bluuebunny/crossref_metadata_2025_split huggingface dataset:
Implementing a Strategy for Shale as Well Barrier in New Wells
Authors: Kristiansen Tron Golder , Delabroy Laurent , Obando Palacio Guillermo Andres , Winther Tonje , Aarseth Nils Andre , Bauer Andreas , Hagenes Karstein , Lindal Anders , Tyberø Pål 
Published: March 2021

Abstract
Shale is an effective barrier material. It has a proven track record of acting as a seal (barrier) for oil and gas reservoirs for millions of years. Shale with high clay content and especially high smectite has low permeability, in the nanodarcy range, compared to standard class G laboratory cement that has permeability in the 10–20 microdarcy range. Weak ductile shales will also have a self-healing behavior should fractures be induced at some point. Shale is approved by regulators to be used as well barriers and part of permanent plug and abandonment (P&A) for oil and gas wells.
Examples of regulations are Norsok D-010, 2013 in Norway and O&G UK, 2012. In Norsok D-010, one suggests the formation of shale barriers to happen due to creep in ductile shales. Creep occurs in many materials and is observed as deformation under constant load and is also well described in rock mechanics literature. In a previous paper (Kristiansen et al., 2018), it was discussed how shale can be activated as a barrier to form around the wellbore in some shale types. This can be done by inducing a pressure drop in the open annulus (rapid drawdown), by heating the shale by a couple of hundred degrees Celsius, or by chemical processes. In that paper, the process found most effective and practical at that time was demonstrated: the activation of shale barriers with a rapid pressure drop in the annulus. It was also shown that the barrier can be verified days after by standard verification methods used in the industry (pressure testing and bond logging). The shale barrier verification criteria are analogous to cement barriers.
In this paper we share the experience from the implementation of a strategy to use shale as well barriers in new wells at Valhall and a second field, Ula, around 100 km away. The method used to activate the shale barriers has revealed some challenges from a well control point of view, but it has also shown that waiting a couple of weeks, or in some cases a couple of months, shale barriers are forming with the same quality as when they were activated or logged later as part of P&A. From this work it can be concluded that the shale barriers logged during P&A are, in some cases, in place only weeks or months after the wells have been drilled. The activation seems to induce an acceleration of time-dependent deformation that will naturally happen over longer time and is consistent with rock mechanics principles of time-dependent deformations in rocks (like creep and consolidation).
Development, Testing and Validation of an Adaptive Drilling Optimization System
Authors: Daireaux Benoit , Ambrus Adrian , Carlsen Liv A. , Mihai Rodica , Gjerstad Kristian , Balov Mohsen 
Published: March 2021

Abstract
An important benefit of drilling automation is the ability to ensure continuous updating of the parameters controlling the drilling process according to the current wellbore conditions. While actively drilling, this means continuously adjusting the weight on bit (WOB), topdrive speed and flowrate according to the current formation properties and drilling system behaviour: ability to transport cuttings, buckling or exceeding the geo-pressure margins. We present here the main principles used to design and develop such an adaptive drilling optimization system, and the first results obtained both in a simulated environment and in real operations.
The system achieves adaptability by combining two separate processes. Firstly, it maintains an updated estimate of the bit-rock interaction mechanism using a stochastic approach coupled with a physical model. This is used to predict the system's response to changes in parameters (WOB, topdrive speed or flowrate), including the possible presence of a founder point, i.e. a WOB threshold above which no gain in rate of penetration (ROP) is achieved, and also to detect changes in formation properties. Then, the second process ensures that the effects of the same drilling parameters are evaluated with respect to their ability to ensure safe drilling: cuttings transport and drillstring mechanical stability are the main constraints here, evaluated in a probabilistic framework. The combination of these two processes provides the generation of both safe and optimum drilling parameters.
The system can be used in two contexts: firstly, as an advisory module which provides set-point recommendations to the driller; secondly, as an integrated module into a drilling automation system. In the latter configuration, the generated set-points are used to actively control the drilling process. Note that the bit-rock interaction prognoses enable quick automated detection of – and therefore reaction to- sudden changes in formation properties. Both modes facilitate real-time monitoring of the bit-rock interaction process, including the estimated formation properties, bit aggressiveness and founder point. Results from active tests in a simulated environment and advisory mode against real field data are presented and discussed.
Systematic Selection of Drill-In and Completion Fluids for Development of the Dvalin HT Gas Field - Part II: Successful Clean-Up Validates Experimental Qualification Approach
Authors: Czuprat Oliver , Eriksen Kjetil , Clinch Duncan , Byrski Piotr , Gibbons Garbhan , Hughes Neal , Øian Tore , Ritschel Robert , Storhaug Jens 
Published: March 2021

