bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical modeling of lignite combustion in a bed: A one-dimensional approach
Authors: Miljkovic Biljana , Pesenjanski Ivan
Published: December 2015

Thermal plant design and choice of suitable technology requires the
understanding of the fuel thermo-chemical properties. The reactions that
consist of different phases may be approached in two ways. One is to
determine the kinetics of each individual reaction and its interaction with
the environment. The other method is to use an integrated approach, when,
based on the results, the summary formula for the behavior of combustible
matter is obtained. This is an empirical approach. Despite possible
objections, particularly regarding its accuracy, the narrow range of
applicability etc., the attractiveness of this procedure is evident due to
direct results, simplicity and far lower costs to the experiment. That is the
reason why this paper focuses on determining the kinetic parameters of the
integrated model of group reactions that are part of the combustion of
lignite at low temperatures. The paper develops a simple mathematical model
of the combustion process for lignite in bed which is then confirmed by
modeling the experimental results.
Weight Loss Decreases Excess Pancreatic Triacylglycerol Specifically in Type 2 Diabetes
Authors: Steven Sarah , Hollingsworth Kieren G. , Small Peter K. , Woodcock Sean A. , Pucci Andrea , Aribisala Benjamin , Al-Mrabeh Ahmad , Daly Ann K. , Batterham Rachel L. , Taylor Roy
Published: December 2015

OBJECTIVE

This study determined whether the decrease in pancreatic triacylglycerol during weight loss in type 2 diabetes mellitus (T2DM) is simply reflective of whole-body fat or specific to diabetes and associated with the simultaneous recovery of insulin secretory function.

RESEARCH DESIGN AND METHODS

Individuals listed for gastric bypass surgery who had T2DM or normal glucose tolerance (NGT) matched for age, weight, and sex were studied before and 8 weeks after surgery. Pancreas and liver triacylglycerol were quantified using in-phase, out-of-phase MRI. Also measured were the first-phase insulin response to a stepped intravenous glucose infusion, hepatic insulin sensitivity, and glycemic and incretin responses to a semisolid test meal.

RESULTS

Weight loss after surgery was similar (NGT: 12.8 ± 0.8% and T2DM: 13.6 ± 0.7%) as was the change in fat mass (56.7 ± 3.3 to 45.4 ± 2.3 vs. 56.6 ± 2.4 to 43.0 ± 2.4 kg). Pancreatic triacylglycerol did not change in NGT (5.1 ± 0.2 to 5.5 ± 0.4%) but decreased in the group with T2DM (6.6 ± 0.5 to 5.4 ± 0.4%; P = 0.007). First-phase insulin response to a stepped intravenous glucose infusion did not change in NGT (0.24 [0.13–0.46] to 0.23 [0.19–0.37] nmol ⋅ min−1 ⋅ m−2) but normalized in T2DM (0.08 [−0.01 to –0.10] to 0.22 [0.07–0.30]) nmol ⋅ min−1 ⋅ m−2 at week 8 (P = 0.005). No differential effect of incretin secretion was observed after gastric bypass, with more rapid glucose absorption bringing about equivalently enhanced glucagon-like peptide 1 secretion in the two groups.

CONCLUSIONS

The fall in intrapancreatic triacylglycerol in T2DM, which occurs during weight loss, is associated with the condition itself rather than decreased total body fat.
Alogliptin, a Dipeptidyl Peptidase 4 Inhibitor, Prevents the Progression of Carotid Atherosclerosis in Patients With Type 2 Diabetes: The Study of Preventive Effects of Alogliptin on Diabetic Atherosclerosis (SPEAD-A)
Authors: Mita Tomoya , Katakami Naoto , Yoshii Hidenori , Onuma Tomio , Kaneto Hideaki , Osonoi Takeshi , Shiraiwa Toshihiko , Kosugi Keisuke , Umayahara Yutaka , Yamamoto Tsunehiko , Yokoyama Hiroki , Kuribayashi Nobuichi , Jinnouchi Hideaki , Gosho Masahiko , Shimomura Iichiro , Watada Hirotaka
Published: December 2015

OBJECTIVE

Recent experimental studies have shown that dipeptidyl peptidase 4 (DPP-4) inhibitors have antiatherosclerotic benefits in glucagon-like peptide 1–dependent and –independent manners. The current study investigated the effects of alogliptin, a DPP-4 inhibitor, on the progression of carotid atherosclerosis in patients with type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

This prospective, randomized, open-label, blinded-end point, multicenter, parallel-group, comparative study included 341 patients with T2DM free of a history of apparent cardiovascular diseases recruited at 11 clinical units and randomly allocated to treatment with alogliptin (n = 172) or conventional treatment (n = 169). Primary outcomes were changes in mean common and maximum intima-media thickness (IMT) of the carotid artery measured by carotid arterial echography during a 24-month treatment period.

