Geological Depth Research Articles

Improved cluster analysis of Werner solutions for geologic depth estimation using unsupervised machine learning

Werner deconvolution is a widely used method for computer-aided solution estimations using magnetic field data. Because of the inherent unpredictability of potential field data, the techniques frequently yield unpredictable results and may not always be able to predict the full extent of the geological structures depicted. The unsupervised clustering algorithm was then used to improve the detection of geological structures generated from magnetic field data. A synthetic magnetic model was created by combining two models that resembled dikes. To add a little more complexity to the model, sporadic noise was applied to the synthetic model. The synthetic model was subjected to Werner deconvolution to produce solutions. The developed solutions resulting from the synthetic data were applied to an unsupervised machine-learning algorithm. The algorithm was able to detect two clusters from the dataset and the centroids generated from the number of clusters formed indicated the depth of the two models, which was 5 m and 8 m respectively. The algorithm was then subjected to a real case dataset from the Banke complex, which is part of the Nigerian Younger Granite region. Three clusters were formed, having centroids of 536 m, 635 m, and 530 m. These depths were validated with previous surveys carried out in the area. This algorithm proved successful in determining the exact position in terms of the depth of the geologic bodies. This proposed approach is fully data-driven and is successful even when there is noise.

Direct Air Capture: Effects of Low-Purity CO2 and Geological Depths on Post-Capture Compression Energy and Storage

Phreeqc software has been successfully employed to study the behaviour of the gypsum rock-water system under different conditions and various levels of impurities present in the injected CO2 stream. The dissolution of gypsum leads to the increase in water quantity because of release of hydration water molecules. Under the conditions at 1km geological depth, an anhydrite (CaSO4) produced remained dissolved in the solution while the pH slightly drops owing to sulphate ions generation. As the pressure and temperature increase at 1.5km depth, more gypsum dissolves until at 2.5km depth where excess rise in temperature inhibits gypsum dissolution. The injection of pure CO2 leads to the production of calcite in the solution, which continues to grow as more CO2 is injected. But, the presence of impurity such as N2 in the CO2 stream inhibits formation of calcite, owing to continuous dissolution/ionization of calcium. Other carbonate crystals were similarly affected while the pH continues to drop drastically. It is inferred that the presence of impurities such as N2 in the CO2 stream complicates carbonation mechanisms and inhibits formations of the carbonate crystals.

Modelling Methane Adsorption Isotherms on Shale at Different Temperatures

Prediction of adsorption isotherms under different temperatures is significant to reserve estimation of shale gas reservoirs. Based on the Polanyi adsorption potential theory and Langmuir adsorption theory, a method was presented to predict adsorption isotherms at different temperatures. In this method, the relationship between Langmuir pressure and temperature was quantified. By utilizing this method, we predicted adsorption isotherms of Longmaxi shale from 45 °C to 120 °C according to experimental data at 30 °C. Meanwhile, by considering the pressure and temperature gradients, we also predicted the adsorption capacity of Longmaxi shale with geologic depth. Results show that the adsorption data predicted by our method are in accord with experimental data and the error coefficient is less than 5%. In addition, the isosteric heat of adsorption for Longmaxi shale can be calculated by predicted adsorption data based on the Clausius–Clapeyron equation of capillary systems. Therefore, our study illustrates theoretical foundations for the efficient evaluation of adsorbed gas content in shale gas reservoirs at geologic conditions.

CO2 mineralization and CH4 effective recovery in orthoclase slit by molecular simulation

