bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Biot Coefficient for Low-Permeability Rocks Accounting for Undrained Loading
Authors: Kim Kiseok , Espinoza D. Nicolas
Published: September 2023

The determination of poroelastic properties for low-permeability porous media (k < 10−18 m2) is often elusive because of long periods required to dissipate or equilibrate pore pressure in tested samples. Poroelastic properties, such as the Biot coefficient, play a key role in determining the effective stresses in-situ and changes due to thermal, hydraulic and mechanical loadings. This paper presents a method to determine the Biot coefficient of low-permeability porous media accounting for undrained loading. We conducted experiments and numerical simulations to show the effectiveness of the method and ran parametric studies by changing the loading rate, equilibrium time, and permeability. The results show that the Biot coefficient, drained bulk modulus and permeability can be determined from a single partially undrained experiment as long as undrained response is considered in the data analysis. This method is advantageous not only because it is faster than previous methods but also because it can determine permeability indirectly. Accurate determination of these properties is critical to predict the response of low-permeability materials such as seal rocks for carbon geological storage among other applications.

INTRODUCTION

Accurately characterizing the poromechanical response of geological formations is critical for the success of subsurface energy projects, such as oil and gas recovery, geologic carbon and hydrogen storage, geothermal energy, and nuclear waste geological storage among others. Low permeability formations (k < 10−18 m2) play a vital role in many cases as sealing layers or containment barriers. Low-permeability formations exhibit a strong hydromechanical coupling, hence, confidently predicting their poromechanical behavior is critical (Bachu 2008; Makhnenko et al. 2017; Espinoza and Santamarina 2017; Zheng et al. 2022). However, accurate measurement of poromechanical properties can be challenging for materials with ultra-low hydraulic diffusivity due to the long period needed to achieve pore pressure equilibrium when external loadings are applied (Kim and Makhnenko 2020).
Drilling Data Based Approach for Equivalent Circulation Density Prediction While Drilling
Authors: Abdelaal Ahmed , Elkatatny Salaheldin , Gamal Hany , Ziadat Wael
Published: September 2023

The current research presents a machine learning application toward predicting the equivalent circulating density (ECD) in real-time while drilling operations. Maintaining high accuracy in estimating equivalent circulating density (ECD) is crucial due to the potential well control issues that can arise from inaccurate ECD values. Inaccurate ECD can lead to problems such as fluid losses, formation fracturing, kicks, and blowouts. Therefore, precise ECD estimation plays a vital role in preventing these issues and ensuring the safety and stability of drilling operations. The fourth industrial revolution provided high technology-based solutions to serve the oil and gas industry and machine learning is considered one of the best tools in research and development. The developed model within this study utilized the drilling hydraulic data in terms of initial mud weight, mud pumping standpipe pressure, and pumping rate to be fed to the random forest model to predict the ECD with good accuracy. A data set of 5,140 data points was used through a comprehensive data analytics workflow to enhance data quality that greatly impacted the model accuracy. The obtained results showed the outperformance of the developed model to predict ECD with a correlation coefficient (R) of 0.99 between the actual and predicted ECD data with a low mean square error of 0.04. The developed model will add more to the drilling automation process toward safe and efficient operations through providing high accurate ECD values while drilling.

INTRODUCTION

The drilling operations are considered the most critical among the other operations in the oil and gas due to safety precautions and well control issues that impact the personnel's life and the operations’ high cost. Monitoring the drilling operations with many sensors along the surface beside downhole sensors will help control the operations. Equivalent circulating density (ECD) is considered one of the parameters during drilling operations and should be given special care while drilling narrow window zones where there is not a wide gap between the pore and formation fracture pressures. ECD represents the hydrostatic pressure of the drilling mud and the annular friction pressure losses while circulating the wells (Haciislamoglu, 1994). Inaccurate estimation of ECD may lead to many well control issues as ECD might increase and cause mud losses or even fracturing the drilled formations, while low ECD value below the drilled zone pore pressure may result in a kick and flow from the drilled formations. Hence, many well control problems will be encountered with inappropriate ECD estimation. Many factors affect ECD such as hole geometry, pressure losses profile, drilling mud rheological characteristics especially mud weight and viscosity, well pressures and temperature profiles, and hole cleaning (Hemphill and Ravi, 2011; Zhang et al. 2013; Abdelgawad et al. 2019).
3D Pore-Scale Modeling of Mineral Dissolution and Precipitation in Fractured Rocks
Authors: Kang Q. , Liu M. , Carey J. W. , Viswanathan H. S.
Published: September 2023

