosity predictions, based on Archie formula, give worse results.

Gravity and Remote Sensing Methods as a Solution in Identifying Geothermal Reservoirs on Volcanoes

Tiris Village, Lamongan Volcano complex is an area that has geothermal potential. The existence of geothermal potential in this study was identified using the gravity method combined with remote sensing methods. Remote sensing method is used to obtain a map of the distribution pattern of the soil surface temperature and a map of the continuity of the straightness and fault structure. The data used in the remote sensing method is secondary data in the form of Landsat-8 imagery and DEM SRTM 1 arc. Processing of the soil surface temperature map was obtained by using thermal infrared processing NDVI. The form of continuity of the straightness or fault structure is obtained by processing Landsat-8 multispectral image data in the form of 567 band composite and DEM SRTM data form of 3D topographic modeling. The data from the composite band 567 was reviewed visually using a 3D topographic model. The gravity method is the main method in this research because it is used to obtain the residual Bouguer anomaly distribution. The residual Bouguer anomaly data was obtained by using the moving average through spectrum analysis. The residual Bouguer anomaly distribution can be used for qualitative interpretation of the distribution of the earth’s gravitational acceleration at the measurement location. The quantitative interpretation of the gravity data is based on the surface density estimation graph using the Parasnis method and 3D inversion modeling, using residual Bouguer anomaly data. The results of 3D inversion modeling provide four types of subsurface rock layers based on the density distribution value, namely, the first rock layer ρ 1 = 2.52 – 2.67 g/cm3, the second rock layer ρ 2 = 2.72 – 2.77 g/cm3, the third rock layer ρ 3 = 2.80 – 2.83 g/cm3, and the fourth rock layer ρ 4 = 2.84 – 2.86 g/cm3. The third rock layer is assumed to be reservoir rock and is estimated to be at a depth of 500–800 meters below the measurement point. The fourth rock layer is assumed to be intrusive igneous rock, which penetrates dominantly in the middle of the measurement location, which is oriented southwest, south to north, which is indicated by the high anomaly continuity on the regional Bouguer anomaly map. Based on the results of 3D inversion modeling and spectrum analysis of the average depth of the regional Bouguer anomaly, it is found that the intrusive rock layer is thought to be at a depth of 350 meters below the measurement point.

Detection of geological boundaries by 3D gravity inversion for density gradients in different directions

The spatial position and dip feature of the density boundary are significant to the study of fault and tectonic frameworks. Edge detection methods generally attach importance to the horizontal position of the boundary, but it is difficult to determine the dip feature expressly. A density gradient inversion method was proposed based on the corresponding relationship among the gravity forward field, forward kernel matrix, and model attributes. The inversion result of this method is that the density gradient value is different from the conventional gravity inversion. It can directly display the 3D distribution features integrated with 3D inversion results of the density gradient in different directions. The theoretical model means that the inversion results can not only identify the horizontal position of the boundary but also qualitatively determine the dip feature of faults. It has been widely applied to fault identification in the Songliao Basin. According to the joint inversion results, the strike feature and the dip feature can be quantitatively and qualitatively identified, respectively, making up for the shortcomings of sparse distribution and poor lateral resolution of existing seismic data.

Windowed 4D inversion for near real-time geoelectrical monitoring applications

Many different approaches have been developed to regularise the time-lapse geoelectrical inverse problem. While their advantages and limitations have been demonstrated using synthetic models, there have been few direct comparisons of their performance using field data. We test four time-lapse inversion methods (independent inversion, temporal smoothness-constrained 4D inversion, spatial smoothness constrained inversion of temporal data differences, and sequential inversion with spatial smoothness constraints on the model and its temporal changes). We focus on the applicability of these methods to automated processing of geoelectrical monitoring data in near real-time. In particular, we examine windowed 4D inversion, the use of short sequences of time-lapse data, without which the 4D method would not be suitable in the near real-time context. We develop measures of internal consistency for the different methods so that the effects of the use of short time windows or the choice of baseline data set can be compared. The resulting inverse models are assessed against qualitative and quantitative ground truth information. Our findings are that 4D inversion of the full data set performed best, and that windowed 4D inversion retained the majority of its benefits while also being applicable to applications requiring near real-time inversion.

3D deep electrical structure and seismogenic environment in the western section of the Zhangjiakou-Bohai fault zone

