bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Body Mass Index on the Relative Revision Rates of Cemented and Cementless Unicompartmental Knee Replacements
Authors: Mohammad Hasan R. , Judge Andrew , Murray David W.
Published: March 2023

Background:

Unicompartmental knee replacements (UKRs) are being performed in an increasingly overweight population. There are concerns that cemented fixation will not last. Cementless fixation may offer a solution, but the relative performance in different body mass index (BMI) groups remains unknown.

Methods:

Ten thousand, four hundred and forty cemented and cementless UKRs were propensity matched. Patients were stratified into 4 BMI groups: underweight (<18.5 kg/m2), normal weight (18.5 to <25 kg/m2), overweight (25 to <30 kg/m2), and obese (≥30 kg/m2). The effect of BMI on the relative performance of UKR fixation groups was studied. Cox regression was used to compare revision and reoperation rates.

Results:

The revision rate per 100 component-years significantly increased (p < 0.001) with BMI for the cemented UKRs. Revision rates per 100 component-years for the normal, overweight, and obese groups were 0.92 (95% confidence interval [CI], 0.91 to 0.93), 1.15 (95% CI, 1.14 to 1.16), and 1.31 (95% CI, 1.30 to 1.33), respectively. This was not observed for the cementless UKR, with revision rates of 1.09 (95% CI, 1.08 to 1.11), 0.70 (95% CI, 0.68 to 0.71), and 0.96 (95% CI, 0.95 to 0.97), respectively. The 10-year implant survival rates for the matched cemented and cementless UKRs in the normal, overweight, and obese groups were 93.8% (95% CI, 89.1% to 96.5%) and 94.3% (95% CI, 90.9% to 96.5%) (hazard ratio [HR], 1.17; p = 0.63), 88.5% (95% CI, 84.2% to 91.7%) and 93.8% (95% CI, 90.2% to 96.2%) (HR, 0.61; p = 0.005), and 90.7% (95% CI, 88.2% to 92.6%) and 91.8% (95% CI, 88.9% to 94.0%) (HR, 0.74; p = 0.02), respectively. There were insufficient numbers in the underweight group for analysis (n = 13). Obese patients had less than half the rates of aseptic loosening (0.46% vs. 1.31%; p = 0.001) and pain (0.60% vs. 1.20%; p = 0.02) in the cementless group as compared with the cemented group.

Conclusions:

Higher-BMI groups had higher revision rates for the cemented UKRs but not for the cementless UKRs. Cementless fixation was associated with reduced long-term revision rates compared with cement fixation in the overweight and obese groups. In the obese group, the rates of aseptic loosening and pain were at least 50% lower in the cementless UKR group.

Level of Evidence:

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
Can the same statistics module be used for service teaching by tailoring the support based on the student’s chosen qualification?
Authors: Calvert Carol , Hilliam Rachel , Steele Emma
Published: March 2023

At the Open University in the UK, students taking undergraduate degree qualifications in areas such as Data Science and Economics are now the largest cohort of students on a second-year undergraduate statistics module, originally written for specialist mathematics and statistics students. This paper outlines an ongoing project to identify how more targeted support could be provided to students who are studying non-mathematics and statistics qualifications. This has involved engaging all the tutors who provided support in the project to create a new way of adapting their teaching styles and tutorial content.  By grouping students who had similar qualification goals together and linking these groups to individual tutors, the new way of working created an atmosphere where students feel able to share their own misunderstandings and see how statistics is useful within their chosen qualifications.
Front Matter
Authors: Mann Tony
Published: March 2023

Front Matter Issue 20-03
Adapting successful online activities for in-person classes - a new challenge
Authors: Russell Ewan
Published: March 2023

Over the past few years, discussion across the sector has rightly been concentrated on how to provide a valuable and engaging online experience for students. The shift back to in-person classes has left many practitioners considering whether there are any lessons from the necessary shift to online teaching that can be applied to in-person teaching. This article will cover experiences stemming from a welcome but unanticipated dilemma - the live online classes for the module in question were extremely popular with students in 2020/21. How should the lecturer approach the return to in-person sessions? Activities for live online classes were designed as consolidation "games" which sought to encourage peer learning and discussion. The positive response to these activities encouraged the lecturer to pursue a flipped classroom model for the 2021/22 academic year.  This article will discuss the various considerations when planning the transition to in-person classes for the 2021/22 academic year. In addition to reflections from the lecturer on the experience, this case study will also present preliminary findings from a formal study aiming to determine whether the activities have any positive effects on student confidence. Specifically, the study will investigate student confidence in areas such as working with peers, preparing for a class using online resources, and communicating mathematics in a written format.
Front Matter
Authors: Owen Alun
Published: March 2023

Front Matter for 21(1)
Editorial
Authors: Owen Alun
Published: March 2023

Editorial for 21(1)
Real-Time Anomaly Detection Methodology for Drilling Fluids Properties
Authors: Borges Filho Moacyr Nogueira , Mello Thalles Pereira , Scheid Cláudia Miriam , Calçada Luís Américo , Waldman Alex Tadeu , Teixeira Gleber , Martins André Leibsohn
Published: March 2023

Online drilling fluid measurement technologies are popping up in the industry as an essential tool for drilling automation, while online density measurements are widespread, the availability of rheology measurements is increasing fast and additional properties (o/w ratio, solids content, electrical stability, filtration, etc) appear as field trials. This article presents the concept of a supervisory/ advisory systems dedicated to support the detection of abnormal events and to provide guidelines for fluid treatment actions.