Knowledge of the competitive adsorption behaviors of shale gas and CO2 in shale is crucial for understanding the fluid storage, exploration and segmentation. In this work, Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations as well as DFT calculation were carried out to study the adsorption mechanisms of CH4 and its mixtures with CO2 in orthoclase slit. The dependence of gas adsorption behavior on geological depth, water content and CO2 mole fraction, yCO2, were explicitly examined. Quantum chemistry calculation characterizes the chemical adsorption of CO2 on orthoclase surface by forming a carbonate-like structure, showing the feasibility of CO2 enhanced shale gas recovery and geological sequestration of CO2 in orthoclase. The enrichment region of pure CH4 in orthoclase slit is inferred to be at the geological depth of approximately 2600 m, which accords with the high methane yield in 2000–3200 m by CO2 injection. The adsorbed methane molecules are favorably loaded at slits with low water content (0–2 wt%). The adsorption capacity of CH4 in the binary mixture decreases with the increasing yCO2. The favorable mining conditions are predicted to at 2000–3200 m with an economical yCO2 of 0.3. Shallow geological depth (200–400 m) is helpful for the sequestration of CO2. This study has gained deep insights into the adsorption and recovery mechanisms of shale gas in orthoclase slit and has shed light on the efficiencies of CO2 enhanced recovery of shale gas and the mineralization of CO2 in shale.

Review on the kerogen deformation mechanism

Shale gas is unconventional natural gas energy stored in shale, and is one of the important substitutes for conventional oil and gas resources. Since amorphous kerogen is the main component of shale organic matter and has a high degree of deformation ability, it is a key factor to improve shale gas recovery. As an emerging mining technology CS-EGR, the CO2 injection method replaces the hydraulic pressure method, thereby alleviating the greenhouse effect and energy crisis. The basic understanding of the microscopic mechanism of the multicomponent competitive adsorption and diffusion of the adsorbate in kerogen will provide a theoretical basis and guidance for further understanding of kerogen deformation and further CS-EGR. Starting from the summary of experimental research, this paper systematically summarizes the kerogen model used for kerogen deformation research and discusses the effects of adsorbate, load, moisture, temperature, pressure, and geological depth on different kerogen structures of different maturity. The effect of kerogen deformation.

Investigation of the Adsorption Behavior of Organic Sulfur in Coal via Density Functional Theory (DFT) Calculation and Molecular Simulation

In this paper, we have investigated the chemical adsorption behavior of O2 on five types of organic sulfur (thiol, sulfoxide, thioether, sulfone, and thiophene) in polycyclic aromatic hydrocarbon (PAH) sheets using density functional theory (DFT) calculations. Here, the adsorption energy of O2-organic sulfur exceeds that of O2-PAH. Sulfone tends to be more favorable for oxidation reactions than other organic sulfur compounds and PAH by energy gap and deformation charge density analyses. A large charge transfer occurs between O2 and organic sulfur compounds by charge analysis. A radical distribution function (RDF) analysis shows that O2/CO2/N2 is preferentially adsorbed on nitrogen/sulfur/oxygen-containing functional groups in coal. To inhibit the reaction of sulfur-containing coal with oxygen, the physical adsorption of pure gas (CO2/O2/N2) and binary mixed gases (CO2 + O2/N2 + O2/CO2 + N2) is conducted at different temperatures and geological depths using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The adsorption capacities of five types of organic sulfur with respect to the pure gases decrease with increasing temperature and increase with increasing depth. For O2/CO2, CO2/N2, and O2/N2 binary gas systems, the order with respect to adsorption amount is CO2 > O2 > N2. The factor of adsorption capacities is also evaluated, and the results show that pore volume plays a key role in adsorption behavior.

Application of in-situ anisotropic parameters in 3D seismic velocity analysis for improved pre-drill pore pressure prediction in the onshore Niger Delta basin, Nigeria

