bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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.
Optimized Electrical Design for Weight Reduction in Offshore Platforms
Authors: Pragasam Sathishkumar
Published: September 2019

Weight control is critical in platforms of offshore oil fields and wind farms. Each engineering discipline is responsible to design their respective system with weight optimization as an important goal. This paper explores the various avenues that are available in electrical system design, that can contribute to weight reduction in an offshore structure.
Experimental Investigation and Modeling of Onset of Liquid Accumulation in Large- Diameter Deviated Gas Wells
Authors: Rastogi Ayush , Fan Yilin
Published: September 2019

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

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

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

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

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

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.
Simulation of Fault Reactivation Using the HISS Model
Authors: Ryu Jenny , Espinoza D. Nicolas , Balhoff Matthew T. , Tavassoli Shayan
Published: September 2019

Long-term integrity and practical storage of CO2 is contingent upon its seal performance and the dynamic sealing capacity of faults for the CO2 storage site. Faults are prone to reactivation with reservoir pressurization caused by CO2 injection. The goal of this study is to create and verify a reservoir elasto-plastic model capable of capturing short-term evolution of fault reactivation and the resulting change of permeability. This model is then used to explore the effects of coupling geomechanics with reservoir fluid flow on the reactivation of faults.

In this paper, we introduce a workflow for modeling of fault reactivation with fault elements as gridblocks instead of surfaces. Reservoir simulation, with coupled fluid flow and geomechanics, was used for this purpose. The simulation models utilize a geomechanical module to capture elasto-plasticity and a compositional numerical scheme based on an equation of state (EOS) to calculate CO2-brine interaction. The geomechanical module used in this study is based on Hierarchical Single Surface (HISS) model that captures strain softening and hardening, and therefore post-yield plastic deformations related to fault reactivation. The compositional numerical scheme based on EOS calculates the amount of CO2 solubilization in brine as well as the density and viscosity of the CO2- and aqueous-rich phase. In this approach, the flow properties, i.e. permeability and porosity, dynamically change in response to geomechanical effects. The dynamic change was captured through a volumetric strain-permeability law.

Our simulation results show that the model is capable of capturing short-term evolution of fault reactivation and the resulting change of permeability along the fault. The dynamic changes of fault properties control the extent of fault reactivation, the pressure relief during injection, and the fault sealing capacity.
Reviving a Mature, Watered-Out Fractured Carbonate Reservoir: An Integrated Approach to Design a Miscible EOR Scheme for the Bigoray Field in Alberta
Authors: Rivero Jose A. , Faskhoodi Majid M. , Mukisa Herman , Zaluski Wade , Ali Lahmar Hakima , Andjelkovic Dragan , Xu Cindy , Ibelegbu Charles , Kadir Hanatu , Sawchuk William M. , Pearson Warren , Ameuri Raouf , Gurpinar Omer
Published: September 2019

The Bigoray area of the Pembina field in western Alberta consists of approximately 50 naturally fractured Nisku carbonate reefs. Production from the Bigoray Nisku D and E pools started in 1978, and shortly after, water injection was initiated to maintain reservoir pressure as a secondary drive mechanism. By 2013, the pools had reached high water cuts, making them uneconomical to produce. In 2017, a decision was made to reactivate the pools and initiate a solvent injection enhanced oil recovery (EOR) project feasibility assessment.

A multidisciplinary team was assembled to review and reinterpret all the geoscience data with modern methodologies to characterize the reservoirs and create new static model descriptions to be used in a dynamic model. Data from well logs, seismic, core measurements, and image logs were integrated into a comprehensive and consistent model that could be used with certainty as a prediction tool.

A history-matching process was carried out by creating different realizations of the static model to honor well-to-well connectivity and water movement within the pools. The history-matching process was performed while ensuring that the model updates were global in nature and consistent with the geological understanding of the reservoirs.

