Predicting variations of the least principal stress with depth: Application to unconventional oil and gas reservoirs using a log-based viscoelastic stress relaxation model

Knowledge of layer-to-layer variations of the least principal stress, S hmin, with depth is essential for optimization of multi-stage hydraulic fracturing in unconventional reservoirs. Utilizing a geomechanical model based on viscoelastic stress relaxation in relatively clay rich rocks, we present a new method for predicting continuous S hmin variations with depth. The method utilizes geophysical log data and S hmin measurements from routine diagnostic fracture injection tests (DFITs) at several depths for calibration. We consider a case study in the Wolfcamp formation in the Midland Basin, where both geophysical logs and values of S hmin from DFITs are available. We compute a continuous stress profile as a function of the well logs that fits all of the DFITs well. We utilized several machine learning technologies, such as bootstrap aggregation (or bagging), to improve the generalization of the model and demonstrate that the excellent fit between predicted and observed stress values is not the result of over-fitting the calibration points. The model is then validated by accurately predicting hold-out stress measurements from four wells within the study area and, without recalibration, accurately predicting stress as a function of depth in an offset pad about 6 miles away.

Controlled Frac Height Growth Technique to Avoid Contacting Water-Bearing Layer

Many techniques have been used to model, diagnose and detect fracture dimension and propagation during hydraulic fracturing. Diagnosing fracture dimension growth vs time is of paramount importance to reach the desired geometry to maximize hydrocarbon production potential and prevent contacting undesired fluid zones. The study presented here describes a technique implemented to control vertical fracture growth in a tight sandstone formation being stimulated near a water zone. This gas well was completed vertically as openhole with Multi- Stage Fracturing (MSF). Pre-Fracturing diagnostic tests in combination with high-resolution temperature logs provided evidence of vertical fracture height growth downward toward water zone. Pre-fracturing flowback indicated water presence that was confirmed by lab test. Several actions were taken to mitigate fracture vertical growth during the placement of main treatment. An artificial barrier with proppant was placed in the lower zone of the reservoir before main fracturing execution. The rate and viscosity of fracturing fluids were also adjusted to control the net pressure aiming to enhance fracture length into the reservoir. The redesigned proppant fracturing job was placed into the formation as planned. Production results showed the effectiveness of the artificial lower barrier placed to prevent fracture vertical growth down into the water zone. Noise log consists of Sonic Noise Log (SNL) and High Precision Temperature (HPT) was performed. The log analysis indicated that two major fractures were initiated away from water-bearing zone with minimum water production. Additionally, in- situ minimum stress profile indicated no enough contrast between layers to help confine fracture into the targeted reservoir. Commercial gas production was achieved after applying this stimulation technique while keeping water production rate controlled within the desired range. The approach described in this paper to optimize gas production in tight formation with nearby water contact during hydraulic fracturing treatments has been applied with a significant improvement in well production. This will serve as reference for future intervention under same challenging completion conditions.

School Principals’ Stress Profiles During COVID-19, Demands, and Resources

The present study examined latent profiles of school principals’ stress concerning students’, teachers’, parents’, and principals’ own ability to cope during the COVID-19 pandemic. In addition, the role of job demands (workload, remote work stress, difficulty to detach from work, COVID-19 crisis, COVID-19 infections at school, impact of COVID-19 on future teaching), resources (buoyancy, effective crisis leadership, social appreciation, successful transition to remote teaching), and occupational well-being (measured as job burnout and engagement) in predicting the latent profiles of stress sources was examined. The participants were 535 (59% women) school principals across Finland, who answered to a questionnaire concerning their sources of stress and occupational well-being during spring 2020. Three latent profiles were identified according to principals’ level of stress: high stress (41.4% of the school principals), altered stress (35.9%), and low stress (22.7%) profiles. Work burnout, workload, COVID-19 related concerns, and difficulty to detach from work increased the probability of principals belonging to the high or altered stress profile rather than to the low stress profile. Work engagement, buoyancy, and social appreciation increased the probability of principals belonging to the low rather than to the high or altered stress profile.