We present a pore-scale numerical modeling study of coupled fluid flow, solute transport, and mineral dissolution/precipitation in 3D fractured carbonate rocks. The injected fluid can dissolve the carbonate and release carbonate ions into the solutions, which react with Ba2+ resulting in barium carbonates (BaCO3) precipitation. Both a simplified fracture and a complex fracture geometry extracted from real shale images are considered. Simulations with a wide range of Pe and Da numbers are carried out to systematically study their effects on dissolution/precipitation patterns and on evolution of fracture geometry, porosity, and permeability. The results show that the coupled physicochemical process is strongly dependent on the Pe and Da. While similar trend of the permeability-porosity variations is obtained for the two fractures at the same Pe and Da numbers, the evolution of fracture morphology is different due to the difference in initial structure heterogeneity and wall roughness. This work reveals the interplay of advection, diffusion, and reaction in determining the fracture evolution and improves our understanding of fluid-mineral interactions in fractures.

INTRODUCTION

Fractures play an important role in providing preferred flow pathways in low-permeability formations and significantly enhance their permeability. They can improve gas production for shale reservoirs but can also increase the risks for leaking of CO2 from geological storage sites.

The fluid-mineral reactions, including dissolution or precipitation, can cause the alteration of porous medium matrix or fracture wall. Particularly, mineral dissolution (precipitation) can increase (decrease) the pore/aperture size and hence the permeability of porous or fractured media. While there have been a lot of studies on mineral dissolution in porous or fractured media considering resultant pore-structure change (Chen, Kang, Viswanathan, et al., 2014; Kang et al., 2014; Kang et al., 2002; Liu & Mostaghimi, 2017; Rasoulzadeh et al., 2020; Starchenko et al., 2016; Verberg & Ladd, 2002; Verhaeghe et al., 2005, 2006), studies on mineral precipitation are much less (Deng et al., 2021; Kang et al., 2005; Kang et al., 2003; Menefee et al., 2020), and studies on coupled dissolution and precipitation are scarce (Chen, Kang, Carey, et al., 2014; Kang et al., 2010). Particularly, there is no high-resolution pore-scale modeling study on coupled dissolution and precipitation in three-dimensional (3D) fractures with evolving fracture geometry to our best knowledge. Consequently, the complex coupled processes including fluid flow, solute transport, dissolution/precipitation, and evolution of pore structure are not well understood.
Coupled Pore Pressure and Geomechanical Modeling of a Naturally Fractured Reservoir
Authors: Yao Qiuliang , Madyarov Andrew
Published: September 2023

Natural fractures play a significant role in oil and gas production by serving as the primary fluid pathways in reservoirs with low matrix permeability. However, their behavior is sensitive to stress change. The depletion of reservoir pressure will increase the effective stress and may cause natural fractures to close. Closure of opened fractures may create pressure barriers and impede further depletion. Numerical simulation of a naturally fractured reservoir remains challenging. A fully coupled finite element model is developed in this study using commercial finite element method (FEM) software. The interaction between total stress and reservoir pressure is computed using a Biot-Gassmann poroelastic model, and the depletion is modeled as pressure diffusion using Darcy's law. The closure of natural fractures is modeled by associating the permeability to stress using a subroutine that reads the stress at each time iteration to compute the corresponding permeability and update the material property at each material point. A scenario study successfully demonstrates the modification of the depletion pattern because of the closure of natural fractures.

INTRODUCTION

When natural fractures develop within a reservoir, geomechanical and hydraulic properties interact with one another (Davies & Davies, 2001). The initial spatial distribution of opened fractures has a significant impact on fluid flow and pressure depletion (Heffer et al., 1994). The in-situ stress field responds to reservoir pressure changes according to porous media constituting material laws. On the other hand, hydraulic properties of natural fractures are sensitive to stress conditions. Closure of opened fractures creates a pressure barrier and can impede further depletion. Such interactive behaviors are highly dynamic and should be modeled in a coupled manner (Jin et al., 2000). Most current modeling approaches involve two separate simulation platforms: (1) fluid flow and reservoir pressure modeled with reservoir simulators and (2) stress evolutions modeled using FEM simulators (Myers et al., 2017). Such approaches depend on a large amount of data repeatedly transferred between the two platforms. Recently lots of efforts of coupled modeling have been reported or implemented into commercial software. Generally, the reservoir simulator is the master or host in the coupled process, therefore the focus is on fluid simulation, but the stress is typically handled oversimplified. Furthermore, properly modeling the modification of fracture transport properties attributed to stress variations remains challenging (Gao & Gray, 2022).
Nanoindentation Characterization of Vaca Muerta Formation Shale Rocks and Its Relation to Geomechanical Model and Core Plugs Properties
Authors: Noya M. , Celleri H. , Camilion E. , Caneiro A. , Floridia A. , Grasetti C. G. , Ramallo J. I. , Fuertes M. C.
Published: September 2023