The proposed methodology consisted of two stages: experimental data acquisition in a flow loop and data processing for the validation of the algorithm. In the data acquisition stage, multiple properties of the drilling fluids were continuously measured by using automatic sensors. In the second stage, the drilling fluid's properties were processed in a fault detection algorithm. The algorithm used Principal Component Analysis (PCA) to train the process model through the calculation of the principal components of the steady state of the fluid, which represents the healthy state of the drilling fluid.

Once the process was trained, the algorithm monitored new data samples obtained in the data acquisition stage and compared them to the trained model by calculation of the mean square prediction error (MSPE) of the model and the T² of Hoteling. Persistent changes in MSPE and T² values indicated that an anomaly was occurring in the drilling fluid. The new methodology was validated based on the data obtained in a flow loop where fluid properties were monitored using online sensor under different operational conditions. The algorithm was able to detect faults and anomalies in the drilling fluid even identifying the source of the anomalies through the decomposition of the MSPE and T² statistics. The proposed algorithm performed well in real-time conditions, pointing out that it can be used as a diagnostic tool in-field oil well drilling operations.
Mitigation of Drilling Dysfunction: Data Analysis and Physical Modelling Shine a New Light on HFTO
Authors: Johnson Ashley , Balka Muhammad Sarfraz , Bhoite Sameer , Crerar Paul , Simon Aaron , Quinones John
Published: March 2023

High frequency torsional oscillation (HFTO) is still one of the most disruptive drilling dysfunctions we encounter. Vibrations are observed with fundamental frequencies as high as 400 Hz and torque sweeps from 0 to 7000 lbf.ft. The resulting damage includes drilling collar cracking, damaged electronics, and backed-off tools.

By measuring the amplitude and the fundamental frequency of this dysfunction, we present a model to characterize its drivers. This is a critical step in defining the mitigation strategies.

Although there are a multitude of drilling dynamics tools deployed to record these effects, the nature of HFTO, with large amplitude harmonics on top of the fundamental modes, means that simply deploying a sensor and data acquisition tool is not sufficient to characterize the dysfunction. There are critical requirements for these recorders in terms of sampling frequency and anti-aliasing filters, without which a unique interpretation of the dynamics is impossible.

We have a next-generation MWD tool that will detect HFTO. By calculating a fast fourier transform (FFT) in real time, it will also deliver a log of HFTO throughout the operation, that can be delivered to the driller in real time.

With this we have developed and demonstrated a suite of mitigation strategies. These are specific to the type of HFTO detected and include increasing the collar speed or reducing the WOB (for Type 2) or reducing the rate at which the WOB is increased (for Type 1). We also show that by changing the contact points on the tool to reduce the side force (friction), the operator can mitigate the Type 2 HFTO and achieve a considerable improvement on this drilling dysfunction and its impact.
New One BHA Solution for High Dogleg Severity Curve and Lateral Drilling
Authors: Noel Anan , Mendoza David , Li Denis , Perez Freddy , Andreasen Greg , Tang Kien Hoe , Buitrago Oscar , Sardjono Ryan , Oluwadare Sola
Published: March 2023

The highly productive Permian Basin requires wells with high dogleg severity (DLS) curve and long lateral sections. After many years of development and participation by all major industry players, most 8.5in size wells are still being drilled using two bottomhole assemblies (BHAs); one for the curve and a second for the extended lateral section. This increases cost, time, and risks. With development of our new solution, curve and lateral sections of Permian wells can now be consistently drilled in one run.

Using in-house digital modeling and dynamic drilling simulation software of the complete drilling system and complex lithology profiles, design attributes were evaluated for directional performance before initial prototypes were created. These models increased efficiency and cost savings in the design process.

Analysis revealed that shortening the distance from the RSS pad actuators to the bit (L1), increases the build-rate capability, increases the DLS output in the curve section, and provides tight trajectory control in long laterals. The system design also has a proprietary bit box connection and polycrystalline diamond compact (PDC) cutters on the bias unit.

