bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bringing Uncertainty to the Forefront of Informed Decision Making in Oil and Gas Exploration and Development
Authors: Wanjau Paul , Bloomfield Rory , Bauer Jennifer , Rose Kelly 
Published: September 2019

Abstract
As data computing and big data driven analytics become more prevalent in a number of spatial industries, there is increasing need to quantify and communicate uncertainty with those data and resulting spatial analytical products. This has direct implication in oil & gas exploration and development where big data and data analytics continue to expand uses and applications of spatial and spatio-temporal data in the industry without providing for effective communication of spatial uncertainty. The result is that communications and inferences made using spatial data visuals lack crucial information about uncertainty and thus present a barrier to accurate and efficient decision making. With increasing cost awareness in oil & gas exploration and development, there is urgent need for methods and tools that help to objectively define and integrate uncertainty into business decisions.
To address this need, the Variable Grid Method (VGM) has been developed for simultaneous communication of both spatial patterns and trends and the uncertainty associated with data or their analyses. The VGM utilizes varying grid cell sizes to visually communicate and constrain the uncertainty, creating an integrated layer that can be used to visualize uncertainty associated with spatial, spatio-temporal data or data-driven products.
In this paper, we detail the VGM approach and demonstrate the utility of the VGM to intuitively quantify and provide cost-effective information about the relationship between uncertainty and spatial data. This allows trends of interest to be objectively investigated and target uncertainty criteria defined to drive optimal investment in improved subsurface definition. Examples are presented to show how the VGM can thus be used for efficient decision making in multiple applications including geological risk evaluation, as well as to optimize data acquisition in exploration and development.
Today, uncertainty, if it is provided at all, is generally communicated using multiple independent visuals, aggregated in final displays, or omitted altogether. The VGM provides a robust method for quantifying and representing uncertainty in spatial data analyses, offering key information about the analysis, but also associated risks, both of which are vital for making prudent business decisions in oil & gas exploration and development.
Permeability Logging through Constant Pressure Injection Test: In-Situ Methodology and Laboratory Tests
Authors: Manivannan Sivaprasath , Bérest Pierre , Jacques Antoine , Brouard Benoît , Jaffrezic Vincent , De Greef Vincent 
Published: September 2019

Abstract
In wells producing water, oil, gas or geothermal energy, or in access wells to hydrocarbon storages, it is critical to evaluate the permeability of the formation as a function of depth. Continuous permeability logs in these wells are typically derived using tools that measure electrical, nuclear, magnetic or acoustic signals, using empirical relations that are often formation dependent. The permeability logs derived using these empirical relations often show significant differences when compared to the permeabilities obtained from core samples or well tests.
A new technique is proposed in this paper in which the open hole is scanned with an interface between two fluids with a large viscosity contrast. The injection rate into the formation depends on interface location and well pressure history. An inverse problem is solved to estimate permeability as a function of depth from the evolution of flow rates with time. During the test, the well is equipped with a central tube, typically a drill string, and the scanning is done by injecting in the central tube a liquid that is different from the liquid in the annulus, at a constant wellhead pressure. Injection and withdrawal rates are measured at the tubing and the annulus wellheads, respectively; the difference between these two rates gives the formation injection rate. Interface location is also estimated from the flow rates and pressure at the wellhead and an injection profile in the open hole is derived.
A permeability log is derived from this injection log by considering a radial, monophasic flow in each layer and same skin value for all formation layers. Initial formation pressure and storativity, estimated from other logs, are also used as inputs. The sensitivity of the permeability log to these inputs is estimated using analytical expressions. The proposed methodology is applicable to oil or water bearing formations drilled using oil or water-based muds, respectively.
A continuous permeability log is estimated from the synthetic test data using the proposed interpretation workflow; it shows a correlation of 0.95 (on a scale of 0 to 1) when compared to the input permeability log. A laboratory model that mimics a multi-layered formation is used to study the repeatability of the technique and the validity of the uniform skin assumption by creating a mudcake at the inner radius. Four consecutive tests were performed on the same set of samples and the interpreted permeability logs are compared to the benchmark permeability log; correlations are greater than 0.94.
An Accelerated Adjoint Method for Model Maturation to Update Static Models with Time-Lapse Reservoir Surveillance Data
Authors: Alpak Faruk O. , Jennings James W. 
Published: September 2019

