bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simplifying Well Abandonments Using Shale as a Barrier
Authors: van Oort Eric , Juenger Maria , Aldin Munir , Thombare Akshay , McDonald Mike 
Published: February 2020

Abstract
Well abandonment is one of the biggest challenges in the oil and gas industry, both in terms of cost and effort as well as the technical hurdles associated with wellbore isolation for an indefinite term. A mechanism that may be exploited to simplify well abandonments is using natural shale formations for the creation of annular barriers. Currently, uncemented annuli often require casing milling and pulling before abandonment plugs can be set, which necessitates the use of a drilling rig. This is an expensive, time- and labor-intensive process, particularly offshore. However, shale creep may naturally form a barrier behind uncemented casing sections. With a qualified annular shale barrier in place, the well may only require the setting of abandonment plugs within the existing casing string(s), a task that can often be done rigless and with significantly less effort.
The work described in this paper presents the results of a rock mechanical investigation into the creep behavior of North Sea shales and their ability to form effective annular barriers. Field core from the Lark-Horda shale was used to conduct dedicated, customized experiments that simulated the behavior of shale confined under downhole effective stress, pressure and temperature conditions to fill in an annular space behind a simulated casing string. Full scale tri-axial rock mechanics equipment was used for testing cylindrical shale samples obtained from well-preserved field core in a set-up that mimicked an uncemented casing section of a well. The deformation behavior of the shale was monitored for days to weeks, and the formation of the annular barrier was characterized using dedicated strain measurements and pressure pulse decay probing of the annular space.
The large-scale lab results clearly show that the Lark-Horda shales will form competent low permeability annular barriers when left uncemented, as confirmed using pressure-pulse decay measurements. They also show that experimental conditions influence the rate of barrier formation: higher effective stress, higher temperature and beneficial manipulation of the annular fluid chemistry all have a significant effect. This then opens up the possibility of activating shale formations that do not naturally create barriers by themselves into forming them, e.g. by exposing them to low annular pressure, elevated temperature, different annular fluid chemistry, or a combination. The results are in very good agreement with field observations reported earlier by several North Sea operators.
Low-Density Invert Emulsion Drilling Fluid Enables Recovery of Oil Reserves in Extremely Depleted Reservoirs: A Case History From Valhall, Norway
Authors: Askø Arne , Alsvik Eva Teresia , Danielsen Trond Helge , Haga Marton Audun 
Published: February 2020

Abstract
A drilling fluid designed for drilling long horizontal wells in extremely depleted chalk reservoirs within the limitations of a narrow mud weight window, high overbalance, high solids contamination and static periods was successfully implemented when drilling a water injection well on Valhall Flank North in the southern Norwegian Continental Shelf.
In parts of the Valhall reservoir the depletion is estimated to 313 bar (4500 psi). The estimated pressure gradients in the planned trajectory were pore pressures between 0.64 sg and 0.70 sg (5.3 ppg to 5.8 ppg) and with a corresponding fracture gradient of 0.95 sg (7.9 ppg). These conditions required a drilling fluid which could be maintained at a density as low as 0.78 sg (6.5 ppg) combined with a low viscosity, strict fluid loss control, tolerance towards contamination of chalk and high stability. No conventional drilling fluid would provide a sufficiently low density to drill this section, thus an unconventional solution had to be found. The proposed solution was to add hollow glass spheres (HGS) rated to withstand pressures up to 1310 bar (19,000 psi) to reduce the density of a conventional fluid. However, previous experience using HGS as an additive in drilling fluid was limited. Therefore, the design and qualification of this drilling fluid had to be conducted both in the laboratory as well as on a larger scale yard-trial.
Laboratory testing and the yard trial verified the feasibility of mixing the HGS in a large-scale production and confirmed their ability to withstand the expected downhole pressure and mechanical strain while drilling. The 1750 m (5740 ft) 8.5" injection well on Valhall Flank North was drilled in one run, with no drilling fluid-related problems. The drilling fluid density was maintained between 0.78 sg (6.5 ppg) and 0.85 sg (7.1 ppg) while the maximum measured equivalent circulation density (ECD) increased from 0.83 sg (6.9 ppg) at start of the section, to 0.96 sg (8.0 ppg) at section TD.
Completing this well was resulted in an increase of 7.5 mmboe recoverable oil demonstrating that implementing HGS in drilling fluids provides an expanded operational envelope and access to so far inaccessible oil reserves.
Early Identification of Drilling Collision Risk Using MWD Survey Quality Data
Authors: Cosca Nicolas , Willerth Marc 
Published: February 2020