Prototype testing was done on high-DLS curve and lateral wells with major operators delivering wells per client requirements. The new solution successfully landed high DLS curve sections in 14 wells. The solution achieved a new milestone of delivering the 8.5-in curve on target and much faster than the conventional motor in the same application. After the curve sections the same BHA drilled into the long lateral section without making a trip between the curve and lateral sections. Several records were broken in some of these 14 wells, including 19% more daily footage than the previous record. Almost all these wells were also drilled using a remote operations center utilizing latest digital capabilities, reducing onsite footprint. Based on the most conservative figures from field test results and projected usage, the increased efficiency and faster well delivery time can significantly impact sustainability, reducing CO2 emissions per well drilled by this new solution.
Numerical Simulation of Production Declines in Tight Naturally Fractured Carbonate Reservoirs
Authors: Altman Raphael , Tineo, Roberto , Afifi Mostafa
Published: March 2023

Tight naturally fractured carbonates are "hybrids" between conventional and unconventional reservoirs and are becoming increasingly important in an operator’s portfolio. Wells produce if natural fractures are present and not damaged. Otherwise, large stimulation jobs are required. The steep initial production declines in these reservoirs are influenced by matrix-fracture transients, near-wellbore damage / production impairment, and factors that that cause the natural fracture conductivity to change (decrease) during the production. In this paper we focused on the simulation of the matrix-fracture transient.

Our work focused on reservoir simulation of naturally fractured carbonates with matrix permeabilities in the 0.0001 to 0.1mD range. We used our existing knowledge from simulating these reservoirs to build conceptual models for modelling transient behavior in these reservoirs. We considered dynamic models with both structural and unstructral grids to understand the impact of these in modelling production transient effects. The structural grid simulations used 100m by 100m gridcells with dual porosity, while the unstrucutral grids were built using a single porosity (SP) and complex gridding with variations in grid size to capture natural fractures.

History matching production data using conventional simulation models was challenging because families of natural fractures are typically not uniform as we move away from the wellbore and large structural grids will have difficult capturing this discontinuity. In these scenarios we have seen that dual porosity structural grids will provide too much pressure support causing the well’s simulated bottom hole pressure to be overestimated. Conversely, SP models with complex unstructured grids gave much better results. They were effective in matching the data after the initial production decline because of greater accuracy in accounting for the matrix contribution. They also provide a more accurate representation of discrete fracture network models as opposed to an upscaled approximation.

Production decline rates in tight naturally fractured reservoirs can be highly variable and have a strong impact on EUR and project economics. Therefore, understanding the mechanisms that influence these declines and modeling them accurately through fit-for-purpose dynamic simulations as shown in this work, are an important step for optimizing the development of these reservoirs.
Integrated Rock Physics Model to Predict Sweet Spots in an Unconventional Jurassic Carbonate Source Rock
Authors: Mohammed Ammar , Altowairqi Yazeed
Published: March 2023

The exploration of unconventional hydrocarbon resources mainly targets the tight source rock reservoirs where hydraulic fracturing is needed for an effective hydrocarbon production. This project aims to predict new areas with high hydrocarbon production potential that can be effectively stimulated/fractured, known as sweet spots, in a tight Jurassic carbonate source rock.

A rock physics model was developed to link the seismic properties to rock properties of the target formation. Three main rock properties are used in this study to define the sweet spots: total organic content (TOC), Young's modulus (YM) and Poisson's ratio (PR). TOC is a geochemical property that is related to the production potential and is obtained in the laboratory from core, while YM and PR are rock elastic properties that are related to the frackability and are obtained from density and sonic (compressional and shear) logs. Sweet spots are generally characterized by high values of TOC, high values of YM and low values of PR. Using well data, these three properties were cross-plotted against two derivative elastic properties (lambda-rho and mu-rho) that are calculated using sonic (compressional and shear) and density logs to obtain a linear relationship. Lambda and mu are measures of incompressibility and shear rigidity, respectively, while rho is density. Cutoffs of lambda-rho and mu-rho were chosen to represent the sweet spots. The distribution of sweet spots in the study area was then mapped using a rock physics model that is built by integrating two inverted 3D seismic volumes; lambda-rho and mu-rho.

Results show that sweet spots are characterized by low values of lambda-rho and mu-rho, and are well distributed in the study area. In addition, results show that TOC has an inverse relationship with frackability which means that there should be a balance between reservoir quality and completion quality when targeting sweet spots for more economical hydrocarbon production.
Investigation of Thermal Fracturing and Permeability Enhancement in Tight and Shale Rocks During In-Situ Heating
Authors: Wei Zijian , Sheng James , Zhou Yicheng
Published: March 2023

