bluuebunny/crossref_metadata_2025_split huggingface dataset:
Decline Curve Analysis Using Machine Learning Algorithms: RNN, LSTM, and GRU
Authors: Vega-Ortiz Carlos , Panja Palash , Deo Milind , McPherson Brian 
Published: September 2023

ABSTRACT
The traditional Arp's decline model failed to predict production from many oil and gas reservoirs due to some inherent assumptions like boundary-dominated flow contrary to long transient flow. Fundamentally, this is a time series curve fitting and forecasting problem. Advanced machine learning (ML) algorithms can be used to capture the unusual trend in hydrocarbon production decline. The objective of this study is to develop various ML algorithms such as Recurrent Neural Network (RNN), Long Short-Term Memory (LSTM), and Gated Recurrent Unit (GRU) in forecasting future production performance and estimating ultimate recovery (EUR).
Decline curve analysis (DCA) is a straightforward and rapid way to estimate future production simply by suitable curve fitting. However, the traditional Arp's method overestimates the production from many reservoirs, resulting in new empirical methods such as Power Law Exponential Analysis (PLE by Ilk, 2008), Logistic Growth Analysis (LGA by Clark 2011), and Duong Method (DM by Duong 2011). The outcomes of these recent models also depend on the quality of the data and the reservoir flow regimes. The machine learning algorithm is applied to overcome the drawbacks and limitations of the empirical decline curve models. Machine learning algorithms such as RNN, LSTM, and GRU are compared. The first 80% of time-series data is used for training the models and the last 20% is used for testing. The trained models are employed to forecast future rates and to calculate EUR. The value of NSE close to unity suggests good model performance. A normalized Nash-Sutcliffe model efficiency coefficient (NNSE) and Normalized Root Mean Squared Error (NRMSE) are selected for assessing the efficacy of different models. The LSTM models have several unique advantages over typical supervised machine learning algorithms. The models are flexible in handling multiple inputs in time series. The ML models developed in this work can be coupled with an economic model considering the future oil price and operational costs.
Machine learning is a research area quickly growing across several industries providing valuable insights. Machine algorithm for time series forecasting in the oil and gas industry has not been comprehensively explored. Results from this work will provide the literature with another application perspective with strong opportunities in production data analysis.
Monitoring of Shear Failure Along Rock Fractures in Limestone and Granite with Seismic Wave Transmission
Authors: Han K. , Pyrak-Nolte L. J. , Bobet A. 
Published: September 2023

ABSTRACT
A key challenge in using geophysical monitoring to assess the stability of rock fractures is the ability to identify precursory signatures to slip. Laboratory direct shear tests were conducted on induced tensile fractures in Indiana limestone and Sierra White granite under an effective normal stress of 2 MPa, to determine the geophysical signatures of slip along the fractures under both dry and saturated conditions. During the experiments, the normal load, shear load and shear displacement were recorded along with compressional (P) and shear (S) waves that were propagated across the fracture. For dry limestone and granite fractures, the amplitudes of both the transmitted P- and S-waves showed a distinct peak prior to shear failure. Such peak is taken as a precursor to shear failure. However, for saturated limestone and granite fractures, the amplitude of the P-waves displayed either a small increase or a continuous decrease, while a distinct peak in wave amplitude was still observed in the S-waves. This phenomenon can be explained by the increase in the normal fracture specific stiffness due to the presence of highly incompressible fluid, water, which leads to a decreased P-wave sensitivity to changes of the normal stiffness of the asperities under saturated conditions. Also under saturated conditions, a dramatic change in the decrease rate of the P-wave amplitudes was observed that either coincided or occurred close to the peak amplitude of the S-waves, which can be then considered also as a seismic precursor to shear failure. This observation was consistent through different tests and for both limestone and granite rocks under saturated conditions.

