Fractured Reservoir Research Articles

Optimizing geothermal reservoir modeling: A unified bayesian PSO and BiGRU approach for precise history matching under uncertainty

This research focuses on optimizing geothermal reservoir modeling tackling issues related to non-uniqueness, subsurface uncertainties, and computational intensity. The proposed workflow integrates Bayesian Particle Swarm Optimization (PSO) and a Bidirectional Gated Recurrent Unit (BiGRU) network to enhance the efficiency of history matching in the context of geothermal resource development under uncertainties. The methodology involves four key steps: firstly, identifying crucial uncertainty parameters such as injection rates and reservoir temperature; secondly, constructing the BiGRU network to capture the nonlinear relationship between these parameters and time series outputs, with Bayesian PSO automating hyper-parameter tuning; thirdly, using Bayesian PSO for the inversion of uncertainty parameters, utilizing the BiGRU as a forward model to reduce computational costs; and finally, conducting a thorough analysis and refinement of errors in predicted responses between the high fidelity model and Bayesian PSO, ensuring the accuracy of the history-matching process. Validation using a 3D fractured geothermal reservoir scenario demonstrates the Bayesian PSO and BiGRU method's efficacy in inverting uncertainty parameters with narrow uncertainties. The Obtained results are compare the performance of predicting the recovery factor (RF) using different surrogate methods, including Gaussian Processes (GP), Radial Basis Function (RBF), and Random Forest Regression (RFR). The proposed Bayesian PSO and GRU-based history-matching approach proves highly accurate and robust for efficiently addressing significant uncertainties in geothermal extraction processes.

Comprehensive heat extraction performance and fractured reservoir cooling effect analysis of a novel mine enhanced geothermal system

Mining deep metal mines poses significant challenges due to the high-temperature conditions in such environments. However, the vast untapped geothermal energy within these mines holds great prospects for development and application. Herein, we proposed a novel technology for the deep mine cooling and enhanced geothermal system (DMC-EGS), which transforms the relationship between deep mining and geothermal resources from a source of heat harm to heat benefit, while also providing conditions for underground mining environment cooling. Understanding the fluid flow and heat transfer processes in the deep mine thermal reservoir is crucial for developing DMC-EGS. Based on the local thermal equilibrium theory, a three-dimensional thermal–hydraulic coupled model of the thermal reservoir in the Sanshan Island Mine containing multiple fractures was established. The impact of natural fractures and fracture number on the thermal recovery performance and cooling effect of the system was considered, and the optimization scheme of heat recovery wellbore was proposed for the deep thermal reservoir of Sanshan Island Mine. It can be found that fractures play a crucial role in fluid-rock heat exchange. Compared with scenarios without fractures, hydraulic fractures could significantly improve the heat transfer capacity and rock cooling effect, resulting in a 45.7% increase in the amplitude of rock matrix temperature decrease and more than a 1.76-fold increase in overall heat recovery efficiency. In addition, the number of fractures significantly impacted the temperature distribution within the rock formation, and an increased number of fractures was associated with more efficient heat recovery performance. When the number of fractures was 7, the cumulative thermal production could reach 6.767 × 109 J. Among the three thermal exploitation schemes compared, the DMC-EGS under the triple-well mode yielded the best heat recovery performance during the 40-year extraction period, superior to the conventional dual-well mode, while the one injection and two production mode demonstrated better heat recovery capacity and cooling effect.

Influence of Mineral Composition on Initiation Pressure of Waterflood-Induced Fractures in Tight Sandstone Reservoir.