Abstract
We develop a novel ensemble model-maturation method that is based on the Randomized Maximum Likelihood (RML) technique and adjoint-based computation of objective function gradients. The new approach is especially relevant for rich data sets with time-lapse information content. The inversion method that solves the model-maturation problem takes advantage of the adjoint-based computation of objective function gradients for a very large number of model parameters at the cost of a forward and a backward (adjoint) simulation. The inversion algorithm calibrates model parameters to arbitrary types of production data including time-lapse reservoir-pressure traces by use of a weighted and regularized objective function. We have also developed a new and effective multigrid preconditioning protocol for accelerated iterative linear solutions of the adjoint-simulation step for models with multiple levels of local grid refinement. The protocol is based on a geometric multigrid (GMG) preconditioning technique. Within the model-maturation workflow, a machine-learning technique is applied to establish links between the mesh-based inversion results (e.g., permeability-multiplier fields) and geologic modeling parameters inside a static model (e.g., object dimensions, etc.). Our workflow integrates the learnings from inversion back into the static model, and thereby, ensures the geologic consistency of the static model while improving the quality of ensuing dynamic model in terms of honoring production and time-lapse data, and reducing forecast uncertainty. This use of machine learning to post-process the model-maturation outcome effectively converts the conventional continuous-parameter history-matching result into a discrete tomographic inversion result constrained to geological rules encoded in training images.
We demonstrate the practical utilization of the adjoint-based model-maturation method on a large time-lapse reservoir-pressure data set using an ensemble of full-field models from a reservoir case study. The model-maturation technique effectively identifies the permeability modification zones that are consistent with alternative geological interpretations and proposes updates to the static model. Upon these updates, the model not only agrees better with the time-lapse reservoir-pressure data but also better honors the tubing-head pressure as well as production logging data. We also provide computational performance indicators that demonstrate the accelerated convergence characteristics of the new iterative linear solver for adjoint equations.
Experimental Investigation and Modeling of Onset of Liquid Accumulation in Large- Diameter Deviated Gas Wells
Authors: Rastogi Ayush , Fan Yilin 
Published: September 2019

Abstract
The challenges related to liquid loading have been observed during flow-back after hydraulic fracturing, as well as during the production phase, and are further aggravated with the high inclination angles found in deviated wellbores. An experimental study was carried out to investigate the onset of liquid loading in a 6-inch production casing at various inclination angles. A unified mechanism model for the onset of liquid loading is developed for a large-diameter production casing.
The experimental setup includes a 6-inch acrylic test section which can be inclined from 0° to 90°. The study involves two-phase air-water flow in low liquid loading conditions to simulate a gas well. A dye- injection-system was used to detect the onset of liquid film reversal.
The experimental data demonstrates that the major factor that induces liquid accumulation is the liquid film reversal at pipe bottom. The critical gas velocity associated with the onset of liquid film reversal shows a strong function with the inclination angle and liquid flow rate in the current experimental study. Comparison with previous experimental data reveals that it also depends on the gas density and pipe diameter, i.e. it decreases with increasing gas density and increases when pipe diameter increases. Comprehensive model evaluation was conducted in the current study, showing a large discrepancy for inclination angles higher than 45° and few existing models capture all the effects of deviation angle, liquid flow rate, pressure, and pipe diameter. A new model is developed based on the physics of the onset of liquid film reversal, coupled with a new model for the liquid film thickness distribution around the pipe perimeter. It captures well the effects of deviation angle, liquid flow rate, gas and liquid density, viscosity, and pipe diameter on the critical gas velocity, outperforming all other existing models.
The experiments in this study provide new insights into the onset of liquid accumulation in large- diameter deviated wells. The new mechanics model fills the critical gap to enhance accuracy when predicting the onset of liquid loading especially for deviated and large-diameter wells. It can be easily implemented, which will benefit the industry practically. It is also applicable to gas condensate pipelines where smaller inclination angles exist.
Experimental and Molecular Insights on Mitigation of Hydrocarbon Sieving in Niobrara Shale by CO2 Huff-n-Puff
Authors: Zhu Ziming , Fang Chao , Qiao Rui , Yin Xiaolong , Ozkan Erdal 
Published: September 2019