The inaccurate prediction and characterization of anisotropic properties of hydrocarbon reservoirs during seismic processing have been a major obstacle to optimal time-to-depth conversion, well-to-seismic ties, and a robust fit-for-purpose velocity model for accurate seismic pore pressure (SPP) imaging. Though some levels of exploration successes have been achieved using isotropic velocity models in parts of the Niger Delta Basin, serious challenges however abound at the deeper shale-dominated intervals of the basin because of the intrinsic anisotropic properties of shale. The application of in situ anisotropic parameters in 3D seismic velocity analysis for improved pore pressure prediction in the study area was carried out with the objectives of applying the appropriate anisotropic parameters for optimal processing of seismic velocity field for overpressure studies. Anisotropic parameters for vertical transverse isotropic (VTI) wave-field were estimated from available wire-line logs using standard empirical relationships and were used to correct for shale anisotropy on a 6.0-km offset seismic data. The migrated velocities were further converted to geological depth and calibrated to wells. Isotropic and anisotropic pre-stack depth migrated (preSDM) velocities were inverted to seismic pore pressure prediction. Results of the study revealed that the anisotropic preSDM velocities yielded higher resolution in the vertical and lateral positioning of geological features when compared with the isotropic velocity model. Also, the seismic velocity fields generated from the anisotropic preSDM seismic velocities were observed to optimally tie to the well and accurately imaged the reservoir pore pressures at deeper intervals. These findings, therefore, revealed the appropriateness of the applied anisotropy parameters (−0.05 ≤ δ ≤ 0.05 and 0.08 ≤ η ≤ 0.48) in predicting elasto-thermal properties of the area. These parameters can therefore be incorporated into anisotropic velocity modeling and processing of long offset seismic data for accurate prediction of pore pressure, lithological, and fluid properties of reservoirs in the area.

The W transform

Time-frequency spectral analysis methods such as the S transform cannot appropriately present low-frequency anomalies in seismic traces because they generate a time-frequency spectrum with a low resolution in time at low frequencies. I have developed the W transform to improve the time resolution of the spectrum at low frequencies, for an effective detection of seismic anomalies related to hydrocarbon reservoirs in petroleum exploration and abnormal features in near-surface geophysics. The W transform has three features: (1) the spectral energy is concentrated around the dominant frequency of a seismic waveform, rather than being shifted toward higher frequencies by the S transform; (2) the implementation is numerically stable because it avoids any potential frequency singularity in the S transform; (3) the Gaussian window function is defined using a nonstationary frequency weight, rather than using a stationary frequency weight in the S transform, because the dominant frequency is a time-dependent function. Therefore, the time-frequency spectrum generated by the W transform appropriately represents seismic properties varying with geologic depth, and it has an improved time resolution at low frequencies that makes it suitable for characterizing reservoirs in petroleum geophysics and for detecting karsts in construction engineering.

Optimization for Emission Frequency of Oceanic Impulse Sound Source Logging

Gao, X.; Zhu, J.; Fu, H., and Hao, X., 2020. Optimization for emission frequency of oceanic impulse sound source logging. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 124–129. Coconut Creek (Florida), ISSN 0749-0208.In the exploration and development of offshore oilfields, the requirements for the detection distance and accuracy of underground geological structures are increasing day by day. When the traditional acoustic logging technology is used in oceanic logging, the formation structure is complex, and the reflected signal is very weak, which makes it difficult to extract the reflected signal and accurately identify the reflector orientation. The plasma impulse sound source is used as the emission source of the technology of ocean exploration while drilling, which has the characteristics of high power, wide frequency band, energy accumulation, and controllable and repeatable excitation, which can not only enhance the detection distance of traditional acoustic logging, but also detect the geological structure, fracture types, and strike around the well. In this article, sound depth detection technology is applied to study the selection of the dominant emission frequency band of the stimulated sound source based on the establishment of the geological interface depth detection model with different borehole diameter parameters. The results show that: when the well diameter is 0.1524, 0.2159, 0.2445, and 0.3112 m, 5, 3.8–4.2, 3.5–4, and 3 kHz are selected as the dominant excitation frequency bands, and the detection distance can reach tens of meters or even hundreds of meters. This research provides a reference for the subsequent application of impulse source in offshore logging.

Physico-chemical and dielectric parameters for the monitoring of carbon sequestration in basalt and silica media

