bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation Damage Diagnosis Facilitates a Successful Remedial Treatment Design and Execution in Sandstone Horizontal Oil Producer: A Laboratory and Field Case Study
Authors: Bataweel M. A. , Al-Ghamdi A. H. , Osode P. I. , Almubarak T. A. , Azizi E. S. , Sarhan Eddy , Al-Faifi M. G.
Published: May 2015

Well-control fluids were used during a routine overbalanced workover operation in an offshore well completed in high permeability sandstone. As expected, a fluid loss control pill was used to control the excessive losses encountered during this operation. However, due to the high permeability of the reservoir and the absence of sized particles in the pumped pill; large amount of fluids were lost to the formation before losses were controlled. The deep invasion of fluids laden with high concentration of polymer had inevitably resulted in severe formation damage and impaired production. Several attempts to clean out the wellbore and revive the well flow were unsuccessful with no injectivity either. The well was consequently suspended while a multidisciplinary team was formed to identify the cause of the impairment and recommend a treatment plan.

A comprehensive review of detailed field operation and data related to the fluid losses accompanied with laboratory work to identify the damaging mechanism and formulate an optimized remedial treatment was conducted. The lab work included jar testing to assess compatibility and emulsion tendency when different wellbore fluids are mixed with each other and with formation fluids. Analysis of the samples collected from the wellbore was carried out and different treatment fluid options were evaluated using actual field samples. Core flood experiments were also conducted to assess the impact of high-viscosity pills on permeability and ability of remedial treatment in restoring the original permeability.

Experimental results revealed partial removal of the polymer invading the core using organic acid. The designed pre-flush composed of mutual solvent with surfactant package was effective in breaking the emulsion from field samples and laboratory-prepared emulsions. A significant improvement in production from this well was realized by application of a cost effective formic acid-based chemical treatment. Proper treatment design with effective displacement technique were also attributed to the successful damage removal and regained well productivity.
A Fast Simulation Tool for Evaluation of Novel Well Stimulation Techniques for Tight Gas Reservoirs
Authors: Egberts P.J.P. , Peters E.
Published: May 2015

For stimulation of tight fields, alternatives to hydraulic fracturing based on hydraulic jetting are becoming available. With hydraulic jetting many (10 to 20) laterals can be created in a (sub-) vertical well. The laterals are 100 to 200 m long, typically 4 laterals are applied with a small inclination at a single kickoff depth. This type of well configuration will be called a radial well. A simulation tool based on a semi-analytical method is developed to computate the production performance of a radial well. The tool provides an efficient way to assess the production potential of a stimulated well for many different well designs. The method is particularly suitable for performing a sensitivity analysis to preselect a limited number of designs to be further analysed. The results of the tool show excellent agreement with those of a numerical reservoir simulator. As an example, the tool is applied to a stacked field with three separate reservoirs, wich have permeability ranging from 1 to 5 mD. The radial well increases cumulative gas production by 10% for the reservoir with 5 mD and by 50-70% for the reservoirs with 1 mD permeability.
A Better Formulation of Objective Functions for History Matching Using Hausdorff Distances
Authors: Bouzarkouna Z. , Nobakht B. Nezhad
Published: May 2015

History matching aims at finding one or several reservoir models that closely reproduce the past behavior of the reservoir. Objective functions are often used to measure the quality of these models.

Indeed when using assisted history matching techniques, a good formulation of the objective function is crucial since it increases the likelihood to get an acceptable history match. Moreover, for manual history matching, and in particular for large fields, objective functions can also be used in order to compare between runs and to help understanding the field.

In this paper, we investigate an alternative new formulation of the objective function. The proposed formulation does not take into account only the difference between the production data (point by point) but also discrepancies in the shape. The proposed formulation is based on an appropriate Hausdorff distance.

The proposed approach is applied on different data from different real history matching studies. Results are compared with the standard mean squared error formulation, and shown to satisfy more reservoir engineering principles when comparing between runs.
Life of Field Reservoir Surveillance and Optimization Using Cased-Hole Log Measurements
Authors: Kaawan Emad , Juha Lutfi , Elmanghush Aziza
Published: May 2015

Reservoir management is about optimizing reservoir performance to achieve long-term recovery goals. This can be accomplished through a systematic application of integrated, multidisciplinary technologies to positively impact financial performance and achieve synergy. Multidisciplinary integration leads to better understanding of reservoir performance for proper decisions on remedial actions such as water shut-off, additional perforations, stimulation; for long-term planning and enhanced oil recovery to optimize production at the well and field levels. The case of the As-Sarah field in Libya shows how cased-hole logging and production-monitoring contributed to successful reservoir management.