Revealing the impact of core mineral composition on the initiation pressure of waterflood-induced fractures (WIFs) in tight sandstone reservoirs is a crucial aspect of studying the initiation mechanism of WIFs. In this paper, through quantitative characterization of the core mineral composition from six samples of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, and modified experimental cores and displacement equipment for WIF experiments, the influence of the core mineral composition on the initiation pressure of WIFs in tight oil reservoirs is investigated. The conclusions are as follows. (1) The rock mineral composition of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, includes quartz, feldspar calcite, and clay, characterizing it as a typical feldspar sandstone reservoir. Quartz and calcite are considered as brittle minerals, while feldspar and clay are categorized as lithologic minerals. (2) For feldspar sandstone reservoirs, including quartz, feldspar, calcite, and clay minerals, when the combined content of quartz and feldspar exceeds 600% of the total mineral content, the changes of quartz and feldspar content will affect the initiation pressure of WIFs. As the ratio of the quartz content to feldspar content Rqf increases, the initiation pressure of WIFs exhibits a logarithmic function decrease. (3) Considering the contribution of diagenetic minerals to rock brittleness, the calculation method for the brittleness index of feldspar tight sandstone reservoirs is improved. (4) The relationships between Rqf, brittleness index, and initiation pressure of induced fractures suggest that an increase in Rqf leads to a power-law increase in the brittleness index, while the initiation pressure of WIFs relative to the brittleness index shows a power-law decrease. This phenomenon indicates an increased likelihood of WIFs occurring during the long-term water injection process in feldspar sandstone reservoirs. This work contributes to understanding how core minerals affect the initiation pressure of WIFs in tight sandstone reservoirs.

Analysis of competition and interference mechanisms of multiple hydraulic fractures in deep-sea hydrate reservoirs in the South China Sea

Improving the fundamental theory of hydraulic fracturing in deep-sea hydrate reservoirs is of great significance in enhancing the efficiency of gas hydrate mining. In this paper, a multi-cluster fracturing model for a horizontal well was established with a three-dimensional extended finite element method and the measured geo-mechanical data from hydrate reservoirs in the South China Sea. The performance, fracture initiation, and expansion mechanisms of multi-hydraulic fractures are investigated under different fracturing sequences, hydrate saturation and cluster deployment patterns. Some interesting results have been discovered: In the case of three-cluster, the fractures produced by sequential fracturing are notably more affected by pre-existing fractures. Furthermore, the effect of fracture interference between simultaneous and sequential fracturing is reflected in the middle fracture is compressed by the fractures on its left and right sides. The increase in hydrate saturation enhances the cementing ability of the sediments and results in an increased difficulty of fracture initiation for the five-cluster simultaneous fracturing. It also results in a decrease in the geo-stress field, where the interaction between fractures plays a dominant role in the process of fracture expansion, leading to non-uniform expansion.

Study on the Complex Electrical Response Characteristics of Loaded Coal and the Control Mechanism of the Main Fracture System Structure.

The structure of coal seam fractures is the main physical property of coalbed methane reservoir evaluation, and the complex resistivity method is a potential geophysical evaluation method for coal seam fractures. In this study, cylindrical coal samples with axial directions perpendicular to the bedding, face cleat, and butt cleat were prepared. The complex electrical parameters of the loaded specimens were tested with test frequencies ranging from 1 Hz to 10 kHz. The complex electrical response characteristics of the loaded coal are summarized, and the control mechanism of the main fracture system structure is analyzed. The results indicated that (1) as the loading pressure increased, the resistance R and the absolute values of reactance X(|X|) gradually decreased, especially in the frequency band where R slowly decreased and the characteristic frequency of X, the decreased amplitude was more significant, and the cutoff frequency of R and the characteristic frequency of X all gradually increased. (2) The complex electrical properties of coal show obvious anisotropic characteristics. Both R and |X| decreased sequentially according to the direction perpendicular to the bedding, face cleat, and butt cleat; the cutoff frequency of R and the characteristic frequency of X all increased sequentially. (3) The dispersion phenomenon of the complex electrical properties of coal is attributed to the induced polarization; the elevated loading stress enhances the polarization effects of the molecular-induced moments of the coal skeleton, and the anisotropic difference of the complex electrical properties is due to the difficulty in the degree of transport of charged particles induced by structural differences of the main fracture system. (4) The resistance R3 and capacitance Xc were selected as the complex electrically sensitive parameters of the loaded coal orthogonal fracture structures. A logarithmic inversion model reflecting the main fracture system structure of coal was constructed. This provides a certain theoretical basis for efficient electrical exploration of coal reservoir fracture structures.