Abstract
In nanoporous rocks, potential size/mobility exclusion and fluid-rock interactions in nano-sized pores and pore throats can turn the rock into a semi-permeable membrane, blocking or hindering the passage of certain molecules while allowing other molecules to pass freely. In this work, we conducted several experiments to investigate whether CO2 can mitigate the sieving effect on the hydrocarbon molecules flowing through Niobrara samples. Molecular dynamics simulations of adsorption equilibrium with and without CO2 were performed to help understand the trends observed in the experiments. The procedure of the experiments includes pumping of liquid binary hydrocarbon mixtures (C10 C17) of known compositions into Niobrara samples, collecting of the effluents from the samples, and analysis of the compositions of the effluents. A specialized experimental setup that uses an in-line filter as a mini-core holder was built for this investigation. Niobrara samples were cored and machined into 0.5-inch diameter and 0.7-inch length mini-cores. Hydrocarbon mixtures were injected into the mini-cores and effluents were collected periodically and analyzed using gas chromatography (GC). After observing the membrane behavior of the mini-cores, CO2 huff-n-puff was performed at 600 psi, a pressure much lower than the miscibility pressure. CO2 was injected from the production side to soak the sample for a period, then the flow of the mixture was resumed and effluents were analyzed using GC. Experimental results show that CO2 huff-n-puff in several experiments noticeably mitigated the sieving of heavier component (C17). The observed increase in the fraction of C17 in the produced fluid can be either temporary or lasting. In most experiments, temporary increases in flow rates were also observed. Molecular dynamics simulation results suggest that, for a calcite surface in equilibrium with a binary mixture of C10 and C17, more C17 molecules adsorb on the carbonate surface than the C10 molecules. Once CO2 molecules are added to the system, CO2 displaces C10 and C17 from calcite. The experimentally observed increase in the fraction of C17 thus can be attributed to the release of adsorbed C17. This study suggests that surface effects play a significant role in affecting flows and compositions of fluids in tight formations. In unconventional oil reservoirs, observed enhanced recovery from CO2 huff-n-puff could be partly attributed to surface effects in addition to the recognized gas-liquid interaction mechanisms.
Sieve Distribution vs Sand Retention: The Impact of Mono-Sieved Gravel on Sand Control
Authors: Fuller Michael , Palisch Terry , Fischer Christine 
Published: September 2019

Abstract
Traditional sand control sizing has typically been based on "standard", wide-sieve gravel distributions (i.e. 20/40, 16/30, etc). Historic sand retention testing has therefore been limited to these standard gravel (i.e. proppant) sizes. With the emergence of new proppant technologies, extensive testing has recently been performed to evaluate the impact of mono-sieved gravel on sand retention performance.
Sand retention testing was performed using a number of industry test protocols [Martch 2012] to ascertain the impact of sieve distribution on gravel sizing rules. The testing involved multiple formation particle size distributions (PSDs) and compared the sand retention characteristics of standard-sieve gravel, to comparably sized mono-sieve gravel. Over a dozen PSDs were taken from actual formations containing both uniform and non-uniform distributions, over a wide range of mean particle diameters (d50). Multiple gravel sizes were also tested. Performance indicators measured include produced solids, size of largest produced solids and retained gravel permeability.
Comparison of the mass of produced sand through various combinations of formation/gravel are useful in identifying the preferred gravel to manage solids production. This study will show that sand control performance of mono-sieved gravel is comparable to that of standard-sieve distribution gravel. This is illustrated by comparing the mass of produced sand and measurement of permeability in the various formation/gravel combinations. The paper will demonstrate that numerous "rules of thumb" employed for gravel sizing (including use of "Saucier's ratio") during the gravel- and frac-pack design process can be applied to any sieve distribution gravel, whether standard- or mono-sieved. In addition to the test results, this paper will reference multiple GOM applications with frac-pack completions in which sand control is performing as designed using mono-sieved gravel.
This paper is critical for all completions engineers who are designing gravel or frac-pack completions. Sand retention testing on mono-sieved gravel is novel, and these results complement existing testing. The results of this testing have already been applied by several exploration and production companies, and this paper will allow others to benefit from the work.
Real-Time 3D Inversion of Ultra-Deep Resistivity Logging-While-Drilling Data
Authors: Wilson Glenn , Marchant David , Haber Eldad , Clegg Nigel , Zurcher Derick , Rawsthorne Luke , Kunnas Jari 
Published: September 2019

Abstract
Ultradeep resistivity logging-while-drilling (LWD) is now a routine service for real-time well landing,geosteering, and reservoir and fluid contact evaluation. Progressing beyond layered earth inversions to three-dimensional (3D) inversions helps improve real-time decisions to deliver better well placement, completion, and production. To this end, the first real-time 3D inversion of ultradeep resistivity LWD data is realized by exploiting the fact that the sensitive volume of a given transmitter-receiver pair is far smaller than the total logging volume. This implies that the global mesh can be decoupled into multiple independent, localized inversion and modeling meshes that are tractable for the efficient solution of the forward and inverse problems in real time using moderate computer resources. The authors' implementation is based on a 3D finite-volume method discretized on locally refined octree meshes. It uses the regularized Gauss-Newton method for minimizing the objective function for data subsets on local inversion meshes, which iteratively update the global mesh. Nonlinear Kalman filtering is applied using prior information on each local inversion mesh from the updated global mesh to introduce new observations optimally. A model study and a case study of trilateral well placement in a mature reservoir in the Norwegian Continental Shelf demonstrate the efficacy of the method. Run times on modest computer resources enable the first real-time 3D inversion of ultradeep resistivity LWD data.
Integrated Operations Centers – Planning and Delivering Improved Operational Performance Through IOC Initiatives
Authors: Clark Alexander , Larsen Henrik W. , Nordtvedt Jan-Erik , Stafford Bart T. , Stewart Kevin , Tvedt Bård-Henning , Tveit Ådne 
Published: September 2019