Cased-hole production and pulsed-neutron-logging have been used extensively since the early life of As-Sarah field for reservoir surveillance and to identify opportunities for remedial actions. A significant number of thermal--decay-time, reservoir saturation and production logging campaigns have been performed. The aims of these campaigns were to estimate the propagation of the oil/water contact (OWC), determine the residual oil saturation profile, identify watered-out zones for isolation, and define zonal contribution. A re-interpretation project of all As-Sarah field cased-hole logs was completed and presented in a comprehensive time-lapse display. The results of this project guided the fluids movement during history-matching in the dynamic model.

Using reservoir saturation measurements along with the production logging data ensured data consistency and reliability. This helped the operator to be certain that there was no movable-oil left in the formation, enabling confidence in the decision to plug-back the water-entry zones. This integration was used for tar-mats mapping, characterization of the low-productivity D and E units at the top of the reservoir, re-evaluating the recovery factor, and anticipating the OWC for infill-well planning.

Building time-lapse water saturation and flow profiles is not straightforward. The water and remaining oil saturations must be calculated for each well to evaluate the fluids' mobility. The project included detailed saturation processing taking into account the field-wide reservoir residual oil saturation. Presenting the results in this unique format provides quick and easy access to a huge amount of data, thus providing an at-a-glance understanding of the reservoir behavior and aquifer strength. It also contributed to optimizing liquids' off-take, minimizing bypassed reserves and selecting wells for further monitoring. The log results were correlated with production history to calibrate and validate the dynamic model that is being used for field development.
Solar Generated Steam Injection in Hamca, Venezuelan Extra Heavy Oil Reservoir; Simulation Study for Oil Recovery Performance, Economical and Environmental Feasibilities
Authors: Yegane Mohsen Mirzaie , Ayatollahi Shahab , Bashtani Farzad , Romero C.
Published: May 2015

Application of solar energy compared to conventional gas-burning boilers for steam generation in thermal Enhanced Oil Recovery processes is a newly attended technology, which brings significant benefits to the petroleum industry through environmental and economical aspects. This technique is especially designed for the regions in which gas-burning steam generation is not viable in large scale. The objective of this study is to investigate about viability of using solar energy to generate steam instead of using conventional steam generators in a Venezuelan extra heavy oil reservoir. Limited gas production policy of the Venezuelan government is the major challenge for utilizing gas steam generators for extra heavy oil reservoirs in this country. Besides, the efficient daylight duration, economic and environmental advantages, are the main features to propose solar-generated-steam injection in Venezuelan extra heavy oil reservoirs. In this study, various scenarios of steam injection on Hamaca-Venezuelan heavy oil reservoir-have been investigated using commercial thermal simulator software and the main results of oil production for similar time periods (5 years) are compared. To compensate the energy needed for the steam generators during the night time, dual types steam generators were proposed to utilize solar and fossil energies during day-time and night time respectively. The simulation results for this extra heavy oil reservoir indicated that the oil production was not significantly improved when solar method is used regardless of the amount of the nightly injection of fossil-fuel generated steam for flow back prevention. This finding illustrated high economic efficiency for solar-generated steam injection compared to dual type (solar and fossil-fuel) steam generator method. Furthermore, the results indicated that in typical imposed cyclic steam injections in integrated solar thermal projects, there is no significant difference in oil productions in various scenarios with different pattern and rate of steam injection if the total amount of injected steam is constant. In addition, this study shows the significant reduction of CO2 and Sulfur Oxides emissions if this new technology is implemented. Besides, various scenarios (with and without natural gas backup) were designed for exact day light duration profile in vicinity of the reservoir in order to optimize the oil production as well as accurate economic and environmental evaluation for each scenario.
Novel Integrated Approach Simultaneously Optimising AFI Locations Plus Number and (A)ICD Sizes
Authors: Dowlatabad Mojtaba Moradi
Published: May 2015

The optimal design of Advanced Well Completions (AWCs) is an important step in field development planning nowadays. However, determination of optimum design of (Autonomous) Inflow Control Devices [(A)ICDs] and their integration with Annular Flow Isolations (AFIs) in an advanced well completed across a heterogeneous reservoir is a challenge which has not been addressed properly yet. Most used, variable strength (A)ICD completion design, workflows by industry are based on trial and error evaluations of a static well-reservoir models. Several researchers also suggested relating the strengths of the devices to near wellbore static reservoir properties such as permeability of the encountering layers. Both of these approaches do not capture the dynamic interactions between the well and constantly changing reservoir conditions. Moreover, neglecting mutual dependency of AFI location and (A)ICD design in the traditionally step-by-step (A)ICD-AFI design workflows, may result in a design delivering low overall productivity throughout the field life.

A novel, integrated (A)ICD-AFI completion design workflow is presented in this paper. The workflow simultaneously optimises (A)ICDs strengths and number plus locations of AFIs in the horizontal and/or multilateral wells based on field's production lifetime. The approach includes stochastic optimisation algorithm coupled with a reservoir simulator and an in-house completion design programming code. The code is developed to automatically generate various (A)ICD-AFI completion configurations required to determine the optimum completion design while honouring practical concerns and economics. A novel AFI modelling technique developed allows integration of AFIs in the optimisation process.