RESULTS

Alogliptin treatment had a more potent glucose-lowering effect than the conventional treatment (−0.3 ± 0.7% vs. −0.1 ± 0.8%, P = 0.004) without an increase of hypoglycemia. Changes in the mean common and the right and left maximum IMT of the carotid arteries were significantly greater after alogliptin treatment than after conventional treatment (−0.026 mm [SE 0.009] vs. 0.005 mm [SE 0.009], P = 0.022; −0.045 mm [SE 0.018] vs. 0.011 mm [SE 0.017], P = 0.025, and −0.079 mm [SE 0.018] vs. −0.015 mm [SE 0.018], P = 0.013, respectively).

CONCLUSIONS

Alogliptin treatment attenuated the progression of carotid IMT in patients with T2DM free of apparent cardiovascular disease compared with the conventional treatment.
Modified Asphalt Binder with Natural Zeolite for Warm Mix Asphalt
Authors: Dubravský Marián , Mandula Ján
Published: December 2015

In recent years, warm mix asphalt (WMA) is becoming more and more used in the asphalt industry. WMA provide a whole range of benefits, whether economic, environmental and ecological. Lower energy consumption and less pollution is the most advantages of this asphalt mixture. The paper deals with the addition of natural zeolite into the sub base asphalt layers, which is the essential constituent in the construction of the road. Measurement is focused on basic physic – mechanical properties declared according to the catalog data sheets. The aim of this article is to demonstrate the ability of addition the natural zeolite into the all asphalt layers of asphalt pavement. All asphalt mixtures were compared with reference asphalt mixture, which was prepared in reference temperature.
The Idea of an Innovated Concept of the Košice Geothermal Project
Authors: Bujanská Alena , Böszörményi László
Published: December 2015

Slovakia has very limited amounts of fossil resources. However, it has a relatively high potential of geothermal energy which use is far below its possibilities. The most abundant geothermal resource, not only in Slovakia but throughout the central Europe, is Košice basin. Since the publication of the first ideas about the ambitious goal to exploit the geothermal potential of this site, 20 years has passed and three geothermal wells has been made but without any progress. In the article the authors present the idea of a fundamental change in the approach to improve the energy and economic efficiency of the project.
Application of Chemical Grouting as an Option of Removing Soil Moisture - a Case Study in the Reconstruction of the Church
Authors: Katunská Jana , Katunský Dušan
Published: December 2015

The article provides an analysis of removing moisture from the soil masonry walls. The chemical pressure insulation may be considered as one of the alternatives. This paper describes the chemical waterproofing and points to a case study, which is a small church in the town of Košice. Renovation of the church took place in two stages, made using pressure chemical insulation for chemical grouting of envelope masonry. The appropriateness and effectiveness of the applied chemical methods can be seen in the conclusions of this contribution.
Engineered Solution to Reduce the Impact of Lost Circulation During Drilling and Cementing in Rumaila Field, Iraq
Authors: Arshad Umar , Jain Bipin , Ramzan Muhammad , Alward Wassem , Diaz Lenin , Hasan Ibrahim , Aliyev Ali , Riji Chen
Published: December 2015

Over the last 60 years in the oil and gas industry, lost circulation has been the major nonproductive time (NPT) issue worldwide during well construction (12% of total NPT). According to industry figures, more than USD 2 billion are spent combating circulation loss each year. In the Rumaila field of Iraq, the NPT due to lost circulation is significant, estimated to be 46% of the total NPT recorded.

The Rumaila oil field is a super-giant oil field in southern Iraq; the field is estimated to contain 17 billion barrels, which accounts for 12% of Iraq's oil reserves. In the Rumaila field, at least 45% of the wells experience severe to total circulation loss at depths of 450 to 650 m true vertical depth (TVD) while drilling in the karst facies of the Dammam formation. Numerous strategies, requiring up to 24 days of rig time or 15 cement plugs in some extreme cases, have been applied by different service companies without consistent results. This has resulted in higher operating costs and delayed production. Some of the identified reasons for the low success rate are poor wellbore characterization, weak assessment of the problem, and improper execution.

The foundation of the proposed engineering and operational approach is the characterization of the wellbore with the caliper and formation image logs for better understanding of fractures and estimation of fracture volume. The approach also includes two cement slurry-type options—an increased slurry rheology with reduced density and a slurry with rapid gel strength development. The proposed approach is made complete with the engineered estimation of cement slurry volume, based on loss rate, and proper field deployment.

Developed on the basis of previous experiences and optimization of hydrostatic pressure, cement slurry rheology, and gel strength development, the engineered lost circulation solution significantly improves the lost circulation control results. Extended evaluation of cement plug jobs with the engineered design and proper execution has proven the effective impact of the solution, curing losses during the drilling phase (<3 days). This solution has proven to be an effective and key element, contributing to the increased success rate of the subsequent primary cementing operation and overcoming the challenges of zonal isolation.
Sensitivity Analysis and Optimization of Alkaline-Surfactant Flooding in a Thin Clastic Reservoir
Authors: Ghadami Nader , Das Apurba K. , Tunio Kamran H. , Sabzabadi Ali
Published: December 2015

Chemical EOR is one of the promising methods to improve the oil recovery. However, due to high cost of the process, there are challenges to minimize the cost and maximize the oil recovery. Some influencing parameters should be taken into account in a systematic approach to find their impact on oil recovery and accordingly optimizing the process.

