Shale Development Research Articles

Characteristics of horizontal wellbore Stoneley and shear waves responses to faults in unconventional shale reservoir

Understanding and identifying faults is crucial in revealing the structure and dynamic mechanisms of the Earth's interior, predicting seismic activity, and extracting petroleum resources. In unconventional shale reservoir exploration and development, the faults developed through horizontal wells can increase rock permeability. Still, they also pose a risk of casing deformation and inter-well pressure interference during hydraulic fracturing processes. Most of these faults have a small fault throw (<5 m), making it difficult to determine them using seismic exploration methods accurately. Therefore, this study investigates fault identification based on high-frequency sonic logging data. Three-dimensional numerical models, including shale reservoir, horizontal well, and fault, are designed, and forward simulations are conducted. The study investigates the response characteristics of Stoneley wave and dipole shear wave to small-scale and large-scale faults. In addition, the types of fault-filling media and fault width are analyzed. The results show that Stoneley wave and dipole shear wave are sensitive to faults. A thin fluid layer within the fault significantly increases the attenuation of both wave amplitudes. However, fault width is not a sensitive parameter. Based on the forward simulation studies, this paper proposes a method to identify faults using borehole mode waves and further determine key parameters such as fault throw and fault-filling media types. The effectiveness of the fault identification method is verified through a field example. This technique offers noteworthy benefits in detecting small-scale faults and in the subsequent assessment of vital fault parameters.

Research on the Characteristics and Mechanisms of Supercritical CO2 Displacement of Shale Oil Under Nanoscale Confinement

ABSTRACTShale reservoirs, characterized by compact pores, poor physical properties, and high organic matter content, exhibit significant differences in microscopic flow behavior compared to conventional oil reservoirs. These distinctions complicate the accurate assessment of shale oil reserves and the selection of optimal exploration and development strategies. Understanding the mechanisms and factors influencing microscopic flow in shale oil is crucial for both theoretical and practical aspects of shale oil exploration and development. In this study, molecular dynamics simulations employing the Grand Canonical Monte Carlo method were used to develop a microscale molecular dynamics model for n‐octane (C₈H₁₈) adsorption on various adsorbents. Adsorption energies for organic materials (kerogen), brittle minerals (quartz, albite), carbonate minerals (calcite), and clay minerals (illite, kaolinite, montmorillonite) were calculated to evaluate the adsorption strength of shale oil and CO2 on these adsorbents. Furthermore, a nonequilibrium molecular dynamics (NEMD) approach was utilized to model the CO2 displacement of shale oil in different slit pores, exploring the flow characteristics and displacement mechanisms of supercritical CO2 under nanoscale confinement. This investigation also considered the effects of CO2 density, slit pore surface properties, and driving force magnitudes, providing essential theoretical and technical insights for assessing shale oil reserves and refining exploration and development strategies.

Characteristics of shale reservoir development under the influence of sedimentary differentiation: A case study of the Cambrian Qiongzhusi Formation in the Deyang-Anyue rift trough of the Sichuan Basin

Characteristics of shale reservoir development under the influence of sedimentary differentiation: A case study of the Cambrian Qiongzhusi Formation in the Deyang-Anyue rift trough of the Sichuan Basin

Basis of Identification, Type of Syngenetic Assemblage, and Pattern of Development of Coal and Oil Shale in the Tanshan Area of the Eastern Liupanshan Basin, China

The Yan’an Formation in the Liupanshan Basin hosts substantial coal and oil shale resources. However, coal and oil shale often exhibit different types of associated or syngenetic combinations, which makes it difficult to recognize coal and oil shales, and research on the patterns of development of coal and oil shales is lacking. In this study, field outcrop, core, logging, and analytical data are comprehensively utilized to describe the characteristics of coal and oil shale, classify their syngenetic combinations, and establish a developmental model. Analytical results from the Tanshan area reveal that coal exhibits a lower density and higher oil content than oil shale. Specifically, coal shows oil contents ranging from 7.22% to 13.10% and ash contents of 8.25–35.66%, whereas oil shale displays lower oil contents (3.88–6.98%) and significantly higher ash contents (42.28–80.79%). The oil and ash contents of both coal and oil shale in the Tanshan area show a negative correlation, though this correlation is significantly stronger in coal than in oil shale. In long-range gamma-ray and resistivity logs, coal exhibits substantially higher values compared to oil shale, whereas in density logs, oil shale shows greater values than coal. Acoustic time difference logging reveals marginally higher values for coal than for oil shale, though the difference is minimal. There are five combination types between coal and oil shale in this area. The oil shale formed in a warm, humid, highly reducing lacustrine environment within relatively deep-water bodies, while coal developed in swampy shallow-water environments; both derive organic matter from higher plants. Variations in depositional settings and environmental conditions resulted in five distinct combination types of coal and oil shale.