The application of the new and the traditional workflows are illustrated using heterogeneous reservoir simulation models. A significant improvement in total oil production for the wells, designed by the new workflow, was achieved comparing with the wells designed by the traditional workflows. The study aims to help well engineers in designing optimal advanced well completion delivering maximum possible field's added-value.
A New Bayesian Approach for Analogs Evaluation in Advanced EOR Screening
Authors: Siena Martina , Milano Politecnico di , Guadagnini Alberto , Rossa Ernesto Della , Lamberti Andrea , Masserano Franco , Rotondi Marco
Published: May 2015

We present and test a new screening methodology to discriminate amongst alternative and competing Enhanced Oil Recovery (EOR) techniques to be considered for a given reservoir. Our work is motivated by the observation that, even if a considerable variety of EOR techniques have been successfully applied to extend oilfield production and lifetime, an EOR project requires extensive laboratory and pilot tests prior to field-wide implementation and preliminary assessment of EOR potential in a reservoir is critical in the decision-making process. Since similar EOR techniques may be successful in fields sharing some global features, as basic discrimination criteria we consider fluid (density and viscosity) and reservoir formation (porosity, permeability, depth and temperature) properties. Our approach is observation-driven and grounded on an exhaustive data-base which we compile upon considering worldwide EOR field experiences. A preliminary reduction of the dimensionality of the parameter space over which EOR projects are classified is accomplished through Principal Component Analysis (PCA). A screening of target analogs is then obtained by classification of documented EOR projects through a Bayesian clustering algorithm. Considering the cluster which comprises the EOR field under evaluation, an inter-cluster refinement is then accomplished by ordering cluster components on the basis of a weighted Euclidean distance from the target field in the (multidimensional) parameter space. Distinctive features of our methodology are that (a) all screening analyses are performed on the database projected onto the space of principal components, and (b) the fraction of variance associated with each principal component is taken as weight of the Euclidean distance we determine. As a test bed, we apply our approach on three fields operated by eni. These include light, medium and heavy-oil reservoirs, where Gas, Chemical and Thermal EOR projects have been respectively proposed. Our results are (a) conducive to the compilation of a broad and extensively usable data-base of EOR settings and (b) consistent with the field observations related to the three tested and already planned/implemented EOR methodologies, thus demonstrating the effectiveness of our approach.
Evaluation of Petrophysical and Mechanical Features for Shale Gas Reservoirs in South Sichuan Basin, China
Authors: Zhang Rui , Ning Zhengfu , Yang Feng , Zhao Huawei
Published: May 2015

Shale gas, as an unconventional resource, has become an exploration and exploitation hotpoint in China. In this paper, a series of experiments were conducted to investigate petrophysical and mechanical properties on the gas shales in Longmaxi Formation south Sichuan Basin, China. Mineralogical and organic geochemical analysis results indicate shale matrix shows strong heterogeneity and structure complexity. A positive correlation between TOC and quartz indicates that bioclastics are the main source of both siliciclastic and organic matters in anaerobic environment. Pore structure was investigated by mercury injection and nitrogen adsorption measurements. The dominant pore size distributes below 3.7nm measured by mercury injection, while 3-5nm by nitrogen adsorption. Micronsized fractures and nanopore structure of shale samples had been identified through mercury saturation curves and adsorption-desorption isotherms. The average maximum mercury saturation is less than 50% at 414MPa, and all of the nanopores were slit-shaped (Type H3 adsorption-desorption isotherms). The BET specific surface area which was calculated from nitrogen adsorption ranges between 7-19 m2/g and have an obvious positive relationship with TOC (total organic matter content) and illite-montmorillonite mixed layer content. Pulse decay measurement reveals that an exponential function can describe the permeability deterioration upon applied effective stress. The stress-dependent permeability of shale is more sensitive than sandstone because of high pore compressibility (low aspect ratio of pore and elastic moduli). The stress-dependent permeability data of samples with micronsized fractures can also be excellently fitted by Walsh model (fractured porous media permeability model), and fitting results show that the fractures in shale samples have high roughness and small aperture compared with sandstone. Static Young's modulus of shale samples increase with increasing quartz, and decrease with increasing TOC and clay minerals content. Due to the weak mechanical property of montmorillonite, shale samples show viscoelastic behaviour and relatively weak mechanical parameters (low Young's modulus, cohesive strengths and friction coefficients, high possion's ratio) under triaxial compression conditions. With the increasing of confining pressure, shales gradually transform from brittleness to ductileness. A comparison of static mechanical parameters between our samples and North America indicates that black siliceous shales of Longmaxi formation have moderate Young's modulus and Poisson's ratio.
Optimization of Well Pad & Completion Design for Hydraulic Fracture Stimulation in Unconventional Reservoirs
Authors: Schofield J. , Rodriguez-Herrera A. , Garcia-Teijeiro X.
Published: May 2015

Reservoir stimulation by means of hydraulic fracturing has enhanced the production of hydrocarbons from shale. The latest methods concentrate on reducing the detrimental interference between fractures within the same well. The theory behind this is well understood, however the concept of constructive interference between fractures in adjacent wells is not so developed.