In this study, we present a robust optimization workflow of alkaline-surfactant (AS) flooding into a thin clastic reservoir of a field in the Malay Basin. There are coreflood experiments and pilot tests on this field that can be quite helpful to provide a basis to find out the appropriate range of input parameters. Optimization work is based on response surface methodology (RSM) and particle swarm optimization (PSO) technique that aid us to indicate the optimum oil recovery from chemical flooding. In order to get the utmost advantage of this workflow, the waterflooding should be optimized prior to the chemical flooding optimization to maximize the sweep efficiency and oil recovery from the chemical flood.

Evaluation of coreflood and pilot tests indicated that some parameters need supplementary evaluation to investigate their effect on reservoir performance and flow dynamics. These parameters include residual oil reduction by chemical, relative permeability curves, chemicals adsorption, chemical concentration, slug size, injection rate, and initiation time of chemical injection. Based on the result of tornado chart, residual oil reduction and injection rate exhibited highest and lowest impact on oil recovery. RSM was used to explore the relationship between input variables and objective function. Some design parameters such as chemical concentration, slug size and initiation time were examined in this stage. Afterwards, proxy models have been built using polynomial regression and neural network methods. The results showed that the proxy model by neural network method revealed better performance for prediction of the simulation results. The proxy model was used to calculate the oil recovery for any combination of input parameters. Besides, it was used to assess the parameter sensitivity and identify the impact of any input parameter on oil recovery. At the next stage, PSO method was utilized to optimize the oil recovery by chemical flooding. It was found that the optimized water injection rate and pattern for water flooding scenario need further optimization to improve the sweep efficiency and thereby oil recovery by AS flooding at later stage. Running numerous simulation cases is normally expected to optimize the process by conventional methods and the proposed PSO approach can be used to reduce the number of runs significantly. Sensitivity analysis provided a very good understanding about reserve ranges for the different influential parameters. Optimizing the cost of chemical flooding and improving oil recovery are other outcomes of this study.
Methanol Production Enhancement Using Captured Carbon Dioxide Injection
Authors: Abdelsalam Omar
Published: December 2015

Study had been conducted to enhance methanol production via CO2 injection. This injected CO2 will be recovered from existing Reformer Flue Gas. The advantage of CO2 injection had resulted in attractive economical outcome for methanol production.

In Addition, the crucial effect of Decreasing Greenhouse effect by decreasing the CO2 Gas missions and its environmental impact was a main target of this paper and design project.

Not only production increase is the remarkable achievement in this study, but also the CO2 source, which is recovered from existing steam reformer Flue Gas in any Methanol Production plant. Detailed Material and Energy Balance has been done over the whole plant before and after modification, Accompanied with Preliminary economic analysis to the project.

As a Brief description of the project: flue gas will be sucked from pre-reformer stack via blower, and then cooled down by direct contact with water. Next, flue gas will be treated in two-column absorption technology using amine-based solvent to capture CO2. Purified CO2 will be injected in the methanol process.

As a conclusion, the outcome was remarkable and the increase in the plant productivity was in average of 5%, CO2 Gas emissions released and did made use of it for the same plant.
CO2 Well Injectivity: Effect of Viscous Forces on Precipitated Minerals
Authors: Sokama-Neuyam Yen Adams , Ursin Jann Rune
Published: December 2015

Carbon Capture and Storage (CCS) is particularly attractive for the oil and gas industry due to the potential of Enhanced Oil Recovery (EOR). The presence of adequate well injectivity is identified as a prerequisite for CCS and CO2 EOR projects. Mineral precipitation in the vicinity of the well is suggested as a possible injectivity impairment mechanism. After mineral precipitation and formation dryout, continuous injection of CO2 into the formation could redistribute precipitates and alter injectivity. In this work, we investigated the effect of viscous force on precipitated minerals and the resulting consequences on permability and injectivity. The influence of supercritical CO2 injection rate, initial core permeability and saturating brine salinity were investigated. We observed that, injectivity impairment has a maximum immediately after mineral precipitation. Continuous injection of supercritical CO2 into the core after mineral precipitation is seen to reduce injectivity impairment induced by precipitated minerals. In most numerical and geochemical models, static injectivity impairment as a result of mineral precipitation is often assumed. Our findings suggest that injectivity remains dynamic throughout the injection process. Therefore, changes in CO2 injectivity after mineral precipitation could be complex to model and understanding of the processes is a good point to start.
Industrial Application for the Removal of Kinetic Hydrate Inhibitor (KHI) Co-Polymers from Produced Water Streams
Authors: Al Redoua Ali , Hamid Saed Abdul
Published: December 2015

To avoid hydrate formation, Kinetic Hydrate Inhibitor (KHI) is injected into the upstream wet gas pipelines. KHI eventually remains in the produced water which is treated for H2S and oil removal before it is re-injected into deep disposal wells. Industry regulators in the State of Qatar have concluded that the presence of KHI polymers in the injected wastewater leads to long term reservoir damage… Hence it is essential to remove KHI polymers from re-injected wastewater streams.

