Authors: Fabio Parrozza; Federico Cracolici; Daniele Farina; Vanessa Silvia Iorio; Luca Dal Forno; Lucio Bertoldi; Kris Ravi; Michael Prohaska; Felix Hahn; Stefan Lebwohl
Paper presented at the OMC Med Energy Conference and Exhibition, Ravenna, Italy, October 2023.
Paper Number: OMC-2023-380
OnePetro
Published: October 24 2023

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Abstract
Carbon Capture and Storage became of paramount importance in the global effort to reach carbon neutrality targets as it represents the most suitable technology for hard-to-abate industry emissions. One of the crucial challenges of CCS technologies is constituted by permanent CO2 placement in the selected geological storage site. To reach this target cement plays a fundamental role as it must provide good sealing between the well and the rock formations avoiding any possible leakage route.

Standard laboratory procedures, such as API Specification RP 10, are used to investigate cement performance and properties after extended CO2 exposure in pressurized autoclaves at controlled pressure and temperature conditions. At the end of the exposure period, cement properties are finally evaluated through mechanical, chemical and mineralogical tests. Unfortunately, this test configuration takes a significant amount of time to reach the first results and does not provide any dynamics evolution of the CO2 carbonation front. Consequently, an innovative setup was designed to improve the quality of the cement-fluids interaction assessment.

To better replicate downhole conditions, a cylindrical sandstone core is encapsulated by cement to represent inverted annular conditions. During a test, CO2 is radially injected through the sandstone core into the cement annulus, typically over a test duration of three months. An innovative in-situ test cell is developed that allows to retrieve real-time information about the evolution of the carbonation front from a CT-scanner, while the test is ongoing. In addition, CO2 consumption and system permeability measurement can also be measured under in-situ conditions.

The newly developed in-situ test cell enables instant evaluation of CO2 effect on cement, without compromising sample integrity. Thus, new insights into this complex behaviour of cement/CO2 interactions have been gained.

Authors: Paul Wagner; Kris Ravi; Michael Prohaska

Paper presented at the SPE Trinidad and Tobago Section Energy Resources Conference, Virtual, June 2021.
Paper Number: SPE-200931-MS
https://doi.org/10.2118/200931-MS
Published: June 28 2021

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Abstract

Global warming is one of the most significant issues the world is facing. Capturing carbon dioxide from the atmosphere or industrial processes and storing it in geological formations (carbon capture and storage, CCS) can help counteract climate change. Nevertheless, the interaction between well barrier elements such as cement, casing, tubulars, packers, and valves can lead to possible leakages. To accomplish successful carbon dioxide sequestration, injecting the carbon dioxide in its supercritical state is necessary. The supercritical carbon dioxide can corrode steel and elastomers and react with the calcium compounds in the cement, dissolving them and forming calcium carbonate and bicarbonate in the process. This carbonation can lead to channels forming on the cement-to-rock interface or cracking due to the carbonate precipitation, resulting in a loss of well integrity.

This study focusses on finding ways that enable the continuous monitoring of cement integrity, under in-situ conditions, in a lab setup. The construction of an autoclave, capable of withstanding supercritical conditions of carbon dioxide, facilitates the in-situ monitoring. This autoclave also makes CT-scans of the pressurized sample possible, as well as acoustic measurements, using state-of-the-art piezo elements. The first tests will establish a baseline using neat Class G Portland cement to verify the design and sensors. The set up consists of a rock core in the middle of the autoclave surrounded by a cement sheath. A prepared channel in the center of the core expedites the distribution of the carbon dioxide. Once the ability of the sensors to monitor the integrity is verified, different cement compositions and their interaction with supercritical carbon dioxide can be studied.

The experimental setup and the procedure discussed here closely simulate the downhole condition. Hence, the results obtained using this setup and procedure is representative of what could be observed downhole. The direction is not to remove the sample from the autoclave for analysis, as is the current industry practice, but to measure cement integrity under in-situ conditions over an extended period of time. Digitalization is powering the in-situ analysis in these tests.