In this paper, contemporary hydraulic fracturing techniques are numerically simulated to analyze both the rock and fluid mechanic effects on the generation of fractures within a reservoir. The techniques involve various geometrical patterns of well and fracture spacing, followed by methods of sequencing the different stages of stimulation. These methods aim to reduce the compressive stress normal to fractures and increase the size o f tensile regions between fractures in adjacent wells. To measure the performance of different methods, the simulated microseismic energy released is used to calculate the stimulated rock volume (SRV). Production profiles have been generated for several key hydraulic fracturing scenarios, with the results predominantly showing an optimum well spacing to exist.
Lessons Learned from Further Development of the Peregrino Heavy Oil Field Offshore Brazil
Authors: Haugen Einar , Østbye Nils O. , Grønvold Tore , Straith Knut , Theting Thomas G.
Published: May 2015

The Peregrino heavy oil field is located 85 km off the coast of Cabo Frio, Rio de Janeiro. The water depth in the area is approximately 120 m. Phase I of the development comprises a FPSO and two wellhead/drilling platforms. Production of oil started in April 2011. Statoil is operator with 60% equity and partner Sinochem holds 40%. To date, more than 80 million barrels of 14° API oil has been lifted and close to 30 development wells have been drilled. The drive mechanism of the reservoir is reinjection of produced water and pressure support from the aquifer.

The new Phase II development involves a third wellhead platform tied back to the FPSO. It targets oil resources that cannot be reached from the two existing wellhead platforms. An extensive exploratory drilling program with a total of six reservoir penetrations and a detailed data collection program were undertaken in 2011-2012. From the drilling campaign the Peregrino field was found to have a large southern extension with additional 1-2 billion barrels of oil in place that could be developed. In spite of many similarities with the geology in Phase I, the new reservoirs held a number of surprises with respect to reservoir fluid (lighter oil was found) and different reservoir properties.

This paper describes the experiences and challenges with developing this offshore heavy oil field from a subsurface point of view: These include appraisal strategy for optimum data collection, reservoir modelling, and impact on design parameters such as production capacities. Many of these challenges are generic for heavy oil fields: how to handle large amounts of water circulation, identifying reservoir data that are critical for field planning such as absolute and relative permeability. Heavy oil reservoirs with oil viscosity of several hundred centipois are usually high quality reservoirs with relatively homogenous sandstone, as is the case with the Peregrino field for the most part. This paper discusses critical factors in determining reservoir performance for a wide range of reservoir parameters, and includes a section on how this was implemented in the uncertainty analysis.

Safe water injection into the oil zone to avoid fracturing the cap rock is very important. This has been assured both through theoretical work and data from an injection well in the Peregrino field. All producers in Peregrino are horizontal wells (with open-hole gravel packs) in order to improve productivity and drainage. Flow assurance and oil-water transport in wells and flow lines are also described. Use of inflow control valves in horizontal wells have shown potential in Peregrino and will be described in the paper.
Using Tracer Data to Determine Polymer Flooding Effects in a Heterogeneous Reservoir, 8 TH Reservoir, Matzen Field, Austria
Authors: Laoroongroj Ajana , Lüftenegger Markus , Kadnar Rainer , Puls Christoph , Clemens Torsten
Published: May 2015

Polymer injection pilot projects aim at reducing the uncertainty and risk of full-field polymer flood implementation. The interpretation of polymer pilot projects is challenging owing to the complexity of the process and fluids moving out of the polymer pilot area. The interpretation is increasingly more complicated with the heterogeneity of the reservoir.

In the polymer pilot performed in the 8 TH reservoir of the Matzen Field in Austria, a polymer injection well surrounded by a number of production wells was selected. A tracer was injected one week prior to polymer injection. The tracer showed that the flow-field in the reservoir was dramatically modified with increasing amounts of polymers injected. Despite short breakthrough times of 4-10 weeks observed for the tracer, polymer breakthrough occurred only after more than 12 months although injection and production rates have not been substantially changed.

The tracer signal indicated that the reservoir is heterogeneous with high flow velocities occurring in high permeable layers. By injecting polymers, the mobility of the polymer augmented water was reduced compared with water injection and lead to flow diversion into adjacent layers. The tracer response showed that the speed of the tracer moving from injection to production wells was reduced with increasing amount of polymers injected.