As there are no industrially proven technologies for removal of KHI, pilot tests were conducted for removal via evaporation. At the same time, futher options were being assessed by other operators, including Wet Air Oxidation and KHI replacement with MEG. All options were assessed on technical, economical, planning, environmental, and safety criteria. The evaporation technology was found to be most suitable.

The pilot tests showed that KHI can be removed via evaporation to produce a distillate stream, equal to more than 99% of the incoming flow, with KHI polymers residual concentration lower than the detection limit of 25 mg/l, which will be suitable for re-injection; plus a concentrate stream that includes the concentrated KHI polymers and other salts and solids.

The process scheme was developed during the FEED (Front End Engineering and Design) stage, as follows. First, a pre-treatment step ensures breaking of the emulsions and the removal of oil and sludge. This mainly consists of coagulation and pH adjustment tanks, Dissolved Air Flotation and centrifuge packages. This is followed by a two-stage evaporator package which incorporates mechanical vapor recompression, cross heat exchangers, coolers, and cleaning in place techniques. Two outlet streams are created as a result; one distillate stream (free from KHI) which is sent for deep well injection, and one concentrate stream (with KHI), which will be sent to the concentrate storage facilities and will be loaded onto trucks for incineration by a third party.

The removal of KHI from produced water streams using evaporation technology has never been done on an industrial scale. The success of this project would ensure that continuing the utilization of KHI products to avoid hydrate formations in the wet gas streams is suitable for the natural gas industry, whilst also avoiding any potential damage of the reservoirs in the long term.
Carbon Dioxide Sequestration in Coal Formations
Authors: Ibrahim Ahmed Farid , Nasr-El-Din Hisham A.
Published: December 2015

Carbon dioxide (CO2) is the major greenhouse gas emitted in all activities. CO2 sequestration in coal seams has become an attractive carbon sequestration technology where the injection of CO2 enhances methane production from coalbeds (ECBM), in addition to storing CO2. CO2 can be retained in coal via three ways: free gas within the pore space or fractures in the coal, adsorbed molecules on the organic surface of coal, and dissolved in groundwater within the coal.

This study investigates the effects of the salinity (NaCl) of coal seam water, injection flow rate, and CO2 state (formation pressure) on the CO2 sequestration in volatile bitumen coal. To achieve this objective; coreflood tests were conducted on different coal cores. The change in the effective water-coal permeability after CO2 injection was examined. Also, the displacement efficiency of water by CO2 was estimated. The experimental data was cross-matched with numerical simulation to estimate the relative permeability curves.

The coreflood experiments showed that the effective water permeability in coal decreased during CO2 injection due to its adsorption onto the coal surface, and reduction of the relative water permeability. Higher formation pressure led to permeability reduction as a result of higher CO2 adsorption onto the coal surface. The effective water permeability decreased by 8% at 50 psi back pressure, compared to 48% at 1100 psi back pressure. Furthermore, as the injection flow rate increased, the contact time of CO2 to the coal surface decreased. Hence, the CO2 adsorption to the coal matrix decreased and the change on effective water permeability slightly decreased. Specifically, the effective water permeability decreased by 48% at 1 cm3/min comparing to 41% at 4 cm3/min. As salt concentration increased, the change in pressure drop across the core slightly increased, but this effect decreased as formation pressure increased. As the water salinity increased, the coal become more CO2 wet, and the residual gas saturation increased. Based on these observations, the injection of CO2 into highly volatile bitumen coal seams for CO2 sequestration and ECBM purposes is more efficient as the salt concentration increases and high injection pressure.
Enhanced Well Testing Solution to Improve Operation Safety and Reliability
Authors: Selvaraj Jagannath
Published: December 2015

In this paper, we review three methods that were utilized by Qatar Shell to improve process safety and reliability of Well Test Operations.
Probabilistic History Matching in a Shallow Marine Deltaic System: A Frequentist Approach
Authors: Jimenez Eduardo A , Jin Long , Essen Gijs van , Kullberg Ingrid
Published: December 2015

Within recent years there have been significant research efforts towards building an ensemble of reservoir models to quantify subsurface uncertainty. The data assimilation and model calibration strategy is rapidly moving away from conditioning just a single model as in almost every forecast exercise the predictability of a single model is rather limited. In this paper we will present a frequentist inference basis for the dynamic data integration problem in subsurface modeling. Specifically, we’re after deriving small representative sets of reservoir images and how dynamic data affects them.

Our approach starts with screening a large ensemble of subsurface realizations holding between 104–106 members (or more) where we’re after representatives that are mutually different in terms of their relevant reservoir flow behavior. We propose a reduced representation of the probability distribution of the high-dimensional vector space of all reservoir images defined by flow-like snapshots. This process allows defining a metric space where it's possible to execute cluster analysis and/or heuristic sampling of the high-dimensional geologic space. The result of this stage is a smaller ensemble of dynamically unconditioned eigen-reservoirs without compromising uncertainty that can be used in any stage of field development planning that involves reservoir dynamics.