Logging evaluation method for organic geochemical parameters of shale in Jurassic Formation

Black shale is the main source rock of the Jurassic Liangshan Formation shale reservoir in basin A, and its organic geochemical parameters TOC, S1, and S2 are very important for the quantitative evaluation of shale reservoir exploration and development potential. TOC, S1, and S2 logging evaluation methods are established according to the principle of “core calibration logging” because of the possession of logging and core analysis data in basin A. Firstly, improved △logR and multiple regression analysis methods are used to establish a quantitative TOC logging method based on slowness, resistivity, and gamma-ray logging. Secondly, based on acoustic time difference, resistivity, and gamma logging, a quantitative calculation method of S2 is established by multiple regression analysis. Finally, based on the statistical relationship between TOC and (S1+S2) of core analysis and S2 calculation results, a logging method for quantitative calculation of S1 is obtained. The application results show that the TOC calculated based on multiple regression analysis is in good agreement with the TOC of core analysis, with A relative deviation of 9%. The modified △logR method results in a large deviation from the TOC of core analysis due to the influence of the error of coefficient A and overlap coefficient K. The relative deviation of S1 and S2 calculated by logging and S1 and S2 by core analysis is 6% and 7%, which can meet the evaluation requirements of hydrocarbon generation potential of source rocks.

The geochemical, pore development and water-bearing characteristics of deep and ultra-deep marine shales and their effects on gas content: New implications from the shales of the first Lower Cambrian high-yield gas well (Z201) in China

The geochemical, pore development and water-bearing characteristics of deep and ultra-deep marine shales and their effects on gas content: New implications from the shales of the first Lower Cambrian high-yield gas well (Z201) in China

Freshwater green algae and fungi from Upper Triassic strata of the Cuyana Basin, central-western Argentina: indicators of palaeoenvironment and petroleum source potential

Freshwater green alga microfossils and dispersed fungal spores were recovered from among rich terrestrial palynofloras of the upper Potrerillos Formation, at the Quebrada del Durazno locality in the Cacheuta depocentre of the Cuyana Basin, Mendoza Province, central-western Argentina. Sedimentological data suggest that the Upper Triassic Potrerillos Formation comprises deltaic plain deposits with significant development of black carbonaceous shales and coal facies formed in semi-permanent swamps and/or ponds with intermittent flooding that progressed into the lacustrine Cacheuta Formation. These sub-environments enabled the development of autochthonous freshwater organic-walled green microalgae. Here, we present the first description of developmental stages for the colonial alga Botryococcus braunii (Chlorophyta, Trebouxiophyceae) from the Potrerillos Formation. The fossil algae have economic importance because they are the major organic constituents of oil shales in the Cuyana Basin. We further document (1) diverse zygospores of zygnematacean green algae (Charophyta) representing the genera Ovoidites and Schizosporis; (2) prasinophyte algae (Cymatiosphaera), sphaeromorph acritarchs (incertae sedis) and fungal representatives assigned to Portalites. A new species of Ovoidites is described, and a newly emended description and affinity are given for Greinervillites undulatus. Comparisons with modern freshwater algal habitats and sedimentology suggest that the zygnematacean zygospores indicate shallow stagnant water bodies, while abundant colonial green Botryococcaceae algae represent ponded water in paludal or lacustrine environments. The terrestrial vegetation and autochthonous freshwater green algae likely developed under warm temperate, humid to sub-humid, strongly seasonal megamonsoonal climatic conditions. Ana María Zavattieri* [amzavattieri@gmail.com], Unidad de Paleopalinología, Departamento de Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, Av. A. Ruíz Leal s/n, Parque General San Martín, M5502IRA Mendoza, Argentina; Pedro Raúl Gutiérrez [pedroraulgutierrez@gmail.com], Museo Argentino de Ciencias Naturales ‘B. Rivadavia’ – CONICET, Sección Paleopalinología, Área Paleontología. Buenos Aires, Argentina; Av. Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina.