This response was used to assess the changes of the amount of water flowing from injection to production well. After a match for the tracer curve was obtained, adsorption, residual resistance factor and dispersivity were calculated. The results showed that even for heterogeneous reservoirs without having good conformance of the pilot, the critical parameters for polymer injection projects can be assessed by analyzing tracer and polymer response. These parameters are required to determine whether implementation of polymer injection at field scale is economically attractive.

Along the flow path, an incremental recovery of about 8 % was achieved. The polymer retention and inaccessible pore volume in the reservoir was in the same range as in core floods. Incremental oil recovery owing to acceleration along the flow path was estimated at contributing to about 30 % to the overall incremental oil production due to polymer injection and 70 % to improved sweep efficiency.
Operational Challenges and Monitoring of a Polymer Pilot, Matzen Field, Austria
Authors: Lüftenegger Markus , Kadnar Rainer , Puls Christoph , Clemens Torsten
Published: May 2015

Four main areas of uncertainty can be described in polymer injection projects: Are we able to deliver the polymer solutions at the required quality to the wellhead?Are we able to inject polymers at the required quantity and quality?Are we producing sufficient incremental oil?Are we able to cost-effectively separate, and treat oil and water after polymer breakthrough?

The monitoring program which was developed for the polymer injection pilot aims at reducing the uncertainty and at fast identification of operational difficulties - details are described below:

Polymer quality at the wellhead: the polymer concentration and viscosity of the “mother” solution and injected polymer solution was measured at various locations in the surface facilities. A quality check of the delivered polymer, including a filter ratio test of the dissolved polymer was performed, the biological activity monitored, iron content measured and polymer solution investigated for “fish-eyes”. The monitoring program enabled us to identify challenges related to shearing the polymers after changing the operating envelope, to identify problems related to biological activity and to ensure data quality for interpretation of the pilot. Injectivity and Degradation: monitoring involved wellhead and bottom-hole-pressure measurements and repeated fall-off tests as well as visual monitoring of the polymer solutions in the well. The results showed the mobility reduction of the polymer solutions versus water mobility and an indication of induced fractures. Combining the various measurements led to identification of an operational issue: the injectivity decreased more than expected from polymer rheology and prepilot water quality assessment. The reason was the combination of polymers and biological activity in combination with fines and oil (despite being small). This challenge is currently tackled by reducing the biological activity. Incremental oil: accurate measurement of the water cut of the producing wells is key; in particular of the wells producing at water cuts above 90%. In addition, water salinity at the producing wells was measured and a repeated tracer program was set up. The results have been used to assess the reservoir architecture and incremental oil related to polymer injection. The challenges in the interpretation of the pilot related to conformance of the pilot could be resolved using this data. Polymer, oil, water treatment: the surface facilities are constantly monitored for separation efficiency and plugging owing to back produced polymers. Operating challenges are seen in all treatment steps for full field polymer injection implementation due to separation but also handling of the polymers in water treatment facilities.
Effects of Rock Anisotropy on Integrated Modelling
Authors: Li L. , Bakk A. , Fjær E. , Bauer A. , Stenebråten J.F. , Holt R.M.
Published: May 2015

Associated with reservoir monitoring towards optimizing production of oil and gas and maximizing the recovery, or ensuring safe CO2 storage, it may be beneficial to introduce integrated geomechanics, rock physics and seismic modelling in the work flow. The geomechanics modelling estimates the effective stress change and deformation in the reservoir and surrounding rocks induced by reservoir pore pressure change. The rock physics modelling estimates the subsequent change of the seismic wave velocities in the rock. Then the seismic modelling estimates detectable changes in the seismic signals. Rock anisotropy may affect every component in such integrated modelling. In this paper we performed the integrated modelling study and compared two simplified cases: In one case, all the rocks were assumed isotropic in stiffness, while in another case, the overburden and sideburden were assumed transeversely isotropic. The geomechanical modelling showed that the in situ stresses which were assumed pure results of rock gravity were already different in two cases. After reservoir depletion, the stress changes were different in two cases as well. A rock physics model was used to calculate the changes of seismic wave velocities as results of the changes of rock stresses and rock deformation. The rock physics model is based on the diffenrential effective medium theory and assumes the rock as a solid with spherical void inclusions and penny-shaped cracks, aiming at capturing stress-sensitive and anisotropic wave velocities. Seismic wave two way travel times and time shifts were calculated along different paths, with different offsets but the same reflection midpoint. The results show the difference between the isotropic case and the anisotropic case. Such difference increases with increasing offset. We conclude that such integrated modelling is important to understand the physical processes in the subsurface because those processes are interdependent. Rock anisotropy plays an important role in the physical processes and has significant impacts on the results of the integrated modelling.
Joint Interpretation of Interwell Connectivity by Integrating 4D Seismic with Injection and Production Fluctuations
Authors: Yin Zhen , MacBeth Colin , Chassagne Romain
Published: May 2015