We have used derivative-based techniques available in our in-house simulator to deterministically history match the eigen-reservoirs and provide a solution to the dynamic data conditioning problem. We provide results of the workflow application in a shallow marine deltaic system where 28 years of production data has been successfully assimilated. Our results show a remarkable improvement in the predictability of reservoir models, which is a vital component in the entire hydrocarbon maturation cycle.
Near Surface Velocity Model of Dukhan Field from Multi-Physics Survey to Enhance PSDM Seismic Imaging
Authors: Setiyono K. , Gallo S. , Boulange C. , Bruere F. , Moreau F. , Rondeleux B. , Snow J.
Published: December 2015

Dukhan Field affords an opportunity to assess alternative near surface velocity modeling workflows that specifically integrate Microgravity (MGR) and Vertical Electrical Sounding (VES). A pilot study of the Dukhan seismic data demonstrates that integration of MGR/VES into Pre-Stack Depth Migration (PSDM) improves the fidelity of seismic images and results in an improved depth match.

In many giant carbonate reservoirs, variations in surface and near surface geology result in velocity issues that are not necessarily corrected by standard seismic data processing workflows. A novel approach integrates MGR and VES inversion into processing workflows. Initial calibration and testing of MGR/VES data were computed on a pilot area (165 sq.km) at Dukhan which improved the near surface geological model between the surface and the first observed seismic reflector - Simsima Formation. Processing sequences utilizing microgravity and resistivity inversion resulted in a new velocity model. Combined with structural information, the VES resistivity model constrained the gravity inversion in depth. Gardner and Faust equations facilitated building the final near surface velocity model.

The resultant MGR/VES PSDM pilot model improved the velocity model between the surface and top Simsima Formation based on 1) visible impact on the deeper structure obtained from imaging and 2) better fit between the seismic depth horizons and well measured depths. Based on the results of this study, QP acquired MGR/VES data over the entire Dukhan survey area and will utilize these data in any future PSDM full-field processing. Other giant carbonate reservoirs may benefit from utilizing this workflow to further refine and enhance seismic imaging.
Gas Driers KO Drum Design Shortfall
Authors: O'Neill Stephen , Whateley Thomas , Al Hajri Abdulla
Published: December 2015

The objective of this paper is to describe a deterioration that was observed in the performance of molecular sieve type Gas Driers, to summarize the work that was done to identify the root cause, to describe the modifications that were implemented to resolve this problem, and to explain the extent to which these modifications were effective in resolving this problem.

During early 2012 the pressure drop across the Gas Driers in two trains within the onshore gas processing facility in Ras Laffan began increasing at a faster rate than usual. This change correlated with an increase in the CO2 content of gas feeding the concerned Gas Driers. Through liaison with molecular sieve vendors, it was established that the accelerated rate of bed deterioration had been caused by liquids carryover from the upstream Driers Inlet Separator co-inciding with an increase in CO2 content of the gas. Since it was preferred to maintain the increased CO2 concentration of the gas, efforts were made to re-design the Driers Inlet Separator to minimize liquid carryover into the Gas Driers.

The effectiveness of gas/liquid separation in the existing Driers Inlet Separator was first assessed by means of computational fluid dynamics (CFD) studies conducted by a third party. These studies demonstrated that the separation efficiency of liquids from gas in the existing vessel was inadequate, and that the effectiveness of separation could be greatly enhanced by implementation of various internal modifications without the need to replace the existing vessels.

It was proposed to remove the existing vane pack from within this vessel and to install new internals including a vane type inlet distributor, mesh pad, and cyclone separators. The effectiveness of these new internals was first demonstrated using proprietary software by the same third party. Upon completion of detailed engineering, these internals were manufactured and installed within the existing vessels.

The rate at which molecular sieve deterioration occurs downstream of these modified Driers Inlet Separators was assessed, and details regarding the methodology for this assessment as well as the outcome of the assessment are provided.

This paper will be of interest to anyone involved in the design or operation of molecular sieve Gas Driers and upstream gas/liquid separation facilities. It will provide useful information regarding the importance of effective gas/liquid separation upstream of these Gas Driers, especially when the CO2 concentration of the gas is high. This paper also describes novel internals modifications that can be considered for implementation in existing two or three phase separators that do not provide adequate separation of liquids from gas.
Residual Trapping of CO2 in Water-Wet and Mixed-Wet Carbonates for Carbon Utilization in Mature Carbonates Oil Fields
Authors: Al-Menhali A. , Krevor S.
Published: December 2015

