Adjacent Wells Research Articles

Evolution mechanism of deviated well fiber-optic strain induced by single-fracture propagation during fracturing in horizontal wells

Considering the high construction cost of horizontal adjacent well monitoring and the lack of vertical adjacent well fiber optic for obtaining fracturing information, this paper proposes the use of deviated wells with fiber optics for monitoring purposes. To demonstrate the advantages of deviated well fiber optics and the feasibility of their deployment, this paper constructs a forward model based on the finite element coupled with cohesive element approach to simulate the strain induced by the propagation of a single hydraulic fracture in horizontal wells on deviated well fiber optics, and conducts a numerical simulation analysis of the strain induced by the propagation of a single hydraulic fracture on deviated well fiber optics. The results show that the strain evolution induced by single-fracture propagation in deviated well fiber optics can be divided into four stages: strain-enhancing, strain-converging, tensile strain-expanding, and linear strain-converging. The strain evolution characteristics of deviated well fiber optics are manifested as follows: a “heart-shaped” tensile strain convergence zone with a certain deviation appears in the middle, which subsequently converges into a tensile strain convergence band, with compressive strain convergence zones on both sides, and an expanding tensile strain convergence zone on the outer side of the compressive strain convergence band. The analysis finds that when the well inclination angle is greater than 45°, the strain response characteristics of deviated well fiber optics are mainly governed by the width expansion of the fracture, and when less than 45°, they are mainly governed by the height expansion of the fracture. Changes in the azimuth angle can cause a deviation of the “heart-shaped” tensile strain area and the compressive strain convergence zone in the fiber-optic strain waterfall plot, with larger deviations corresponding to smaller azimuth angles. The depth at which the deviated well fiber optics are deployed, reaching the depth of the horizontal section of the horizontal well, can reflect the upward expansion of the fracture height. The results of the analysis illustrate the advantages of deviated well fiber optics in obtaining both fracture width and height expansion information simultaneously and propose a method for selecting suitable deviated well fiber-optic construction parameters based on fracturing monitoring needs. This research can reduce the construction cost of deploying fiber optics in adjacent wells and has significant implications for guiding the layout of adjacent well fiber optics.

Effect of acid viscosity on conductivity during online acid-fracturing in ultra-deep carbonate reservoir

The influence of viscosity change in the same acid system on etched-fracture morphology and conductivity was often neglected in many studies that conducted multi-stages alternative acid-etching experiments using different acid systems. In order to address this knowledge gap, the present study investigated the impact of single injections of low viscosity and high viscosity acid, as well as an alternative stages of low and high viscosity acid, on the acid-etched fracture morphology and conductivity. While the online acid-fracturing technology was proposed based on experimental results firstly in ultra-deep wells. The results show that injecting acid with different viscosities is more effective than using a single viscosity acid-etching, as it improves fracture morphology and conductivity. Additionally, the stages of alternating acid have a significant impact on conductivity. Experimental studies reveal that employing three stages of alternating acid with different viscosities enhance the fracture conductivity in the research area. Based on these findings, the P6 well successfully is implemented online acid-fracturing in an ultra-deep well reaching 8000 m firstly in Sichuan Basin. Compared to adjacent wells, this technique exhibited lower friction resistance, enabling higher acid-injection rates.

Numerical Simulation Study on Dynamic Interaction between Two Adjacent Wells during Hydraulic Fracturing