Stratigraphic and Petrophysical assessment of ASL sandstone reservoir in northern and central October Field, Gulf of Suez

ABSTRACT This study analysed the depositional environment and diagenesis of the ASL Member reservoir in the October oil field located in the Gulfof Suez Basin, Egypt. Sedimentological and petrophysical techniques were used to interpret data from four wells: OCT-J7B, GS173-2, GS184-4A, and GS195-3, penetrating various rock types, including sandstone, carbonate, and fractured basement reservoirs. Log correlations of OCT-J7B and GS173-2 showed they penetrated pre-Miocene strata, while GS184-4A and GS195-3 reached the Rudeis section. Based on seismic-based structural maps, all wells except GS173-2 were drilled down-dip of the main Clysmic fault. The Hawara shale and the older shales in the Rudeis section were found to be the reservoir’s lateral seal, and the Lagia shale was found to be its vertical seal. Core analysis of OCT-J7B revealed the ASL as limestone interbedded with shale and sandstone deposited in a proximal submarine fan lobe, while GS184-4A and GS195-3 were located in amid-fan carbonate system. The comparisons of core and log data from the four wells yielded excellent matches, and the iso-parametric mapping delineated reservoir quality horizontally and hydrocarbon potentiality. The study recommends sitting future wells away from uplifts and suggests further reservoir characterization and evaluation of potential zones in the ASL Member.

Performance of multistage-fractured horizontal wells with secondary discrete fractures in heterogeneous tight reservoirs

AbstractA significant portion of tight sandstone reservoirs commonly displays intricate fluvial channels or fault systems. Despite various attempts at analytical/semi-analytical modeling of multistage-fractured horizontal wells (MFHWs) in unconventional reservoirs, the majority of studies have focused on scenarios with homogeneous original physical properties, neglecting cases where MFHWs traverse multiple regions in channelized heterogeneous reservoirs. Comprehending the influence of heterogeneous and leaky faults on the performance of MFHWs is essential for efficient development. This study presents an innovative semi-analytical model to analyze the pressure transient behavior of MFHWs with secondary fractures as they traverse multiple regions in banded channel heterogeneous reservoirs, particularly considering the presence of partially-communicating faults. The approach combines the source method and Green’s function method to obtain solutions, introducing a novel technique for discretizing fractures without discretizing interfaces. The effects of the reservoir heterogeneity, partially-communicating faults and fractures system on pressure behavior are analyzed. The results indicate that the pressure behavior of MFHWs passing through regions with different physical properties exhibits distinctive characteristics, differing from both the homogeneous case and the heterogeneous cases where the well does not traverse distinct regions. Permeability heterogeneity influences the curves of all other flow regimes, except the early and late flow regimes. Faults affect transient pressure behavior only when not positioned in the middle of each two primary fractures. Region area heterogeneity primarily influences the medium flow regimes. This work provides valuable insights into the performance of MFHWs in channelized heterogeneous reservoirs, offering technical support for well testing in these reservoirs.

A multi-mechanism numerical simulation model for CO2-EOR and storage in fractured shale oil reservoirs