Perfecting Straddle Packer Microfrac Stress Contrast Measurements for Hydraulic Fracturing Design in UAE Tight Oil Reservoir

The objective of this work was to quantify the in-situ stress contrast between the reservoir and the surrounding dense carbonate layers above and below for accurate hydraulic fracturing propagation modelling and precise fracture containment prediction. The goal was to design an optimum reservoir stimulation treatment in a Lower Cretaceous tight oil reservoir without fracturing the lower dense zone and communicating the high-permeability reservoir below. This case study came from Abu Dhabi onshore where a vertical pilot hole was drilled to perform in-situ stress testing to design a horizontal multi-stage hydraulic fractured well in a 35-ft thick reservoir. The in-situ stress tests were obtained using a wireline straddle packer microfrac tool able to measure formation breakdown and fracture closure pressures in multiple zones across the dense and reservoir layers. Standard dual-packer micro-injection tests were conducted to measure stresses in reservoir layers while single-packer sleeve-frac tests were done to breakdown high-stress dense layers. The pressure versus time was monitored in real-time to make prompt geoscience decisions during the acquisition of the data. The formation breakdown and fracture closure pressures were utilized to calibrated minimum and maximum lateral tectonic strains for accurate in-situ stress profile. Then, the calibrated stress profile was used to simulate fracture propagation and containment for the subsequent reservoir stimulation design. A total 17 microfrac stress tests were completed in 13 testing points across the vertical pilot, 12 with dual-packer injection and 5 with single-packer sleeve fracturing inflation. The fracture closure results showed stronger stress contrast towards the lower dense zone (900 psi) in comparison with the upper dense zone (600 psi). These measurements enabled the oilfield operating company to place the lateral well in a lower section of the tight reservoir without the risk of fracturing out-of-zone. The novelty of this in-situ stress testing consisted of single packer inflations (sleeve frac) in an 8½-in hole in order to achieve higher differential pressures (7,000 psi) to breakdown the dense zones. The single packer breakdown permitted fracture propagation and reliable closure measurements with dual-packer injection at a lower differential reopening pressure (4,500 psi). Microfracturing the tight formation prior to fluid sampling produced clean oil samples with 80% reduction of pump out time in comparison to conventional straddle packer sampling operations. This was a breakthrough operational outcome in sampling this reservoir.

No Impact of Psychosocial Stress on Glioblastoma Development

Purpose: Psychosocial stress represents an important source of questions in the potential implication of origin of cancer. The aim of the study was to assess stress prevalence prior to diagnosis of wild-type IDH glioblastoma.Methods: This prospective single-center study enrolled consecutive new cases of wild-type IDH glioblastoma diagnosed between December 2019 and March 2021 at the University Hospital of Bordeaux. A standardized patient self-assessment stress questionnaire explored both the presence of stressor exposure and the intensity of patient stress level prior to the diagnosis. Four groups were included: high stressors/high stress, high stressors/low stress, low stressors/low stress, and low stressors/high stress. Patient characteristics were collected. Statistical analysis was based on the Chi-square test and the Kaplan-Meier survival estimator.Results: Sixty-four patients with a median age of 66 years were included. Glioblastoma involved predominantly the frontal lobe (39%). Thirty-six patients (56.3%) presented a low stressor/low stress profile. Stress corresponded mainly to the death of a loved one or to family health problems. Among working professionals, 20 patients (67.5%) reported low-intensity work stress. A history of depression was found in 30%. Progression-free survival at 6 months was 45.3% and median overall survival was estimated to be 16.5 months. Level and presence of stress did not differ based on location of tumour. No association was found between stress and tumour progression or overall survival.Conclusion: A majority of patients in this study had low exposure to stressors as well as low stress level. Psychological stress did not seem to favour the emergence of glioblastoma or survival.