The history-matched model was used to optimize the location of new producers and injectors based on remaining oil saturations and reservoir structure. Optimization of the EOR scheme involved testing a matrix of scenarios to investigate the effect of injection rates and solvent volumes as well as production pressures and voidage ratios. Additionally, in an effort to improve displacement efficiency, a large number of simulation runs were devoted to test and establish the most efficient locations for the well perforations in both the new injectors and producers.
A Semi-Analytical Approach for Analysis of Wells Exhibiting Multi-Phase Transient Linear Flow: Application to Field Data
Authors: Hamdi Hamidreza , Behmanesh Hamid , Clarkson Christopher R.
Published: September 2019

Rate-transient analyses (RTA) is a useful reservoir/hydraulic fracture characterization method that can be applied to multi-fractured horizontal wells (MFHWs) producing from low permeability (tight) and shale reservoirs. In this paper, a recently-developed three-phase RTA technique is applied to the analysis of production data from a MFHW completed in a low-permeability volatile oil reservoir in the Western Canadian Sedimentary Basin.

This new RTA technique is used to analyze the transient linear flow regime for wells operated under constant flowing bottomhole pressure conditions. With the new method, the slope of the square-root-of-time plot applied to any of the producing phases can be used to directly calculate the linear flow parameter, xf√k, without defining pseudo-variables. The method requires a set of input PVT data and an estimate of two-phase relative permeability curves. For the field case studied herein, the PVT model is constructed by tuning an equation of state (EOS) from a set of PVT experiments, while the relative permeability curves are estimated from numerical model history-matching results.

The subject well, a MFHW completed in 15 stages, produces oil, water and gas at a nearly constant (measured downhole) flowing bottomhole pressure. This well is completed in a low-permeability, near-critical volatile oil system. For this field case, application of the new RTA method leads to an estimate of xf√k that is in a close agreement (within 7%) with the results of a numerical model history-match performed in parallel. The RTA method also provides pressure-saturation relationships for all three phases that are within 2% of those derived from the numerical model. The derived pressure-saturation relationships are central to the use of other RTA methods that require calculation of multi-phase pseudo-variables.

The new three-phase RTA technique developed herein is a simple-yet-rigorous and accurate alternative to numerical model history-matching for estimating xf√k when fluid properties and relative permeability data are available.
Reducing Cost of BOE and Extending Field Life with Intelligently Controlled Multilaterals
Authors: Mark Glaser , Andreas Grossmann
Published: September 2019

While many factors in the reservoir cannot be controlled, there are three controllable factors in field development that make a significant impact. More reservoir contact leads to more oil produced. Controlling sand and water means lower treatment costs, and in-situ reservoir management leads to higher cumulative production. While the underlying technologies have been around for up to 20 years, it is only recently that their synergies and true value are understood. This paper will demonstrate the effect each of these technologies has on increasing overall production rates, improving recovery, and reducing the cost per Barrel of Oil Equivalent (BOE).

The successful implementation of multilaterals in the North Sea will be analyzed. Since 1996, over 300 multilateral junctions have been installed on the Norwegian continental shelf fields with currently approximately 30 junctions completed each year.

Additionally, simulations will be used to demonstrate the incremental improvements in oil recovery that can be obtained by using properly designed advanced completions that include multilaterals, sensors, and passive/active flow control equipment.

The paper will evaluate production performance of a vertical well field development base case against scenarios using horizontal and multilateral wells. It will show how fields can be optimized, leading to increased oil and decreased water production.

Production rates can be significantly improved by combining multilaterals with other advanced completion techniques, such as intelligent completions and inflow control devices. The subject field simulation can be further optimized to manage gas and water production.

With a tailored multilateral field design, combined with properly designed advanced completions systems, the simulation succeeds in terms of achieving maximum contact with the oil reservoir and meeting improved ultimate recovery objectives.

It can be concluded that as reservoir contact is increased, a reduced decline in production rate is observed leading to both a higher Estimated Ultimate Recovery (EUR) and optimized drawdown profile distributions. Additionally, results will be presented that have considered oil production and a method to lower production of unwanted fluids or gas.

This paper also demonstrates the value of field development design from the perspective of reservoir simulation. It is through reservoir insight that a level of understanding is created that can help define the optimum well and completion design to meet field expectations.