Abstract
Digital Transformation in oil and gas is bringing a new wave of opportunities that will transform the industry. In operations, these technologies can lead to new Ways of Working and deliver next generation Integrated Operations Centers (IOCs); empowering them to be the digital watering holes at the center of world-class operations. Several companies have publicized the effectiveness of their IOC initiatives in terms of cost savings, reduced losses and increased production. However, the success of Integrated Operations initiatives is not guaranteed; many IOCs have been deployed that have failed to live up to expectations.
Based on decades of experience delivering IOCs, this paper will explore the underlying principles that should be behind every IOC program, as well as the key program elements and delivery methodology that, while not guaranteeing success, go a long way to addressing the issues common to unsuccessful projects.
The principles proposed as the drivers behind an IOC initiative all support the philosophy that delivering an IOC is a long-distance race, not a sprint that ends when the center opens. The consequence of this is that any IO program should think of the center as a capability that should be delivered as manageable chunks into an operations culture that embraces evolution and change. To support these principles, the paper discusses eight key elements to include as part of the delivery program. These elements do more than support the delivery program, they also ensure the sustainability of the IOC capability. Finally, the paper discusses the advantages of adopting a delivery methodology from software development that has been shown to significantly improve the delivery of value, the engagement of stakeholders and the programs ability to cope with evolving changes.
New Acid-Tunneling Insights from Full-Scale Water- and Acid-Jetting Tests
Authors: Livescu S. , McDuff D. , Comeaux B. , Singh A. , Lindsey B. J. 
Published: September 2019

Abstract
Acid-tunneling is an acid jetting method for stimulating carbonate reservoirs. Several case histories from around the world were presented in the past showing optimistic post-stimulation production increases in open-hole wells, comparing to conventional coiled tubing (CT) acid jetting, matrix acidizing, and acid fracturing. However, many questions about the actual tunnel creation and tunneling efficiency are still not answered. In this paper, the results of an innovative full-scale research program involving water and acid jetting are reported for the first time.
The tunnels are constructed through chemical reaction and mechanical erosion by pumping hydrochloric (HCl) acid through conventional CT and a bottom-hole assembly (BHA) with jetting nozzles and two pressure-activated bending joints that control the tunnel initiation directions. If the jetting speed is too high and the acid is not consumed in front of the BHA during the main tunneling process, then unspent acid flows toward the back of the BHA and creates main wellbore and tunnel enlargement with potential wormholes as fluid leaks off, lowering the tunneling length efficiency.
Full-scale water and acid jetting tests were performed on Indiana limestone cores with 2-4 mD permeability and 12-14% porosity. Many field-realistic combinations of nozzle sizes, jetting speeds, and back pressures were included in the testing program. The cores were 3.75-in. in diameter by 6-in. in length for the water tests, and 12-in. in diameter by 18-in. in length for the tests with 15-wt% HCl acid. The jetting BHA was moved as the tunnels were constructed, at constant force on the nozzle mole, to minimize the nozzle stand-off distance. Six acid tests were performed at the ambient temperature of 46F and two at 97F. The results from the acid tests show that the acid tunneling efficiency can be optimized by reducing the nozzle size and pump rate. The results from the water and acid tests with exactly the same parameters to match the actual CT operations in the field show that the tunnels are constructed mostly by chemical reaction and not by mechanical erosion. The acid tunneling efficiencies obtained from the full-scale acid tests are superior to the average tunneling efficiency of more than 500 actual tunnels constructed during more than 100 acid tunneling operations performed to date worldwide.
The paper describes the full-scale water and acid jetting tests on Indiana limestone cores. The major novelty of this test program consists of performing all measurements with back pressure, unlike all previous water and acid jetting studies reported in literature, to more accurately mimic the downhole well conditions. The novel understanding of the combined effect of the nozzle size, pump rate, and back pressure significantly improves the actual acid-tunneling efficiency.