Experimental study on fractures quantitative characterization of shale during uniaxial compression

IntroductionFractures are crucial to the development of shale oil and gas because they operate as a seepage pathway. The key to ensuring effective development is the fractures strong connection. Therefore, it is of great significance to carry out experimental research on the development of shale fractures.MethodsThis research thoroughly assesses the quantitative features of shale fractures using a number of criteria by combining the indoor uniaxial compression test with 3D CT reconstruction.Results and discussionThe findings indicate that the bedding angle has a significant impact on the distribution characteristics of shale fractures and that its quantitative features cannot be well described by a single metric. The volume weight of many fractures can be used to determine the new fracture angle and complexity coefficient, which more accurately reflect the actual fracture distribution given the complexity of fracture growth under 3D reconstruction. The connectivity examination also shows that the axial shear and radial tensile mixed fractures have higher connection than the single shear fracture, suggesting that the radial tensile fracture may lead to a higher overall connectedness. The parameters (fracture rate, fracture complexity coefficient, connectivity) used in this paper have a good correlation with the fractal dimension correlation coefficient R2 > 0.7, which indicates that these parameters are suitable parameters for quantitative characterization of shale fracture distribution characteristics. The influence mechanism of bedding angle on shale fractures is also suggested based on experimental results and earlier research. This mechanism is that the bedding angle will alter the effect of principal stress on interlayer micro-pores, micro-fractures, and cementation of bedding planes, leading to a significant anisotropy of fracture morphology created by macroscopic fracture.

Prediction of Total Organic Carbon Content in Shale Based on PCA-PSO-XGBoost

Total organic carbon (TOC) content is an important parameter for evaluating the abundance of organic matter in, and the hydrocarbon production capacity, of shale. Currently, no prediction method is applicable to all geological conditions, so exploring an efficient and accurate prediction method suitable for the study area is of great significance. In this study, for the shale of the Qingshankou Formation of the Gulong Sag in the Songliao Basin, TOC content prediction models using various machine learning algorithms are established and compared based on measured data, principal component analysis, and the particle swarm optimization algorithm. The results showed that GR, AC, DEN, CNL, LLS, and LLD are the most sensitive parameters using the Pearson correlation coefficient. The four principal components were also identified as input features through PCA processing. The XGBoost prediction model, established after selecting the parameters through PSO intelligence, had the highest accuracy with an R2 and RMSE of 0.90 and 0.1545, respectively, which are superior to the values of the other models. This model is suitable for the prediction of TOC content and provides effective technical support for shale oil exploration and development in the study area.

Research on the comprehensive dessert evaluation method in shale oil reservoirs based on fractal characteristics of conventional logging curves

The traditional logging evaluation of comprehensive sweet spots in shale oil reservoirs has problems such as complex explanatory parameters, incompatible quantitative characterization scales, and low-cost efficiency. A method based on the fractal characteristics of conventional logging curves is proposed to evaluate the comprehensive sweet spots of fractured horizontal wells in shale oil reservoirs. Firstly, the existing evaluation parameters and methods were reviewed, pointing out the limitations of traditional logging evaluation methods. Furthermore, we analyzed 63 fractured sections from three horizontal fractured wells in the Yingxiongling shale oil reservoir of the Qinghai Oilfield, using tracer monitoring data. By applying wavelet transform to reduce noise in high-frequency signals from conventional logging curves, we then used multifractal spectrum analysis and R/S analysis to extract the multifractal spectrum width (∆α) and fractal dimension (D) from four conventional logging attributes: natural gamma logging (GR), acoustic time difference logging (AC), density logging (DEN), and neutron logging (CNL). A multi-attribute comprehensive fractal evaluation index was developed by using the post-fracturing tracer monitoring profile as a constraint and applying the grey relational analysis method. This approach enabled a quantitative classification and evaluation of the key sweet spots in shale oil reservoirs after fracturing. The results show that the comprehensive fractal evaluation index of the high-yield well section after Class I layering is 0.75<∆ α‘<1, 0 < D‘<0.25; 0.35<∆ α‘<0.75, 0.25 < D‘<0.8 in the middle well section of Class II layer; Class III low production well Sect. 0<∆ α‘<0.35, 0.8<∆ α‘<1. Finally, a prediction model for physical property parameters characterized by fractals was introduced using machine learning algorithms, which is 31.9% more accurate than the conventional interpretation physical property parameter prediction model for the comprehensive sweet spot of fracturing. This evaluation method is a concise approach to comprehensively evaluate the sweet spot area based on the extraction of multifractal spectral characteristic parameters from conventional logging data. It is of great significance for characterizing the volume fracturing effect of shale oil and providing technical support for the effective development of shale on a large scale.