Advanced multilaterals continue to grow in popularity with many operators, and it therefore becomes important to evaluate the value of different field development methods. This knowledge can aid operators in unlocking new reservoir targets and optimizing field development, and ultimately will improve recovery factors and overall field economics.
Multi-Objective Optimization of CO2 Enhanced Oil Recovery Projects Using a Hybrid Artificial Intelligence Approach
Authors: You Junyu , Ampomah William , Sun Qian , Kutsienyo Eusebius Junior , Balch Robert Scott , Cather Martha
Published: September 2019

In this paper, a hybrid scheme that couples artificial neural network (ANN) and multi-objective optimizers is structured to co-optimize oil recovery and carbon storage of CO2 - EOR processes. The workflow is developed and validated employing an injection-pattern-based model. A field scale case study is presented to demonstrate the practicability of the workflow.

An injection-pattern based reservoir model employing a compositional numerical simulator is established to develop and test the hybrid-optimization workflow. Such a scheme aims at optimizing objective functions including oil recovery factor, CO2 storage and project net present value (NPV). An ANN expert system is trained and employed as a proxy of the high-fidelity model in the optimization process. The ANN model is trained by a robust optimization procedure which is competent to find the best architecture. Particle swarm optimization (PSO) is coupled with the developed proxy model to optimize a weight-aggregated objective function, and multi-objective functions by a Pareto front approach. A field case study is included in this paper. The reservoir model is well-tuned via a rigorous history matching process using the available field data. The aforementioned workflow is deployed to optimize the tertiary recovery stage of the field development.

In this paper, the validation results of the proxy model will be compared against results from the high-fidelity numerical models. Investigations focus on comparing the optimum solution found by the aggregative objective function and the solution repository (Pareto front) generated by the multi-objective optimization process. The optimization results provide significant insight to the decision-making process of CO2 - EOR project when multiple objective functions are considered.

This study develops a novel hybrid-optimization workflow for CO2 - EOR projects considering multiple objective functions. The robustness of the development is confirmed via a field case study. Moreover, this work investigates the relationship between the solutions of the aggregative objective function and the Pareto front, which provides constraints and reduces uncertainties involved by the multi-objective optimization process.
Investigation of Wettability Alteration by Silica Nanoparticles Through Advanced Surface-Wetting Visualization Techniques
Authors: Li Shidong , Dan Daniel , Lau Hon Chung , Hadia Nanji J , Torsæter Ole , Stubbs Ludger P.
Published: September 2019

Altering the wetting state of a rock surface to more water-wet has been proposed as an enhanced oil recovery (EOR) mechanism for nanoparticles. However, how nanoparticles achieve this is not well understood. The objective of this study is to fill this knowledge gap by using advanced 2D and 3D visualization techniques.

In this study, advanced visualization techniques were used to study how hydrophilic silica nanoparticles change the wettability of a glass surface. First, we used interferograms of an oil drop resting on a nanoparticle-treated glass surface to analyze the effect of nanoparticles on wettability. Second, we used Atomic Force Microscopy (AFM) to characterize the structure of nanoparticles covering a glass surface. Third, we used a 2D microfluidic apparatus to visualize wettability alteration caused by the nanoparticle injection. Fourth, we used a fluoresence imaging method with confocal microscopy to find out the reason for this change.

Interferograms of a nanoparticle-treated glass surface showed bright and dark fringes, indicating the presence of a thin water film covering the glass surface caused by nanoparticle adsorption. Furthermore, the higher the nanoparticle concentration, the thicker was the nanoparticle adsorption layer. A low pH environment can reduce nanoparticle adsorption on the glass surface. AFM results showed that the topography of the glass surface changed from smooth to rough after nanoparticle treatment. Microfluidic experiments showed that nanoparticle injection changed the wettability of the grain surface to more water wet. By using a confocal microscopy, we observed a thin water film covering the surface of glass grains suggesting that nanoparticle adsorption is the main mechanism of wettability alteration by nanoparticles.