A technique is proposed to quantitatively measure interwell connectivity by correlating multiple 4D seismic monitors to historical well production data. We make use of multiple 4D seismic surveys shot over the same reservoir to generate an array of 4D seismic differences. Then a causative relationship is defined between the 4D seismic signals and changes of reservoir fluid volumes caused by injection and production behavior. This allows us to correlate seismic data directly to well data to generate a “well2seis” volume. It is found that the distribution of the “well2seis” correlation attributes reveals key reservoir connectivity features, such as the seal of faults, inter-reservoir shale and fluid flow pathways between wells, and can therefore enhance our interpretation on interwell connectivity. Combining with conventional interwell methods that are based on injection and production rate variations, this multiple 4D seismic method is found to support the conventional interwell approaches and can provide more reliable and detailed interpretation.

Our methodology is tested on a synthetic model extracted from full-field data for a Norwegian Sea reservoir, the fluid flow of which is controlled by fault compartmentalization and inter-reservoir shale. The full structural details and reservoir properties are preserved but three scenarios with different degrees of reservoir connectivity are created. It is found that proposed technique successfully detects the flow paths of the injected fluids in all reservoir scenarios. A volumetric attribute is created that accurately identifies the distinctive types of key flow barriers and conduits for each scenario that are known to be major factors influencing the reservoir dynamics. This proves that the well2seis attribute agrees with geological interpretations better than conventional well connectivity factors based on engineering data only. Additionally, the combination of the two types of methods provides a more robust tool for characterization of the reservoir connectivity by providing both quantitative degree and physical pattern of interwell communication.
Integrated Model Based Decision Analysis in Twelve Steps Applied to Petroleum Fields Development and Management
Authors: Schiozer Denis José , Santos Antonio Alberto , Drumond Paulo Soares
Published: May 2015

This work describes a new methodology based on 12 steps for integrated decision analysis related to petroleum fields development and management considering reservoir simulation, risk analysis, history matching, uncertainty reduction techniques, representative models and selection of production strategy under uncertainty. The example of application is the field UNISIM-I-D which is a benchmark case based on Namorado field, Campos Basin, in Brazil. The main focus of the results is to show that the method can be used in practical applications, i.e., complex reservoirs in different field stages (development and management) because it allows the integration of static (geostatistical images generated by reservoir information) and dynamic data (well production and pressure) to reduce uncertainties allowing risk analysis integrating geological, economic and other uncertainties yielding a decision analysis based on risk-return techniques. In this methodology, no proxy model is used so reservoir simulation is used directly to reproduce field performance. We also show that the methodology is efficient and easy to use, even in complex cases where the computational time is an important concern and in real time operations.
Effects of Water Salinity, CO2 Solubility, and Gas Composition on Coal Wettability
Authors: Ibrahim Ahmed Farid , Nasr-El-Din Hisham A.
Published: May 2015

Geological sequestration of CO2 in coal seams has become an attractive carbon sequestration technology for two reasons. First, the injection of CO2 or mixtures of CO2 and N2 enhances methane production from coalbeds (ECBM). Second, it reduces the effect of global warming by storing CO2. The sequestration of CO2 in Tiffany and Allison fields in the San Juan Basin is an example of this technology. The efficiency of this process is strongly dependent on the wetting behavior of the coal–water–CO2 system and the CO2 diffusion rate from the cleat network, through the micro-cleats, and to the matrix surface, which is improved if the coal is CO2 wet.

This study aims to investigate the effects of the salt type and concentration of coal seam water, the solubility of CO2 in water, and the injected gas composition on the wettability of a highly volatile bitumen coal with 82 wt% carbon content from Bull Hill, Oklahoma. Contact angles in the coal–water–CO2 system were measured using a captive bubble method at pressures up to 1000 psi. Adsorption isotherm measurements were conducted to confirm the effect of salt concentration on the CO2/coal surface adsorption behavior. The zeta potential was measured to examine the effects of the salt concentration on coal hydrophobicity.

The results showed that the coal tended to be CO2 wet as the pressure increased where the contact angle changed from 80° at atmospheric pressure to 125° at high pressure (1000 psi). It was found that the salt concentration increased the coal wettability to the CO2. NaCl increased the contact angle values from 125° to 140° with a NaCl concentration of 15 g/L. It was found that MgCl2 and CaCl2 slightly increased the contact angles. These results were confirmed by measuring the adsorption isotherm and the zeta potential at different water salinities. The CO2 adsorption was improved as the salt concentration increased and the absolute zeta potential value decreased, especially in NaCl cases. It was found that the contact angles of flue gases were generally smaller than those of CO2 and the contact angles did not exceed 90° even at high pressures and high N2 contents (81° at 1000 psi for 100% N2). The solubility of CO2 in water did not affect the stabilized contact angle values but it minimize the stabilization time as the solubility increased.