Nanoindentation has arisen as a promising technique to geomechanically characterize small cutting samples obtained during drilling a well. This technique is a useful tool to characterize unconventional reservoirs during the exploration phase. While we have previously analyzed cutting rock samples from Palermo Aike Fm. (Austral-Magallanes Basin, Argentina) in which not enough data was available to cross check the technique, we now analyze Vaca Muerta Fm. (Neuquen Basin, Argentina) core rock samples that have a thoughtful geomechanical characterization. In this work we compare the properties obtained by nanoindentation to those obtained from a validated geomechanical model. Additionally, we compare nanoindentation data with laboratory tests obtained by static and dynamic experiments at plug scale. The results show that the elastic modulus obtained by nanoindentation matches the elastic modulus obtained with ultrasonic wave test under high confining pressure. Furthermore, it correlates to the ones obtained by triaxial compressive tests as well as with the modulus obtained from a calibrated geomechanical model. Additionally, good correlation is also seen when hardness data from nanoindentation is compared with uniaxial compressive strength (UCS) measured in plugs and with scratch resistance from core samples, but in a different order of magnitude. Using the elastic modulus and hardness obtained from nanoindentation we were able to screen data equivalent to confined dynamic Young modulus, UCS and scratch resistance measured in the cores. Therefore, nanoindentation in cutting is a cheap method to obtain mechanical properties when information or samples are not available, valuing cutting samples obtained prior to drilling new wells and getting cores and logs. Furthermore, it could be useful to determine the variations of these properties in horizontal wells where sonic logs are expensive and difficult to run.

INTRODUCTION

Exploration projects often rely on drill cuttings as the sole source of rock samples from a given area of interest. However, estimating the mechanical properties of these cuttings is a challenge due to the small sizes of the samples. Fortunately, the nanoindentation technique can overcome this issue, as demonstrated by several studies (Shukla et al., 2013; Glover et al., 2016; Ma et al., 2020). This method allows the determination of the indentation modulus, hardness, and fracture toughness of rock samples using a small amount of material from the measurement of load-displacement curves. Previous research has shown that there is a strong correlation between the indentation modulus and the dynamic Young modulus (Kumar et al., 2012; Dang et al., 2017; Celleri et al., 2020, Noya et al., 2021), indicating that the former can be used to describe the elastic behavior of rock samples during dynamic tests at high confining pressures.
Molecular Dynamics Insights into Bioconversion Induced Matrix Strain
Authors: Pandey R. , Sohail T. , Ajibona A. I. , Saurabh S.
Published: September 2023

The total annual US consumption of natural gas is expected to surpass 40 trillion cubic feet in the coming years. Microbially enhanced coalbed methane (MECBM) aims to replicate naturally occurring microbial pathways to generate methane from in-situ coal. In a basic gamut of lab-characterization experiments investigating properties of coal as a reservoir, it was revealed microbial treatment of coal results in swelling of the coal matrix. Bio-strains in the matrix result in changes in connected porosity, and its stress-state which governs the flow behavior throughout the life of the producing reservoir. Use of molecular dynamics (MD) enables us to utilize the bio-strain data to understand the dynamic stress-state development in a MECBM reservoir. The Wiser coal molecule was used as the representative molecule, whose reactive potential was minimized using PCFF. The stable MD system enables application of strain, which enables the analysis of internal stresses. Results indicated internal stresses developed during bioconversion exceeded the Von Mises failure criterion for the sample tested in the laboratory under hydrostatic pressure (0.2 MPa). However, the internal stresses for sample under in-situ stress regimes was suppressed, far from the tensile failure conditions.