Abstract
Formation damage by the drill-in fluid has been identified as a major risk for the Dvalin HT gas field. To ensure the long-term stability and mobility of the mud even after an extended suspension time between drill-in and clean-up of the wells, a novel static aging test under downhole temperature and high pressure was conducted. Experiments have shown that the downhole stability is commonly underestimated when the surrounding pressure is lower than in the field. Thus, a high-pressure cylinder was used in vertical orientation in a heating oven with a pressure pump regulating the pressure up to 200 bar.
The reservoir section was drilled with the optimized organo-clay-free oil-based drilling fluid (OCFOBDF) specified in the qualification phase. Tracers in the lower completion were used to identify clean-up from the upper high-permeability streak and the deeper (relatively lower) high-permeability streak. Due to extended wait on weather after drilling and completion of the first of the four wells, the lag time until clean-up was almost 11 weeks (74 days).
It could be experimentally shown that the qualified OCFOBDF system weighted with micron sized barite remains mobile without phase separation even after static aging at 160 °C and 200 bar for the maximum estimated lag time between drilling and clean-up of 3 months. The absence of a gas cap in the set-up also better represents downhole conditions in the reservoir section and has shown that it improves the fluid´s stability. The clean-up of the well was successful with a maximum flowrate of 3.0 MM Sm3/d. Analysis of the tracers has proven that clean-up was successful for the entire reservoir section, including the deeper part.
It could be concluded that in alignment with the lab tests that the mud fulfilled its requirement to be mobile even up to three months. Because of the superior properties, settling of solids (bridging and weighting material) could be avoided, resulting in no blockage of the (lower part of the) reservoir.
The use HPHT aging has been the key to proving the long-term stability and mobility of the combined Drill-In and Completion Fluid. This technique falls outside of current API RP testing practices but is believed to be highly beneficial for qualification of fluids that will be left in the lower completion for long periods, especially in open hole completions under high temperature and pressure.
Evaluating Data-Driven Techniques to Optimize Drilling on the Moon
Authors: Joshi Deep R , Eustes Alfred W , Rostami Jamal , Dreyer Christopher 
Published: March 2021

Abstract
Several companies and countries have announced plans to drill in the lunar South Pole in the next five years. The drilling process on the Moon or any other planetary body is similar to other exploration drilling by using rotary drills, for example the oil and gas drilling. However, the key performance indicators (KPIs) for this type of drilling are significantly different. This work aimed to develop the drilling optimization algorithms to optimize drilling on the Moon based on the experiences with the terrestrial drilling in related industries.
A test drilling unit was designed and fabricated under a NASA Early Stage Innovation (ESI) grant; A high-frequency data acquisition system was used to record drilling responses at 1000 Hz. Parameters like weight on bit (WOB), torque, RPM, rate of penetration (ROP), mechanical specific energy (MSE), field penetration index (FPI), and the uniaxial compressive strength (UCS) were recorded for 40 boreholes in the analog formations. This work utilizes the large dataset comprising of more than 1 billion data points recorded while drilling into various lunar analogous formations and cryogenic lunar formations to optimize power consumption and bit wear during drilling operations.
The dataset was processed to minimize the noise. The effect of drilling dysfunctions like auger choking and bit wear was also removed. Extensive feature engineering was performed to identify how each of the parameter affects power consumption and bit wear. The data was then used to train various regression algorithms based on the machine learning approaches like the random forest, gradient boosting, support vector machines, logistic regression, polynomial regression, and artificial neural network to evaluate the applicability of each of these approach in optimizing the power consumption using the control variables like RPM and penetration rate. The best performing algorithm based on ease of application, runtime, and accuracy of the algorithm was selected to provide recommendations for ROP and RPM which would result in minimum power consumption and bit wear for a specific bit design.
Since the target location for most lunar expeditions is in permanently shadowed regions, the power available for a drilling operation is extremely limited. The bit wear will significantly affect the mission life too. Algorithms developed here would be vital in ensuring efficient and successful operations on the Moon leading to more robust exploration of the targeted lunar regions.
A Generalised Solution to the Point to Target Problem Using the Minimum Curvature Method
Authors: Sawaryn Steven J. 
Published: March 2021