Research on the Dynamic Apparent Permeability of Shale: Coupling Anisotropic Deformation Characteristics and Multiple Transport Mechanisms.

As shale gas is an unconventional energy source, it is believed to be essential for achieving green resource development and improving the energy supply-demand balance. However, owing to shale's substantial anisotropic properties and various microstructures, its gas flow characteristics and transport mechanisms are exceedingly complex. Therefore, accurately predicting gas permeability evolution in shale pores was considered to be important for energy development. In this study, an examination of the apparent volumetric strain, caused by the synergistic effects of effective stress and gas adsorption, combined with analysis of dynamic changes in pores in different directions has been undertaken. Based on the Knudsen number (Kn), gas flow mechanisms in shale were separated further to create an anisotropic apparent permeability model. The model was validated by publicly available experimental data concerning the permeability under different stress conditions. The influence of different flow regimes and mechanisms on permeability changes during shale reservoir development has been discussed and analyzed with a model parameter sensitivity analysis being carried out. The results demonstrated that if both mechanisms (effective stress and gas adsorption) were ignored, the shale permeability would be underestimated; however, if shale's anisotropic mechanical properties were ignored, the apparent permeability would be overestimated. Our findings could provide theoretical guidance for energy exploitation, which would be beneficial in contributing to sustained and rapid energy development.

Mechanical Properties and Energy Characteristics of Shales Under Conventional Triaxial Compression Conditions Based on Different Initial Prestresses

ABSTRACTConventional triaxial compression tests were conducted on shale specimens under varying initial prestress conditions to investigate their mechanical properties and energy evolution characteristics, thereby revealing the shale damage mechanism. The results demonstrate that the peak differential stress of the shale samples increases with the rising initial prestress, following an exponential function. Based on the maximum and minimum principal stress data of the shale samples and the Mohr‐Coulomb criterion, the cohesive force and internal friction angle of the tested shale were calculated as 29.86 MPa and 38.92°, respectively. By analyzing the ultimate storage energy of shale samples under different confining pressures, it was found that the ultimate storage energy increases exponentially with confining pressure. Additionally, the dissipated energy at peak stress exhibits a linear relationship with increasing confining pressure. This study provides critical insights into the damage mechanisms of shale under complex stress conditions and offers theoretical support for optimizing shale gas extraction engineering practices. The quantitative relationships between stress, energy evolution, and confining pressure contribute to improving the efficiency and safety of shale reservoir development.

Organic matter content and its role in shale porosity development with maturity: Insights from Baltic Basin Silurian shales

Organic matter content and its role in shale porosity development with maturity: Insights from Baltic Basin Silurian shales

Oil Storage Capacity in Organic‐Rich Chang 7 Shale, Ordos Basin: Comparing Evaluation Methods and Controlling Factors

ABSTRACTThis study examines the oil storage capacity and controlling factors of organic‐rich Chang 7 shale in the Ordos Basin, using multistep Rock‐Eval pyrolysis (MREP) and liquid hydrocarbon vapour adsorption (LHVA) techniques. The research evaluates the effectiveness of these techniques in determining oil content and identifies key geological and geochemical factors impacting free and adsorbed oil. Analyses of geochemical, mineralogical, and pore structure characteristics reveal that Chang 7 shale, with high total organic carbon (TOC) content and oil‐prone kerogen, along with moderate thermal maturity, is a high‐quality hydrocarbon source rock. A strong linear correlation between MREP and LHVA results demonstrate the reliability of both methods for assessing adsorbed oil content, though discrepancies emphasise the impact of hydrocarbon loss during sample preparation. Statistical analysis indicates TOC content (&gt; 2%, with &gt; 4% especially favourable) and thermal maturity (Ro = 0.7%–1.0%) as the critical factors for shale oil accumulation and key indicators for identifying sweet spots. These findings improve the understanding of oil occurrence processes in shale and offer practical insights for optimising shale oil exploration and development.