Abstract
By identifying changes in the error characteristics of magnetic surveys while drilling, crews can be alerted early on to a potential close approach with an offset well. This alert does not require expert analysis prior to trigger, enabling safer deployment of remote monitoring and drilling automation systems.
That magnetic interference can be used to identify offset wells has been long known, however identification of the interference pattern is not always straightforward. Safe operation in close-approach situations currently requires proactive monitoring by an expert. This new method uses a conditional expectation of survey quality parameters ("marginal sigma") trained on previously accepted surveys to identify new errors. Quality control data from several wells with known close approaches are analyzed with this technique alongside traditional survey quality assessments. Automatic flagging of high-risk surveys for review would enable proactive monitoring workflows to be replaced with "management by exception" workflows making more efficient use of expertise.
Survey quality data from several close approach scenarios were analyzed using traditional QC methods along with the marginal sigma method. Traditional QC measures are not readily adapted to automated identification of offset wells. Problematic situations include cases where:
Surveys are already failing QC for a known reason, External interference temporarily improving QC data masks the problem, The onset of interference is too small to cause an immediate QC failure.
In light of this, traditional QC parameters still require proactive monitoring by an expert individual. Using the marginal sigma estimation, even small changes in magnetic measurement patterns are identified and escalated for review. These changes are often detected with even a single outlier survey, implying that escalation would occur as quickly as with the most vigilant observer. This system would be of particular value in situations where a limited number of experts are used to oversee a high volume of work, such as remote monitoring in North America Land, or in the future, supervising autonomous drilling systems.
The proposed system changes the drilling supervision requirements for what has previously been a high-risk scenario (collision avoidance drilling). Proactive monitoring by an expert can be safely transitioned to a "management by exception" system enabling better utilization of resources.
Wellbore Integrity During Blowouts: Broaching Prevention and Control
Authors: Michael Andreas , Gupta Ipsita 
Published: February 2020

Abstract
During loss of well control events, fracture initiation occurring during the post-blowout capping stage following uncontrolled discharge, can lead to reservoir fluids broaching to the seafloor. A classic example is Union Oil's 1969 oil spill in Santa Barbara channel, where fracture initiation at various locations caused thousands of gallons per hour to broach in the ocean floor over a period of a month before it could be controlled (Mullineaux, 1970; Easton, 1972). The impacts on California's oil industry are still felt strongly today. Disasters as such could be prevented if the effects of the post-blowout loss of well control stages (uncontrolled discharge and capping) are incorporated into the shut-n procedures and the wellbore architecture.
Analytical models are used to simulate the loads on the wellbore in the different stages during loss of control and predict capping pressure build-up during the shut-in to indicate fracture initiation during the capping stage. Using these models, critical capping pressure and subsequently critical discharge flowrates is calculated for a well below which fracture initiation would occur. A hypothetical case study with typical deepwater Gulf of Mexico parameters is performed demonstrating the likelihood of fracture initiation during different discharge flowrates, discharge periods and shut-in methods (abrupt/"hard" or multi-stage/"soft"). Further discussion addresses reservoir depletion during the discharge stage preceding the capping, as well as the conditions necessary for upward propagation of these fractures towards the seafloor. Through these fractures fluids from the reservoir ultimately broach into the seawater.
The ability to model these fracture failures will enhance the understanding of wellbore integrity problems induced during loss of control situations and create workflows for predicting possible broaching happening during the post-blowout capping stage early on. Dimensionless plots are used to present fracture initiation for different scenarios useful for drilling and wellbore integrity engineers when making contingency plans for dealing with loss of well control situations.
A New Look at Elastic Collapse
Authors: Mitchell Robert 
Published: February 2020

Abstract
Elastic collapse is an important piece of the tubular collapse formulation in API TR 5C3 and ISO 10400. Elastic collapse is significant because it is independent of the strength of the tubing, e.g. K-55 and Q-125 have the same resistance to elastic collapse. Advanced collapse models, such as Klever (2006), require a thick-wall collapse result as part of their formulation.
What would the effect of a thick-wall have on elastic collapse? There really is no way to tell from the classic formulation. What is needed is a formulation that is based on an elastic solution for a thick-wall cylinder, but that can derive the classic solution for a thin-wall.
The elastic equations for a thick-walled cylinder exist, known as the Kirsch equations. This elastic solution was expanded in a series as a function of t/D. Using terms of order t/D only, the boundary conditions were set, and balance of moments yielded the classical result. This shows that the Kirsch equation is a valid starting point for a thick-wall collapse result.
A new set of physically reasonable boundary conditions was proposed for the Kirsch equation, which were then used to determine the collapse resistance for thick-wall pipe. This result also yielded the classic result in the limit as t/D is small.
Analysis of Torsional Stick-Slip Situations Observed with Downhole High-Frequency Magnetometer Data
Authors: Cayeux Eric , Ambrus Adrian , Øy Lars , Helleland Arvid , Brundtland Svein Tore , Nevøy Harald 
Published: February 2020