The heterogeneity in fracture formation significantly influences the hydraulic fracture propagation among adjacent wells, underscoring the urgency to comprehend the underlying fracture mechanisms. Specifically, in shale gas or oil extraction fracturing operations, stress interactions among neighboring fracturing clusters, or mutual interference during the propagation of parallel fractures, are commonplace. At present, there is relatively little research on the sensitivity parameters of adjacent borehole fracture propagation morphology. Consequently, we employed ABAQUS software 2022 to construct a numerical model simulating the fracturing of adjacent boreholes in opposing directions. Upon validating the model’s fidelity, we systematically explored the influence of various engineering and geological factors on fracture morphology and propagation length. Our findings revealed a three-phase evolution: independent fracture propagation, subsequent mutual repulsion, and, ultimately, mutual attraction. It is worth noting that increasing the elastic modulus from 10 GPa to 80 GPa, and increasing the crack length by 16.30%, is beneficial for crack propagation, while the horizontal stress difference profoundly shapes the crack mode, but has a relatively small impact on the overall crack length. When HSD increases from 0 MPa to 15 MPa, the total crack length only changes by 1.24%. In addition, the filtration coefficient of the reservoir is a key determining factor that has a significant impact on the morphology and length of cracks generated by adjacent boreholes. Increasing the filtration coefficient from 1 × 10−14 m3/s/Pa to 5 × 10−12 m3/s/Pa reduces the total length of cracks by 60.77%. Notably, an optimal injection rate exists, optimizing fracturing outcomes. Conversely, the viscosity of the fracturing fluid exerts a limited influence on fracture morphology and length within the confines of this simulation, allowing for the selection of a suitable viscosity to ensure smooth proppant transport during actual fracturing operations. In designing fracturing parameters, it is imperative to aim for sufficient fracture propagation length while harnessing “stress interference” to foster the development of intricate fracture networks. Ultimately, our research findings serve as a solid foundation for engineering practices involving hydraulic fracture propagation in adjacent boreholes undergoing opposing fracturing operations.

Transfer learning for well logging formation evaluation using similarity weights

Machine learning has been widely applied in well logging formation evaluation studies. However, several challenges negatively impacted the generalization capabilities of machine learning models in practical implementations, such as the mismatch of data domain between training and testing datasets, imbalances among sample categories, and inadequate representation of data model. These issues have led to substantial insufficient identification for reservoir and significant deviations in subsequent evaluations. To improve the transferability of machine learning models within limited sample sets, this study proposes a weight transfer learning framework based on the similarity of the labels. The similarity weighting method includes both hard weights and soft weights. By evaluating the similarity between test and training sets of logging data, the similarity results are used to estimate the weights of training samples, thereby optimizing the model learning process. We develop a double experts' network and a bidirectional gated neural network based on hierarchical attention and multi-head attention (BiGRU-MHSA) for well logs reconstruction and lithofacies classification tasks. Oil field data results for the shale strata in the Gulong area of the Songliao Basin of China indicate that the double experts’ network model performs well in curve reconstruction tasks. However, it may not be effective in lithofacies classification tasks, while BiGRU-MHSA performs well in that area. In the study of constructing large-scale well logging processing and formation interpretation models, it is maybe more beneficial by employing different expert models for combined evaluations. In addition, although the improvement is limited, hard or soft weighting methods is better than unweighted (i.e., average-weighted) in significantly different adjacent wells. The code and data are open and available for subsequent studies on other lithofacies layers.

Microbial community interactions on a chip

Multispecies microbial communities drive most ecosystems on Earth. Chemical and biological interactions within these communities can affect the survival of individual members and the entire community. However, the prohibitively high number of possible interactions within a microbial community has made the characterization of factors that influence community development challenging. Here, we report a Microbial Community Interaction (µCI) device to advance the systematic study of chemical and biological interactions within a microbial community. The µCI creates a combinatorial landscape made up of an array of triangular wells interconnected with circular wells, which each contains either a different chemical or microbial strain, generating chemical gradients and revealing biological interactions. Bacillus cereus UW85 containing green fluorescent protein provided the "target" readout in the triangular wells, and antibiotics or microorganisms in adjacent circular wells are designated the "variables." The µCI device revealed that gentamicin and vancomycin are antagonistic to each other in inhibiting the target B. cereus UW85, displaying weaker inhibitory activity when used in combination than alone. We identified three-member communities constructed with isolates from the plant rhizosphere that increased or decreased the growth of B. cereus. The µCI device enables both strain-level and community-level insight. The scalable geometric design of the µCI device enables experiments with high combinatorial efficiency, thereby providing a simple, scalable platform for systematic interrogation of three-factor interactions that influence microorganisms in solitary or community life.