Thermal fracturing could lead to a remarkable enhancement in rock permeability, which is quite crucial for unconventional reservoirs. This study focuses on assessing the capacity of thermal fracturing and permeability improvement in tight and shale reservoirs, and mathematically characterizing the essential relationship between them during the in-situ heating (ISH) process. For this purpose, ISH treatment, pulse-decay permeability (PDP) testing, and computerized tomography (CT) scanning for core samples from tight sandstone and shale reservoirs was carried out in real-time on a self-designed apparatus to explore the dynamic evolutions in permeability and thermal crack during the ISH process. Experimental studies reveal that only the temperature exceeding the critical value of 500 °C, some thermal cracks propagate quickly on a small scale and form a complicated crack system in situ, therefore causing a permeability increment to 11.23 and 29.82 times. Synergizing the mechanism analysis of thermal activity and geochemical data, the large difference in mineral thermal expansion coefficient (DTEC) arising from α/β phase transition in quartz (α/β-QPT) at 573 °C is demonstrated to be the most critical mechanism for thermal fracturing in two rocks. On the basis of crack geometry, thermo elasticity, fracture mechanics, and percolation theory, a permeability model is established. α/β- QPT is fully proven as a dominant reaction through incorporating it into our model and getting preferable permeability matching. Practical guidance and prospect for the actual variations in physical properties of ultra-low permeability reservoirs in situ stimulated by thermal recovery could be provided by this work.
Oil Pipeline Leak Detection Using Deep Learning: A Review on POC Implementation
Authors: AlAzri Ahmed , Alkaabi Sultan , AlZakwani Saud , Altamimi Fadhil , AlMamari Maadh , AlSulaimani Mohammed
Published: March 2023

Oil and gas production operations are key sources of environmental pollution which exposing the people and effect the human activity in the world. Petroleum Development Oman (PDO) is the leading exploration and production oil and gas companies in the Sultanate of Oman which lead to avoid adverse health effects in Oman. Oil pipline leakes could be undetected for a long time. However, the precise methods could help improve the oil leaking detection response process in channel required resources with more effectively to be concerned regions. Existing Synthetic-aperture radar (SAR) approaches are limited by their algorithm complexity which difficult to work with imbalanced data sets, doubts to select optimal features, and the relatively slow detection. Using deep learning approach could speed up the oil detection. convolutional neural network U-Net segmentation models based on oil leaking detection could be achieve promising automated results. However, there are insufficient features extraction due to loss of target to detect oil leaking or shadows in drone images that commonly appear in various size, shapes, and brightness levels, which the images that captured under many conditions. To overcome all these limitations, we utilized a deep learning model named Pyramid Scene Parsing Network (PSPNet). The proposed algorithm can probabilistically detect oil leak from drone imagery at the frequency of data collection. Thus, PDO Oman could reduce millions of Dollars when direct action from operators that received a quick true alarm of oil leaking. The effectiveness of the proposed method is demonstrated through A proof of concept (POC) based on a realistic dataset that collected history data that our deep learning algorithms achieved the perfect predict the oil leaking before occurs.
Automated Geomechanics Modelling Workflow Supports Real-Time Decision Making and Risk Mitigation in Challenging Horizontal Wells
Authors: Dorantes Arnott , Franco Nata , AlSameen Rawan , Amer Syed Mohamed , Karpfinger Florian , Corona Mauricio , Levario Jesus , Abdul Kader Mansoor
Published: March 2023

Geo-steering a horizontal well to the pay zone is commonly deployed across the globe but combining it with real-time geomechanics is very advantageous under challenging wellbore conditions. The normal practice is to have the geomechanics expert receiving the measurements data, updating the pre-drill model and giving recommendations. This paper will describe efficiency improvements brought by an innovative workflow of automation of the geomechanics model in real-time from the remote operations center.

Horizontal drilling can be very challenging, especially if the wellbore stability starts deteriorating. This can hugely impact operations, such as downhole fluid losses, extensive back-reaming, stuck pipe incidents and in extreme cases, sidetrack, and re-drilling the section might be needed. To further improve support to drilling team, a thorough review of the geomechanics process was carried out. A performance improvement opportunity was identified in the way real-time geomechanics was conducted in the project and the potential benefits of a more automated process would bring.

The Automated Geomechanics Modelling Workflow enabled real-time updates of the geomechanics model when logging-while-drilling (LWD) is transmitted to a Real-time Operations Center (RTOC). The pre-drill geomechanics model was built for a given wellbore trajectory by experts, shared with the RTOC and connected to real-time LWD drilling data. The model was automatically updated while drilling and made available to the RTOC specialist, who identified the breakout zones from caliper log, and porosity trend from density image, and could initiate immediately the communication protocol with drilling operations team. The same information was also shared in real-time with geomechanics expert for interpretation and recommendations.

Enabling real-time update of the geomechanics model accelerates the interpretation, recommendation, and reaction from both geomechanics expert and drilling team. Identification of critical intervals by changes of trends of hole enlargement, geological failure or porosity can be immediately communicated to act accordingly. The drilling, tripping and fluids practices can be adjusted on spot, and the main impact is the minimization of wellbore instability and stuck pipe incidents. The benefits from the automated geomechanics modelling are numerous, including safe drilling operations at lower non-productive time, better hole and reservoir quality, and cost saving opportunity.