Abstract
An explicit solution to the general 3D point to target problem based on the minimum curvature method has been sought for more than four decades. The general case involves the trajectory's start and target points connected by two circular arcs joined by a straight line with the position and direction defined at both ends. It is known that the solutions are multi-valued and efficient iterative schemes to find the principal root have been established.
This construction is an essential component of all major trajectory construction packages. However, convergence issues have been reported in cases where the intermediate tangent section is either small or vanishes and rigorous mathematical conditions under which solutions are both possible and are guaranteed to converge have not been published. An implicit expression has now been determined that enables all the roots to be identified and permits either exact, or polynomial type solution methods to be employed. Most historical attempts at solving the problem have been purely algebraic, but a geometric interpretation of related problems has been attempted, showing that a single circular arc and a tangent section can be encapsulated in the surface of a horn torus. These ideas have now been extended, revealing that the solution to the general 3D point to target problem can be represented as a 10th order self-intersecting geometric surface, characterised by the trajectory's start and end points, the radii of the two arcs and the length of the tangent section.
An outline of the solution's derivation is provided in the paper together with complete details of the general expression and its various degenerate forms so that readers can implement the algorithms for practical application. Most of the degenerate conditions reduce the order of the governing equation. Full details of the critical and degenerate conditions are also provided and together these indicate the most convenient solution method for each case. In the presence of a tangent section the principal root is still most easily obtained using an iterative scheme, but the mathematical constraints are now known. It is also shown that all other cases degenerate to quadratic forms that can be solved using conventional methods.
It is shown how the general expression for the general point to target problem can be modified to give the known solutions to the 3D landing problem and how the example in the published works on this subject is much simplified by the geometric, rather than algebraic treatment.
Development and validation of a prognostic nomogram for predicting the survival of HIV/AIDS adults who received antiviral treatment: a cohort between 2003 and 2019 in Nanjing
Authors: Jiang Fangfang , Xu Yuanyuan , Liu Li , Wang Kai , Wang Lu , Fu Gengfeng , Wang Liping , Li Zhongjie , Xu Junjie , Xing Hui , Wang Ning , Zhu Zhengping , Peng Zhihang 
Published: March 2021

Abstract
Background

Although great achievements have been made since free antiviral treatment (ART) was available, an in-time and accurate prediction of survival for people living with HIV (PLHIV) is still needed for effective management. We aimed to establish an effective prognostic model to forecast the survival probability of PLHIV after ART.
Methods

The participants enrolled were from a follow-up cohort between 2003 and 2019 in Nanjing from Nanjing AIDS Prevention and Control Information System. The nested case-control study was employed with HIV-related death, and propensity-score matching (PSM) approach was applied at a ratio of 1:4 to allocate the patients. Univariate and multivariate Cox hazards analyses were used based on the training set to determine the risk factors. The discrimination was qualified using the area under the curve (AUC) and concordance index (C-Index). The calibration was evaluated using the calibration curve. The clinical benefit of prognostic nomogram was assessed by decision curve analysis (DCA).
Results

Predictive factors including CD4 cell count (CD4), body mass index (BMI) and food blood glucose (GLU) were determined and contained in the nomogram. In the training set, AUC and C-index (95% CI) were 0.826 and 0.793 (0.740, 0.846), respectively. The model of validation set still revealed good discrimination with an AUC and a C-index (95% CI) of 0.750 and 0.776 (0.711, 0.839). The calibration curve also exhibited a high consistency in predicting the survival of PLHIV (especially in the first three years after starting ART). Moreover, DCA demonstrated that the nomogram was clinically beneficial.
Conclusion

The nomogram is effective and accurate in forecasting the survival rate of PLHIV, and therefore accessible for medical workers in health administration.
Postoperative Hypoalbuminemia: Prevalence, Risk Factors, Association with Postoperative Pneumonia in Brain Tumors Patients Undergoing Craniotomy
Authors: Zhao Da-wei , Zhang Xu-yang , Wei Kai-yan , Jiang Yi-bin , Liu Dan , Zhang Shui-xian , Feng Hua , Hu Rong 
Published: March 2021

Abstract
Hypoalbuminemia is associatied with poor outcome in patients undergoing surgery intervention. The main aim for this study was to investigate the incidence and the risk factors of postoperative hypoalbuminemia and assessed the impact of postoperative hypoalbuminemia on complications in patients undergoing brain tumor surgery. This retrospective study included 372 consecutive patients who underwent brain tumors surgery from January 2017 to December 2019. The patients were divided into hypoalbuminemia (< 35 g/L) and non-hypoalbuminemia group (≥ 35 g/L) based on postoperative albumin levels. Logistic regression analyses were used to determine risk factors. Of the total 372 patients, 333 (89.5%) developed hypoalbuminemia after surgery. Hypoalbuminemia was associated with operation time (OR 1.011, P < 0.001), preoperative albumin (OR 0.864, P = 0.015) and peroperative globulin (OR 1.192, P = 0.004). Postoperative pneumonia had a higher incidence in patients with than without hypoalbuminemia (41.1% vs 23.1%, P = 0.029). The independent predictors of postoperative pneumonia were age (OR 1.053, P < 0.001), operation time (OR 1.003, P = 0.013) and lower postoperative albumin (OR 0.946, P = 0.018). Postoperative hypoalbuminemia has a higher incidence with the increase of operation time, and is associated with postoperative pneumonia in patients undergoing brain tumor surgery.
Identification of the co-expression module-trait relationships and hub genes associated with the diffuse-type gastric cancer
Authors: Ye Zaisheng , Zheng Miao , Zeng Yi , Xie Yunqing , Wei Shenghong , Wang Yi , Lin Zhitao , Chen Shu , Wang Zhiwei , Zheng Qiuhong , Chen Luchuan 
Published: March 2021