Study of the evolution characteristics of fiber-optic strain induced by the propagation of bedding fractures in hydraulic fracturing

Shale reservoirs contain numerous bedding fractures, making the formation of complex fracture networks during fracturing a persistent technical challenge in evaluating shale fracture morphology. Distributed optical fiber sensing technology can effectively capture the process of fracture initiation and propagation, yet the evaluation method for the initiation and propagation of bedding fractures remains immature. This study integrates a distributed optical fiber sensing device based on optical frequency domain reflectometry (OFDR) with a large-scale true tri-axial fracturing physical simulation apparatus to conduct real-time monitoring experiments on shale samples from the Lianggaoshan Formation in the Sichuan Basin, where bedding is well-developed. The experimental results demonstrate that two bedding fractures in the shale sample initiated and propagated. The evolution characteristics of fiber-optic strain in a horizontal adjacent well, induced by the initiation and propagation of bedding fractures, are characterized by the appearance of a tensile strain convergence zone in the middle of the optical fiber, flanked by two compressive strain convergence zones. The initiation and propagation of the distal bedding fracture causes the fiber-optic strain in the horizontal adjacent well to superimpose, with the asymmetric propagation of the bedding fracture leading to an asymmetric tensile strain convergence zone in the optical fiber. Utilizing a finite element method coupled with a cohesive element approach, a forward model of fiber-optic strain in the horizontal adjacent well induced by the initiation and propagation of hydraulic fracturing bedding fractures was constructed. Numerical simulation analyses were conducted to evaluate the evolution of fiber-optic strain in the horizontal adjacent well, confirming the correctness of the observed evolution characteristics. The presence of a "wedge-shaped" tensile strain convergence zone in the fiber-optic strain waterfall plot, accompanied by two compressive strain convergence zones, indicates the initiation and propagation of bedding fractures during the fracturing process. These findings provide valuable insights for interpreting distributed fiber-optic data in shale fracturing field applications.

Collaborative-driven reservoir formation pressure prediction using GAN-ML models and well logging data

Formation pressure is the foundation and prerequisite for achieving efficient drilling and risk control in complex geological formations. However, intelligent prediction of formation pressure faces challenges such as insufficient sample sizes, poor prediction performance, and low prediction accuracy, which severely restrict the realization of safe and efficient drilling. To address this, this paper proposes a new method based on Generative Adversarial Networks (GAN) and Machine Learning (ML), aiming to improve adaptation to complex geological conditions and effectively capture the nonlinear relationship between logging data and formation pressure for intelligent prediction of formation pressure. The research results show that the GAN technology successfully amplified the 125 cable-measured formation pressure data by 204.8 times. Compared to machine learning predictions without using GAN technology, the constructed GAN-ML model reduced the average root mean square error by 0.59 MPa and the average absolute error by 0.71 MPa in the training set. The GAN-ML model predicted the formation pressure of adjacent wells with an average root mean square error of 1.59 MPa and an average absolute error of 1.96 MPa compared to the cable-measured formation pressure values. This achievement significantly enhances the robustness and generalization performance of intelligent models, demonstrating the potential of GAN-ML in addressing small sample data problems. It opens a new technical path for data-driven intelligent prediction and provides innovative data analysis and prediction methods for the field of geological exploration.

Real-time monitoring of rock fracture by true triaxial test using fiber-optic strain monitoring in adjacent wells

The real-time monitoring of fracture propagation during hydraulic fracturing is crucial for obtaining a deeper understanding of fracture morphology and optimizing hydraulic fracture designs. Accurate measurements of key fracture parameters, such as the fracture height and width, are particularly important to ensure efficient oilfield development and precise fracture diagnosis. This study utilized the optical frequency domain reflectometer (OFDR) technique in physical simulation experiments to monitor fractures during indoor true triaxial hydraulic fracturing experiments. The results indicate that the distributed fiber optic strain monitoring technology can efficiently capture the initiation and expansion of fractures. In horizontal well monitoring, the fiber strain waterfall plot can be used to interpret the fracture width, initiation location, and expansion speed. The fiber response can be divided into three stages: strain contraction convergence, strain band formation, and postshutdown strain rate reversal. When the fracture does not contact the fiber, a dual peak strain phenomenon occurs in the fiber and gradually converges as the fracture approaches. During vertical well monitoring in adjacent wells, within the effective monitoring range of the fiber, the axial strain produced by the fiber can represent the fracture height with an accuracy of 95.6% relative to the actual fracture height. This study provides a new perspective on real-time fracture monitoring. The response patterns of fiber-induced strain due to fractures can help us better understand and assess the dynamic fracture behavior, offering significant value for the optimization of oilfield development and fracture diagnostic techniques.