This paper presents findings of new techniques to study wettability alteration by nanoparticles, including thin-film interferometry, surface characterization by AFM, and fluoresence imaging with confocal microscopy. Observations showed that nanoparticles adsorption on a glass surface results in a thin water film that prevents the oil from contacting the surface. This is the main mechanism of wettability alteration by nanoparticles. This is the first time use of these advanced visualization techniques to study wettability alteration by nanoparticles is reported.
Anticipating Geo-Drilling Hazards by Sharing Geo-Drilling Events Information Nationwide
Authors: Hoetz Guido , Nijhuis Ivo
Published: September 2019

Drilling hazards can lead to significant cost overruns during the drilling phase and might cause unsafe situations or potentially harm the environment. Often the local geology, when poorly understood, is the trigger of a drilling incident. By sharing past drilling experience and in particular observations on Geo-Drilling Hazards, via a suitable platform, well planning and risk assessment can be carried out more effectively. After analysing historic drilling reports, observations on drilling incidents have been compiled using a structured approach. Classification schemes allow systematic capture of key information in a format suitable for a database. In this process the observations (facts) during the drilling operation are analysed and classified into a limited number of event types. By interpreting the data in the geological context, the underlying geohazard type has been determined by selecting from a defined (and limited) number of geological causes. The resulting information can be accessed via an online user interface with GIS functionality and advanced analysis options.

The Geo-Drilling Events (GDE) database currently covers some 1000 boreholes from the Netherlands. Around 1400 geo-drilling events have been analysed systematically allowing to identify drilling hazard hotspots in a statistically meaningful sense. Examples of geo-drilling events include stuck tool, gains, losses, H2S. The underlying geological phenomena i.e. the "geo-drilling hazards" include geological conditions such as: fault, swelling clay, or anomalous pressures. By correlating these with other information, in particular seismic data, the risk of geo-drilling hazards in a planned well can be assessed. For example; it appears that 65% of the (strong) overpressures observed in de Zechstein formation are linked to the Platten dolomite member. This unit can often be identified on seismic and this hazard is therefore, to some degree, predictable.

Planned well trajectories can now be screened efficiently for geo-drilling hazards. The GDE Tool based on advanced classification criteria allows to share relevant well information across all operators active in the Netherlands. This includes newcomers, like geothermal operators who carry out a lot of drilling nowadays. The GDE Tool allows everyone to learn from the experience on drilling hazards gathered over the years by oil companies.
Application of Seismo-Dynamic Analysis to the Development of Oilfields Located in Tectonically Complex Structures
Authors: Salimov Farit , Kotenev Maxim , Kotenev Artem
Published: September 2019

Zones of increased fracture density related to the tectonic disturbances and connected to the protrusions and recesses of the consolidated basement were identified with the application of seismo-dynamic analysis of the seismic data. This is done for the first time on Povkhovskoe oil field located in Western Siberia.

Daily and monthly rates of the producing wells in relation to their location within the geological structure were analyzed. The analysis showed a pattern of increased well productivity by more than 2 times when approaching the areas with high density of fractures. At a distance of more than 500 m from the tectonic disturbances the fluid inflow rates significantly decrease and the performance of hydraulic fracking provides only short-term effect. The deterioration of the reservoir properties is due to a decrease in the value of the reservoir rock permeability because of the decrease in the proportion of fractures and the predominance of the pore space. Reservoir type changes from fractured or fractured-porous reservoir type to porous-only type.

The dependence of high oil saturation of the productive formation from the presence of the tectonic disturbances was recorded. Exploitation of producing wells confirms the assumption of oil moving along the sub-vertical zones of destruction and contributing to the primary target Upper Jurrasic-1 reservoir. Drilling of sidetracks from low oil rate and high water saturation wells in the areas with increased fracture network identified by seismo-dynamic analysis showed a high efficiency of the operations leading to a high-rate production including a substantially lower water-cut oil production (up to 5% of water) at the site where the surrounding production wells have water-cut of 99-100%. Meanwhile, reservoir characteristics of the Upper Jurrasic-1 formation are identical. Based on the results of research identified were prospective deposits for the drilling of production wells on the edges of the hydrocarbon accumulation in areas with high fracture density and suggested were the borehole sidetracks of wells that are plugged and abandoned.