Under the policy background and advocacy of carbon capture, utilization, and storage (CCUS), CO2-EOR has become a promising direction in the shale oil reservoir industry. The multi-scale pore structure distribution and fracture structure lead to complex multiphase flow, comprehensively considering multiple mechanisms is crucial for development and CO2 storage in fractured shale reservoirs. In this paper, a multi-mechanism coupled model is developed by MATLAB. Compared to the traditional Eclipse 300 and MATLAB Reservoir Simulation Toolbox (MRST), this model considers the impact of pore structure on fluid phase behavior by the modified Peng–Robinson equation of state (PR-EOS), and the effect simultaneously radiate to Maxwell–Stefan (M–S) diffusion, stress sensitivity, the nano-confinement (N-C) effect. Moreover, a modified embedded discrete fracture model (EDFM) is used to model the complex fractures, which optimizes connection types and half-transmissibility calculation approaches between non-neighboring connections (NNCs). The full implicit equation adopts the finite volume method (FVM) and Newton–Raphson iteration for discretization and solution. The model verification with the Eclipse 300 and MRST is satisfactory. The results show that the interaction between the mechanisms significantly affects the production performance and storage characteristics. The effect of molecular diffusion may be overestimated in oil-dominated (liquid-dominated) shale reservoirs. The well spacing and injection gas rate are the most crucial factors affecting the production by sensitivity analysis. Moreover, the potential gas invasion risk is mentioned. This model provides a reliable theoretical basis for CO2-EOR and sequestration in shale oil reservoirs.

Coupled thermo-hydro-mechanical modeling on geothermal doublet subject to seasonal exploitation and storage

Combining the conventional high-temperature aquifer thermal energy storage system with the common geothermal reservoir development system is a potential alternative to increase energy access, but effects of natural parameters like fracture aperture and reservoir permeability and development parameters like flow rate and injection temperature on the efficiency of energy exploitation and storage have seldomly been investigated. In this study, three assessment parameters and three evaluation criteria were defined to evaluate the sustainability and efficiency of deep geothermal reservoirs with seasonal energy exploitation and storage, and a robust approach of optimizing the development parameters was proposed by combining numerical reservoir model, experimental design and surrogate model, and multiple response optimization method. Based on a case study of the geothermal doublet in Tsinghua University, China, the robustness and reasonability of the developed optimization method were demonstrated. The results show that the optimal development parameters can not only maximize the total recoverable energy and effective recovery efficiency, but also satisfy the requirements of sustainably developing deep geothermal reservoirs. The recoverable heat energy can increase about 20% by adding artificial thermal storage into geothermal reservoir development. Therefore, it is strongly recommended to add energy storage into the future geothermal reservoir development system.

Nonlinearly Constrained Pressure Residual (NCPR) Algorithms for Fractured Reservoir Simulation

Nonlinearly Constrained Pressure Residual (NCPR) Algorithms for Fractured Reservoir Simulation

Proppant distribution characteristics based on the coring well analysis

It is significant to clarify the proppant distribution pattern under real fracturing conditions to optimize the sand addition process in hydraulic fracturing of the Mahu tight conglomerate reservoir. However, the laboratory experiment is far from the real fracturing condition due to the limitations of scale, pumping scale, and stress conditions. In this paper, the proppant in cuttings and mud was obtained by screening and cleaning samples from the high-deviated coring well of the Mahu conglomerate reservoir in Xinjiang. The sphericity of particles was observed by a continuous variable magnification microscope, and the transparency (TR) of particles and the red-blue difference (RBD) of reflected light were followed by transmitted light. Considering these three factors, the proppant identification method in cuttings was established to obtain the spatial location and distribution of proppant along the whole well section. The effect of proppant transport and placement was evaluated. The results show that: (1) Compared with the formation of mineral particles, the proppant has better sphericity, TR>20%, and RBD > 30. Combined with the surface roughness, luster, and associated minerals, the particle can be evaluated as a proppant. (2) The content of proppant with small particle size (40/70 mesh) is significantly higher than that with large particle size (20/40 mesh), which ranges from 10‰ to 450‰ and 5‰ to 280‰, respectively. (3) Horizontally, 20/40 mesh proppant migrates approximately 10m, and 40/70 mesh proppant migrates approximately 23 m in the hydraulic fracture. (4) In the longitudinal fracture, 20/40 mesh proppant was concentrated at a 12 m vertical distance from the adjacent well, while 40/70 mesh proppant was placed at a larger longitudinal range, approximately 10 m above and 10 m below the adjacent well. The research results have certain reference significance for the improvement measures of the sand-adding process in the Mahu tight conglomerate reservoir.