INTRODUCTION
Monitoring of frictional rock discontinuities, such as fractures, joints, and faults, is crucial to the evaluation of the mechanical instability of rock for the design of geotechnical structures as well as to the identification of potential natural hazards. Geophysical wave measurements, such as compressional (P) and shear (S) wave propagation, have been widely used as remote and non-destructive methods to monitor changes in the contact area and the state of stress along rock discontinuities. In laboratory experiments, changes in P- and S-waves in the transmitted, reflected, and converted modes have been used to assess local changes in frictional contact surfaces and subsequently understand slip initiation and propagation (Nakagawa et al., 2000; Hedayat et al., 2014a, 2014b; El Fil et al., 2019, 2021; Gheibi et al., 2021, Han et al., 2022a). For example, Mutlu and Bobet (2006) showed that slip along non-homogenous interfaces does not occur simultaneously at all locations along the interface. Also, significant progress has been made to identify and detect seismic precursors to shear failure of artificial rock (gypsum) discontinuities where frictional interfaces have been molded or saw-cut (Hedayat et al., 2014a, 2014b; El Fil et al., 2019, 2021).
Numerical Study on Rock-Breaking Mechanisms of Triangular-Shaped PDC Cutter
Authors: Wenhao He , Xue Li , Runqing Zhang , Zhenliang Chen , Huaizhong Shi , Zhongwei Huang , Chao Xiong , Jinming Sun , Chengtao Hu 
Published: September 2023

ABSTRACT
Conventional PDC cutter usually gets broken when drilling into deep formations due to high hardness and strong abrasion. To help solve such a problem, triangular-shaped PDC cutters have been developed and utilized in the design of hybrid-cutters PDC bit, which have achieved enhanced rate of penetration and high life cycle. Nevertheless, few researches have focused on the rock-breaking mechanisms of triangular-shaped PDC cutter. This research carries out a series of numerical simulations to reveal the rock-breaking mechanisms of the triangular-shaped PDC cutter. Parametrical analysis has also been conducted to reveal effects of cutting parameters, rock strength, and cutter structural parameters on the rock breaking performances of the triangular-shaped PDC cutter. Numerical analysis results show that the triangular PDC cutter is more easily to crush the rock than the conventional PDC cutter by predominantly decreasing the cutting force. Given the same cutting depth and the cutting angle, the triangular-shaped PDC cutter can exhibit higher rock-breaking performances than that of the conventional PDC cutter. Also, optimal analysis should be done for the design of the triangular-shaped PDC cutter. These research findings help the readers understand the rock-breaking mechanisms and the further application of the triangular-shaped PDC cutter in deep hard formations.

INTRODUCTION
Along with the development of PDC bit technologies, PDC bits have accounted for more than 90% drilling footage around the world(Dan & Scott, 2015). Meanwhile, given increasing demand on energy consumption, the exploitation depth gradually shifts into deep and ultradeep formations beyond 6000 m, which are usually distinguished by high hardness and abrasion. In those formations, conventional PDC cutters usually get broken in the drilling process due to high impact, large vibration, and strong abrasion, leading to low rate of penetration (ROP), long drilling duration, and unnecessary non-productive time(NPT) (Durrand et al., 2010; J. Liu et al., 2019; Shahrul Amar et al., 2020; Shi et al., 2018; Zhu et al., 2019). To improve the drilling performances, by modifying the planar cutting surface into 3D cutting structure, innovative kinds of PDC cutters have been proposed to enhance the resistance of PDC bits to high impact and strong wear, such as the conical PDC cutter, the axe-shaped PDC cutter, and the triangular-shaped PDC cutter. In detail, the cutting structures of conical, axe-shaped, and triangular-shaped PDC cutters are respectively a conical, ridged, and trustum of pyramid cutting element. Following the available literature findings, many of the non-planar PDC cutters have exhibited better rock-breaking performances than that of the conventional planar PDC cutter.
Hydraulic Fracturing with Supercritical CO2 in the Laboratory: Ultrasonic Monitoring of Fracture Propagation at in Situ Stress and Temperature
Authors: Kovalyshen Y. , Giwelli A. , Sarout J. , Kiewiet L. , Shulakova V. , Esteban L. , Banks S. , Sarmadivaleh M. , Kato Y. , Katou M. , Takeuchi T. , Kuramoto D. , Chen Y. , Ishida T. 
Published: September 2023

ABSTRACT
The paper reports results of hydraulic fracturing experiments. The fracturing was completed under in situ conditions in 15 cm cube of American Black granite and Montney shale samples using supercritical CO2. Different modes of ultrasonic monitoring have been used. The final fractures were also imaged with fluorescent resin. In contrast to previously reported tests, here we use very strong rocks, high confinement, and stress contrast.