INTRODUCTION AND BACKGROUND

There has been a sustained increase in the demand for clean energy sources such as hydrogen and methane, especially as the world works towards meeting sustainable climate goals (Jun et al., 2016). Natural gases like methane have lower carbon footprint, as it generates approximately 50% of the carbon when compared to burning oil and coal for electricity generation (Tollefson, 2012). As such, natural gases are set to go up in production rates to meet environmental demands. Recent data indicates that the world demand for natural gas is expected to increase till 2045, with a significant portion of this demand to be met by increasing production from unconventional resources, such as coalbed methane (CBM) (Birol, 2017; Gonzales, 2021; IEA, 2022). CBM refers to naturally occurring methane extracted from coal and coal seams, which is an unconventional source of natural gas (Haldar, 2018). However, to meet the increasing demand for natural gas, researchers have made efforts to find ways to increase the production of coalbed methane. One such method is to replicate the natural production of methane formed by microbial breakdown of organic components present in coal (Flores et al., 2008; Strapoć et al., 2008; Midgley et al., 2010; Penner et al., 2010). This process of producing microbial methane from coal is referred to as Microbially Enhanced Coalbed Methane (MECBM) (Scott, 1999).
A Novel End-To-End Solution for Developing Geomechanical Models Along Horizontal Wells Without Well Logs
Authors: Soroush Hamed , Gentry Emilie , Madyarov Andrew , Harmouche Jinane
Published: September 2023

Knowledge of rock properties and in-situ state of stress along the horizontal laterals is essential to optimize frac and stage designs for maximum recovery and avoid casing deformation during fracturing. Also, the integrity of the borehole is directly dependent on the stress profiles along the well trajectory and appropriate design of the drilling and stimulation operations. However, lack of wireline logs such as dipole sonic, porosity, image, and density, which are required for estimation of geomechanical properties, prevents operators from having this valuable information and, thus, optimizing their operations. Our solution to this data challenge is Drilling Dynamic Geomechanics (DDG) technology that utilizes downhole drilling dynamics data to calculate continuous 1-D profiles of the rock mechanical properties, pore pressure, and principal stresses along the entire well length. Using a combination of Bit Vibration Signals (measured down-hole) and Electronic Drilling Recorder, EDR, data (routinely measured at surface) provides a low-cost high-value solution to this major problem. It uses readily available data, imposing no additional time for data acquisition. Drilling dynamics data are high resolution high scanning-rate and are available along the entire well length providing higher resolution estimates of geomechanical properties with significantly larger coverage in comparison to well logs. This paper describes our methodologies and results of field testing the technology in different basins.

INTRODUCTION

To ensure safe and cost-effective subsurface operations, knowledge of the state of stress is essential. Characterizing rock properties and the in-situ stress state in the complex reservoirs and cap rocks is critical for optimizing well designs and completions. Also, the integrity of the borehole is directly dependent on the 3D stress profile along the well trajectory and appropriate design of the drilling and stimulation operations. In-situ stresses are notoriously difficult to determine.

The currently available methodologies for stress estimation are heavily dependent on well logs such as density, sonic, porosity, etc. These inferences are based on simplified models or correlations which generally result in stress profiles with a large range of uncertainties and requirement to be calibrated against expensive field tests such as Extended Leak-off Test (XLOT), minifrac, and Diagnostic Fracture Injection Test (DFIT). The required logs are rarely available in horizontal wells, where understanding the lateral changes in the state of stress is very important. Also, seismic data that cover a larger volume of subsurface formations are not of sufficient spatial resolution for the required subsurface characterization, especially for carbon storage purposes.
Development of a Weak But Brittle Analog Sediment Rock for Experimental Study
Authors: Wibisono Doandy Y. , Gutierrez Marte , Majumder Dipaloke , Gautam Pradeep K.
Published: September 2023

Laboratory-tested results in rock mechanics have played a crucial role in understanding rock behavior and failure mechanisms. This paper outlines the development of an analog rock, similar to sandstone, for an experimental study that yields a low unconfined compressive strength yet exhibits brittle failure characteristics. The F-75 Ottawa sand, Type I/II commercial grade Portland cement, air entrainment admixture, and water constitute the raw mixtures of the developed analog rock. The result is a reproducible homogeneous and isotropic rock. The effect of the air entrainment admixture and freezing-thawing cycle on the analog rock are investigated. This study amplifies the notable macroscopic fracturing after a limited post-yield strain. The unconfined compressive strength has been bounded at around 1.5 MPa, and the material continues to exhibit brittle behavior at a range of confinement. A set of Brazilian indirect tensile tests was used to assess the tensile strength, including the brittle failure analysis governed by the ratio between the unconfined compressive strength and tensile strength. In addition, the material physical properties were obtained, along with the thin-section-based porosity analysis. The synthetic sandstone is developed for a scale-model experimental study of brittle failure in tunnels using a true-triaxial apparatus that include spalling, dog-earing, and rockburst.