Quantitative Prediction of the Development and Opening Sequence of Fractures in an Ultradeep Carbonate Reservoir: A Case Study of the Middle Ordovician in the Shunnan Area, Tarim Basin, China

Summary Quantitative prediction of reservoir tectonic fracture development characteristics, opening pressures, and opening sequences is critical in the exploration and development of oil- and gas-bearing reservoirs and thus has received widespread attention. Using numerical simulations of the paleostress field during the formation of tectonic fractures and the rock fracture criterion, we predict the development and occurrence of fractures in the Middle Ordovician Yijianfang Formation in the Shunnan region of the Tarim Basin, China. The local paleostress fields reflected by the mechanical properties and occurrence of tectonic fractures obtained from core descriptions, acoustic emission (AE) experiments, paleomagnetic experiments, sound velocity measurements, and borehole breakouts were used to determine the regional paleostress and in-situ stress. We established a geomechanical model by combining the mechanical parameters of the rocks with the finite element method (FEM), optimizing the boundary conditions with a self-adaptive constraint algorithm, and conducting numerical simulations of the in-situ stresses. Fracture occurrence and numerical simulation results of the in-situ stress field were used to determine the opening pressure (Pk) and opening sequence of the fractures. The level of fracture development decreases away from the strike-slip fault in the study area. Fracture development is positively correlated with the Young’s modulus, paleostress difference, and paleostress difference coefficient of the rock. The direction of the maximum horizontal principal stress is from north-northeast (NNE) to northeast (NE). Initially, shear fractures and tensional fractures oriented NNE 30°–35° and NE 40°–45°, respectively, open during the water injection process. Pk is positively correlated with the horizontal stress difference coefficient and the angle between the fracture strike and the maximum horizontal principal stress. At the structural highs (burial depths shallower than 6450 m) and the structural lows (burial depths deeper than 6450 m), the burial depth correlates negatively and positively with Pk, respectively. This investigation of the development, occurrence, Pk, and opening sequence of tectonic fractures and their principal controlling factors will have a positive impact on the future exploration and production opportunities of similar fractured reservoirs.

Shale brittleness evaluation under high temperature and high confining stress based on energy evolution

Deep and ultra-deep shale gas reservoirs are crucial targets for future natural gas development. Extensive research has shown the shale brittleness is closely associated with the hydraulic fracture network quality. However, the shale brittleness may be altered in deep reservoirs due to the high temperature and high geo-stress. At present, commonly used shale brittleness evaluation methods cannot distinguish the differences in energy evolution caused by different mineral components in shale rock. In order to distinguish this difference, this study innovatively proposes a shale brittleness evaluation method that considers mineral composition based on energy evolution. A high-temperature triaxial compression experiment was carried out on the Longmaxi Formation shale, its fracture mode was analyzed, and the brittleness of the shale was evaluated based on this innovative method. The results indicate that with increasing confining stress, the shale fracture mode transitions from brittle tensile-shear multi-crack penetrating fracture to brittle-plastic shear single-crack fracture, and the brittleness of shale shows a decreasing trend. Under low confining stress, the shale brittleness decreases with temperature. Under high confining stress, temperature is the non-main controlling factor of shale brittleness. This study provides valuable guidance for the design and optimization of hydraulic fracturing in deep shale reservoirs.

Investigation of the Combination Mechanism of Spontaneous Imbibition and Water Flooding in Tight Oil Reservoirs Based on Nuclear Magnetic Resonance