Abstract
Diffuse-type gastric cancer (DGC) is a gastric cancer subtype based on Laurén histological type, with poor prognosis when compared intestinal-type gastric cancer. It is necessary that comprehensive analysis identifies pathways and genes involved in DGC. RNA expression data of DGC (including 52 samples, top 5000 genes) and fourteen patient clinic traits were downloaded from The Cancer Genome Atlas (TCGA) database. Co-expression modules and module-trait relationships were constructed by weighted gene co-expression network analysis (WGCNA). The identified ten co-expression modules were obtained from DGC samples. The co-expression turquoise module positively correlated with longest dimension. The co-expression magenta module positively correlates with gender, and person neoplasm cancer status. The co-expression green module also positively correlates with pathologic N stage and pathologic stage. Besides, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment obtained some cancer related signal pathways in the co-expression turquoise and green module, such as proliferation, drug resistance, cell metabolism. Additionally, we identified the hub genes in the co-expression turquoise, green and magenta modules. Protein-protein interaction (PPI) and biological processes (BP) analysis were performed on the hub genes in those modules, suggesting the key role of those modules in the development of the cancer. The hub genes were significantly related to Overall survival analysis showed some important hub genes were significant in DGC patients, including ANK2, GNAO1, MAP6, RERG (turquoise module), MEP1A, GUCY2C, ALDOB (green module), XIST, TTTY15, NCRNA00185, CYorf15B (magenta module). The study provided new biomarkers and potential mechanisms in DGC.
An effective prediction of biomagnification factors for organochlorine pollutants
Authors: Zhang Ming Cai , Zhai Hong Lin , Bi Ke Xin , Zhao Bin Qiang , Shao Hai Ping 
Published: March 2021

Abstract
Biomagnification factor (BMF) is an important index of pollutants in food chains but its experimental determination is quite tedious. In this contribution, as the feature descriptors of molecular information, Tchebichef moments (TMs) were calculated from their structural images. Then stepwise regression was employed to establish the prediction model for the logBMF of organochlorine pollutants. The correlation coefficient with leave-one-out cross-validation (Rcv) was 0.9570; the correlation coefficient of prediction (Rp) and root mean square error (RMSEp) for external independent test set reached 0.9594 and 0.2129, respectively. Compared with traditional two-dimensional (2D) quantitative structure-property relationship (QSPR) and the reported augmented multivariate image analysis applied to QSPR (aug-MIA-QSPR), the proposed approach is more simple, accurate and reliable. This study not only obtained the model with better stability and predictive ability for the BMF of organochlorine pollutants, but also provided another effective approach to QSPR research.
Decreased renal function increases the nighttime urine volume rate by carryover of salt excretion to the nighttime
Authors: Takezawa Kentaro , Kuribayashi Sohei , Okada Koichi , Sekii Yosuke , Inagaki Yusuke , Fukuhara Shinichiro , Kiuchi Hiroshi , Abe Toyofumi , Fujita Kazutoshi , Uemura Motohide , Imamura Ryoichi , Nonomura Norio 
Published: March 2021

Abstract
Purpose: To determine the pathophysiology of nocturnal polyuria associated with renal dysfunction.Methods: Patients who underwent laparoscopic nephrectomy were studied prospectively. The diurnal variation in urine volume, osmolality, and salt excretion were measured on preoperative day two and postoperative day seven. The factors associated with an increase in the nighttime urine volume rate with decreased renal function were evaluated by multiple linear regression analysis.Results: Forty-nine patients were included. The eGFR decreased from 73.3 ± 2.0 to 47.2 ± 1.6 mL/min/1.73 m2 (P < 0.01) and the nighttime urine volume rate increased from 40.6% ± 2.0% to 45.3% ± 1.5% (P = 0.04) with nephrectomy. The nighttime urine osmolality decreased from 273 ± 15 to 212 ± 10 mOsm/kg (P < 0.01) and the nighttime salt excretion rate increased from 38.7% ± 2.1% to 48.8% ± 1.7% (P < 0.01) with nephrectomy. Multiple linear regression analysis revealed that the increase in the nighttime urine volume rate was strongly affected by the increase in the nighttime salt excretion rate.Conclusion: A decrease in renal function causes an increase in the nighttime urine volume rate, mainly due to an increase in nighttime salt excretion.Trial registration number: UMIN000036760 (University Hospital Medical Information Network Clinical Trials Registry)Date of registration: From June 1st, 2019 to October 31th 2020