Based on these observations, for CO2 storage and ECBM purposes, injection of CO2 into highly volatile bitumen coal seams is more efficient as the salt concentration content increase. However, other types of coals might show different behaviors due to their varying rank and mineral compositions.
A Study of the Interaction Mechanism between Hydraulic Fractures and Natural Fractures in the KS Tight Gas Reservoir
Authors: Zhang Fuxiang , Qiu Kaibin , Yang Xiangtong , Hao Jun , Yuan Xuefang , Burghardt Jeffrey , Liu Hongtao , Dong Jianyi , Luo Fang
Published: May 2015

The KS reservoir is a naturally fractured, deep, tight gas sandstone reservoir under high tectonic stress. Development wells for this reservoir are of depths in excess of 6,500 m TVD. Stimulation is required to provide production rates that sufficiently compensate for the high cost of drilling and completing wells to access this deep reservoir. Hydraulic fracture design and execution must be optimal to ensure economic production. To effectively stimulate a more than 200-m thick sandstone reservoir yielding consistently high performance, it is critical to understand the interaction between hydraulic fractures and natural fractures, as the natural fractures significantly affect the growth and geometry of hydraulic fractures.

To this end, a comprehensive study was conducted involving frac pressure analysis of previously stimulated wells, microseismic data analysis, hydraulic fracturing modeling by using a fracturing simulator that honors the natural fracture system, near-wellbore 4D geomechanical simulation of mechanical response of natural fractures during hydraulic fracturing, and large block hydraulic fracturing tests. This study reveals that existing natural fractures results in complexity of hydraulic fracture systems both in the near wellbore region and in the far field region. The complexity in the far field is largely controlled by the intersection angle (defined as the angle between the natural fracture strike and the maximum horizontal stress direction) given the large differential horizontal stress in this field.

Based on an understanding of the interaction mechanism, an optimization of the hydraulic fracturing strategy was implemented in KS field. Improvements were made in staging, perforation, diversion, and the pumping schedule, which increased the averaged production rate more than 50% compared with previously stimulated wells.
Use of Emulator and Canonical Correlation to Incorporate 4D Seismic Data in the Reduction of Uncertainty Process
Authors: Ferreira Carla J. , Davolio Alessandra , Schiozer Denis J. , Vernon Ian , Goldstein Michael
Published: May 2015

In petroleum engineering, simulation models are used in reservoir performance prediction and in the decision-making process. These models are complex systems, typically characterized by a vast number of input parameters. Typically, the physical state of the reservoir is highly uncertain and, thus, the appropriate parameters of the input choices are also highly uncertain. 4D seismic data can reduce significantly the uncertainty of the reservoir because it has a high area resolution, as opposed to the observed well rates and pressure. However, two main challenges are faced to calibrate the simulation model using 4D seismic data. The process can be time consuming because most models go through a series of iterations before being considered sufficiently accurate to give an adequate representation of the physical system. The consideration of 4D seismic data as an observed parameter in the form of maps would lead to an unfeasibly large number of variables to be matched. To overcome such issues, the construction of an emulator that represents the simulation model and the use of the canonical correlation technique to incorporate 4D seismic data can be used. The present study constructed a stochastic representation of the computer model called an emulator to quantify the reduction in the parameter input space. 4D seismic data was incorporated in the procedure through the canonical correlation technique. The water saturation map derived from seismic data was converted into seven canonical functions. Such functions represent the observable characteristics to be matched in the uncertainty reduction process. A high number of evaluations was necessary to identify the range of input parameters whose outputs matched the historical data (4D seismic data). The large number of evaluations justifies the use of an emulator and the reduction of uncertainties with areal characteristics shows that 4D seismic data was successfully incorporated. The emulator methodology represents a powerful tool in the analysis of complex physical problems such as history matching. The incorporation of 4D seismic data as an observable output to be matched leads to a difficult problem to be solved. However, the canonical correlation permitted a successful incorporation of such data into the problem.
Beyond Q-Resolution and Prenex Form: A Proof System for Quantified Constraint Satisfaction
Authors: Chen Hubie
Published: May 2015

We consider the quantified constraint satisfaction problem (QCSP) which is to
decide, given a structure and a first-order sentence (not assumed here to be in
prenex form) built from conjunction and quantification, whether or not the
sentence is true on the structure. We present a proof system for certifying the
falsity of QCSP instances and develop its basic theory; for instance, we
provide an algorithmic interpretation of its behavior. Our proof system places
the established Q-resolution proof system in a broader context, and also allows
us to derive QCSP tractability results.
Call-by-value, call-by-name and the vectorial behaviour of the algebraic \lambda-calculus
Authors: Assaf Ali , Díaz-Caro Alejandro , Perdrix Simon , Tasson Christine , Valiron Benoî t
Published: May 2015