As conventional oil reservoirs are gradually being depleted, researchers worldwide are progressively shifting their focus towards the development and comprehensive study of tight oil reservoirs. Considering that hydraulic fracturing is one of the main approaches for developing tight sandstone reservoirs, it is of great significance to explore the mechanism of spontaneous imbibition and waterflooding behavior after hydraulic fracturing in tight oil reservoirs. This research delves into the analysis of tight sandstone core samples obtained from the Shahejie Formation in the Bohai Bay Basin. All core samples are used for a series of experiments, including spontaneous imbibition and water flooding experiments. An additional well-shut period experiment is designed to understand the impact and operational dynamics of well shut-in procedures in tight reservoir development. Utilizing nuclear magnetic resonance (NMR) technology, the pore sizes of a sample are divided into three types, namely, macropores (>100 ms), mesopores (10–100 ms), and micropores (<10 ms), to thoroughly assess the fluid distribution and changes in fluid signals during the spontaneous imbibition and water flooding stages. Experimental outcomes reveal that during the spontaneous imbibition stage, oil recovery ranges from 12.23% to 18.70%, predominantly depending on capillary forces. The final oil recovery initially rises and then falls as permeability decreases, while the contribution of micropores progressively grows as the share of mesopores and macropores deceases. With water flooding processes carried out after spontaneous imbibition, enhanced oil recovery is observed between 28.26% and 33.50% and is directly proportional to permeability. The well shut-in procedures can elevate the oil recovery to as high as 47.66% by optimizing energy balance.

Carbon Storage Potential of Shale Reservoirs Based on CO2 Fracturing Technology

The development of shale reservoirs is important in ensuring China’s national energy security by achieving energy independence. Among the key technologies for shale oil production, CO2 fracturing is an effective method that can not only enhance oil recovery but also promote large amounts of CO2 storage, thereby supporting China’s goals of achieving a carbon peak and carbon neutrality. This research paper aims to study the impacts and prospective applications of CO2 fracturing in shale reservoirs, using real exploitation parameters from the GYYP1 well in the Songliao Basin. By utilizing numerical simulation, the dynamics of CO2 production are analyzed. Adsorption and diffusion are identified as pivotal mechanisms for CO2 storage in shale reservoirs. After the analysis of the fracturing process, approximately 22.13% of CO2 is found to be adsorbed, which decreases to 11.06% after ten years due to pressure decline. Diffusion increases the volume of CO2 interacting with a greater extent of shale, thereby enhancing the adsorption mechanism. Over time, the diffusion process results in a remarkable increase of 26.02% in CO2 adsorption, ensuring the long-term and stable storage of CO2 within the shale reservoir. This investigation delves into the contribution of these two crucial mechanisms of CO2 storage in shale reservoirs, ultimately predicting that, by 2030, approximately two million tons of CO2 can be effectively stored in the Daqing Oilfield through CO2 fracturing in shale oil reservoirs. Such an achievement will undoubtedly contribute to the sustainable development of the energy sector and foster the transformation and upgrading of China’s energy structure.

Optimization method of refracturing timing for old shale gas wells

Based on the elastic theory of porous media, embedded discrete fracture model and finite volume method, and considering the micro-seepage mechanism of shale gas, a fully coupled seepage-geomechanical model suitable for fractured shale gas reservoirs is established, the optimization method of refracturing timing is proposed, and the influencing factors of refracturing timing are analyzed based on the data from shale gas well in Fuling of Sichuan Basin. The results show that due to the depletion of formation pressure, the percentage of the maximum horizontal principal stress reversal area in the total area increases and then decreases with time. The closer the area is to the hydraulic fracture, the shorter the time for the peak of the stress reversal area percentage curve to appear, and the shorter the time for the final zero return (to the initial state). The optimum time of refracturing is affected by matrix permeability, initial stress difference and natural fracture approach angle. The larger the matrix permeability and initial stress difference is, the shorter the time for stress reversal area percentage curve to reach peak and return to the initial state, and the earlier the time to take refracturing measures. The larger the natural fracture approach angle is, the more difficult it is for stress reversal to occur near the fracture, and the earlier the optimum refracturing time is. The more likely the stress reversal occurs at the far end of the artificial fracture, the later the optimal time of refracturing is. Reservoirs with low matrix permeability have a rapid decrease in single well productivity. To ensure economic efficiency, measures such as shut-in or gas injection can be taken to restore the stress, and refracturing can be implemented in advance.