INTRODUCTION

Brittle failure in the underground excavation can be sudden and catastrophic, resulting in large cracks and fractures such as spalling and rockburst. This stress-induced failure is typically encountered in sparsely fractured or massive rocks at deep underground excavations (Martin et al., 1997). Therefore, understanding the nature of undesirable rock mass brittle failure is essential to provide mitigation plans for the associated risks.

One approach to enhance the understanding of behavior and failure mechanisms of rocks is through laboratory testing. However, it is challenging to collect natural, homogeneous, and undisturbed rock specimens of varying sizes from the field. Additionally, the natural specimen may introduce alterations to the variables that could differentiate the investigation plan in terms of reproducibility (Johnston & Choi, 1986). Hence, developing a repeatable analog rock mix can be considered with a flexibility range of controlled properties. In this case, the prepared analog rock specimens must have the characteristics of the investigated phenomenon (i.e., brittle behavior).
Investigating Grain Size Influence on the Stress-Dependent Permeability of Porous Rocks Using Particulate Discrete Element Method
Authors: Pothana Prasad , Ifrene Ghoulem , Ling Kegang , Garcia Fernando E.
Published: September 2023

Reservoir in-situ stresses continuously evolve during the reservoir life cycle because of the production of hydrocarbons, injection of water and CO2 for enhanced oil recovery, storage of CO2, and nuclear waste disposal. The induced changes to the stress state deform the reservoir rock, including the pores and fractures in the rock, and hence change the permeability of the rock. Studies demonstrate that grain size significantly affects the mechanical properties and strength of rock, yet little research exists on the effect of grain size on stress-sensitive seepage behavior.

In this study, we investigated the effect of grain size on the stress-dependent flow behavior of a porous rock using the three-dimensional discrete element method. We modeled the porous rock geometry using randomly generated rigid spherical grains of given size distribution enclosed in a cuboid. Particle-particle interactions and wall-particle interactions are governed by the Flat-Joint contact model. Rigid boundary walls are used, and a constant strain rate is applied to the boundaries to reach a pre-defined confining stress state. Subsequently, we used the pore scale finite volume method to model the steady-state fluid flow of single-phase fluid at each confining stress state of the model.

The permeability-stress relationship data is best described by the exponential model, and the exponent of the exponential model (stress-sensitive coefficient) indicates how rapidly the permeability changes with stress. Our results show that the stress-sensitive coefficient varied very little with the grain size and shows a general decreasing trend with an increase in the mean grain size of the spherical pack. We argue that the effect of other parameters such as pore morphology, micro-cracks, and cementation has a greater influence on the stress-sensitive permeability than the grain size alone.

INTRODUCTION

The subsurface in-situ stresses exhibit dynamism, which is attributed to the influence of several anthropogenic factors such as reservoir depletion during hydrocarbon extraction, CO2 sequestration, geothermal activities, nuclear waste disposal, and natural causes arising from tectonic movements. Such stress variations significantly impact the physical properties of rocks, particularly their porosity, permeability, and dynamic elastic properties. Given the practical applications associated with these effects, the geoscience community has shown significant interest in this aspect.
The Role of Shear Deformation on Shale Fracture Reactivation and Conductivity Evolution
Authors: Yu Jiayi , Wang Jiehao , Li Yan , El-Fayoumi Amr , Wu Ruiting , Liu Xiaolong , Rijken Peggy , Rathbun Andrew P. , Elsworth Derek
Published: September 2023