This workflow is a breakthrough on how wellbore instability is monitored in the wells in the gas project, creates a unique interaction of geoscience and drilling disciplines to monitor hole condition and to manage risks. This work will benefit other operators and service companies in the region to deploy similar process, driving efficiency while lowering well construction costs.
Hydraulic Fracturing of Highly Azimuthally-Deviated Horizontal Wells Enhanced by Wellbore Notching
Authors: AlTammar Murtadha J. , Alruwaili Khalid M. , Al-Dakheel Hussain K. , Aidagulov Gallyam , Abbad Mustapha
Published: March 2023

Multistage hydraulic fracturing is an effective stimulation method as it opens communication between the wellbore and larger reservoir volumes. Nevertheless, there are cases where the formation cannot be fractured within the completion pressure limitations. This problem can be addressed by placing weak points, such as perforations and notches, so fractures could initiate there at lower pressure. This paper discusses this remedy applied in horizontal open holes that are highly deviated from the minimum horizontal stress.

In this study, cement grout block samples (24×18×18 in.) were prepared to cast precisely weak points and boreholes. The cured blocks were completed with 1.25×12 in. (diameter × length) long openhole section in the center. Hydraulic fracturing experiments were conducted inside a polyaxial load-frame to simulate the wellbore under strike-slip stress regime. Boreholes of two azimuthal deviations from minimum stress were considered: 0° (straight) and 35° (inclined). For each, two weak points were tested: V-notch and single perforation. Fracturing fluid was injected at low rate into the borehole. The obtained injection pressure trends were interpreted with open holes cored out to analyze the initiated fractures.

Both fracture initiation pressure (FIP) and fracture breakdown pressure (FBP) (i.e., the maximum) were selected for comparisons, as the former is not influenced by the fracture size nor by the fluid-rock interactions during propagation. FIP was estimated indirectly as deviation from linearity in the borehole injection pressure trend. The results revealed remarkably that the notch significantly reduces FIP and FBP, compared with the reduction by the single perforation, in both the straight and inclined boreholes. Each of the weak points delivered very similar FIP and FBP in straight and inclined boreholes. All the weak points initiated a fracture that is transverse to the borehole axis, which provides the advantage of 360° communication with the reservoir. It was noticed that the inclined borehole with one perforation initiated a transverse fracture with a distinct angle from the preferred plane. To summarize, even if the wellbore is drilled at a high angle of deviation from the minimum horizontal stress in the strike-slip regime, the notch still outperforms perforation in terms of FIP reduction.

This work presents experimental comparisons of hydraulic fracturing pressure reductions caused by notches and single perforation holes placed in horizontal open holes aligned with and highly deviated from the minimum horizontal stress. The experiments showed how notches outperform conventional perforation, and by this, provide insights for stimulation design of horizontal wells where trajectories were influenced by factors other than stimulation, such as geology and reservoir location.
A Simulator for Minimizing Openhole Breakdown Pressure through Notch Shape Optimization
Authors: Han Yanhui , AlTammar Murtadha J. , Alruwaili Khalid M.
Published: March 2023

Wellbore breakdown pressure is an important parameter utilized in hydraulic fracturing stimulation design. Because of the stress concentration around wellbore and formation strength, the borehole breakdown pressure is often much higher than the minimum confining stress plus tensile strength. To overcome the barrier of the stress concentration and locate the fracture initiation spot, well is often perforated or notched before the hydraulic fracturing treatment. Qualitatively, it is well observed and accepted that perforations and notches can reduce the breakdown pressure; quantitatively, however, there is a demand for reliable and accurate method to predict how much various perforating or notching configurations can help reduce the breakdown pressure. In this paper, a computational mechanics simulator is developed to predict the breakdown pressure inside a notched wellbore subjected to loading of in-situ stresses. The simulator can predict the breakdown pressure for a well with a given notch stimulated with fluid injection. It can also be used to optimize the design of a notching tool which can minimize the breakdown pressure during hydraulic fracturing. The simulator is applicable to cases of both longitudinal and transverse notches.
Toward Combining Multi Seismic Attributes, A Novel Machine Learning Approach
Authors: Alshuala Mustafa
Published: March 2023

The objective of this study is to develop and examine a machine learning model that combines multiple seismic attributes in a way that preserves all the features of the combined attributes with, hopefully, better resolution and efficiency than the conventional seismic attributes integration method. We used the Auto- Encoder algorithm, which is a neural network method. It consists of two identical networks known as encoder and decoder. Auto-Encoder was initially developed to compress data in the encoder part, and then the same structure is used to decompress data in the decoder part. Our interest is in the output of the encoder which is the reduced version of the input.

For fault and fracture detection, we examined and compared the results of Octree as a conventional multi- seismic quantization method and Auto-Encoder as a new machine learning technique. The study used five 3D volumes, one for each of the five attributes Raw Data, Skeleton, Detect, Negative Curvature 1 and Negative Curvature 3. Each 3D volume is divided into 100 slices. One slice per attribute (i.e. a set of five slices) comprise an input dataset to the encoder. The process is iterated 100 times to obtain 100 slices of encoded attributes.