The Zhangjiakou-Bohai fault zone (ZBFZ) is an important NW-trending active tectonic zone in North China. The western section of ZBFZ is characterized by frequent moderate and strong earthquakes. This is a typical tectonic area for studying seismic and volcanic activities. The three-dimensional (3D) deep electrical structure of the region was revealed by using 3D electromagnetic inversion of 143 magnetotelluric stations. The results suggest that the deep electrical structure in the western part of the ZBFZ is laterally heterogeneous. To the north of the Shangyi-Chicheng Fault (F4), the upper crust has a high resistivity structure (R), corresponding to the exposed Hanuoba basalts and metamorphic rocks. To the south of F4, high and low resistivity zones alternate, which is attributed to the complex faults and basin-range structures. In the middle crust, the low-resistivity structures (C1 and C2) gradually appear in the northwest and southeast of the study area, showing the characteristics of a high-resistivity structure sandwiched between two low-resistivity structures. In the lower crust, the two low-resistivity structures (C1 and C2) gradually join each other and the whole region becomes characterized by low resistivity. The Shangyi-Chicheng Fault (F4), the northern margin fault of the Huai’an Basin (F7), and the northern margin fault of the Huaizhuo Basin (F11) are definite electrical difference zones, which are connected to a low-resistivity layer in the crust. The results indicate that the focal depth of the 1998 M6.2 Zhangbei earthquake was between 12 km and 15 km and its seismogenic fault was the Dahezhen-Hailiutu Fault (F3), which is concealed beneath the Hanuoba basalt area. It is speculated that owing to the neotectonic activities, the magma originated in the asthenosphere mantle rose and erupted on the surface near Datong, forming the Datong volcanic group. Then the magma continued to migrate and overflow along with the fractures in the NE direction, forming the Hannuoba basalts in the Zhangbei area. The existence of mantle thermal material in this area led to the migration of accompanying fluids to the middle and upper crust, resulting in fault sliding and frequent occurrence of moderate and strong earthquakes in this region.

Shape Dynamic Time Warping for Seismic Waveform Inversion

ABSTRACT We illustrate shape dynamic time warping (ShapeDTW) for 1D structure waveform inversion with examples from Tanzania, East Africa, and Northeastern Oklahoma. Seismograms of the Mw 5.9 Lake Rukwa, Tanzania, earthquake (18 August 1994) recorded by regional broadband seismographic stations of the Tanzania Broadband Seismic Experiment are used to demonstrate the method. We also test the inversion through solving for 1D crustal velocity structure of the Cherokee Platform in Oklahoma using seismograms of the 2011 Mw 5.7 Prague, Oklahoma, earthquake recorded by the EarthScope Transportable Array. Dynamic time warping (DTW) bypasses the time expense required for manual identification of seismic phases and shows potential for linking discrete seismic phases between two similar waveforms. ShapeDTW improves inversion performance by characterizing the character of the time series near each amplitude point. Applying Sakoe-Chiba band limits to ShapeDTW and an additional amplitude constraint improves the overfitting problem that occurs with the classic DTW method. We apply ShapeDTW to estimate optimal time shifts between observed and synthetic waveforms with time shifts reduced through inversion. The crustal velocity model of Tanzania found using ShapeDTW is close to that found using “phase time inversion” of numerous regional seismic phases observed in the three-component waveforms in a previous study but avoids the necessity of isolating and interpreting different seismic phases in the waveforms. Reducing the ShapeDTW functional misfits can overcome the cycle-skipping problem that often occurs with direct comparison of amplitudes in waveform inversion. This method may be useful in generating starting models for other 1D and 3D inversion methods.

Deep-Learning-Based Noniterative 2D-Inversion of Unfocused Lateral Logs

Abstract —The work deals with the development of methodological and algorithmic tools for the quantitative interpretation of oil well resistivity logs. We review the results of applying the neural-network-based approach to the inversion of resistivity logs measured at thinly bedded high-contrast environments. The capabilities of the proposed approach are demonstrated by the example of the algorithm for noninterative express inversion of unfocused lateral logs (BKZ). BKZ is the unfocused array logging method widely used in the Commonwealth of Independent States for oil well studies. BKZ logs are known for their complexity: The signals of unfocused gradient probes are highly affected by the medium properties below and above the measuring point. The developed algorithm is based on the inversion of full logs into the parameters of a 2D axisymmetric model of the medium, which allows naturally taking into account the influence of surrounding rocks and borehole conditions. Transition from the “layered” parametrization conventional for BKZ logs interpretation to a quasi-continuous change of properties along the well axis allows extracting meaningful information at every measurement point and constructing high-resolution geoelectric models of the sediments. The noniterative nature of the algorithm provides a high computing efficiency. This opens up the possibility of using the 2D inversion advantages to increase the reliability of the initial express interpretation results. Testing the algorithm on the practical data from West Siberian oilfields has revealed the field of its maximum efficiency, namely, study of impermeable and low-permeability sediments, such as the complex shaly caprocks and bituminous deposits of the Bazhenov Formation. With high-quality input data, the approach is also efficient for studying permeable terrigenous sediments.

Development and practical evaluation of a saturation effect learning simulator for inflow magnetic resonance angiography.