Abstract Currently, there are concerns about the safety of carbon sequestration in the geological media. To assuage this concern, scientists and engineers have the tasks to demonstrate fool-proof and comprehensive techniques that can monitor the movement, or otherwise, concentration of the injected CO2 in the subsurface. In this work, well-defined laboratory experiments were used to demonstrate the key physico-chemical characteristics and dielectric parameters that are useful in monitoring carbon sequestration sites. The porous materials used were basalt and silica sand samples to demonstrate the possibility of CO2 injection into different media. To simulate the resident fluids, distilled and brine water samples were used in separate experimentations. Also, the pressures and temperatures were chosen to correspond to different geological depths which are relevant for CO2 injection. The pH, bulk electrical conductivity ( σ b ) and bulk dielectric permittivity ( e b ) of the system were measured for the two different media. On one hand, the decrease in pH was clearly observed in both the basalt and silica sand after the exposure to CO2. On the other hand, σ b and e b increased as CO2 was injected. Our results further revealed a higher ion mobilisation​ potential in basalt medium than that in silica sand. This results in lower pH and higher electrical conductivity in the basalt medium than the silica medium. Thus, a simultaneous measurement of pH, σ b and e b are proposed as a multiparameter approach to monitor CO2 leakage from the storage reservoir. As far as we are aware, this is the first work in the open literature that reports simultaneous dielectric and electrical behaviours of CO2 –water–porous media system for basalt porous medium in connection with carbon sequestration.

Effect of Geological Depths on CH4 Adsorption, Diffusion, and Swelling in Kaolinite by Molecular Simulations

The demand for energy in the world has increased dramatically, leading to an increase in the geological depth of unconventional natural gas development such as shale gas. Comprehension adsorption a...

A permeation model of shale gas in cylindrical-like kerogen pores at geological conditions

Understanding the diffusion and permeation behavior of shale gas at geological depths is significantly important to exploration of shale gas, while the permeation mechanism of shale gas in shale gas reservoir is closely related to the confined fluid behavior at mesoscopic scale and cannot be described by traditional Fick or Knudsen diffusion models. In this work, we use the dual control volume grand canonical molecular dynamics method to systematically investigate the permeation processes of shale gas in cylindrical -like kerogen pores represented by the carbon nanotube at different geological depths, and hundreds of simulation data in different pressures, temperatures and pore diameter are obtained. By analyzing these simulated data, we propose a new permeation model to describe the permeability of shale gas in cylindrical-like kerogen pores at geological depths. The new model can satisfactorily reproduce the extrapolation testing data of permeability of shale gas, and perfectly bridge the gap between macroscopic Fick model and microscopic Knudsen model, which provides a useful guidance and reference for exploration of shale gas.

PERMEABILITY, SELECTIVITY AND DISTINGUISHING CRITERION OF SILICONE MEMBRANE FOR SUPERCRITICAL CO2 AND N2 IN THE POROUS MEDIA

The possibility of leakage of CO2 from a geological storage reservoir is of serious concern to stakeholders. In this work, high–pressure-temperature laboratory experiments were performed to demonstrate the application of a silicone membrane-sensor system in the monitoring of subsurface gases, especially in the leakage scenario. Mass permeation, membrane resistance to gas permeation, and the gas flux across the membrane are reported for two gases, namely, CO2 and N2. Mass permeation of CO2 through the membrane was more than ten times higher than that of N2, under similar conditions. It was also found to increase with the geological depths. The gas flux remains higher for CO2 as compared to N2. From the results, a simple criterion for distinguishing the presence of the different gases at various geological depths was formulated based on the rate of permeation of gas through the membrane. Results and techniques in this work can be employed in the detection/monitoring of subsurface gas transport, especially in geological carbon sequestration.

ELECTRICAL RESISTIVITY SURVEY FOR GROUNDWATER POTENTIAL AND ESTIMATION OF CLAY DEPOSIT IN ARAGBA-OKPE, OKPE LOCAL GOVERNMENT AREA, DELTA STATE NIGERIA

Electrical resistivity survey employing Vertical Electrical Sounding techniques of Schlumberger arrangement were carried out at seven (7) fairly distributed stations with 154 Vertical Electrical Soundings in Aragba-Okpe. The data obtained from the field were plotted on a log-log graph and interpreted qualitatively by inspection and quantitatively by partial curve matching. The results obtained were improved with the aid of computer iteration using the Winresist Software to delineate the thickness and depth of each layers as well as the resistivity value. These layers were grouped together in to geologic depth intervals known as the Geoelectric sections for interpretations. Using knowledge of both the local geology of Aragba-Okpe and the resistivity of the layers, the Geoelectric sections were interpreted. The study revealed that boreholes for sustainable water supply could be drilled to a depth of 30 m in Aragba-Okpe, However, the fifth layer within Aragba Primary School, Aragba Secondary School and Oviri Aragba Road (VES 1, 5 and 7) are the best locations for sustainable water supply
 The overburden protective capacities of the aquifer in Aragba-Okpe were evaluated using the Dar-zarrouk parameters. The result also revealed poor aquifer protection ratings of less than 0.1 in all the stations. The groundwater in Aragba-Okpe is therefore not protected and prone to contamination in the event of pollution.