We examine the relationship between the algebraic lambda-calculus, a fragment
of the differential lambda-calculus and the linear-algebraic lambda-calculus, a
candidate lambda-calculus for quantum computation. Both calculi are algebraic:
each one is equipped with an additive and a scalar-multiplicative structure,
and their set of terms is closed under linear combinations. However, the two
languages were built using different approaches: the former is a call-by-name
language whereas the latter is call-by-value; the former considers algebraic
equalities whereas the latter approaches them through rewrite rules. In this
paper, we analyse how these different approaches relate to one another. To this
end, we propose four canonical languages based on each of the possible choices:
call-by-name versus call-by-value, algebraic equality versus algebraic
rewriting. We show that the various languages simulate one another. Due to
subtle interaction between beta-reduction and algebraic rewriting, to make the
languages consistent some additional hypotheses such as confluence or
normalisation might be required. We carefully devise the required properties
for each proof, making them general enough to be valid for any sub-language
satisfying the corresponding properties.
Weak Cat-Operads
Authors: DOSEN Kosta , Petric Zoran
Published: May 2015

An operad (this paper deals with non-symmetric operads)may be conceived as a
partial algebra with a family of insertion operations, Gerstenhaber's circle-i
products, which satisfy two kinds of associativity, one of them involving
commutativity. A Cat-operad is an operad enriched over the category Cat of
small categories, as a 2-category with small hom-categories is a category
enriched over Cat. The notion of weak Cat-operad is to the notion of Cat-operad
what the notion of bicategory is to the notion of 2-category. The equations of
operads like associativity of insertions are replaced by isomorphisms in a
category. The goal of this paper is to formulate conditions concerning these
isomorphisms that ensure coherence, in the sense that all diagrams of canonical
arrows commute. This is the sense in which the notions of monoidal category and
bicategory are coherent. The coherence proof in the paper is much simplified by
indexing the insertion operations in a context-independent way, and not in the
usual manner. This proof, which is in the style of term rewriting, involves an
argument with normal forms that generalizes what is established with the
completeness proof for the standard presentation of symmetric groups. This
generalization may be of an independent interest, and related to matters other
than those studied in this paper. Some of the coherence conditions for weak
Cat-operads lead to the hemiassociahedron, which is a polyhedron related to,
but different from, the three-dimensional associahedron and permutohedron.
Ranking Templates for Linear Loops
Authors: Leike Jan , Heizmann Matthias
Published: May 2015

We present a new method for the constraint-based synthesis of termination
arguments for linear loop programs based on linear ranking templates. Linear
ranking templates are parameterized, well-founded relations such that an
assignment to the parameters gives rise to a ranking function. Our approach
generalizes existing methods and enables us to use templates for many different
ranking functions with affine-linear components. We discuss templates for
multiphase, nested, piecewise, parallel, and lexicographic ranking functions.
These ranking templates can be combined to form more powerful templates.
Because these ranking templates require both strict and non-strict
inequalities, we use Motzkin's transposition theorem instead of Farkas' lemma
to transform the generated $\exists\forall$-constraint into an
$\exists$-constraint.
Domain Representations Induced by Dyadic Subbases
Authors: Tsuiki Hideki , Tsukamoyo Yasuyuki
Published: May 2015

We study domain representations induced by dyadic subbases and show that a
proper dyadic subbase S of a second-countable regular space X induces an
embedding of X in the set of minimal limit elements of a subdomain D of
$\{0,1,\perp\}\omega$. In particular, if X is compact, then X is a retract of
the set of limit elements of D.
Extracting verified decision procedures: DPLL and Resolution
Authors: Berger Ulrich , Lawrence Andrew , Forsberg Fredrik Nordvall , Seisenberger Monika
Published: May 2015

This article is concerned with the application of the program extraction
technique to a new class of problems: the synthesis of decision procedures for
the classical satisfiability problem that are correct by construction. To this
end, we formalize a completeness proof for the DPLL proof system and extract a
SAT solver from it. When applied to a propositional formula in conjunctive
normal form the program produces either a satisfying assignment or a DPLL
derivation showing its unsatisfiability. We use non-computational quantifiers
to remove redundant computational content from the extracted program and
translate it into Haskell to improve performance. We also prove the equivalence
between the resolution proof system and the DPLL proof system with a bound on
the size of the resulting resolution proof. This demonstrates that it is
possible to capture quantitative information about the extracted program on the
proof level. The formalization is carried out in the interactive proof
assistant Minlog.
The extensional realizability model of continuous functionals and three weakly non-constructive classical theorems
Authors: Normann Dag
Published: May 2015

We investigate wether three statements in analysis, that can be proved
classically, are realizable in the realizability model of extensional
continuous functionals induced by Kleene's second model $K_2$. We prove that a
formulation of the Riemann Permutation Theorem as well as the statement that
all partially Cauchy sequences are Cauchy cannot be realized in this model,
while the statement that the product of two anti-Specker spaces is anti-Specker
can be realized.