bluuebunny/crossref_metadata_2025_split huggingface dataset:
Full Waveform Inversion With Extrapolated Low Frequency Data
Authors: Li Yunyue Elita , Demanet Laurent 
Published: March 2016

Abstract
Low frequency data are crucial for the success of full waveform inversion (FWI) because it defines the low wavenumber component of the velocity model and determines the kinemat- ics of the seismic waves at higher frequencies. When low frequency data are missing, FWI with inaccurate starting models suffers severely from cycle skipping and yields erroneous inversion results. However, acquiring low frequency data from the field is a challenging and expensive task. In this paper, we explore the possibilities of synthesizing low frequencies from high frequency data. Low frequency extrapolation from the band-limited recordings is feasible by first separating the seismic record into individual events and extrapolating their frequency content to a lower frequency band based on the nondispersive assumption. The extrapolated low frequency data are reasonable approximations to the true low frequency data, with higher fidelity in phase than in amplitude. To demonstrate the reliability of the extrapolated low frequencies for FWI, we initialize FWI at low frequencies using the extrapolated phase information. The resulting low wavenumber models are then used to initialize full waveform inversion at higher frequencies. We demonstrate that FWI with extrapolated low frequency data produces reasonable estimations of the low wavenumber velocity model, which further help FWI escape the local minima.
Application of VTI Fast Marching Eikonal Solver to Improve Seismic Imaging
Authors: Alashloo S. Y. M. , Ghosh D. , Bashir Y. 
Published: March 2016

Abstract
Sedimentary layers in the Earth's subsurface result in seismic anisotropy which makes the wave velocity dependent to the propagation angle. This phenomenon causes complexities and errors in seismic imaging such as mispositioning of migrated events. One of the challenging issues in seismic imaging is the computation of seismic wave traveltime from source to receiver via the reflection point. A powerful method to compute traveltime is applying finite difference to solve the eikonal equation. In this study, we employ a fast marching eikonal solver in isotropic and VTI concept to obtain the seismic traveltime required for Kirchhoff depth migration algorithm. Rather than using elliptical eikonal equation which is commonly used in industry, we consider an anelliptic approximation since it is more realistic and accurate. Comparing the contours of isotropic and VTI traveltimes demonstrates a considerable lateral difference of wavefronts for both conditions. After Kirchhoff imaging, results show that the VTI imaging algorithm generates images with higher resolution than the isotropic one specifically in deeper parts where reflectors are more continuous and their patterns are more clear and traceable.
Single-Trip Abandonment Approach
Authors: Denmon Michael , Harive Kevin , Irvine Bruce 
Published: March 2016

Abstract
As the number of mature wells that are no longer economically viable increases, so does the need for effective well abandonment processes that meet stringent environmental and regulatory conditions. Because of varying well configurations and types, a unique or more tailored engineering approach is required to meet plug and abandonment governmental requirements, as well as operator-specific objectives for varying well designs. Through proper planning and design, this method also decreases operational and health, safety, and environmental (HSE) risks for a variety of challenging scenarios. This paper presents case histories of the successful use of a single-trip abandonment approach that saves time for the producers by addressing specific well types by simplifying the abandonment process in an economical and flexible manner through engineering planning and shaped-charge performance design.
The single-trip abandonment approach can drastically reduce associated costs common in well abandonment campaigns, including rig time and support services that are involved in making multiple trips in and out of the well. With an average rig rate of USD 500,000 per day for floaters, USD 100,000 per day for jackups, and USD 60,000 per day for barges (Rigzone 2015), any reduction in rig time exposure can be beneficial to the producer. By providing a method of successfully abandoning a well in one trip, as opposed to separate trips involving the cutting and removal of casing strings, the single-trip well abandonment approach allows producers to successfully plug and then spot cement in a combined action, permitting an expedited well abandonment process.
Through extensive testing and development of both tool technology and shaped-charge design, the single-trip well abandonment approach has proven to be a versatile and an effective system for a variety of well abandonment scenarios. Providing flexibility in operational capabilities for abandoning a well, squeezing off zones, providing limited casing entry, and allowing annular cement squeezing for remedial work, the single-trip abandonment approach has proven to be reliable and efficient, particularly in operations in the AsiaPac region. Using the engineering aspects of advanced tubing-conveyed perforating (TCP) design and capabilities as a building block in the single-trip system allowed for the successful implementation of required abandonment procedures while also providing the capability to be deployed in a variety of casing sizes, weights, and wellbore conditions.
This paper provides an in-depth study of the technical design, advanced modeling, multiconditional testing, and shaped-charge optimization of the systems for the single-trip abandonment approach. Additionally, the paper provides beneficial information that could be applied to well abandonment projects around the world.
Behind Casing Inspection Using Active Gamma-Gamma Technique
Authors: Hu Yike , Guo Weijun 
Published: March 2016