Stratigraphically Controlled Stress Variations at the Hydraulic Fracture Test Site-1 in the Midland Basin, TX

We investigated the relationship between stratigraphy, stress, and microseismicity at the Hydraulic Fracture Test Site-1. The site comprises two sets of horizontal wells in the Wolfcamp shale and a deviated well drilled after hydraulic fracturing. Regional stresses indicate normal/strike-slip faulting with E-W compression. Stress measurements in vertical and horizontal wells show that the minimum principal stress varies with depth. Strata with high clay and organic content show high values of the least compressive stress, consistent with the theory of viscous stress relaxation. By integrating data from core, logs, and the hydraulic fracturing stages, we constructed a stress profile for the Wolfcamp sequence, which predicts how much pressure is required for hydraulic fracture growth. We applied the results to fracture orientation data from image logs to determine the population of pre-existing faults that are expected to slip during stimulation. We also determined microseismic focal plane mechanisms and found slip on steeply dipping planes striking NW, consistent with the orientations of potentially active faults predicted by the stress model. This case study represents a general approach for integrating stress measurements and rock properties to predict hydraulic fracture growth and the characteristics of injection-induced microseismicity.

Geomechanical Model as the Key Step to Proppant Fracturing Success in Shallow Carbonate Reservoir of Bahrain

Geomechanics play an important role in stimulation design, especially in complex tight reservoirs with very low matrix permeability. Robust modelling of stresses along with rock mechanical properties helps to identify the stress barriers which are crucial for optimum stimulation design and proppant allocation. Complex modeling and calibration workflow showcased the value of geomechanical analysis in a large stimulation project in the Ostracod-Magwa reservoir, a complicated shallow carbonate reservoir in the Bahrain Field. For the initial model, regional average rock properties and minimum stress values from earlier frack campaigns were considered. During campaign progression, advanced cross dipole sonic measurements of the new wells were incorporated in the geomechanical modeling which provided rock properties and stresses with improved confidence. The outputs from wireline-conveyed microfrac tests and the fracturing treatments were also considered for calibration of the minimum horizontal stress and breakdown pressure. The porepressure variability was established with the measured formation pressure data. The geomechanically derived horizontal stresses were used as input for the frack-design. Independent fracture geometry measurements were run to validate the model. The poro-elastic horizontal strain approach was taken to model the horizontal stresses, which shows better variability of the stress profile depending on the elastic rock properties. The study shows variable depletion in porepressure across the field as well as within different reservoir layers. The Ostracod reservoir is more depleted than Magwa, with porepressure values lower than hydrostatic (∼7 ppg). The B3 shale layer in between the Magwa and Ostracod reservoirs is a competent barrier with 1200-1500psi closure pressure. The closure pressures in the Ostracod and Magwa vary from 1000-1500psi and 1100-1600psi, respectively. There is a gradual increasing trend observed in closure pressure in Magwa with depth, but no such trend is apparent in the shallower Ostracod formation. High resolution stress profiles help to identify the barriers within each reservoir to place horizontal wells and quantify the magnitude of hydraulic fracture stress barriers along horizontal wells. The geomechanical model served as a key part of the fracturing optimization workflow, resulting in more than double increase in wells productivity compared to previous stimulation campaigns. The study also helped to optimize the selection of the clusters depth of hydraulic fracturing stages in horizontal wells. The poroelastic horizontal strain approach to constrain horizontal stresses from cross dipole sonic provides better variability in the stress profile to ultimately yield high resolution. This model, calibrated with actual frac data, is crucial for stimulation design in complex reservoirs with very low matrix permeability. The geomechanical model serves as one of the few for shallow carbonates rock in the Middle East region and can be of significant importance to many other shallow projects in the region.