Integration of Geophysical and Hydrochemical Methods to Determine the Groundwater Contamination in Al-Hosayniat Landfill South East Mafraq City, Jordan

An integration of Geophysical – Electromagnetic and hydro-chemical methods was used to investigate the potential of groundwater contamination due to Al-Hosayniat Municipal Landfill (HL) southeast of Mafraq city. Twenty-five Time Domain Electromagnetic (TDEM) soundings were carried out inside and outside the HL in addition to one WNW-ESE Very Low Frequency (VLF) profile. The TDEM's results help to define the subsurface geology and structures down to 240m depth. The results also depict the presence of a major fault striking NW-SE that crosses the whole landfill, this fault is documented in the surface geological map, and it was delineated and imaged by TDEM measurements and detected at larger depths. VLF results also detected the presence of a major fault beneath the landfill. The presence of the fault just beneath the HL may enhance the leachate movement which can imply groundwater contamination hazards for a longer period as it is a preferential pathway for contaminants. The results of water quality analyses of adjacent wells show higher concentrations of Na+, SO-24, TDS in some wells and this can be ascribed to agricultural activities and over-pumping in the area rather than landfill leachate. The heavy metal concentrations were found to be within the permissible limits and did't indicate direct contamination due to the HL. However, Fluorite (F-) shows a high concentration of (1.3mg/l) in WS4 and WS5 wells and approaches the permissible limit (1.5mg/l) according to the Jordan Water Standards (JWS). Bromide (Br) shows high concentration of (0.6mg/l) in well Al-2462.

Frac-hits and connections of multi-well hydrofracturing fracture network involving the variable factors: well spacing, perforation cluster spacing and injection rate

PurposeWith the development of fracturing technology, the research of multi-well hydrofracturing becomes the key issue. Frac-hits in multi-well hydrofracturing has an important effect on fracture propagation and final production of fractured well; in the process of hydrofracturing, there are many implement parameters that can affect frac-hits, and previous studies in this area have not systematically targeted the influence of a single parameter on multi-well hydrofracturing. Therefore, it is of great significance to study the occurrence rule and influence of frac-hits for optimizing the design of fracturing wells.Design/methodology/approachBased on the proposed numerical models, the effects of different fracturing implement parameters (perforation cluster spacing, well spacing and injection rate) on frac-hits are compared in numerical cases. Through the analysis of fracture network, stress field and microseismic, the effects of different fracturing implement parameters on frac-hits and connections are compared.FindingsThe simulation results show that the effect of perforation cluster spacing and well spacing on frac-hits is greater than that of injection rate. Smaller well spacing makes it easier for fractures between adjacent wells to interact with each other, which increases the risk of frac-hits and reduces the risk of fracture connections. Smaller perforation cluster spacing results in larger individual fracture lengths and greater deflection angles, which makes the possibility of frac-hits and connections greater. The lower the injection rate, the lower the probability of frac-hits.Originality/valueIn this study, the influence of different fracturing implement parameters on frac-hits and connections in multi-well hydrofracturing is studied, and the mechanism of frac-hits and connections is analyzed through fracture network, stress field and microseismic analysis. Different simulation results are compared to optimize fracturing well parameter design and provide reference for engineering application.