Abstract
During the completion of well drilling, cement is pumped into the annulus behind the casing to provide zonal isolation and a pressure barrier. The cement integrity inside the annulus is crucial for environmental and safety concerns. This paper describes a subsurface evaluation technique to evaluate the cement integrity behind the casing using an active gamma-gamma technique.
The target was a layered structure consisting of single or multiple layers of casing, cement in the annulus, and formation. The tool in use includes a radioactive gamma source and a gamma ray detector, which is designed to be sensitive only to the annular space away from the inner casing. Monte Carlo N-particle (MCNP) simulation based on high-energy photons transport was conducted to simulate the energy spectrum that would be measured by the gamma ray detector. Cement channels were represented by the void located in the annulus, which is characterized in volumetric terms and the localized area coverage of the voids. The detector responses change with different cement integrities. There are two attributes describing the gamma ray spectrum: count rates (CR) ratio and dipping point value. Through extensive computer modeling, the correlation between cement integrity and spectrum information was established, which are in terms used when generating equal CR-ratio curve and equal-dipping point curves. When investigating cement of unknown integrity, its gamma ray response is recorded by the detector and processed by algorithms. The dipping point value (Edip) and count rates ratio (CRratio) can be computed from the as-recorded gamma ray spectrum, and a volume-position chart can be generated in which the equal CR-ratio curve and equal-dipping point curve are plotted. The cement integrity information, the amount and the position of the void, are found simultaneously as the intersection of those two curves.
As compared to the conventional acoustic methods used in cement evaluation, this paper proposes an evaluation method using nuclear technology. The new method provides a data processing methodology to determine the void amount and position inside the cement, which could be used to image the void channel inside the cement.
Dry Tree Semisubmersible for Cost-Effective Deepwater Development
Authors: Tan J. H. , Kiprawi F. , Teng Y. , Kyoung J. , O'Sullivan J. F. , Nazri J. A. 
Published: March 2016

Abstract
Dry tree floating platforms for deepwater offshore developments are typically Spars and Tension Leg Platforms (TLPs). All production semisubmersibles in operation support only wet tree systems because the hull motions are not sufficiently small to allow the use of riser tensioning systems which connect vertical production risers from the subsea wells directly to the topsides. The wet tree semisubmersible designs can potentially be improved for dry tree applications with reduced heave motions. The advantages of dry tree semisubmersibles for deepwater development are presented in this paper with focus on the hull global performance and the cost benefits.
This paper presents a dry tree semisubmersible design with low heave motion and reduced vortex-induced-motion (VIM), hence named Heave and VIM Suppressed (HVS) semisubmersible. A case study of the HVS semisubmersible is performed for the dry tree application to support a relatively small topsides payload of 7,000 MT and five top tensioned risers (TTRs) in benign South East Asian environment. Through numerical simulations using Computational Fluid Dynamics (CFD) and conventional motion analysis based on potential flow theory, the hull global performance and maximum riser tensioner stroke range are provided. The stability analysis results for intact and damaged conditions are presented. The constructability and stability in pre-service conditions are briefly discussed to address the practical application of this hull with respect to cost effectiveness.
The results demonstrate technical readiness of this hull design by showing its ability in supporting dry tree systems with field proven riser tensioners and its superior stability for drilling operations. The application of this dry tree semisubmersible is technically feasible today in mild-to-moderate environmental conditions and thus it is an attractive option for new deepwater development with potential cost benefits.
Perforating the Largest High-Pressure Wells in the Gulf of Mexico
Authors: Brinsden M. , Gavric Z. , Le C. , Baumann C. , Smart M. , Stulb C. 
Published: March 2016