Enhanced gas recovery by CO2 sequestration in marine shale: a molecular view based on realistic kerogen model

Injection of CO2 into shale reservoir is regarded as one potential scenario for CO2 sequestration and enhanced gas recovery (CS-EGR). In this work, a realistic molecular model of kerogen in Chinese Silurian marine black shale was generated using molecular dynamics (MD) simulations. The competitive adsorption of CH4 and CO2 was simulated by the grand canonical Monte Carlo (GCMC) method under different reservoir pressures, temperatures, geological depths, CO2 mole ratios, and moisture contents of kerogen model. Results show that CO2/CH4 adsorption selectivity decreases with increasing reservoir pressure, indicating that CS-EGR can be more efficient if CO2 injection is conducted at the late development stage. The temperature has a negative effect on the selectivity, which indicates that thermal stimulation has an adverse effect on the efficiency of CS-EGR. Also, the selectivity decreases with increasing geological depth, suggesting that shallow shale formations are more suitable for CS-EGR. At low pressures, the selectivity increases with increasing CO2 mole ratio, while at high pressures, the selectivity decreases with the increase of CO2 mole ratio. This result suggests that CO2 mole ratio should be dynamically adjusted with the production so as to adapt to the changing reservoir pressure. At higher pressure condition, both the amounts of CO2 sequestration and CH4 desorption increase with the increase of CO2 mole fraction. However, the adsorption stability of CO2 weakens with increasing injection amounts of CO2. Moreover, the adsorption selectivity decreases initially, and then increases with the moisture content of kerogen. Thus, the performance of CS-EGR may be improved by increasing the kerogen moisture content for Silurian shale gas reservoirs. This study gains enhanced insights on the effect of reservoir pressure, temperature, geological depth, CO2 mole ratio, and kerogen moisture content on CO2/CH4 competitive adsorption, and the results can provide applicable guidances for CS-EGR in shale gas reservoirs.

Application of seismic reflection wave method in high water content sand-layered dike detection

There is a pretty long history of dike construction in China. The filling materials of many dike bodies are sand-layer. It is easy to lead to seepage destruction at the interface between sand layer and different soil layers. Because of the large volume and high water content of dike project, the detection effect of resistivity and geological radar was bad. Three sections of Yangtze river dike in Zhangjiagang with different filling materials such as Nantong ash dam, jiuqi dike and Chaodong dike were detected by seismic reflection wave method, and a comparative study by geological exploration to demonstrate the feasibility of seismic reflection wave method for high water content sand-layered dike detection was made. The tests indicate that under the condition of high water content (above 30%) the seismic reflection wave method is can not only identify sandy soil layers and hidden dangers, but also ascertain shallow geological sand layers and groundwater depth. Research results will provide references for operation and management levee engineering.