In an energy hungry world, fossil fuels are predicted to remain the dominant source of energy for a long time. Burning more fossil fuels will increase CO2 emissions in the atmosphere and will consequently increase the challenges of climate change mitigations. Carbon capture and storage (CCS) in deep saline aquifers is an important process for CO2 reduction on industrial scales but it is not economically attractive. Residual trapping of CO2 through capillary forces within the pore space of the reservoir is one of the most significant mechanisms for storage security and is also a factor determining the ultimate extent of CO2 migration within the reservoir. Carbon capture, utilization and storage (CCUS) in mature oil reservoirs can have a significant energy, economic and environmental benefits and is considered an important component in achieving the widespread commercial deployment of CCS technology. Residual trapping in mixed-wet systems, however, is assumed to be less efficient than in water-wet systems. In this study, we compare residual trapping efficiency in water-wet and mixed-wet carbonates systems on the same rock sample before and after wettability alteration by aging with crude oil. The observations were made at reservoir condition in a core-flooding system that included high precision pumps, temperature control, the ability to recirculate fluids for weeks at a time and an x-ray CT scanner for in situ saturation monitoring. The wetted parts of the flow-loop are made of anti-corrosive material that can handle co-circulation of CO2 and brine at reservoir conditions. We report the initial-residual CO2 saturation curve and the resulting parameterisation of hysteresis models for both water-wet and mixed-wet systems. A novel core-flooding approach was used, making use of the capillary end effect to create a large range in initial CO2 saturation in a single core-flood. Upon subsequent flooding with CO2-equilibriated brine, the observation of residual saturation corresponded to the wide range of initial saturations before flooding resulting in a rapid construction of the initial residual curve. Also, multiphase flow observations were made on a single carbonates core sample. It was made first on its original water-wet state, then were measured again after altering the wetting properties to a mixed-wet system. In particular, CO2 trapping was characterized before and after wetting alteration so that the impact of the wetting state of the rock is observed directly.
Multifunctional Nanoadditive in Water Based Drilling Fluid for Improving Shale Stability
Authors: Taraghikhah S. , Kalhor Mohammadi M. , Tahmasbi Nowtaraki K.
Published: December 2015

Wellbore stability and formation damage are of great interest and significance in drilling industry. It is estimated, each year, millions of dollars are lost due to wellbore instability problems which are resulting from exposure of shale to drilling muds. The main objective of this research activity is to improve shale inhibition and wellbore stability by using Silica nanoparticles in mud formulation. Furthermore, it is also intended to use this nanoadditive as a multifunctional mud additive to decrease fluid loss, improve lubricity, avoid shale swelling and modify rheological properties. In order to achieve these objectives, experimental procedures have been planned in the following sequences; A) Different concentrations of Silica nanoparticles are used in conducting experiments in order to determine the nanoparticles concentration range that yields the optimum shale inhibition. B) Further experiments are conducted on the evaluation of rheological properties and fluid loss via API standard methods. C) Lubricity and shale swelling tests are performed via relevant standards. D) Overall evaluation of laboratory-prepared water based drilling fluid is performed and the results are presented and compared with the blank samples. In conclusion, according to the acquired results including nanoadditives in drilling fluid and comparing them with blank samples, it was found that the most economical and effective concentration of nanoparticles is below 1% w/v, which lead to an acceptable shale inhibition effects by plugging the nanosized pores. These effects are analyzed and reported graphically. Various charts and figures show the enhancement in rheological properties such as yield point by adding small amount of nanoadditive in comparison with ordinary vicosifiers in drilling fluids. The most significant achievement in this research is the cost effectiveness of the nanoadditive. Not only can we improve mud performance with a lower cost in comparison with previously used drilling additives, but also by further modifications, these additives can replace the ordinary drilling additives. Needless to say that such change has a considerable reduction in drilling fluids costs. Several works have accomplished in relation with applying Silica nanoparticles in drilling fluid formulation and approximately in all of these works, only higher concentrations of nanoparticles (more than 10%wt) can be applicable in the shadow of surfactants and ultrasonication methods for sufficient dispersion. The striking feature of this research is the consuming of nanoparticles in lower concentrations (maximum 1% w/v) and without the assistance of surfactants.
Reservoir Modeling of Complex Thin-Bedded Deep Water Deposits Integrating Well Data, Seismic Inversion and Depositional Model from Offshore Sabah, Malaysia
Authors: Souche Laurent , Mahdavi Ramin , Mahmod Nor Mahira , Alim Syarafina , Masoudi Rahim , Basu Debnath
Published: December 2015

The studied field, located offshore Sabah, Malaysia is composed of a succession of thick-bedded sand lobes, thin-bedded heterolithics and shale dominated mass transport deposits (MTDs). While the thinly bedded units contain significant hydrocarbon reserves, the distribution and continuity of sand bodies within these units cannot generally be derived from well data alone. Modern analogues suggest that these thin beds are likely composed of small scale sandy lobes embedded into a shale background. In order to better understand the vertical and lateral connectivity of these turbiditic elements, a numerical model integrating well data and seismic inversion results was built, constrained by a conceptual depositional model based on analogue data.