The first two tests of this study, using the afore mentioned autoclave, investigated the carbonation behaviour of two Class G Portland cement slurrys, one with a low and one with a high slurry-density. The low-density slurry showed extensive degradation and even the high-density slurry showed carbonation, but only close to the sandstone core.

The results from this study can lead to the prevention of leakage of carbon dioxide to the environment and other formations, which defeats the purpose of carbon dioxide sequestration. These results should improve the economics of these wells as well as the health, safety, and environmental aspects.

Authors: Sahar Keshavarz, Petr Vita, Elmar Rückert, Ronald Ortner, Gerhard Thonhauser
Paper presented at the SPE Symposium Leveraging Artificial Intelligence to Shape the Future of the Energy Industry, Al Khobar, Saudi Arabia, January 2023.
Paper Number: SPE-214465-MS
https://doi.org/10.2118/214465-MS
Published: January 19 2023

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Abstract
The drilling industry is permanently seeking to reduce operational costs by improving the efficiency of the drilling process. The complexity and uncertainty of the drilling process and limited information during the well construction lead to difficulty in applying standard control methods and detecting and monitoring the actual ongoing state of the operation. All these represent challenges in order to achieve a fully autonomous drilling sequence.

An autonomous decision-making framework for a systematic plan update based on the current well construction status and available surface and downhole information is presented. The primary objective, minimization of the time to reach the total depth (TD) of a well, has to be fulfilled in multi-level finite operational horizons within the next few minutes up to the TD while keeping associated short- and long-term risks at acceptable levels. The problem is represented as a mathematical description called Markov Decision Process (MDP) defining the ongoing rig state, operational actions, and policies.

The methodology has been implemented on a wait-to-slip hole conditioning operation to demonstrate the viability of the approach using surface sensor information. The value of states is estimated by performing infinite state-action transition evaluations, a method of Reinforcement Learning, to prescribe the best possible set of actions to commit to the combined reward and penalty objectives. In the context of this research, the environment dynamic has been assumed to be fully known to apply Dynamic Programming approaches. The sensitivity analysis was performed confirming the selection of model parameters. The results show the potential for reducing non-necessary operation activities.

The paper presents a novel method for well construction operation planning that connects decision-making over multi-level operation levels. The proper design of such a system is an essential step toward a fully automatized well construction decision-making system.

Authors: Asad Mustafa Elmgerbi; Clemens Peter Ettinger; Peter Mbah Tekum; Gerhard Thonhauser; Andreas Nascimento
Paper presented at the SPE/IADC Middle East Drilling Technology Conference and Exhibition, Abu Dhabi, UAE, May 2021.
Paper Number: SPE-202184-MS
https://doi.org/10.2118/202184-MS

Published: May 25 2021

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Abstract
Over the past decade, several models have been generated to predict Rate of Penetration (ROP) in real-time. In general, these models can be classified into two categories, model-driven (analytical models) and data-driven models (based on machine learning techniques), which is considered as cutting-edge technology in terms of predictive accuracy and minimal human interfering. Nevertheless, most existing machine learning models are mainly used for prediction, not optimization. The ROP ahead of the bit for a certain formation layer can be predicted with such methods, but the limitation of the applications of these techniques is to find an optimum set of operating parameters for the optimization of ROP. In this regard, two data-driven models for ROP prediction have been developed and thereafter have been merged into an optimizer model. The purpose of the optimization process is to seek the ideal combinations of drilling parameters that would lead to an improvement in the ROP in real-time for a given formation.

This paper is mainly focused on describing the process of development to create smart data-driven models (built on MATLAB software environment) for real-time rate of penetration prediction and optimization within a sufficient time span and without disturbing the drilling process, as it is typically required by a drill-off test. The used models here can be classified into two groups: two predictive models, Artificial Neural Network (ANN) and Random Forest (RF), in addition to one optimizer, namely genetic algorithm. The process started by developing, optimizing, and validation of the predictive models, which subsequently were linked to the genetic algorithm (GA) for real-time optimization. Automated optimization algorithms were integrated into the process of developing the productive models to improve the model efficiency and to reduce the errors.