Thus, the detailed structural and tectonic structure of the basement surface and the Jurassic sediments allows to select complex, small-scale geological features, which will be very prospective for the detection of small oil deposits, to specify the location of exploration wells, to start the search for deposits in areas of sub-vertical degradation in the Middle and Lower Jurassic sediments, basement rocks in areas with overlying hydrocarbon deposits already in development. Identifying zones of high density fracturing, including those associated with horizontal shear zones, allows to adjust the contour outlines of the alleged existing deposits and to discover prospective areas with the increased permeability. Described zones and areas are likely to be located close to faults originating in the basement.
Mechanical Properties of Drill Cuttings Based on Indentation Testing and Contact Mechanics Solutions
Authors: Martogi Debora , Abedi Sara , Saadeh Crystal , Mitchell Ian
Published: September 2019

Rock strength evaluation is commonly performed on extracted core samples. The retrieval process of core samples is costly and with high risk, especially in unconventional wells. Besides, mechanical testing carried out on core samples could be time-consuming, particularly for low permeability rocks such as shales. In contrast, tons of shale cuttings are generated and discarded at the end of drilling. Small scale testing, such as instrumented indentation test, could be performed on shale cuttings to obtain the mechanical properties of shale rocks. Unlike core samples, however, the bedding orientation, critical to the definition of mechanical properties of shale cuttings as transversely isotropic material, is indistinguishable on cuttings. A methodology has been developed in the following work to deduce the mechanical properties based on indentation testing of randomly oriented artificial shale cuttings.

Estimation of shale cuttings' elastic constants was carried out using microindentation and constrained inverse algorithm developed based on contact mechanics solutions. Microindentation testing was performed on multiple oriented artificial shale cuttings to obtain the indentation modulus as the function of the unknown bedding orientation. The contact mechanics solutions for both transversely isotropic and anisotropic material were utilized to correlate the indentation modulus to the stiffness tensor components of transversely isotropic shale. An inverse problem was formulated with imposed constraints to identify the mean values of the quantities of interest that best fit the data. The constraints represent the physical information about the bounds on elastic properties as well as a mathematical constraint on the structure of elasticity tensor ensuring the accuracy and robustness of the solutions to this optimization problem. Lastly, Ultrasonic Pulse Velocity (UPV) test was performed to validate the modeling results and good agreement was found between the results of the experimental and modeling efforts and results from UPV tests performed on the same material.

Mechanical properties of shale rocks hold great importance in the design and implementation of drilling and production programs. Retrieval of traditional core samples is known to be expensive and risky as a failure in the recovery process could lead to well abandonment. By using several cuttings with unknown varying bedding orientations, the elastic constants of shales were inferred based on the microindentation testing and the algorithm developed in this work. Successful implementation of this work would allow for a more efficient and economical mechanical characterization of shales.
Depletion-Induced Poroelastic Stress Changes in Naturally Fractured Unconventional Reservoirs and Implications for Hydraulic Fracture Propagation
Authors: Jin Lei , Zoback Mark
Published: September 2019

Numerous questions surround stimulation and depletion in unconventional reservoirs with many important implications. Understanding depletion-induced stress changes is critical for designing in-fill drilling and avoiding phenomenon such as hydraulic fracture growth into depleted areas and hydraulic fractures from in fill wells affecting pre-existing wells (the frac-hit or parent well/child well phenomenon). In this paper, we utilize a fully coupled fracture-poro-mechanical computational model described by Jin & Zoback (https://doi.org/10.1002/2017JB014892) to evaluate the pressure and stress changes associated with pore-scale flow from the low permeability matrix into a much more permeable discrete fracture network. These fractures represent pre-existing natural fractures stimulated in shear during hydraulic fracturing as well as the hydraulic fractures themselves. Because of the marked permeability contrast, depletion is rather heterogeneous and can be visualized as halos adjacent to the more permeable shear fractures and hydraulic fractures. While this might be expected, the calculations are helpful in understanding the extent of depletion and limitations of utilizing the concept of a stimulated reservoir volume to predicting production. To examine the evolutions and characteristics of depletion-induced stress changes, we consider three cases representing different initial pore pressure, horizontal stress anisotropy and pressure drawdown. We show that while the total normal stress decreases overall due to depletion as expected, the changes are anisotropic due to the pressure gradient oriented predominantly perpendicular to the well; the changes are also highly heterogeneous due the presence of fractures and unexpected local increases among fractures can occur. Additionally, newly induced shear stress also develops with heterogeneous distributions. These changes jointly produce complex magnitude variations and rotational patterns of the horizontal principal stresses. For the base case we consider (high initial stress anisotropy, low initial overpressure and insignificant depletion), rotations occur mostly surrounding the fractures and the degree of rotation is mild. In marked contrast to this, in a case in which there is high initial overpressure, little horizontal stress anisotropy and significant depletion, rotations become less dependent on fractures and is prominent throughout the domain to a degree such that the directions of the two horizontal principal stresses are essentially flipped. Taken together, these calculations help illustrate how depletion-induced stress changes can affect problems like in-fill drilling and re-stimulation and therefore provide insights into better drilling and completion designs.
Metal Expandable Annular Sealing Systems for High Pressure Open Hole Zonal Isolation and Stimulation
Authors: Esquitin Yosafat , Schwanitz Brian , Moreno Guido , Avella Natalia , Henao Oscar
Published: September 2019