Paleoenvironmental factors controlling the development of the lacustrine shale interbed in the Jurassic Dongyuemiao Member of the Sichuan Basin, China

Paleoenvironmental factors controlling the development of the lacustrine shale interbed in the Jurassic Dongyuemiao Member of the Sichuan Basin, China

Intelligent seismic AVO inversion method for brittleness index of shale oil reservoirs

Intelligent seismic AVO inversion method for brittleness index of shale oil reservoirs

Development of PCM-Impregnated Expanded Shale Incorporated High Strength Thermal Energy Storing Concrete

Development of PCM-Impregnated Expanded Shale Incorporated High Strength Thermal Energy Storing Concrete

Case Study: Innovative Approach To Increase Well Productivity by Adapting Drilling Targets and Completion Methodology

_ The discourse regarding US land exploration and production has tended to primarily focus on shale development. While this has pushed the industry to adopt many technologies or applications, the general recipe has been to be faster and cheaper with hopefully more predictable BOE/ft production. However, there are limitations with this approach as it tends to boil down to a choice of substitution rather than true engineering to improve return on investment or improved net present value. The relationship of parent and child well production has introduced a variable that does not necessarily respond to faster and cheaper. In fact, operators may agree that a dissolvable frac plug has application to reduce completion costs while completely disagreeing on the methodology to manage field development and the parent-child interaction. Extensive field study and calibration can determine an optimal solution with varying degrees of predictability (SPE 211899). For example, reservoir depletion and fracture communication can be difficult to accurately plan for in advance. These and several additional parameters are specific to a section, field, or bench and the design and planning process begins anew when drilling locations move a sufficient distance away from the asset in question. The best outcome during the drilling and completion of a child well is to limit the negative impact on parent well production while delivering an economically viable addition to existing production. Acceptable ranges of underperformance with the child well vary, but can be summarized as 20 to 30% less than the parent well (SPE 209171). Additionally, contact from an offset child well fracturing operation can detrimentally affect parent well production temporarily or permanently by increasing water production and decreasing hydrocarbon production. Introduction This case study presents the development of a methodology for optimizing and controlling the hydraulic fracturing process’s parameters by increasing cluster efficiency to 100% and overcoming formation leakoff with eight to 10 times rate per cluster when compared with industry standards. The developed framework is validated through field completion and production data taken from wells located on the Northwest Shelf, within the San Andres formation, specifically straddling the state line of New Mexico and Texas with operations primarily in northeast Lea County, New Mexico, and Yoakum County, Texas. For the purposes of this study, parent wells are wells drilled during Segment 1 (2013 to 2016) and/or the first wells drilled in a section. Child wells are defined as any subsequent wellbore placed in a section amongst current producers Segment 2 (2017 to 2020) and Segment 3 (2022 to 2023). The offset true vertical depth (TVD) of the child wells relative to the parent wells is less than 100 ft and no geologic barrier exists, thus the contribution to production is from the same rock matrix regardless of well vintage.

Pore Structure and Fractal Analysis of Low-Resistivity Longmaxi Shale in the Southern Sichuan Basin Combining SEM, Gas Adsorption, and NMR.

Pore structure can affect the reservoir property, petrophysics, and fluid migration/adsorption, which is critical for shale evaluation and development. In this paper, the pore structure, fractal characteristics, and their influencing factors on low-resistivity shale (LRS) from the Longmaxi Formation in the Southern Sichuan Basin were analyzed by combining geochemistry experiments, physical property analysis, X-ray diffraction, scanning electron microscopy (SEM), N2/CO2 gas adsorption experiments, and nuclear magnetic resonance (NMR). The results indicate that in LRS, the layered clay mineral/pyrite distribution and more developed pores with a larger size and better connectivity can build a complex and superior conductive network. In gas adsorption tests, the pore volume (PV) is primarily contributed by mesopores in sizes of 2-4, 10-30, and 40-50 nm; the specific surface area (SSA) is mainly controlled by mesopores of 2-4 nm and micropores of 0.5-0.7 nm. The pore structures characterized by NMR, gas adsorption experiments, and SEM are consistent. In addition, gas adsorption is more suitable than NMR for describing the fractal dimension, where the development of micropores enhances the heterogeneity and complexity of the pore surface and pore structure. The gas-producing LRS has larger D1 and D2 than water-producing LRS. Moreover, TOC contributes to the development of micropores to some degree. Quartz and illite are negatively correlated with the PV and SSA of mesopores and total pores, while pyrite, clay mineral, and illite/smectite (I/S) are converse with a positive relationship. There exists only one negative relationship between chlorite and D2, and chlorite is weakly positively correlated with the large pore volume and negatively correlated with the micropore SSA.

Mechanical properties of shale during pyrolysis: Atomic force microscopy and nano-indentation study

Mechanical properties of shale during pyrolysis: Atomic force microscopy and nano-indentation study