INTRODUCTION
Injection of carbon dioxide (CO2) into subsurface rock formations presents multiple benefits, including reduction in greenhouse gas emissions into the atmosphere. One way of improving the economics of geo-sequestration is to use CO2 as a fracturing fluid to enhance gas productivity in unconventional reservoirs. CO2 can also be used to enhance production of coal seam reservoirs (CO2-ECSB). Understanding fracture initiation/propagation in presence of CO2 is also crucial for the long-term containment of the storage. Monitoring remotely fracture propagation can be achieved using seismic methods. To improve the interpretation of seismic monitoring data in the field we conducted hydraulic fracturing (HF) experiments with supercritical CO2, sc-CO2, in the laboratory under true triaxial stress conditions. We used ultrasonic methods to monitor fracture propagation in cubic rock samples 150 mm in size. For verification purposes the resulting fracture network was visualised after filling it with fluorescent resin. We present here the results of experiments conducted on low permeability American Black granite and shale rock samples.

EXPERIMENTAL SETUP

Equipment
The experiments were conducted in a true triaxial stress cell (TTSC) developed at Curtin University. The maximum compressive load is 1575kN in each spatial direction, while the maximum temperature is about 60°C.
The loading stress is transferred to the sample via steel plates (see Figure 1). Further details about the TTSC and the experimental setup can be found in Wang et al. (2019). Each plate accommodates 10 ultrasonic transducers (pink circles in Fig 1). The transducers are spring loaded against the sample's surface. For this study we used commercially available P-wave ultrasonic transducers (Olympus V103-SM) with a resonant frequency of 1 MHz and a bandwidth from 0.5 to 1.5 MHz. The outer diameter of the transducer is 18 mm, and the crystal size is 13 mm. The transducers were connected to a detection/recording system developed in-house at CSIRO. Due to the system limitations at the time of testing, we could only use 32 ultrasonic transducers out of 60 available (see Figure 2).
Influence of Fault Rupture Velocity on Directivity Effect in Near-Fault Ground Motion
Authors: Zhiyuan Li , Hazarika Hemanta , Guangqi Chen , Zishuang Han , Chaofan Feng 
Published: September 2023

ABSTRACT
Considering the destruction caused by the directivity effect of near-fault ground motion, finite difference models with different source modes are established to explain the directivity effect mechanism, the directivity characteristics of ground motion in the 2016 Kumamoto earthquake are analyzed, and the influences of fault rupture velocity (Vr) on the directivity effect are analyzed. The following conclusions can be made: (1) The directivity effect is mainly caused by the superposition of energy in the forward direction of the fault rupture, which is most significant when the Vr approaches the shear wave velocity (Vs). (2) The ground motion caused by the 2016 Kumamoto earthquake has a distinctive directivity. (3) The Vr is a critical factor influencing the directivity effect, the directivity effect enhances with increasing Vr.