In this study, we conduct laboratory experiments reproducing fracture slip on both propped and unpropped fractures in Marcellus shale to explore the role of shear deformation as a primary control on permeability evolution and its correlation with initial stress state, shear stress magnitude and loading rate, and proppant loading concentration. For tests on unpropped fractures, we incorporate the complexity in both form and response of natural fracture topography by using pristine natural fractures directly split along bedding planes. Under low shear stress, unpropped fracture is prohibited from slipping by strongly mated interlocking asperities. As we increase shear stress exceeding the frictional strength of the contact, it exhibits great conductivity enhancement upon fracture reactivation followed by immediate and continuous decay. If shear stress is loaded incrementally instead of instantaneously – broadly representing different fracking fluid injection rate – fracture conductivity response to shear deformation is considerably muted. Unpropped fracture behaviors are also found to be strongly related to fracture roughness and fidelity of the interlocking asperities, while less sensitive to background stress state. For propped fractures, we use manually ground fractures to specifically focus on the proppant impacts. In contrast to unpropped fractures, conductivity enhancement upon shear reactivation only presents where proppant is placed as non-uniformly distributed monolayer, which can be attributed to the generation of interparticle highly permeable flow paths. Otherwise, conductivity decreases as a result of proppant embedment, crushing, and compaction, however the reduction is muted with thicker proppant pack.

INTRODUCTION

The shale gas revolution dramatically changed the mix of energy supply in the United States over the past decade. The deployment of horizontal drilling and massive hydraulic fracturing to generate highly permeable flow paths has unlocked the massive store of hydrocarbons held in deep, ultralow-permeability shale reservoirs (Warpinski and Teufei, 1987; Maxwell et al., 2002; Taleghani and Olson, 2011; Taleghani et al., 2016).
Quantifying the Potential for Induced Seismicity and the Associated Hazard and Risk for EGS Projects in Nevada and Oregon
Authors: Wong Ivan , Bubeck Alodie , Gray Brian , Lewandowski Nora , McGregor Ian , Smith Sarah , Wu Qimin , Chowdhury Ishika , Yenihayat Nesrin , Akerley John , Garrison Geoffrey , Cladouhos Trenton
Published: September 2023

As part of the development of Induced Seismicity Mitigation Plans (ISMPs) for four proposed enhanced geothermal system sites in Nevada and Oregon, we are evaluating the potential for induced and triggered seismicity and the associated seismic hazard and risk at each site in line with the seven steps described in the U.S. Department of Energy's (DOE) Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems. In Step 1, preliminary screening-level risk analyses are being performed to assess the potential impacts on the local communities and stakeholders during routine operations, including a possible worst-case scenario. In Step 3, criteria for ground vibration and noise are being reviewed and selected to assess the existing ground vibration and noise environments to establish a baseline, and evaluate the anticipated impacts. In Step 5, the seismic hazard at each project site is being estimated due to both natural and induced seismicity. The former provides a baseline from which to evaluate the additional hazard that may be imposed by induced earthquakes. In Step 6, a robust estimate of the seismic risk is being developed prior to the project and associated with the stimulation. The risk analysis helps evaluate alternative operational procedures, including those that could mitigate negative effects and minimize the risk from induced seismicity.

INTRODUCTION

As part of the development of Induced Seismicity Mitigation Plans (ISMPs) for four proposed enhanced geothermal system (EGS) sites in Nevada and Oregon, we are (1) evaluating the potential for induced and triggered seismicity, (2) performing probabilistic seismic hazard analyses (PSHAs) that address the hazard from both natural tectonic seismicity and potential induced seismicity, and (3) evaluating the associated seismic risk at each site. The ISMPs are being developed consistent with the seven steps described in DOE's Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems (Majer et al., 2012).

The overarching purpose of the Protocol is to promote the safety of EGS projects and to help gain acceptance of geothermal development from the general public. The Protocol represents best practices regarding geothermal-induced seismicity and provides guidelines that should be followed to mitigate potential adverse effects from induced earthquakes.
Research on Targeted Hydraulic Fracturing Control Method Based on Theoretical Model
Authors: Wang W. Z. , Yang G. , Wang H. G. , Zhou Z. , Wang L.
Published: September 2023

Targeted Hydraulic Fracturing (THF) is an effective method to increase oil or gas well production. This method involves injecting fluid into the reservoir to create fractures and stimulate the flow of hydrocarbons. Vuggy carbonate reservoirs provide a unique structure, allowing THF to optimize production. The key to successful fracturing is accurate targeting of the reservoir and the creation of artificial fractures connecting with the reservoir through construction methods. Therefore, in vuggy carbonate reservoirs, the turning radius of fractures is critical. The turning radius is affected by various factors, including the pre-existing fracture angle and construction parameters. A fracture expansion model that considers the influence of fluids was established to simulate the trend of fluid energy dissipation and the effect of internal fluid pressure on the expansion of fractures. Moreover, an accurate quantitative evaluation was conducted on the factors affecting the fracture turning range.