Evaluation of the Anti-Oxidative Effects of Monocyte Cells Treated with Bone Marrow Mesenchymal Stem Cells Supernatant on Experimental Colitis in BALB/c Mice

Background: Alternate activation of monocytes could induce anti-inflammatory impacts. This study aimed to investigate whether monocyte cells treated with bone marrow mesenchymal stem cells supernatant (MSC-Sp) could improve anti-inflammatory responses as a cell transfer therapy for colitis. Materials and Methods: The induction of experimental colitis was done by acetic acid in four groups of male BALB/c mice, including the control colitis, treated-monocytes, non-treated-monocytes, and mesalazine groups. Following MSCs culture, the supernatant was harvested, and then 50% conditioned media, or negative control media was added to the monocytes for 24 h. After ten days, peritoneal injection of treated or non-treated-monocytes (105 cells/100µL) was performed in animals' relevant groups of colitis. Ten days later, the oxidative stress profile and histopathological evaluation of colon tissue were assessed. Results: Treated monocytes showed a significant improvement in the oxidative stress profile, namely myeloperoxidase (0.126±0.008), nitric oxide (0.153±0.01), and malondialdehyde (0.148±0.014) compared to the control colitis group (P<0.05). Also, histopathological results revealed that the rate of damage in the treated-monocytes group was less than in normal mice. Conclusion: Our study indicated that the treated monocytes had anti-oxidative potential in colitis mice and were usable as a complementary therapy. [GMJ.2021;10:e2131]

Non-invasive detection for work stress among the professional medical nurses during COVID-19 in Mongolia

COVID-19 pandemic has created a lot of work stress, especially among medical professionals, namely among nurses. The absence of the non-invasive stress detecting method using salivary alpha-amylase test in Mongolia served us to perform this study. We consider that the nurse immunization could be managed and boosted if the work stress is detected, and it would serve as the prevention method from the infections in the clinical settings. The study aims to investigate the stress level among medical professionals, particularly the nurses, using a self-report questionnaire, work stress profile, and salivary alpha-amylase during the initial period of the COVID pandemic. In the mid of March 2020, 356 professional medical nurses from three national tertiary centres of Mongolia were involved in this study. We employed a Work Stress Profile (WSP), a self-administered questionnaire that assists the personnel to identify their perceived stressors and assessing the stress at work. As the physical stress marker, we measured the saliva alpha-amylase level in these participants. The vital signs, heart rate, glucose and blood pressure were measured. The correlation method was used. There were 344 females and 12 males. The participants' mean age was 38±9.6 years old. The stress among the medical professionals was high by WSP - it was counted 342 or 96.1% of the personnel suffering from the stress at work: the WSP average was 151.49±26.81. However, age, education and work experience could influence stress at a certain level. The salivary alpha-amylase and WSP scores were correlated directly (p<0.01; r=0.187). The pulse, diastolic blood pressure and salivary alpha-amylase were interrelated. As one of the important personnel at the hospital, nurses are at high risk to get stressed in Mongolia. We concluded that the overloading of work leads to work stress among professional medical nurses, especially during the COVID-19 pandemic.

Oxidative Stress Profile of Mothers and Their Offspring after Maternal Consumption of High-Fat Diet in Rodents: A Systematic Review and Meta-Analysis

Maternal exposure to the high-fat diet (HFD) during gestation or lactation can be harmful to both a mother and offspring. The aim of this systematic review was to identify and evaluate the studies with animal models (rodents) that were exposed to the high-fat diet during pregnancy and/or lactation period to investigate oxidative stress and lipid and liver enzyme profile of mothers and their offspring. The electronic search was performed in the PUBMED (Public/Publisher MEDLINE), EMBASE (Ovid), and Web of Science databases. Data from 77 studies were included for qualitative analysis, and of these, 13 studies were included for meta-analysis by using a random effects model. The pooled analysis revealed higher malondialdehyde levels in offspring of high-fat diet groups. Furthermore, the pooled analysis showed increased reactive oxygen species and lower superoxide dismutase and catalase in offspring of mothers exposed to high-fat diet during pregnancy and/or lactation. Despite significant heterogeneity, the systematic review shows oxidative stress in offspring induced by maternal HFD.