Characterization of low-frequency distributed acoustic sensing signals in hydraulic fracturing stimulation – A coupled flow-geomechanical simulation approach

Low-frequency distributed acoustic sensing (LF-DAS) is one of the promising diagnostic techniques for detecting and characterizing hydraulic fractures. LF-DAS signals can capture fracture hits and the strain field around the hydraulic fracture. However, the interpretation of field LF-DAS data can be challenging due to the complexity of the underground conditions. This study develops a fracture propagation model to simulate the hydraulic fracturing process. The modelling results are analyzed to examine patterns and trends observed in interpreting field LF-DAS data. The fracture propagation model, coupled with the flow and geomechanical computations, is implemented in the MATLAB Reservoir Simulation Toolbox (MRST). The flow and geomechanical calculations are discretized by the finite volume and the virtual element methods, respectively. The hydraulic fracture is set to propagate along a prescribed path with a specific propagation or activation criterion. The accuracy of our model is validated against the KGD analytical solutions for the leak-off-viscosity, storage-viscosity and leak-off-toughness dominated regimes. The simulated stress and strain features are consistent with those interpreted from field LF-DAS signals. Several case studies and sensitivity analyses demonstrate the approach's utility and examine fracture interference, closure, and stress shadowing effects. The modelling work facilitates interpreting field measurement data by investigating characteristics of fracture hits from adjacent wells. The modelling method provides insights into fracture interference and its implications on optimal designs during hydraulic fracturing stimulation.

Theoretical analysis and field application of cooling bottom hole by mud density reduction during drilling in deep shale gas well

During deep shale gas well drilling process, high bottom hole temperature (≥150 °C) often causes the conventional rotary steerable tool and logging while drilling (LWD) to malfunction. Therefore, it is essential to reduce the bottom hole temperature for safe and efficient drilling. In this paper, a simplified wellbore temperature model for deep shale gas horizontal well was established based on thermodynamic theory, comprehensively accounting for both mechanical and hydraulic heat source. A quantitative analysis was performed to assess the impact of rheological parameters, engineering parameters, thermal parameters and two cooling methods on bottom hole temperature. In addition, a density reduction and cooling scheme for drilling in the horizontal section was developed and implemented on H-29-1 and H-29-6 Well. The results indicated that the temperature model is in good agreement with the Kirbir & Hasan model and real-time measurement data with an error less than ±6 %. Mud density, behavior index, pump rate, weight on bit (WOB) and geothermal gradient had great influence on the bottom hole temperature (up to over 30 °C). If the horizontal section is shorter than 1000 m, reducing the inlet temperature can effectively reduce the bottom hole temperature. But once the horizontal section exceeds 1500 m, reducing mud density is much more effective. With field application on H-29-1 and H-29-6 Well, mud density was reduced from 2.25 g/cm3 to 1.80 g/cm3, resulting in a maximum bottom hole temperature of 143 °C in the horizontal section, and rotary steerable tools and screw worked stably in downhole. Compared to adjacent wells on the same platform that bottom hole temperatures are all above 152 °C, the maximum bottom hole temperature decreased by 9–13 °C. Furthermore, in the horizontal section, the Rate of Penetration (ROP) is increased by more than 48 %, the pump pressure is reduced by 2–5 MPa, and the average hole enlargement rate is only 1.92 %. All findings show that lower mud density can not only effectively reduce the bottom hole temperature, but also improve the drilling efficiency, which has positive significance for the development of deep shale gas.

Zastosowanie „aproksymacji dyfuzyjnej” do opisu procesu zagospodarowania złóż ropy naftowej

Analysis of the interaction of wells in the process of oil field development is based in particular on calculating the correlation coefficient of two adjacent wells. However, due to reservoir heterogeneity, this approach fails to consider the possibility of interactions between wells located at significantly greater distances. The non-equilibrium of the system is attributed to its openness, associated with environmental impacts (flooding process and changes in the stock of existing wells). The oil field development is a complex process, subject to complex works such as well grid compaction, carrying out a wide range of geological and technical operations, etc. From this point of view, the development and exploitation of fields needs a “volumetric” approach, i.e. a diffusion approximation. A crucial aspect of oil production is the timely regulation of both current production rates and water impact on the reservoir system. The oscillatory nature of the time series of measurements of oil, water, and liquid production rates carries information about the state and behavior of the reservoir system. Analysis of the features of oscillatory processes of the technological indicators of well operation across the entire area of the deposit as a whole enables early diagnosis of changes in the state of the system. The approach of the production well stock analysis in terms of the amplitude-frequency characteristics of the dynamics of oil, water, “mobile” water, and flooding, as well as the specific ratios of produced oil to the volume of water injected into the reservoir (an indicator of the effectiveness of water stimulation) allows us to consider the development as a diffusion-like process.