Technology Focus: Seismic (February 2024)

2023 wrapped up nicely with COP28 in Dubai. The key highlights were the commitments by both governments and the private sector to zero-methane production by 2030, net-zero greenhouse gas emissions from operations by 2050, and triple renewable power-generation capacity and double energy efficiency in this decade. There has been tremendous progress on our collective journey toward cleaner energy production, and now we must take it a notch higher. In the past couple of years, JPT’s Seismic feature has been marked by highly innovative seismic techniques and machine-learning work flows focused on reduction of carbon footprint; frontier exploration, expanding heartlands and brownfield development; and improved seismic survey, imaging, and attribute analysis for reservoir characterization and fracture diagnostics, which are in line with the COP28 pledges. This year’s feature is no different. Recent technical-paper titles have further shown the steady increase in the application of advanced seismic techniques and machine learning to mature “stranded” and “advantaged” hydrocarbon-bearing accumulations to production; improve carbon capture, storage, and leak detection; and analyze naturally and artificially induced fractured reservoirs and seismicity. The selected papers are reflective of these themes. In addition, some remarkable applications of seismic techniques are presented in the recommended papers. They include the following: - 2D nonlinear seismic site response analyses used to determine if the capacity of a silty sedimentation could support the load of a pipeline end termination in the event of an earthquake - The results of a pilot test of the Marine Vibrator, an industry-leading seismic-survey technique - High-resolution modeling to infer if an increase in seismicity is caused by an increase in pore pressure from wastewater injection in the Fort Worth Basin of north central Texas - 4D time/depth shifts and strain signals successfully used to estimate pressure depletion in the Gulf of Mexico Others are applying advanced measurement and modeling techniques to optimally place a long horizontal injector well in multilayered heterogeneous sandstone reservoirs and predicting reservoir presence from seismic velocity and pore-pressure prediction. These topics will supply the insights that will help us achieve the COP28 targets while we look forward to more exciting innovations in 2024. Recommended additional reading at OnePetro: www.onepetro.org. OTC 32267 Seismic Stability Assessment of a Mudmat on Liquefiable Seabed by Brian Carlton, Norwegian Geotechnical Institute, et al. OTC 32393 Predicting Reservoir Presence From Seismic Velocity Mapping and Pore-Pressure Prediction by Matthew James Legg, Shell OTC 32741 Marine Vibrator Milestone: A Pilot Seismic Survey by R. Alfaro, TotalEnergies, et al. SPE 212951 High-Resolution Modeling of Pore-Pressure Change, Fault Slip Potential, and Induced Seismicity in the Fort Worth Basin by Changqing Yao, Texas A&M University, et al. URTeC 3870451 Impact of Fracture Roughness on Fines Migration and Fracture-Aperture Growth in Calcareous Shale Rocks During Acidized Corefloods by Hasan J. Khan, King Fahd University of Petroleum and Minerals, et al.

Simulating multiphase flow in fractured media with graph neural networks

Numerical modeling of flow dynamics with multiple fluid phases in subsurface fractured porous media is of great significance to numerous geoscience applications. Discrete fracture-matrix (DFM) approaches become popular for simulating fractured reservoirs in the last decade. Data-driven surrogate models can provide computationally efficient alternatives to high-fidelity numerical simulators. Although convolutional neural networks (CNNs) are effective at approximating the space-time solutions of multiphase flowing processes, it remains difficult for CNNs to operate upon DFMs with unstructured meshes. To tackle this challenge, we leverage graph neural networks (GNNs) for surrogate modeling of an embedded DFM model. The results of two-dimensional cases with complex fracture systems show that the learned surrogates precisely capture the effect of the variations in fracture connectivity and forecast dynamic pressure and saturation solutions with high accuracy. Furthermore, our GNN-based models exhibit promising generalizability to fracture networks with different geometries and numbers of fractures that are not encountered from the training dataset.