In order to validate the functionalities of the developed ROP optimization model, two different cases were studied. For the first case, historical drilling data from different wells were used, and the results confirmed that for the three known controllable surface drilling parameters, weight on bit (WOB) has the highest impact on ROP, followed by flow rate (FR) and finally rotation per minute (RPM), which has the least impact. In the second case, a laboratory scaled drilling rig "CDC miniRig" was utilized to validate the developed model, during the validation only the previous named parameters were used. Several meters were drilled through sandstone cubes at different weights on bit, rotations per minute, and flow rates to develop the productive models; then the optimizer was activated to propose the optimal set of the used parameters, which likely maximize the ROP. The proposed parameters were implemented, and the results showed that ROP improved as expected.

Authors: Asad Elmgerbi; Egor Chuykov; Gerhard Thonhauser; Andreas Nascimento
Paper presented at the International Petroleum Technology Conference, Riyadh, Saudi Arabia, February 2022.
Paper Number: IPTC-22662-MS
https://doi.org/10.2523/IPTC-22662-MS
Published: February 21 2022

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Abstract
Over the past decade, several methods and techniques have been proposed to optimize drilling hydraulic's in real-time; one of these techniques is machine learning, which has shown promising results in prediction and optimization. Nevertheless, the real-time implementation of these techniques is still challenging since most of the published work tried to perform prediction tasks rather than the optimization task. In this regard, this paper tries to tackle the shortcomings of the recently published related methods by presenting a holistic model, based on a machine learning concept, focused on real-time optimization of drilling hydraulic's within a sufficiently short time span and without disturbing the drilling process.

The presented approach relies on using two interconnected models to achieve the goal, which can be classified into, data-driven and analytical models. The real-time optimization process starts by using two predictive models to predict standpipe pressure and annular pressure losses and an analytical model to compute the drill-string pressure loss. Subsequently, the three generated values are used by an optimizer algorithm to generate the optimum combinations of surface drilling parameters, namely, weight on bit, flow rate, and rotation per minute, which are expected to optimize drilling hydraulic.

Two case studies were conducted based on a historical drilling data set to assess the performance of the utilized predictive models and to measure the time required for the model to perform an optimization task. The results reveal that the predictive model demonstrated very high accuracy in terms of predicting SPP and APL as indicated by the determination coefficient value (R2), which was between 0.87 and 0.99. Moreover, the overall simulation time was within a range of between 2 to 4 minutes, which is considered a rational time frame for a real-time optimization task. The methodology applied allowed us to conclude, even showing some limitations, that machine learning techniques can be well used for hydraulic optimization in real-time.

Authors: Shwetank Krishna; Gerhard Thonhauser; Sunil Kumar; Asad Elmgerbi; Krishna Ravi
Journal of the International Measurement Confederation
https://doi.org/10.1016/j.measurement.2022.112152
Published: December 2022

Abstract
A real-time in-line rheological measurement is essential in many sectors to investigate and monitor the performance of the unit, process, and transportation operations. Ultrasound velocity profiling (UVP) technique, combined with pressure differential (PD) data, is among the effective technologies for in-line rheological measurement. This paper reviews and summarizes the basic principle of UVP-PD measurement along with the factors affecting this tool’s performance. The working mechanism of a typical UVP-PD-based experimental setup, according to published literature combined with its limitation, is also discussed in this paper. In addition, a brief description of the experimental procedure used hardware; and data gathering and processing process, along with the expected outcome, are provided. A brief overview of all the published literature on the UVP-PD method is presented per the scope of their industrial applications. Finally, the prospective with the recommendation of this tool application and improvement for precise measurement and analysis are highlighted.