Hydrodynamics control for the well field of in-situ leaching of uranium

In this study, the groundwater hydrodynamics of two adjacent well sites were simulated under different pumping-injection ratios. The aim is to select an optimal pumping-injection ratio that can ensure the groundwater of the two well sites don't affect each other. In addition, the sulfur isotope composition of groundwater in the two well sites were analyzed to verify the simulated results. The results show that the flow velocity at different points outside the edge drilling hole decreases exponentially with the distance between the point and the edge hole. The streamline gradually extends outside of the borehole with the increase of leaching time. It is found that the optimal pumping-injection ratio is 1.003. In this case, the maximum distance between the moving front and the injection borehole is 28.44 m after leaching for 5 years. This indicates that the groundwater flow fields of the two well sites are well controlled. The significant difference in sulfur isotopes between the two well-sites further proves that the SO42− in the acid mining zone does not affect the groundwater in the zone leached by CO2+O2.

Adjacent well casing damage caused by fluid pressure intrusion in multistage fracturing

Nowadays, the large cluster well factory production mode is widely applied, which means that multistage fracturing can cause casing damage not only to the construction well but also to the adjacent well. To explore the cause of casing deformation caused by fluid pressure intrusion in multistage fracturing, a three-dimensional model of multistage fracturing in two wells is established based on natural fractures. The new model has reached dimensions of 1500 m × 300 m × 100 m, essentially achieving a 1:1 scale modeling. In addition, on the basis of large-scale modeling, adjacent wells have been taken into consideration for the first time. The multistage fracturing construction is simulated through the Abaqus finite element model. Results indicate that the multistage fracturing construction of a well not only transforms the stratum near the well, but also the extended hydraulic fractures have a certain effect on the stratum of neighboring wells at a close distance, causing natural fractures near the neighboring wells to slip. In this study, the control variable method was used to evaluate different influencing factors, determine the relationship between influencing factors and adjacent casing deformation, and put forward optimization design suggestions, which provided a reference for preventing and controlling casing deformation caused by fluid pressure intrusion.

Effect of Acid-Injection Mode on Conductivity for Acid-Fracturing Stimulation in Ultra-Deep Tight Carbonate Reservoirs

The conductivity of acid-etched fractures and the subsequent production response are influenced by the injection mode of the fracturing fluid and acid fluid during acid fracturing in a carbonate reservoir. However, there has been a lack of comprehensive and systematic experimental research on the impact of commonly used injection modes in oilfields on conductivity, which directly affects the optimal selection of acid-fracturing injection modes. To address this gap, the present study focuses on underground rock samples, acid systems, and fracturing fluid obtained from ultra-deep carbonate reservoirs in the Fuman Oilfield. Experimental investigations were conducted to examine the conductivity of hydraulic fractures etched by various types of acid fluids under five different injection modes: fracturing fluid + self-generating acid or cross-linked acid; fracturing fluid + self-generating acid + cross-linked acid. The findings demonstrate that the implementation of multi-stage alternating acid injection results in the formation of communication channels, vugular pore space, and natural micro-cracks, as well as grooves and fish-scales due to enhanced etching effects. The elevation change, amount of dissolved rock, and conductivity exhibited by rock plates are significantly higher in comparison to those achieved through the single-acid injection mode while maintaining superior conductivity. It is recommended for optimal conductivity and retention rate in the Fuman Oilfield to adopt two stages of alternating acid-fracturing injection mode. Field application demonstrated that two-stages of alternating acid-fracturing generate more pronounced production response than the adjacent wells.