Depth-conversion techniques and challenges in complex sub-Andean provinces

The reliability of depth conversion in complex land areas is particularly challenging. Accuracy and precision are usually difficult to achieve simultaneously because of the limited amount and quality of seismic data and sparse control from well data. Ideally, depth-migration methods would be the right tools to produce such data for interpreters. However, despite recent significant breakthroughs in seismic imaging, the ability to provide precise depths is not always achievable with depth-imaging techniques. Therefore, depth conversion remains a crucial tool for converting a seismic image and its interpretation to geologic depth. We have developed an overview of the techniques used for depth conversion through a carefully selected set of geologically diverse field examples. We determine the challenges faced while applying each methodology and, more importantly, share our own experiences and pitfalls. We also evaluate the steps taken to overcome these limitations. All these studies highlight the pragmatic application of techniques and their common pitfalls to improve the workflows that can be implemented to solve other depth-conversion problems. Depth-conversion techniques can be classified depending on the approach used for velocity model building (VMB) (i.e., time-depth and instantaneous velocity functions, layer-cake models, or geostatistical velocity interpolations) and also depending on the ray-tracing procedure (i.e., vertical stretching or image ray). To verify the reliability of the VMB, we establish the following criteria for an acceptable velocity model: (1) honors hard data, (2) integrates all the available sources of velocity information, and (3) makes geologic sense. We reinforce the latter in complex areas where geologic control drives the chosen approach. For instance, in cases with strong velocity gradients (e.g., basement-involved structures), vertical depth conversion may not be able to solve all possible scenarios, resulting in an incomplete assessment of the structural uncertainty. To model such situations, we use a time-to-depth conversion based on the image-ray concept.

Formation geological depth image according to refraction and reflection marine seismic data

The possibility of forming of the geological depth image from marine seismic data observed with the method of reflected waves by multiple overlaps and the refracted method by deep seismic sounding was investigated. The difference in the algorithms for the creating of depth image using the finite-difference migration on the field of reflected and refracted waves is shown. Also there is presented the possibility of comparing and generalizing their results. Researches were carried out using the example of seismic data, observed with the method of reflected waves by multiple overlaps and the refracted method by deep seismic sounding in the area of the Azov Sea.

A mesoscale model for diffusion and permeation of shale gas at geological depth

The demand on energy is rising and shale gas as an important unconventional energy resource has received worldwide attention. It has shown a significant effect on the world's energy structure after the commercial exploitation of shale gas in the United States. Understanding diffusion and permeation of shale gas at geological depths is quite essential, but it cannot be described by traditional Fick or Knudsen diffusion models. In this work, we use dual control volume–grand canonical molecular dynamics method to systematically investigate the permeation process of shale gas in montmorillonite (i.e., a clay mineral of shale) at different geological depths. Results indicate that temperature, pressure, and pore size have an important effect on the permeability, and Knudsen equation cannot describe the permeability of shale gas. Accordingly, on the basis of these simulated data, we propose a new mesoscale model to describe the permeability of shale gas at geological depths. The new mesoscale model shows extensive applicability and can excellently reproduce the extrapolation testing data, and it satisfactorily bridges the gap between Knudsen diffusion and Fick diffusion, which provides important fundamentals for exploitation of shale gas. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1059–1066, 2018

Using BP Neural Networks to Prioritize Risk Management Approaches for China’s Unconventional Shale Gas Industry

This article is motivated by a conundrum: How can shale gas development be encouraged and managed without complete knowledge of the associated risks? To answer this question, we used back propagation (BP) neural networks and expert scoring to quantify the relative risks of shale gas development across 12 provinces in China. The results show that the model performs well with high predictive accuracy. Shale gas development risks in the provinces of Sichuan, Chongqing, Shaanxi, Hubei, and Jiangsu are relatively high (0.4~0.6), while risks in the provinces of Xinjiang, Guizhou, Yunnan, Anhui, Hunan, Inner Mongolia, and Shanxi are even higher (0.6~1). We make several recommendations based on our findings. First, the Chinese government should promote shale gas development in Sichuan, Chongqing, Shaanxi, Hubei, and Jiangsu Provinces, while considering environmental, health, and safety risks by using demonstration zones to test new technologies and tailor China’s regulatory structures to each province. Second, China’s extremely complex geological conditions and resource depths prevent direct application of North American technologies and techniques. We recommend using a risk analysis prioritization method, such as BP neural networks, so that policymakers can quantify the relative risks posed by shale gas development to optimize the allocation of resources, technology and infrastructure development to minimize resource, economic, technical, and environmental risks. Third, other shale gas industry developments emphasize the challenges of including the many parties with different, often conflicting expectations. Government and enterprises must collaboratively collect and share information, develop risk assessments, and consider risk management alternatives to support science-based decision-making with the diverse parties.