Abstract
The use of downhole rotational speed measurements made at 300Hz gives new insight into the conditions under which stick-slip torsional oscillations occur. Observations made with high-frequency magnetometers while drilling two reservoir sections have shown, that for these wellbores, using top-drive speeds below 140rpm leads to severe downhole torsional oscillations, also in off-bottom conditions. Additionally, it was observed that downlinking the rotary steerable system (RSS) initiated heavy stick-slip and that reaming downward had a negative damping effect on downhole torsional stability.
These observations have been compared and partly matched with estimations made with a transient hydro-mechanical model. Some ill-defined information had to be estimated, like the amount of flow diversion during the downlinking procedure, the coefficients of static and kinetic friction along the borehole, or the bit efficiency and aggressivity.
Downhole measurements have shown that when the drill-string is subject to strong stick-slip conditions, the downhole rotational speed changes from stationary to more than 400rpm in just a fraction of a second. It is therefore important to utilize sampling rates that are compatible with such very fast events. In practice, that means several hundred Hertz.
A challenge associated with analysis of downhole high frequency data is time synchronization and drift of clocks between the surface and downhole measurements. After time synchronization and correction, it appears that the downhole rotational movement is delayed by several tens of seconds compared to the actual top-drive speed. This leads to question whether rotating the drill-string off-bottom, typically done in order to break gelled-up mud prior to establishing circulation, has any significant the intended effects deviated wells as torque along the drill-string must be built up.
Direct observations of downhole rotational speed at high frequency help in discovering conditions that were not suspected to lead to large torsional oscillations. This new information can be used to improve drilling operational procedures and models of the drilling process, therefore enabling increased drilling efficiency.
Digital Twins for Drilling Fluids: Advances and Opportunities
Authors: Shirangi Mehrdad G , Ettehadi Reza , Aragall Roger , Furlong Edward , May Roland , Dahl Thomas , Samnejad Mahshad , Thompson Charles 
Published: February 2020

Abstract
In this work, we present our unique technology to develop and apply digital twins for drilling fluids and associated wellbore phenomena during drilling operations. A drilling fluid digital twin is a series of interconnected models that incorporate the learning from geological uncertainty, complexity of drilling fluids and operational parameters to support well planning and real-time operations. We transform data collected throughout the years from all aspects of drilling fluids to value-added applications and include real-world conditions such as operation at extended temperatures and pressures, consideration for sensitive zones with tight control of the equivalent circulating density (ECD), and hole cleaning in deviated wellbores. With the advances presented in this work, cuttings bed height along the wellbore can be determined more accurately, and hence the ‘fluid plan’ together with operational parameters (such as mud flow rate and rate of penetration (ROP)) can be optimized to a higher level. In addition to the cuttings bed, an accurate workflow for monitoring of downhole fluid rheological properties at the rigsite is developed. Through the use of a digital twin, accurate high-pressure high-temperature (HPHT) properties can be determined at the rigsite, which can more easily enable efficient and safe operations, as opposed to lab experiments that are often conducted remotely. We demonstrate the application of automated machine learning (autoML) to represent computational simulations and lab experiments. We also use test datasets and rotating cross-validation methods to ensure accurate and robust results. In both cases, very accurate models were obtained, and point the way for the inclusion of more aspects of the drilling operation including ROP optimization, fluid-loss control, drilling fluid properties management, and power transmission.
Simulation of Immiscible Water-Alternating-Gas Injection in a Stratified Reservoir: Performance Characterization Using a New Dimensionless Number
Authors: Nygård Jan Inge , Andersen Pål Østebø 
Published: February 2020