The result of the Auto-Encoder solution is compared with that of Octree. The Auto-Encoder accurately preserved the three faults from the input attribute images whereas Octree preserved only one fault. Additionally, the details of the fractures in the Curvature attributes are also preserved with more clarity in the Auto-Encoder solution than Octree. The machine learning technique (Auto-Encoder) preserves all the features (i.e. faults and fractures) from the combined attributes and shows better resolution than Octree. It can also combine unlimited number of attributes whereas Octree is limited to eight attributes only.
A Workflow to Estimate Critical Drawdown Pressure Utilizing 1-D Geomechanics Modelling
Authors: Qatari Ammar
Published: March 2023

The active mobility of sand particles during the production phase has put extra burden on the efficiency of hydrocarbon extraction for both oil and gas. It plays a significant role on completion design during the drilling phase. Minimizing the effect of sanding has been a major topic to tackle due to the added operational costs and time associated. Unconsolidated sand reservoirs are vastly affected worldwide due to the nature of sand particles accompanying hydrocarbon during the production phase. Sand production poses potential risks for surface and subsurface equipment within the completion design. The objective of this paper is to estimate and quantify the potentials of sand production and wellbore instability using 1-D Mechanical Earth Model (MEM). A clear workflow of the utility of raw petrophysical and 1-D geomechanics modelling data is showcased to aid production and completion operational personnel.

Excessive stress concentrated around the wall of a borehole can cause the release of sand particles into the hydrocarbon stream. This process poses risks for drilling and completion operations as it affects the productivity of a well along with potential equipment damage. Unconsolidated sand reservoirs are prone to rock failure which induces the mobility of sand particles. Stress orientation regimes are properly captured by assessing the orientation of current petrophysical data. Acoustic data is also reviewed for proper in-situ rock strength property calculation. Formation pressure testing is vital to the process to estimate pore pressure gradients. Once MEM is finalized, Critical Drawdown Pressure (CDDP) is analytically calculated using the linear elastic methodology to predict sand production.

The use of 1-D MEM sand management analysis to predict critical drawdown pressure is vital to avoid equipment damage and production limitations associated with sand production in a weakly consolidated reservoir. A workflow to produce an in-depth critical drawdown pressure analysis captures the changes that might occur for a perforation completion over time as it undergoes depletion. A representation of sand potential prediction and critical bottom-hole flowing pressure as a function of reservoir pressure is to be illustrated in a single depth format which allows for sensitivity analysis.

This paper examines the direct impact of the analytical estimation of critical drawdown pressure as a guide to predict the potentials of sand production intervals within a certain reservoir. The mechanical properties, petrophysical raw data, and depletion status are the ingredients to produce a thorough analysis to guide drilling, production, and completion personnel to minimize sand production effects operationally. Further improvement to the model can be made by the integration of production data and reservoir properties that are captured over time.
Strengthening of Carbonate-Based Formation Rocks Natural, Sustainable Materials
Authors: Alarawi Abeer A. , AlTammar Murtadha J. , Alruwaili Khalid M. , Alrubeh Jasim A.
Published: March 2023

Generating hydraulic fractures with good conductivity is essential for well productivity in unconventional formations. However, hydraulic fractures gradually lose conductivity with hydrocarbon production as fracture surfaces creep closer due to proppant embedment or failure of fracture asperities under increasing effective in-situ stresses and high temperatures. This work proposes adding a widely available, natural-based metal carbonate (MC) to fracturing treatments in carbonate formations to make fractures mechanically harder and enhance long-term well productivity. An MC-based formula of varying concentrations was prepared and tested on homogenous carbonate core samples. Two solutions were formulated by mixing 10 and 20 gm of MC powder in 100 ml of organic solvent. The core samples were immersed in different solutions for seven days, and the samples were thoroughly characterized before and after exposure to the solutions. Rebound hammer tests were also conducted to show the effect of the solutions on the samples’ mechanical properties, such as Young's modulus and compressive strength. The test results show that the physical properties such as dry weight, bulk density, and bulk volume of all core samples increased noticeably after treatment, reflecting the success of the precipitation reaction and the penetration of used MC into the bulk of the rock samples. Rock treatment with the 10-20 gm-powder solution led to a significant enhancement of the samples’ mechanical properties, where Young's modulus (E) and Unconfined Compressive Strength (UCS) were observed to increase by up to 34% compared to untreated rock samples. Rock hardening in fracturing applications is a relatively new concept. Compared to the consolidation additives in the literature, the proposed MC formula is ubiquitous, widely available, and inexpensive. Lastly, the MC formula is also a by-product of a few oilfield operations, making it a sustainable solution to industrial waste in the oil industry.
Role of Geomechanical Modeling and Analysis in Sand Management and Control
Authors: Ashtiani Abdi Hadi , Alward Wassem
Published: March 2023

Sand production erodes hardware, blocks tubulars, creates downhole cavities, and must be separated and disposed of on the surface. Completion methods that allow sand-prone reservoirs to be exploited often severely reduce production efficiency. The challenge is to complete wells to keep formation sand in place without unduly restricting productivity.

To avoid sands, the dependence of rock failure on drawdown must be analyzed properly using geomechanical methods. A wide range of methods has been used in the past for sand production prediction. Modeling and designing bottom hole features, mostly perforation geometry and wellbore trajectory, based on sand body mechanical properties and near wellbore stresses is the key to mitigating or eliminating sand production issues in clastic reservoirs.