Authors: Arash Nasiri;Kris Ravi;Michael Prohaska-Marchried;Monika Feichter;Johann Raith;Christian Coti;Emanuele Baronio;Carlo Busollo;Andrea Mantegazzi;Vincenzo Pozzovivo;Stefano Pruno
Paper presented at the SPE EuropEC - Europe Energy Conference featured at the 84th EAGE Annual Conference & Exhibition, Vienna, Austria, June 2023.
Paper Number: SPE-214423-MS
https://doi.org/10.2118/214423-MS
Published: June 05 2023

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Abstract
Underground gas storage plays an important role in achieving energy security. Hydrogen has been proven to be an important player in energy transition, and, thus, underground hydrogen storage (UHS) will become a focal point in the future of gas storage. This brings uncertainties regarding the behavior of mixtures of hydrogen and natural gas in storage wells. Therefore, a deeper investigation must be conducted to characterize the impact of hydrogen exposure compared with natural gas (methane) on well elements. This study focuses on the cement interaction with the mentioned mixture to prove the readiness of existing and new wells for UHS.

Cylindrical samples were prepared out of three types of cement (class A, class G, Special Cement: SC) and were confined in autoclaves in contact with different mixtures of H2/CH4 under 100 bars of pressure and ambient temperature for varying periods of time starting from three weeks. Tests were conducted to investigate the impact of hydrogen exposure on different aspects, namely the mineralogical (X-ray Diffraction; Scanning Electron Microscopy; and Element Distribution Map), mechanical (Uniaxial-Compressive-Strength), and petrophysical (Gas-Permeability). The investigation aimed to establish a comparison of the samples’ characteristics before and after the gas treatment. The pressure was monitored and the gas inside the autoclave was analyzed at the end of each phase. Moreover, samples were visually inspected and weighed prior to and after each phase to evaluate any material deterioration.

A rim was observed around the tested samples (mainly in cement type A), proving gas diffusion. Sample drying out played a significant role in the changes seen in permeability, weight, and Uniaxial Compressive Strength (UCS). The scale of gas-permeability change was found to be around 10-1 – 10-2 mD, within measurement uncertainty. This leads to the conclusion that cement samples evaluated under the experimental conditions and durations with the different mixtures show strong similarities in the results. The observed changes cannot be associated to hydrogen since the increase in its percentage did not introduce major impacts nor scale up the observed effects and the exposition at 100% H2 and 100% CH4 environment shows comparable results. This conclusion is based on the comparison of the test performed with the gas mixture at 100 bar and ambient temperature, for an average experimental duration and exposure of 23 days in the laboratory.

The paper highlights the novel and multidisciplinary approaches implemented for this study with different gas compositions and sets a baseline for future experimentation regarding the effects of hydrogen on storage wells. The results confirm that hydrogen exposure would not lead to loss of integrity in the tested conditions and environments. The project was conducted through cooperation with the gas storage industry, service company and different university departments.

Authors: Abdelfattah Lamik; Gerhard Pittino; Michael Prohaska-Marchried; Ravi Krishna; Gerhard Thonhauser; Thomas Antretter
Paper presented at the SPE/IADC Middle East Drilling Technology Conference and Exhibition, Abu Dhabi, UAE, May 2021.
Paper Number: SPE-202186-MS
https://doi.org/10.2118/202186-MS
Published: May 25 2021
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Abstract

This paper presents the results of laboratory static and dynamic tests on casing-cement-rock systems exposed to axial loads under ambient conditions. A new testing method has been developed.

The casing-cement-rock system mostly fails due to tension and shear stresses. In various applications such as HPHT, deep-water, (steam) injection or geothermal wells, the cement-casing bond is exposed to cyclic thermomechanical loads resulting in casing elongation, contraction, expansion and subsequently in cyclic radial and axial stresses at the cement-casing-rock system. Cement is a brittle material which can fail when subjected to repeated application of stresses lesser in magnitude than the statically determined strength. A novel atmospheric test cell has been designed and constructed. In order to achieve the fatigue limits of the cement-casing bond, a set of testing procedures has been established. Several tests are conducted to evaluate de-bonding. The focus on de-bonding is achieved by allowing the casing to move through the test while preventing any cement movement. Thus, when a force is applied in the axial z-direction - either the casing is pulled out (tension) or pushed down (compression) - the casing has enough space to move in both directions. The advantage of this testing method is that different stress ratios can be applied during the test.