Metal expandable annular sealing systems were used in a 4 ½" completion as an effective high-pressure isolation method inside 6" open hole mudstone formation in the Foothills Basin of Colombia. Effective isolation proved to be historically difficult to achieve.

The operator was approached with a solid metal expandable sealing system with rotation capabilities as an annular barrier for a preferred cementless completion. The sealing system needed to be assembled on a full-bore liner able to deliver robust deployment with a high-pressure seal in a worse case washed-out scenario. The deployment of the system consisted of one annular barrier placed above and one annular barrier placed below the mudstone zone.

Following careful job planning with the operator, the rotationally capable completion was deployed without any incidents. To achieve pressure integrity to set the metal expandable annular barriers, a ball seat sealing system was incorporated to allow the system to be closed and the annular barriers to be set.

After putting the well onto the pipeline, the client recorded a 52% increase in their expected produc-tion from previous wells. Successful results were accomplished as effective isolation was achieved and enhanced production was obtained because of the effective stimulation. This paper overviews the appli-cation, design, implementation and results of the use of new metal annular sealing systems in a 4 ½" completion as an effective high-pressure isolation method inside a 6" open hole, drilled in fractured sandstone and mudstone formations.
Developing an Integrated Real-Time Drilling Ecosystem to Provide a One-Stop Solution for Drilling Monitoring and Optimization
Authors: Cao Dingzhou , Ben Yuxing , James Chris , Ruddy Kate
Published: September 2019

The paper provides a technical overview of an operator's Real-Time Drilling (RTD) ecosystem currently developed and deployed to all US Onshore and Deepwater Gulf of Mexico rigs. It also shares best practices with the industry through the journey of building the RTD solution: first designing and building the initial analytics system, then addressing significant challenges the system faces (these challenges should be common in drilling industry, especially for operators), next enhancing the system from lessons learned, and lastly, finalizing a fully integrated and functional ecosystem to provide a one-stop solution to end users.

The RTD ecosystem consists of four subsystems as shown in architecture Figure 1. (I) The StreamBase RTD streaming system, which is the backbone of the ecosystem. It takes the real-time streaming log data as well as other contextual well data (for example, OpenWells), processes it through analytical models, generates results, and delivers them to the web-based user interface; (II) The analytics models, which include the Machine Learning (ML)/Deep Learning (DL) models, the physics-based models and the stream analytical/statistical models; (III) The digital transformation solution, which wasdesigned to address contextual well data digitization issues to enable real-time physics-based modeling. Contextual well data like bottom hole assemblies (BHAs) and casing programs are challenging to aggregate and deliver to models, as this data is often stored in locations across multiple systems and in various formats. The digital transformation applications are designed to fit into the drilling teams' workflows and collect this information during the course of normal engineering processes, enhancing both the engineering workflow and the data collection process; (IV) the cloud based ML pipeline, which streamlines the original ML workflows, as well as establishes an anomaly detection and re-training mechanism for ML models in production.

Figure 1 RTD ecosystem architecture

All of these subsystems are fully integrated and interact with each other to function as one system, providing a one-stop solution for real-time drilling optimization and monitoring. This RTD ecosystem has become a powerful decision support tool for the drilling operations team. While it was a significant effort, the long term operational and engineering benefits to operators designing such a real-time drilling analytics ecosystem far outweighs the cost and provides a solid foundation to continue pushing the historical limitations of drilling workflow and operational efficiency during this period of rapid digital transformation in the industry.