Multi-point geostatistics (MPS) were used as a platform to combine geological knowledge - in the form of a realistic training image, well measurements and geophysical trends. In order to reproduce observed facies proportions and architecture, the training images were generated using a novel user-guided, semi-automated workflow based on object-distance simulation. Reproducing the vertical heterogeneity of the model observed in thinly bedded units while retaining the lateral variability evidenced by seismic inversion was achieved by creating first set of facies probability cubes from the seismic inversion results using supervised neural-network estimation, then refining these probabilities by calibrating them to vertical proportion curves extracted from high-resolution facies logs. This technique enabled reproducing complex depositional patterns such as compensational stacking and hierarchical distribution of facies. It also allowed sedimentary bodies directly visible on the seismic inversion results to be integrated explicitly into the facies model. The simulated facies distribution was then used to constrain petrophysical property population, yielding detailed and realistic dynamic models.

While the presented approach is specifically tailored to the modeling of thinly bedded deep water environments, the innovative techniques proposed for generating a "photorealistic" training image and for integrating seismic-scale results with high resolution well data could also be used for representing a varied set of depositional settings.
Microporosity Spatial Modeling In A Giant Carbonate Reservoir
Authors: Stanley Rowan , Guidry Sean , Al-Ansi Hussain
Published: December 2015

A challenge for carbonate rock classification in reservoir models is the seemingly chaotic variability in the total pore system which ultimately controls petrophysical and dynamic behaviour. The aim of this study is to describe and spatially model a unified rock-typing scheme aligning the dual requirement for: 1) hydraulically consistent rock classes suited to numerical flow simulation, and 2) heterogeneity shaped according to field-scale geological anisotropy. Description of a suite of samples derived from the Jurassic Arab Formation reservoirs in the Dukhan Field, Qatar, facilitated the following:

Definition of petrophysical rock classes based on consistent pore and capillary pressure characteristics. Evaluation of the rock-type 3D spatial distributions to ensure conformance with inferred geological patterns. Computation of absolute permeability ranges based on measured responses to the fractional proportions of pore systems. Creation of an initial saturation model accounting for the compound saturation fractions related to the pore system components. Implementation of the concepts in a novel geomodeling workflow.

Statistical analyses of almost a thousand pore throat radius distributions and capillary pressure responses reveal a remarkably consistent set of micro-textural associations. Hierarchical clustering analyses define an ordered system of building blocks comprising five dominant pore systems. The macro-porous samples (>2µm pore throat radius – PTR) are distinctly bimodal in two classes (Macro1 and Macro2), while the micro-porous samples have typically unimodal PTR and form three clusters: Micro1 (2 – 0.2µm), Micro2 (0.2 – 0.02µm) and Micro3 (<0.02µm).

Each rock element is a variable mixture of the five textural building blocks and the relative proportions are utilized to define the rock classification. Spatial continuity and anisotropy are shaped by geological trend vectors interpreted from collocated lithological and depositional texture distributions. This approach meets a dual objective of accounting for the myriad of geological processes implicit in the rock fabric while also providing a rock classification applicable for reservoir engineering and flow simulation purposes.
The Effect of Reservoir Conditions on Wetting and Multiphase Flow Properties in CO2-Brine-Rock System
Authors: Al-Menhali A. , Niu B. , Krevor S.
Published: December 2015

The wettability of CO2-brine-rock systems will have a major impact on the management of carbon sequestration in subsurface geological formations. Recent contact angle measurement studies have reported sensitivity in wetting behaviour of this system to pressure, temperature and brine salinity. We report results of an investigation into the impact of reservoir conditions on capillarity and multiphase flow through effects of wetting. The semi-dynamic capillary pressure core flooding technique was used with in situ saturation monitoring. The observations were made using a reservoir condition core-flooding laboratory that included high precision pumps, temperature control, the ability to recirculate fluids for weeks at a time and an x-ray CT scanner. The wetted parts of the flow-loop are made of anti-corrosive material that can handle co-circulation of CO2 and brine at reservoir conditions. Eight reservoir condition capillary pressure characteristic curves were measured using CO2 and brine in single fired Berea sandstone at pressures (5 to 20 MPa), temperatures (25 to 50°C) and ionic strengths (0 to 5 M kg-1 NaCl) representative of subsurface reservoirs. A ninth measurement using an N2-water system provided a benchmark for capillarity with a strongly water wet system. In all cases, the capillarity of the system, scaled by the interfacial tension, were equivalent to the N2-water system within measurement uncertainty. Thus reservoir conditions did not have a significant impact on the capillary strength of the CO2-brine system through a variation in wetting. In this work we report the results of the first study looking systematically at the impacts of reservoir conditions on the effective wettability in the CO2-brine-sandstone system. A new method is presented to quantify shifts in effective wetting properties with changing reservoir conditions. We find no impact within the range of reservoir and flow conditions relevant to CO2 storage, consistent with traditional multiphase flow theory but despite observations by others suggesting that wetting properties and multiphase flow in this system are sensitive to pressure, temperature and brine salinity. This provides definitive confirmation that the CO2- brine system performs as a strongly water-wet system in sandstone rocks and the use of analogue fluids for this characterisation may be useful when the full reservoir conditions cannot be replicated in the laboratory. The spatial saturations were also investigated using x-ray computed tomography and were found to be invariant with different reservoir conditions in homogeneous samples. The findings confirm the role of residual trapping in capacity estimates and provide a comprehensive dataset for flow modelling in water wet reservoirs.
Mitigating Drilling Dysfunction Using a Drilling Advisory System: Results from Recent Field Applications
Authors: Payette Gregory S. , Pais Darren , Spivey Benjamin , Wang Lei , Bailey Jeffrey R. , Pastusek Paul , Owens Michael
Published: December 2015