The quality of visualization in inflow magnetic resonance angiography (MRA) depends highly on the excitation state of the longitudinal magnetization obtained using specified imaging parameters. In addition, signal intensity changes controlled by the preparation pulse-such as inversion recovery (IR) and saturation recovery (SR)-can potentially be used as quantitative physiological values. Although having practitioners understand these relationships both qualitatively and quantitatively is important, handling clinical equipment in practical learning or experiments involves limited opportunities. The simulator corresponds to a three-dimensional spoiled gradient echo sequence and allows users to freely input multiple virtual excitation effects in space and time. The purpose of this study was to quantitatively evaluate the agreement between the measured MRAs obtained in flow phantom tests and virtual MRAs simulated under similar conditions. We imaged two vascular flow phantoms on a 3.0T MR system using three-dimensional (3D) time-of-flight (TOF) MRA and 3D inversion recovery tissue signal suppression (IR-suppression) MRA protocols. We evaluated quantitative values for consistency between the measured and virtual MRAs images with matched spatial resolution. Then we assessed the coincidence by reformatting maximum-intensity projection images with 1mm isotropic pixels, with it ranging from 89.6 to 92.0% and 89.1 to 92.9% for TOF MRA and IR-suppression MRA, respectively. These results may be useful as a reference index for the theoretical study of MRA images by practitioners, for complementary validation by phantom testing, or for the development of MRI-related simulators.

Geophysical surveying for the detection of ferrous-based objects: possibilities for depth estimative combining analytic signal and vertical integral of the anomalous magnetic field

The detection of buried clandestine objects challenges forensic and archeologic search group teams on varying terrains, and variable scales of research. Therefore, the study of controlled buried objects is useful for trainings in geophysical acquisition and processing. In this study, we applied ground survey data for testing the magnetic method at controlled geophysical sites for the location of ordinary objects and firearms. We used data filtering techniques in order to facilitate the location of magnetic targets. Also, we experienced the 3D inversion of analytic signal of the vertically integrated magnetic field (ASVI), for the location of targets in depth. As a result, the study determined the location of four magnetic targets, and a three-dimensional view was constructed from the estimated magnetic susceptibility. We concluded that modeling transformed magnetic data is an affordable technique for application in near-surface investigations. Also, this experiment exemplifies the relevance of magnetic methods for location of excavation sites on the basis of geophysical methods.

Myocardial scar detection in free-breathing Dixon-based fat- and water-separated 3D inversion recovery late-gadolinium enhancement whole heart MRI

The aim of this study was to investigate the diagnostic accuracy and reader confidence for late-gadolinium enhancement (LGE) detection of a novel free-breathing, image-based navigated 3D whole-heart LGE sequence with fat–water separation, compared to a free-breathing motion-corrected 2D LGE sequence in patients with ischemic and non-ischemic cardiomyopathy. Cardiac MRI patients including the respective sequences were retrospectively included. Two independent, blinded readers rated image quality, depiction of segmental LGE and documented acquisition time, SNR, CNR and amount of LGE. Results were compared using the Friedman or the Kruskal–Wallis test. For LGE rating, a jackknife free-response receiver operating characteristic analysis was performed with a figure of merit (FOM) calculation. Forty-two patients were included, thirty-two were examined with a 1.5 T-scanner and ten patients with a 3 T-scanner. The mean acquisition time of the 2D sequence was significantly shorter compared to the 3D sequence (07:12 min vs. 09:24 min; p < 0.001). The 3D scan time was significantly shorter when performed at 3 T compared to 1.5 T (07:47 min vs. 09:50 min; p < 0.001). There were no differences regarding SNR, CNR or amount of LGE. 3D imaging had a significantly higher FOM (0.89 vs. 0.78; p < 0.001). Overall image quality ratings were similar, but 3D sequence ratings were higher for fine anatomical structures. Free-breathing motion-corrected 3D LGE with high isotropic resolution results in enhanced LGE-detection with higher confidence and better delineation of fine structures. The acquisition time for 3D imaging was longer, but may be reduced by performing on a 3 T-scanner.

Characterization of gas‐bearing sediments in the coastal environment using geophysical and geotechnical data

AbstractSeismic investigation in marine gas‐bearing sediments often fails to get information below the acoustic mask created by free gas. To circumvent this problem, we combined collocated multichannel ultra‐high resolution seismic imaging, marine electrical resistivity tomography and core sampling to study the physical properties of gas‐bearing sediments in the Bay of Concarneau (France). We obtained sections of compression (P‐) wave velocity () from the multichannel processing and 2D resistivity models from the marine electrical resistivity tomography data inversion. We observed low resistivity (∼0.5 Ω·m) and low (∼1200 m/s) values where free gas was identified in the seismic data. We tested a joint processing workflow combining the 1D inversion of the marine electrical resistivity tomography data with the 2D P‐wave velocity through a structural coupling between resistivity and velocity. We obtained a series of 2D resistivity models fitting the data whilst in agreement with the data. The resulting models showed the continuity of the geological units below the acoustic gas fronts, which are associated with paleo‐valley sediment infilling. We were able to demonstrate relationships between resistivity and velocity differing from superficial to deeper sediments. We established these relationships at the geophysical scale and then compared the results to data from core sampling ( and porosity). We inferred the porosity distribution from the marine electrical resistivity tomography data. At the core locations, we observed a good agreement between this geophysical scale porosity and the core data both within and outside the gas‐bearing sediments. This agreement demonstrated that resistivity could be used as a proxy for porosity where no was available below gas caps. In these regions, the observed low resistivity showed a high porosity (60%–70%) down to about 10–20 m in depth, in contrast with the surrounding medium that has a porosity of less than 55%. These results support the hypothesis that failures inside the paleo‐valley sediment could control the gas migration.