Fiber-Optic Strain Measurements Aid Fracture Characterization

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3864861, “Geomechanics Modeling of Strain-Based Pressure Estimates: Insights From Distributed Fiber-Optic Strain Measurements,” by Wei Ma and Kan Wu, Texas A&M University, and Ge Jin, Colorado School of Mines. The paper has not been peer reviewed. _ The combination of Rayleigh frequency shift distributed strain sensing (RFS-DSS) and pressure-gauge measurements has been reported recently in field applications. The main objective of the study detailed in the complete paper is to investigate the relationship between strain change and pressure change under various fractured reservoir conditions and provide guidelines for better using this novel strain/pressure relationship to estimate conductive fractures and pressure profiles. Introduction With a spatial resolution of 20 cm and a sensitivity of less than 1 με, RFS-DSS can measure mechanical strain changes along the fiber with higher accuracy and sensitivity than low-frequency distributed acoustic sensing measurements. The field applications of RFS-DSS have improved the understanding of near-well and far-field fracture characteristics and the relationship between stimulation and production in unconventional reservoirs. Although some numerical modeling works have been conducted to study the mechanisms of RFS-DSS data sets, the sensitivity, or influencing factors, of the relationship between strain change and pressure change along the fiber are still unclear. In this work, the authors use a coupled geomechanics and fluid-flow simulator to simulate the strain change and pressure change measured along the producing and monitoring wells during both stable production and shut-in periods. Methodology A 3D multilayer reservoir model with dimensions of 300×400×55.82 m was created using Permian Basin data sets. The reservoir was discretized into 553×129×5 gridblocks. To ensure accurate simulation of field RFS-DSS measurements, the mesh was refined around the fracture and wellbore. The fracture width was set to be the same as the RFS-DSS spatial resolution (0.2 m), and the grid size was set to 5 m except for the refined region. As shown in Fig. 1, the reservoir had 11 perforation clusters along the producing well and the monitoring well was 65 m away from the producing well. A fiber cable was installed on both wells to measure the RFS-DSS data set. The producing well was operated for 240 days before being shut in for 4 days, followed by a 1-day reopening and then continued production for 1 year. The pressure decline was 30–40 psi during the 1-day stable production period. Note that the moment after producing 239 days was taken as the reference time to calculate the strain change during the 1-day production (239–240 days) and the moment after 240 days as the reference time to calculate the strain change during the shut-in period (240–244 days).

Computational Fluid Dynamics Modeling and Analysis of Axial and Radial Temperature of Wellbore during Injection and Production Process

Summary To solve problems such as additional tubing/casing load, casing deformation, and packer failure caused by changes in annular temperature during oil and gas reservoir fracturing and production, based on the well structure of oil and gas reservoirs and transition transient heat transfer mechanism, a four-field coupling simulation model of the temperature field in the main fluid domain of the tubing, the temperature field in the solid domain of the tubing, the temperature field in the annular fluid domain, and the temperature field in the solid domain of the casing is proposed. Considering the coupling of fluid temperature, pressure, and physical parameters, boundary conditions are established based on reservoir characteristics, wellbore heat transfer characteristics, and fracturing and production conditions, and are compiled into Fluent software for simulation through the user-defined function (UDF) method. The effects of the temperature and flow rate of injected fracturing fluid and produced oil and gas on the distribution of the wellbore temperature field and temperature gradient are studied. The research results show that by applying D14-1 and D5-5 gas wells to the model, the simulated temperature is in good agreement with the measured wellbore temperature, and the maximum errors of the simulated values of the two different wells are 6.4% and 4.3%, respectively. As the injection and production operation time increase, the heat transfer between the wellbore and the formation gradually stabilizes. At this time, the injection and production flow rate have little impact on the wellbore temperature field, while the injection and production temperature have a greater impact on the wellbore temperature field. The injection and production temperature will cause changes in annular temperature and temperature gradient, leading to an increase or decrease in pressure within a limited annular volume, resulting in local stress on the tubing and casing. The research results can provide a theoretical basis for the analysis of the temperature field and pressure field of the wellbore during fracturing and oil and gas production, ensuring the safety and stability of fracturing and production.