Summary
Water alternating gas (WAG) is a well-established enhanced-oil-recovery process where gas and water are injected in alternating fashion. Good volumetric sweep is achieved as water and gas target both the oil residing in low and high portions of the reservoir, respectively. Other important features in three-phase hysteretic flow include phase trapping, which is believed to be more strongly associated with the gas phase. With these aspects in mind, a vast simulation study has been performed investigating immiscible WAG injection focusing on mechanisms such as mobility, gravity, injected volume fractions, reservoir heterogeneity, gas entrapment, and relative permeability hysteresis.
The aim of our work is to investigate the interplay between these mechanisms for a model system with sufficient complexity to be of relevance and then scale recovery performance using a new dimensionless number that incorporates the relevant model input parameters. A horizontally layered reservoir is considered where oil is displaced by water and gas alternately injected toward a producer. The model is a modified black-oil type, where hysteresis in the gas phase is modeled using the Land (1968) model for trapping and the Carlson (1981) model for relative permeability hysteresis. It is seen that gravity segregation in uniform models and increased heterogeneity in no-gravity models both lead to lower oil recovery. However, in heterogeneous models, gravity can divert flow from high-permeability layers into low-permeability layers and improve recovery. Hysteresis lowers gas mobility and hence improves gas/oil mobility ratio and reduces gravity segregation. The first effect is always positive, but the second is mainly positive in more uniform reservoirs where gravity segregation has a negative effect on recovery. In heterogeneous reservoirs, reducing gravity segregation can lead to the oil in low-permeability layers remaining unswept.
The newly derived characteristic dimensionless number is effectively a WAG mobility ratio, termed M*, expressing how well the injected-fluid mixture is able to displace oil, whether it is because of fluid mobilities, heterogeneity, or other effects. At a value of M* near unity, optimal recovery is achieved, whereas logarithmic increase of M* reduces recovery.
Prevalence and risk factors of chronic kidney disease and diabetic kidney disease in a central Chinese urban population: a cross-sectional survey
Authors: Duan Jiayu , Duan Guang-Cai , Wang Chong-Jian , Liu Dong-Wei , Qiao Ying-Jin , Pan Shao-Kang , Jiang Deng-Ke , Liu Yong , Zhao Zi-Hao , Liang Lu-Lu , Tian Fei , Liu Zhang-Suo 
Published: February 2020

Abstract
Background : This study was conducted to evaluate and update the current prevalence of and risk factors for chronic kidney disease (CKD) and diabetic kidney disease (DKD) in China.
Methods : From December 2017 to June 2018, a total of 5231 subjects were randomly enrolled from 3 communities in 3 districts of Zhengzhou. CKD was defined as estimated glomerular filtration rate (eGFR) < 60 mL/min.1.73m 2 or urinary albumin to creatinine ratio ≥ 30 mg/g (albuminuria). Diabetic subjects with systolic blood blood pressure > 140 mmHg, albuminuria or an eGFR less than 60 mL/min/1.73 m 2 were classified as having DKD. Participants completed a questionnaire assessing lifestyle and relevant medical history, and blood and urine specimens were taken. Serum creatinine, uric acid, total cholesterol, triglycerides, low-density lipoprotein, high-density lipoprotein and urinary albumin were assessed. The age- and sex-adjusted prevalences of CKD and DKD were calculated, and risk factors associated with the presence of reduced eGFR, albuminuria, DKD, severity of albuminuria and progression of reduced renal function were analyzed by binary and ordinal logistic regression.
Results : The overall adjusted prevalence of CKD was 16.8% (15.8 – 17.8%) and that of DKD was 3.5% (3.0 – 4.0%). Decreased renal function was detected in 132 participants (2.9%, 95% confidence interval [CI]: 2.5 – 3.2%), whereas albuminuria was found in 858 participants (14.9%, 95% CI: 13.9 – 15.9%). In all participants with diabetes, the prevalence of reduced eGFR was 6.3% (95% CI = 3.9 – 8.6%) and that of albuminuria was 45.3% (95% CI = 40.4 – 50.1%). The overall prevalence of CKD in participants with diabetes was 48.0% (95% CI = 43.1 – 52.9%). The results of the binary and ordinal logistic regression indicated that the factors independently associated with a higher risk of reduced eGFR and albuminuria were older age, sex, smoking, alcohol consumption, overweight, obesity, diabetes, hypertension, dyslipidemia and hyperuricemia.
Conclusions : Our study shows the current prevalence of CKD and DKD in residents of Central China. The high prevalence suggests an urgent need to implement interventions to relieve the high burden of CKD and DKD in China.
Assessing the training needs of medical students in patient information gathering; a qualitative study
Authors: Gilligan Conor , Brubacher Sonja , Powell Martine 
Published: February 2020

Abstract
Background Effective communication is at the heart of good medical practice but rates of error, patient complaints, and poor clinician job satisfaction are suggestive of room for improvement in this component of medical practice and education. Methods We conducted semi-structured interviews with experienced clinicians (n = 19) and medical students (n = 20) to explore their experiences associated with teaching and learning clinical communication skills and identify targets for improvements to addressing these skills in medical curricula. Results Interviews were thematically analysed and four key themes emerged; the importance of experience, the value of role-models, the structure of a consultation, and confidence. Conclusions The findings reinforce the need for improvement in teaching and learning communication skills in medicine, with particular opportunity to target approaches to teaching foundational skills which can establish a strong grounding before moving into more complex situations, thus preparing students for the flexibility required in medical interviewing. A second area of opportunity and need is in the engagement and training of clinicians as mentors and teachers, with the findings from both groups indicating that preparation for teaching and feedback is lacking. Medical programs can improve their teaching of communication skills and could learn from other fields s to identify applicable innovative approaches.