Long‐ and Short‐Term Effects of Seismic Waves and Coseismic Pressure Changes on Fractured Aquifers

AbstractTwo adjacent groundwater wells on the North China Platform are used to study how earthquakes impacted aquifers. We use the response of water level to solid Earth tides to document changes after earthquakes and how aquifer and fracture properties recovered to pre‐earthquake properties. We consider two models for the phase and amplitude of water level response to the lunar diurnal (O1) and semidiurnal (M2) tides: a leaky aquifer model, and a model in which fracture orientation determines the response. In the leaky aquifer model, changes arise from changes in permeability and storage; in the fracture model, changes are due to changes in apparent orientation of transmissive fractures. Responses in one well are best explained by the leaky aquifer model, and can explain the large amplitude coseismic water level and permeability changes and the non‐recoverable changes after the largest earthquake. Responses in the other well are consistent with the fracture model and show little coseismic change in water level but changes in apparent fracture orientation. Larger ground motions lead to larger coseismic water level changes and longer recovery times. We propose that the well in the more permeable and shallow aquifer has less variable pore‐pressures around the well. Larger coseismic strains from water level changes may enable longer‐lasting changes in aquifer properties. We conclude that relatively high permeability aquifers are less susceptible to impacts from seismic waves, and thus have small changes in water levels and hydrogeological properties.

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.

Analyzing in situ stresses and wellbore stability in one of the south Iranian hydrocarbon gas reservoirs

This study aims to analyze in situ stresses and wellbore stability in one of the Iranian gas reservoirs by using well log data, including density, sonic (compressional and shear slowness), porosity, formation micro-image (FMI) logs, modular formation dynamics tester (MDT), and rock mechanical tests. The high burial depth, high pore pressure, and strike-slip stress regime of the field require an optimal design of geomechanical parameters based on an integrated data set consisting of static and dynamic data, which is available for this study. Firstly, poroelastic modulus and vertical stress were calculated. Afterward, the Eaton’s equation was used to estimate pore pressure from well logging data. The geomechanical parameters were also calibrated through the interpretation of image data, the use of the modular formation dynamics tester (MDT), and laboratory rock mechanic tests. Employing poroelastic equations, the lowest and highest horizontal stresses were calculated. It was shown that the maximum horizontal stress and minimum horizontal stress correspond to sigma H and sigma h, indicating the strike-slope fault regime. The findings of this research indicated that the equivalent mud weight (EMW) resulted in 10–13 ppg suitable for the Kangan Formation and 11–14 ppg suitable for the Dalan Formation. Additionally, the well azimuth in the NE-SW direction provided the best stability for drilling the encountered formations. Therefore, the results of this study serve as cost-effective tools in planning adjacent wells in carbonate formations of gas field to predict the wellbore stability and safe mud window.

Determination of natural radionuclides and heavy metal concentrations in the groundwater and adjacent areas of the Kattakurgan reservoir, Uzbekistan

Abstract We conducted a comprehensive assessment of the Kattakurgan reservoir, alongside adjacent wells and boreholes, to measure the concentrations of natural radionuclides, heavy metals, and associated radiological hazards. Using NaI(Tl) crystal scintillation gamma spectrometers, we determined radionuclide levels in water and sediment. Inductively coupled plasma mass spectrometry (ICP-MS) was employed for heavy metal analysis. Our results showed radionuclide concentrations in reservoir water for 226Ra (0.8 Bq/L), 232Th (0.4 Bq/L), and 40K (0.4 Bq/L) were within the limits set by the World Health Organization (WHO). In contrast, deep well water samples showed elevated 226Ra concentrations (1.5 Bq/L). Sediment samples’ radionuclide levels were in line with UNSCEAR guidelines. Barium was the most notable heavy metal, with a concentration of 68.08 μg/L. While most radiation hazard indices remained within safety limits, the gamma index recorded a value of 1.057 Bq/kg. Our research provides valuable data for water quality assessment. The methods described can be applied to other reservoir studies. Regular monitoring is recommended for continuous safety evaluation, and further studies on biotic samples are suggested to enhance understanding of the reservoir’s ecosystem health.