In this paper, we present a full-scale geomechanical analysis and modeling using a 1D mechanical earth model (elastic and strength properties and stress field) to address the main challenges and the root causes of sanding in clastic reservoirs in South of Iraq. The analysis includes the following:

Critical Draw Down Pressure (CDPP) profile in different levels of reservoir depletion resulting in sand production. CDPP is the minimum borehole pressure for which no solids are produced from a sand reservoir. Well inclination sensitivity analysis and its role in sand production Sand grain size sensitivity analysis and its role in sand production Unconfined compressive strength (UCS) as rock strength indicator sensitivity analysis and its role in sand production Perforation direction sensitivity analysis relative to stress directions, and its role in sand production.

We present a case study to show how the methodology and workflows have been applied to identify sand-producing intervals for different completion scenarios, determine the optimum drawdown conditions for sand-free production and adjust completion configuration to obtain sand-free production from a clastic reservoir in the South of Iraq.
Pattern Recognition-Driven Automatic Drainage Region Mapping to Accelerate Reservoir Simulations
Authors: Shubbar Ahmed , Maucec Marko , Moriwawon Babatunde
Published: March 2023

History matching is widely considered as the most time- and resource-consuming phase of reservoir simulation modeling. Even with the advent of modern, computer-assisted, history matching methods, the dynamic calibration of large-scale simulation models represents a considerable computational undertake. The challenges become even more pronounced with incorporation of subsurface and production uncertainty.

This paper outlines a step forward in acceleration of reservoir simulation studies by applying a split/merge approach constrained by no-flow boundary drainage region. The method transforms the history-matching process into an accelerated progressive sequence of dynamic model updates in time and space. Each segment defined as distinctive drainage region, the boundaries of the drainage regions are mapped based on no-flow conditions. Each segment is dynamically calibrated and history matched simultaneously in parallel. Lastly, the segments are merged back to reconstruct the original model to run the prediction phase.

The detail of the workflow is described, as well as the implementation of the workflow in a synthetic model. A comparison between the conventional approach and the new approach is discussed. Recommendation and a way forward are shared to capitalize on the accelerated method for future reservoir studies.
Solving the Low Injectivity Challenges in Hydraulic Fracturing Tight Gas Reservoirs - Case Histories Review
Authors: Yudin Alexey , Nurlybayev Nurlan , Al-Jalal Ziad
Published: March 2023

Fracturing in tight and deep gas formations can be challenging when near-wellbore stresses reduce injectivity. The drilling fluid may contribute to a near-wellbore damage, and this will exaggerate the rock breakdown limits additional to the high local stresses. The paper will present case history review of different techniques in addressing low injectivity in tight gas wells to minimize delays in operations and associated risks.

Different stimulation techniques are utilized to enhance the production from tight gas carbonates reservoirs, including multistage fracturing completions and techniques as plug and perf, sliding sleeve systems, coiled tubing conveyed stimulation systems, etc. regardless of completion method type, the damage level could still be present, in addition to the stress cage around the wellbore, hence the injectivity can be very challenging. There are frequent cases, when during the injection stage the pumping rate barely reaches 1 bpm at maximum allowed pressures. And there are several solutions, such as acid squeeze treatment conveyed by coiled tubing, abrasive jet perforations, bullhead acid spearhead stage at lowest pumping rate, completion fluid solvents and others. Each method has different criteria for applicability, depending on the technical scenarios and require critical decision-making process during the operational performance.

Due to damage presence in the near-wellbore zone, the injection rate was observed to be below 1 bpm and surface pressure could be reaching the completion limitations, and the possibility of job cancellation becomes high. Therefore, proper solutions were required to improve the injection prior to fracturing treatment. The case study showcases some statistical analyses of solving the challenges concerning the near-wellbore damage and improving the injectivity prior to main stimulation treatment.

The case studies review will help optimizing the technical decision when injectivity challenges occur in tight gas reservoirs and could be used as a reference in other HPHT fracturing projects.
Managing Adequate Gas EOR for Unstable Asphaltene Stability Field - Asphaltene Flow Assurance Pre-Risk Assessment Case Study for CO2, Enriched Gas, and Lean Gas Options
Authors: Tange Masaaki , Hiraiwa Takeshi , Tareq Khlaifi Khuloud , Sakurai Risa , Bahri Sami , Abed Abdalla Abdelfattah , Uematsu Hiroshi , Makishima Ken , Inokuma Yuto , Sawata Masaru , Alkaabi Sultan Hamdan , Yonebayashi Hideharu
Published: March 2023

To enhance oil production (EOR) in tight carbonate oil reservoirs, gas EOR can be a promising option from injectivity viewpoints compared with water-basis chemical EOR. CO2 is the most attractive injectant with higher recovery factor expectation while responding to the recent decarbonization demands; however, CO2 is also known to accelerate asphaltene flow assurance risks. In actual fact, the previous work revealed a high asphaltene flow assurance potential risk for CO2 injection. Therefore, a further pre-risk evaluation case study was conducted to extract adequate type of potential injection gas among CO2, enriched gas, and lean gas.