Authors: Sharen Monserrat Leon Escobar; Alexander Walzl; Krishna Ravi; Michael Prohaska; Martin Stockinger; Ian Malcolm Richardson; Nazanin Fateh; Stefan Hönig
Paper presented at the SPE/IATMI Asia Pacific Oil & Gas Conference and Exhibition, Jakarta, Indonesia, October 2023.
Paper Number: SPE-215359-MS
https://doi.org/10.2118/215359-MS
Published: October 06 2023

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Abstract

A large and increasing number of wells must be abandoned or repurposed in the next decades. Additionally, there are many wells to be re-entered and repaired due to problems and conditions such as casing leaks, corrosion, annular communication, patch placement, zonal isolation, closing perforations, etc.; therefore, the development of more efficient and cost-effective methods to address these issues is paramount. The main objective of this research includes the proof of concept (POC) of a Wire Arc Additive Manufacturing (WAAM) process under hyperbaric conditions for downhole applications in the Oil and Gas (O&G) industry. This POC will enable the development of a potential downhole WAAM technology that could place corrosion-resistant steel barriers as well as closing holes in the wellbore. Well plugging and abandonment (P&A), and well integrity re-establishment operations are costly and often associated with a low probability of long-term success. Available conventional technologies and techniques mostly use cement as a plugging material. However, steel has several advantages over cement, such as a higher tensile strength, enabling stronger structures with less material; cement is a brittle material while steel is ductile, steel can also resist higher thermal loads. Additionally, steels can be engineered to withstand harsh environments and resist corrosion. Corresponding lab-scale experiments, simulated in an autoclave solely constructed for the proof of concept of hyperbaric WAAM, are carried out to investigate the fundamentals of this process and material properties for downhole applications. The general project description, laboratory set up and design, including process requirements such as voltage, current, shielding gases, and material properties, are presented. With this proof of concept, an alternative technology will be enabled with the potential to revolutionize wellbore P&A. Once this POC has been proven, the deployment method will be assessed. It is foreseen that some of the benefits of developing such tool will be the introduction of rigless or with smaller workover units P&A operations. Additionally, an entirely new way of applying additive manufacturing is proposed to solve compelling challenges in the O&G industry.

Authors: Pouya Ziashahabi; Kris Ravi; Michael Prohaska

Paper presented at the SPE Gas & Oil Technology Showcase and Conference, Dubai, UAE, October 2019.
Paper Number: SPE-198584-MS
https://doi.org/10.2118/198584-MS
Published: October 21 2019

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Abstract

Well integrity is one of the main issues during all life cycles of the well and if any barrier element fails and compromise the integrity of well, remedial strategy may have to be performed to restore the safety and economics of the well. Cement is conventionally used as the isolation material in remedial and primary jobs. However, due to several inherent limitations in cement characteristics, such as cement shrinkage or poor cement slurry compatibility with downhole fluids, it is not always the best solution. Besides, cement slurry is a particle laden fluid which prevents it penetrating in to tight cracks/pathways to ensure isolation during remedial treatments.

This project illustrates the effort to develop a customized polymer system as cement alternative addressing several challenges posed by conventional materials and experimental studies are designed to evaluate its characteristics such as rheology, injectivity and mechanical properties. Furthermore, the compatibility of these systems with drilling fluids contamination and shrinkage behaviour upon cure are evaluated. Afterward, based on the results of measurements, the limitations of each system are determined and the best formulation is optimized.

The results of experiments prove that beside the appropriate rheological properties, the system provides excellent mechanical properties and much lower shrinkage rate upon cure compared to cement. The system withstands and maintains its properties after being contaminated with considerable volume of downhole fluids such as drilling fluids and hydrocarbons and mechanical properties such as compressive strength is not much affected by contamination.

The unique characteristics of customized sealing system as cement alternative could provide benefits to industry by solving several current challenges in achieving secure isolation. Particularly due its ability to penetrate in to tight cracks, this system affords an effective method to mitigate sustained casing pressure or as a remedial solution for casing leakages which cannot be achieved easily by conventional methods.