Abstract
The largest deepwater wells in the Gulf of Mexico have been drilled in the Lower Tertiary play. Most of these wells are completed with single-trip multizone systems have gross perforated lengths exceeding 1,500 ft. The main difficulty in perforating these wells is the ~20,000 psi high-pressure environment. Under these conditions, the challenges include creating sufficiently large entrance holes in the casing, minimizing the high-risk of equipment damage due to gunshock, and reducing the amount of perforating debris created.
Perforating several intervals in a single run is required to complement single-trip multizone systems. Perforating all zones simultaneously in a single trip saves time and reduces risk when compared with stacked frac-pack completions requiring multiple trips for each zone. Safety and cost reduction are extremely important in deepwater operations. Risk control is very important because gunshock and/or debris problems can lead to multimillion dollar losses in nonproductive time, and in extreme cases, gunshock problems can lead to lost wells.
To undertake these challenges, a new Low Perforating Shock and Debris (LPSD) gun system was used. In comparison with standard high-pressure guns, the LPSD gun system produces much less gunshock and negligible amounts of debris; thus, minimizing gunshock risk and reducing cleanup runs typically needed to recover perforating debris. LPSD guns produce negligible amounts of debris because LPSD guns retain all the metallic components inside the guns, including the shaped charge cases, which remain virtually intact inside of the guns. A key element in planning these perforating jobs is gunshock prediction to evaluate if the equipment will be able to withstand the transient loads produced by the perforating guns. The gunshock prediction process is described in detail in this paper.
For a typical 4- to 6-zone 1,500 ft gross length perforating job, the time needed from picking up the first gun to laying out the last gun averages 84 hours. All zones are simultaneously perforated, which eliminates at least three perforating runs per well, saving approximately 9.2 days per well while minimizing personnel exposure. By perforating the largest deepwater high-pressure wells in the Gulf of Mexico's Lower-Tertiary play with LPSD guns, we minimized personnel exposure, minimized debris and reduced execution time up to 72%.
Research of Improvement and Optimization of Critical Flow Rate Model in Condensate Gas Well
Authors: Zhou C. , Wu X. , Li H. , Tang J. , Liu X. 
Published: March 2016

Abstract
Critical flow rate models are widely used for liquid loading prediction in gas wells, take Turner's model as representative, but these models only analyze critical flow rate under wellhead or bottom hole condition, and take surface tension as constant, which results in a relatively large deviation between prediction result and actual liquid loading condition in condensate gas wells. In order to increase precision of liquid loading prediction, critical flow rate models are improved, aiming at solving above-mentioned problems. Different distribution of critical flow rate and surface tension along wellbore are considered, and the largest value of critical flow rate is taken as criterion of liquid loading condition, surface tensions under different temperature and pressure conditions are also calculated. Besides, on the basis of analyzing temperature and pressure distribution in dry gas wellbore by using temperature and pressure coupling method, a reasonable temperature and pressure coupling calculation model for condensate gas well is established, which considers the actual situation that both condensate and formation water exist in wellbore and revises relative density and flow rate of gas accordingly. Through verification by field case, it can be seen that precision of liquid loading prediction of improved critical flow rates models increases compared to that of original models, amongst which the precision of and the increased range of precision of liquid loading prediction of improved Li Min's model is highest. Therefore, the improved Li Min's model is the most suitable model for liquid loading prediction in condensate gas well.
Errors Due to Use of the AGA8 Equation of State Outside of Its Range of Validity
Authors: Glen N. F. , Mills D. , Griffin D. , Fosse S. 
Published: March 2016

Abstract
For many years the AGA 8 method has been the basis for all fluid property calculations related to natural gas supply, and forms an integral part of the measurement infrastructure throughout the world. However, application outside its valid range has the potential to cause significant errors. Case studies are presented that show the potential errors in density and compressibility, and resultant financial exposure, when using the AGA 8 method outside its range of viability.
If all the components are within the specified composition ranges for pipeline quality gas, densities calculated using the AGA 8 method are claimed to have an uncertainty of 0.1 % (at k=2) for temperatures between -10 and 65°C at pressures up to 120 bar(a). However, for mixtures with components in the extended composition range and / or at temperatures and pressures outside the standard limits, the uncertainty increases to between 0.2 and 0.5 % (at k=2) and is effectively indeterminate for compositions outside the extended range of applicability. Comparison with values calculated using the GERG-2008 method generally confirms these claims. However, even for compositions that are within the extended AGA 8 range, the differences can exceed 1 % and the effect of ignoring pseudo-components can cause differences of over 5 %. Given the known limitations of the AGA 8 method and the lack of clarity of the likely uncertainties in calculated densities and compressibilities when used in its extended range, the use of an alternative method would be preferable. Although the GERG-2008 method overcomes some of the limitations of the AGA 8 method, there still remains the problem of ensuring that all the components in the gas stream are measured.
By raising awareness of the limitations of calculating gas properties from composition, this work will help metering system designers, operators and regulators understand the issues that must be addressed when dealing with gas fields whose compositions are outside the pipeline quality gas specification required by the AGA 8 method, as the potential financial exposure can run to hundreds of millions of dollars per annum for a region such as the North Sea.
Pipeline Design Philosophy and Standards – A comparative Study and Recommendations
Authors: Singh Nawin , Nair Sajith 
Published: March 2016