This study focused on subsurface gas-induced asphaltene risks in an offshore heterogeneous oil field showing unstable asphaltene colloidal instability index (CII=2.2), where a crestal lean gas injection has been applied without any asphaltene issues. A single phase bottomhole sample was taken from appropriate candidate well keeping representative reservoir fluid in a clear asphaltene-gradient field: i.e., lesser asphaltenes in shallow depth but more in deeper section.

As a result of this study, no asphaltene onset was detected from original reservoir fluid while asphaltene onset pressures (AOPs) were detected from mixture of reservoir fluid and CO2 or enriched gas or lean gas at two temperatures representing reservoir and wellhead conditions. Experimental gas mixing ratios were carefully designed to distribute the AOPs broadly in operating pressure range: from in-situ reservoir and near wellbore to bottomhole, for securing higher numerical model accuracy by avoiding data extrapolation. A numerical model, calibrated with experimental outputs, predicted risk magnitude by reservoir depth. A comparative analysis revealed higher asphaltene precipitation risks in CO2 injectant than enriched gas and lean gas. Finally, asphaltene particle/aggregate size were discussed for formation damage risks. The visually measured asphaltene solid particle size varied from 1-10 μm for CO2 injection and 1-4 μm for enriched gas injection while no visible for lean gas. From the past injection water quality analysis, the reservoir has threshold particle size between 0.5-1.0 μm to cause plugging. Therefore, it was concluded that risk of asphaltene-induced formation damage is lower in enriched gas injection compared with CO2 injection. In general, higher oil recovery is expected by order of CO2, enriched, and lean gases.

In conclusion, even CO2 EOR is being attractive rapidly from decarbonization viewpoints, the study highlights an importance of balancing business case opportunity and risk from the aspect of injection gas-induced asphaltene flow assurance potential risks.
A Breakdown Pressure Prediction Model with Borehole Geometry Effect Considered
Authors: Han Yanhui , Almutawa Mustafa , Chen Shengli
Published: March 2023

Recently a set of engineering charts have been developed for the time-dependent stress and pore pressure responses at the wellbore surface under the ramp-type, finite-length fluid injection conditions, based on a semi-analytical solution with the use of Laplace-Fourier integral transform technique, to facilitate the prediction of borehole breakdown pressure for hydraulic fracturing operating practice. The charts were presented in a non-dimensionalized form to cover a wide range of borehole/rock parameters, which, in combination with the approximate solution for the impermeable borehole drilling problem, can be conveniently utilized to gain a rapid estimation of breakdown pressure. In this work, a borehole breakdown pressure prediction software was developed to generalize the applications of these engineering charts. Firstly, the engineering charts for an arbitrary borehole interval length-to-radius ratio are constructed from these charts by interpolation or extrapolation. Secondly, the breakdown pressure for a given borehole, in-situ condition, formation properties and pumping schedule, is looked up automatically with higher accuracy and faster speed than the method adopted in previous work.
Restoring Well Integrity: The Innovative Design of Thermally Activated Resin in a Sour Environment
Authors: Khan Danish Ahmed , Acuna Manuel Centeno , Hasan Salah Islam , Merino Lizeth , Chica Pablo , Hussein Ahmed Mudheher , Al Fakih Abdulqawi , Alo Rasho , Normann Svein
Published: March 2023

Loss of Well Integrity introduces the risk of uncontrolled release of formation and well fluids throughout the lifecycle of well. In a Southern Iraq field, one of the wells presented a rather unique challenge that when testing the production liner to 3000 psi, the pressure immediately dropped, and therefore, the integrity of the entire well was compromised. Pressure testing confirmed that the leak was through a liner coupling and USIT log showed that there was almost no cement bond behind the liner in the leak zone. The challenge was to find a safe and cost-effective solution to isolate and repair the hair-line leak, but also to find a solution that caters to the sour environment of the field itself, and that can last for the production lifespan of the well. A tailor-made thermally activated resin was designed in the lab to build a high compressive strength and durability and was not prone to cracking as the target treatment interval would be subjected to a pressure test as part of the conformance analysis.

Conventional approaches to repair this type of leaks, such as microfine cement, are prone to deterioration and cracking over time by which well integrity is compromised. Comparing mechanical barriers such as casing patches or straddle packers were considered as backup solutions as they interfered with production requirements. Downhole Circulating temperature was carefully modeled to avoid premature setting while pumping or delayed gelation of resin once exposed to bottom hole static temperatures. The pill was then squeezed into the leak path utilizing the Bradenhead methodology and the squeeze pressure was maintained throughout the duration of the gel time of the engineered design and the plug was then allowed to fully cure. Once cured, the plug was tagged where expected and milled down to just above the bridge plug. The target treatment interval was then subjected to multiple successful pressure tests confirming the restoration of well integrity.