INTRODUCTION
Near-fault ground motions have gained more attention since the 1994 Northridge earthquake, the 1995 Kobe earthquake, and the 1999 Chi-Chi earthquake (Alavi & Krawinkler, 2004; Bray & Rodriguez-Marek, 2004; Hall et al., 1995; Kalkan & Kunnath, 2006; P. G. Somerville, 2003). The ground motion in the near-fault area is significantly affected by the fault rupture mechanism, rupture process, site location, and permanent ground displacement (X. Chen & Wang, 2020; Y. Zhang et al., 2022). The ground motion in near-fault areas may differ greatly from the ground motion far from the fault areas, which is the near-fault effect of ground motion (Sun et al., 2020; Wu et al., 2021; Yang et al., 2023). The near-fault effect is generally expressed in two aspects: one is the difference with the ground motion characteristics in the area far from the fault, such as the difference in ground motion waveform, spectrum, and duration. The other aspect is the characteristics of ground motion distribution in the near-fault area, such as the distribution characteristics in peak ground velocity (PGV), peak ground acceleration (PGA), and response spectrum amplitude (Farrugia et al., 2017; Jinjun Hu et al., 2011; Mo et al., 2022). Near-fault ground motions are usually characterized by long-period velocity pulses, which have significant destructive effects on large structures and also increase the risk of landslides, debris flows and other disasters (Bray & Rodriguez-Marek, 2004; Lu et al., 2021; Quaranta et al., 2022; P. G. Somerville, 2003; P. G. Somerville et al., 1997; Song et al., 2018). The directivity effect of fault rupture propagation is one of the primary causes of velocity pulse (Bray & Rodriguez-Marek, 2004; P. G. Somerville et al., 1997; Wang et al., 2002).
Manifestation of Negative Compressibility in Partially Saturated Rocks: Theory and Experiment
Authors: Mews K. S. , Lozovyi S. , Holt R. M. , Rozhko A. 
Published: September 2023

ABSTRACT
In this study, laboratory experiments were conducted on partially saturated Mancos shale to investigate the elastic response of the sample under a simultaneous increase by the same magnitude in confining stress and pore pressure in the gas phase. Surprisingly, we observed an extensional volumetric strain of the sample and a simultaneous reduction of shear wave velocities at ultrasonic and seismic frequencies. These observations may be described by apparent effective stress coefficients significantly larger than one. A possible interpretation is a negative shale stiffness leading to the volume increase during compression at constant net stress. To further explain these results, the model of Rozhko (2021) based on the hysteresis of liquid bridges inside microcracks was applied. The stiffness associated with capillary forces is negative, indicating that capillary force may dominate the elastic response inside microcracks with a nanometer-scale aperture. These laboratory experiments and theoretical modeling contribute to a better understanding of multi-phase systems at the nanometer scale comprising of liquid, gas, and solid. Specifically, this research can help in carbon dioxide storage and monitoring through a better understanding of overburden rock's static and dynamic response.

INTRODUCTION
Understanding the mechanical behavior of multi-phase systems consisting of a liquid and a gaseous phase in overburden caprocks is necessary for Carbon Capture and Storage (CCS) monitoring, assessing migration pathways, and pore pressure predictions from seismic velocities. It is important to understand pore pressure effects not only in the liquid phase but also in the gaseous phase.
Elastic properties of porous media with empty and fluid-filled pores are described in classical poroelasticity theory (Gassmann, 1951; Biot, 1962). Brown and Korringa (1975), Rice and Cleary (1976) and Cheng (2021) pointed to the fundamental differences between unjacketed bulk modulus and unjacketed pore modulus, which is neglected in the Gassmann theory. Accounting for global and local flow in the pore space and for patchiness in saturation or rock properties introduces frequency dependence and attenuation related to the viscosity of the pore fluid and the distribution of fluid phases in the pore space. Water can significantly soften due to a change in surface energy (Parks, 1984; Tutuncu and Sharma, 1992).
Multi-Lengthscale Geomechanical Modelling and Monitoring of a Compacting Highly Depleting HPHT Field – A Case Study from Norwegian Continental Shelf
Authors: Zhou C. , Andrews J. S. , Saure-Thomassen A. , Renli L. , Andrew M. J. 
Published: September 2023