The ExxonMobil Drilling Advisory System (DAS™) is a rig-based drilling surveillance and optimization platform that encourages regular (guided) drill-off tests, carefully monitors drilling performance and provides recommendations for controllable drilling parameters to help improve the overall drilling process. It is well known that drilling with dysfunction(s), such as BHA whirl or bit stick-slip, among others, can damage drilling tools, lead to poor borehole quality and result in significant reductions in Rate of Penetration (ROP). The ultimate objective of DAS is to help drillers achieve consistently better and longer bit runs by identifying and mitigating drilling dysfunctions.

In this paper we describe the DAS workflow, provide an overview of many of the key technical components of DAS and summarize results from several recent field applications. The DAS workflow includes a learning (or calibration) mode that encourages the driller to explore different operating parameters by conducting drill-off tests, which in turn allows the system to build an understanding of performance trends. This understanding is then exploited by an application mode which leverages results obtained during the learning (or calibration) phase. The workflow is iteratively applied in real-time as drilling operations and geological conditions change.

Key technical components of the DAS application include: high quality adaptive filtering algorithms for computing various drilling system performance measures (e.g., MSE, ROP, and stick-slip severity, among others), data encapsulation/dimensionality reduction techniques (i.e., the notion of "response points") and reduced order modeling techniques (simplices, smooth response surfaces, etc.) which are ultimately used to generate recommendations for improved performance.

Using examples from recent offshore field applications, we illustrate the use of adaptive filtering and data encapsulation to process noisy real-time data and extract meaningful trends to enable drilling performance optimization. We show how fitting response surfaces to response points can help elucidate, in real-time, the occurrence of classical drilling dysfunctions such as lateral vibrations (as manifest in increased MSE) and stick-slip torsional vibrations. Using results from recent applications of DAS to unconventional pad-drilling operations, we show the impacts of focused drilling performance limiter redesign and real-time DAS parameter changes on improved overall ROP in subsequent wells on a pad.
Fit-for-Purpose Treatment of Produced Water for Hydraulic Fracturing – A Permian Basin Experience
Authors: Sharma Ramesh , McLin Kristie , Bjornen Kevin , Shields Austin , Hirani Zakir , Adham Samer
Published: December 2015

ConocoPhillips is committed to creating a responsible water management plan in developing assets in the Permian Basin of West Texas. Sourcing water for the large multi-frac stimulations in West Texas is a well-known constraint on oil and gas development activities in the area. Additionally, large volumes of produced water (PW) have traditionally required clean up and disposal in injection wells. Rather than viewing these constraints only as challenges, ConocoPhillips realizes the tremendous opportunity to address both issues by treating and reusing PW for hydraulic fracturing operations. With this perspective, water management strategy development has become a truly collaborative, cost-effective, and integrated process that addresses the full life-cycle of water.

ConocoPhillips executed a multi-well reuse pilot program in the Permian Basin. A "fit-for-purpose" treatment scheme was deployed to selectively remove free oil, suspended solids, hydrogen sulfide, and iron as well as to inactivate microorganisms. While gravity separation was adequate for de-oiling and filtration for suspended solids, oxidation followed by coagulation and clarification was necessary for dissolved iron removal. The treated water iron concentration was below 5 mg/L whereas the turbidity was consistently below 10 NTU, making it suitable for well completions. When treating for H2S removal, the oxidation followed by filtration method was sufficient to reduce the H2S concentration to <0.2 mg/L and achieve turbidity below 10 NTU. The treated PW was compatible with the new salt-tolerant friction reducer, achieving similar friction reduction compared to a standard friction reducer and fresh water. The treated PW used in hydraulic fracturing was also compatible with formation water as it was produced from the same formation. The sulfate reducing bacteria were non-detectable in the treated water after four weeks of storage.

The six month pilot operation, demonstrated that PW reuse is technically feasible and can be a cost-effective solution compared to other available water sourcing alternatives. The technical approach developed allowed use of salty produced water (>220,000 mg/L TDS) for completion activities utilizing a new type of friction reducer. Based on the success of the pilot program, a full-field produced water reuse program has been initiated early in the appraisal and development phase of the project to reduce implementation risks and improve economics in a safe and environmentally responsible manner.

Strong collaboration led to success in these projects, and they were designed and executed through a significant team effort made by completion engineers, water treatment engineers, the asset development team, and the operations team. This paper provides an overview of the plan implemented for safe pilot operation, procedures for treatment of produced water and water quality results.