Abstract
The most common method to transport oil and gas within the energy industry is through the pipeline transmission system. However, the pipeline system is very expensive, greatly on account of material and construction costs. One of the key decisive factors for a pipeline project is its capital expenditure (CAPEX). The material cost is primarily driven by "linepipe cost", which is a function of pipeline size and thickness. Several pipeline design standards are followed worldwide based on either the Working Stress Design (WSD) or the Load and Resistance Factor Design (LRFD) approach.
The aim of this paper is to present a comparative study and arrive at recommendations to optimize the material cost of linepipe, through a rational selection of the governing design code for pipelines, design philosophy and material grade. Hence, it is expected that the pipeline industry can benefit, particularly during the initial feasibility stage of evaluating the capital expenditure of a pipeline project.
As the pipeline diameter and operating parameters are fixed in line with process requirements, for purposes of mechanical design, wall thickness will be the governing cost parameter to be assessed. There are broadly two methods of design being followed in the industry to calculate the wall thickness based on pressure containment criteria i.e. WSD (stress criteria) or limit state. Traditionally, pipeline wall thickness is based on WSD, with the allowable design stress considered as a prescribed fraction of Specified Minimum Yield Strength (SMYS). However, there is inherent conservatism in the allowable stress method as only a certain fraction of material strength has been factored.
A recognition of this conservatism by the industry resulted in the limit state approach. A detailed comparison has been performed of available international design standards and the approach followed worldwide to develop the matrix and perform the parametric study. Literature review and parametric analysis indicates that linepipe material cost can be optimized upto 25%. To substantiate the findings, a case study for a typical pipeline project in the Middle East has been performed. FEM tool (e.g. ABAQUS) has been used to ascertain the stress and strain level.
The paper deliberates on the design code, design method and linepipe material and provides recommendations on the judicious selection of these parameters which can ultimately lead to optimum CAPEX. Results of the case study indicate that opportunities exist to optimize the material cost up to 15%.
Successful Tight Gas Development Practice in Ordos Basin of China
Authors: Zhang Xiangning , Zhang Minglu , Ge Chunmei , Deng Huaiqun , Wang Hongyu , Gong Bentao , Zhang Xiaofeng 
Published: March 2016

Abstract
Tight gas is an important resource for PetroChina's foreign cooperation business. PetroChina has cooperated with Shell and TOTAL in tight gas E&P in Ordos basin for years and has made great achievements. It was proved through years of exploration that sets of reservoirs occurred in the Perm-Carb system of the Ordos basin. Benxi, Taiyuan and Lower Shanxi formation are accumulated in marine environment and characterized by sandstones encased in mudstones, while the Upper Shanxi, Shihezi and Shiqianfeng strata are the continental deposits as the favorable targets in the basin.
CB is a cooperation project with Shell in northern Ordos basin. The Permian Shanxi tight gas interval was its target reservoir. CB is the first project deploying dual-lateral horizontal wells to explore the low permeability massive gas field in China and achieved big success. By far, the project has maintained annual production on a high level for 8 years. The second phase appraisal was initiated in 2013 to explore the secondary reservoirs. Recent testing result has seen a good indication and will be very helpful to raise total output to a new level. South Sulige gas field is located in the northwestern Ordos basin and is a project cooperated with TOTAL. To meet the challenges of poor lateral continuity and low reserve richness, an integrated new approach, such as reservoir prediction from 3D seismic Poisson ratio, "chessboard" well patterns from pad development, factory mode drilling and completion operations, were employed which effectively improved well performance and operational efficiency. PetroChina also initiated a joint study with ExxonMobil in Changdong area. The reserves were classified and individual well EURs were estimated by comparing with the U.S. Piceance basin and tight gas E&P practices in Ordos basin. The effective recovery of marginal pay sands will be crucial to the economic.
Total gas consumption in China grew by 7.4% and gas production grew by 6.1% in 2014. Being the largest O&G supplier, PetroChina produced 74.4% of the total national output in 2014. Tight gas accounted for 28% of total annual gas production in PetroChina. Annual natural gas production from foreign cooperation projects reached 6.55 bcm with more than 82% from tight gas reservoirs. Ordos basin, Sichuan basin and Tarim basin are all rich of tight gas resources. Foreign cooperation in tight gas resources in China is enjoying a favorable development circumstances and embracing its bright future.