ABSTRACT
The HPHT field discussed in the paper is one of the major gas production fields on the Norwegian continental shelf. Current depletion is more than 600bar and a unique and comprehensive surveillance program, at multiple length scales, has been in place to monitor the resulting geomechanical effects. This includes: 1) four well re-entries over the last 15 years to log in-situ reservoir compaction measurements based on gamma ray markers, 2) 18 years of continuous offshore platform GPS recording for seabed subsidence and 3) multi-finger caliper measurements for liner deformation at selected producers. In particular, the reservoir compaction has been monitored since 2005 using Compaction Monitoring Instrument (CMI) that measures the compaction between preplaced radioactive markers in the formation. The results from the repeated CMI logging showed that the compaction in the entire reservoir interval is not uniform and is directly influenced by rock mechanical properties. A delayed creeping effect in the producing interval was clearly revealed from core tests and supported by the most recent CMI logging in year 2021. The 1D well-based and 4D field-wide geomechanical models are validated by comparison of predicted deformation with observed casing damage, and by comparison of the predicted surface subsidence with field measurements, respectively. These monitoring results have been used by multidisciplinary teams to improve the understanding of the subsurface, such as sand production, water breakthrough, holdup depth during well intervention, re-perforation and production forecast.

INTRODUCTION
The Norwegian Continental Shelf is a critical supplier of oil and gas to the European market to support energy security. One of the most significant gas production fields on the Norwegian Continental Shelf is a High Pressure High Temperature (HPHT) field, which is the primary focus of this study. Reservoir compaction, which occurs as a result of fluid production and the associated pressure reduction, is an important geomechanical process that requires attention for HPHT fields that will undergo large depletion during primary recovery. The compaction of the reservoir rock and the resulting deformation in the burdens can cause a variety of effects, including well deformation, seabed subsidence, and changes in reservoir permeability. Understanding the effects of reservoir compaction is crucial for maximizing production and ensuring the long-term stability of the reservoir.
Characterization of Gas Transport in Fractured Rocks for Underground Nuclear Explosion Detection
Authors: Li Wenfeng , Neil Chelsea W. , Stauffer Philip H. , Carey J. William , Meng Meng , Frash Luke P. 
Published: September 2023

ABSTRACT
Underground nuclear explosions produce noble gases that can migrate to the surface and become detectable by atmospheric monitoring tools. However, it is challenging to predict radionuclide gas migration in the complex engineered and natural subsurface systems due to several issues. These issues include generation of complex fracture networks near an engineered cavity, reactivation of natural fractures, coupled hydro-thermo-mechanical processes for transport of high-pressure gases in a fractured porous rock system. To improve our understanding of these technical challenges, we used a triaxial direct shear test scheme to characterize coupled hydro-mechanical gas transport in fractured porous rocks. In the experiments, we tested nitrogen (an analog noble gas) flow through two types of rocks with distinct petrophysical properties: porous Bandelier tuff and tight Climax stock granite. For each type, we measured the Biot effective stress coefficient, the rock matrix permeability, and the fracture permeability under various stress states, which allowed us to examine the stress-dependency of the Biot coefficient and investigate rock matrix-fracture interactions for transport of pressurized gas. Comparing the experimental results for the two distinct rock types, we observed some important findings for gas transport in fractured rocks. First, rock fracturing does not necessarily increase samples’ gas permeability when the rock matrix is highly porous. Furthermore, gas permeability of intact rocks can show strong exponential stress dependency even when the rock matrix is very tight. Additionally, Biot effective stress coefficients are not necessarily close to unity for highly porous rocks, especially when rocks are subjected to large effective stresses. In summary, the experimental results can be used to improve the physics in high-fidelity numerical modeling to elevate our understanding of radionuclide gas transport in fractured porous rocks after an underground nuclear explosion event.

INTRODUCTION
Surface radionuclide monitoring is the primary means of determining if an underground explosion is nuclear in nature (Maceira et al., 2017). Following an underground nuclear explosion (UNE), signature noble gas radionuclides, such as Xe-131m, Xe-133, Xe-135, and some krypton radioisotopes, will be produced by nuclear fission (Carrigan et al., 1996; De Geer, 1996; Sun and Carrigan, 2014). They are hard to contain and tend to seep from the underground explosion and migrate to the surface. Surface sampling and detection of these signature gaseous radionuclides, when above some background levels, is a strong indicator of the occurrence of an underground nuclear explosion. By comparison, seismic monitoring cannot definitively discriminate between chemical (for example, TNT) explosions and nuclear events. It is thus important to understand transport of noble gas radionuclides in the subsurface rock strata.