INTRODUCTION

Carbonate reservoirs, widely distributed throughout the world, contain a significant portion of conventional hydrocarbon reserves. Regions such as Tarim Basin in China, Arum River Basin in Turkmenistan, and Arab-D reservoir in Saudi Arabia are notable examples [1,2]. Exploiting these reserves, however, presents difficulties due to characteristics such as high temperature and pressure, depth of burial, low matrix permeability, poor porosity, and complex reservoir structure. Understanding the five primary carbonate formation types: pore, fractured, fracture-pore, fracture-cavern, and pore-fracture-cavern, is essential for reasonable and efficient development of these reservoirs. Due to the fact that the storage space for oil and gas in these reservoirs is primarily natural cavities and fractures, creating seepage channels through hydraulic fracturing is necessary. Acid fracturing has been shown to be the most effective technique for stimulating these reservoirs and making hydrocarbon production viable, with the primary mechanics of acid fracturing being acid dissolving and high-speed impact[9]. Specifically, establishing a targeted fracture propagation and steering model using pre-treatment fracture technology, which forms pre-treatment fractures with controllable direction and length around the well, is critical for achieving the goal of targeted fracturing of carbonate reservoirs.
Spatial Data Analysis of Water Production from Unconventional Reservoirs, Case Study from the Williston Basin, North Dakota
Authors: Bakelli Omar , Kegang Ling , Nesheim Timothy , Mahmood Taufique , Khetib Youcef
Published: September 2023

With the instability of oil prices and the high investment cost associated with developing unconventional reservoirs, oilfield operators, contractors, and service companies are exploring new ways to optimize produced water (PW) management and reduce transportation, treatment, and disposal costs. In addition to this global trend, the Williston Basin faces more challenges due to pressurizing of underground disposal formation and the inadequacy and cost of existing purification technologies. Besides efforts toward the investigation of novel treatment methods that might offer new frontiers for PW reuse, reducing the co-produced water from upstream is still among the top solutions. Recent research showed the potential of spatial data analytics to disclose important information that serves future wells development and minimizes water production. The present study subscribes to these energies to demonstrate the role of spatial data analytics in a better understanding of the PW trend and to identify the high-volume root causes. Production data including multiple fields and producing formations were treated, normalized then visualized for this purpose. The first step, two production sections have been segregated from the data, flow back water and PW section. In the second step, an open-source GIS software was used to generate surface maps. Results analysis showed high values of water oil ratio (WOR) in West, Northeast, and Southwest fields of the Williston Basin with values reaching 94%, and low WOR recorded in central fields with values as low as 10%. The study confirmed the substantial correlation between WOR and the basin's geology configuration. The findings can be used to select a storage facility location and screen out field candidates for water control intervention. The research suggested merging production data with geology, well geometry, and completion data for in-depth insights and analysis.

INTRODUCTION

The petroleum industry is placing increasing focus on optimizing produced water (PW) management and reducing associated costs and environmental impacts. PW from oil and gas production encompasses various sources, including formation water, injected water for enhanced oil recovery EOR, associated chemicals and solids, and flowback water from hydraulic fracturing (Chard & Saunders, 2019).
Integrated Reservoir Simulation and Discrete Fracture Network Modeling for Produced Water Source Identification in Tight Reservoirs, Case Study from the Bakken Formation, Williston Basin
Authors: Bakelli Omar , Chellal Hichem Aimen Ketib , Aoun Ala Eddine , Khetib Youcef , Mellal Ilyas , Kegang Ling
Published: September 2023

The Bakken reservoir in the Williston Basin recorded an increase in produced water volume, previous research suggested two possible reasons: Bakken formation pressure depletion allowing for more water migration and fractures propagation FP enabling fluid flow from the upper Lodgepole and/or from the lower Three Forks formations. The aim of this study is to investigate the two theories and to identify the best match with the real production data. An integrated reservoir model and a discrete fracture network DFN have been used for this purpose, wells and literature data from a Bakken reservoir field were associated to build the reservoir model and then compiled with natural fractures network generated using a DFN modeling tool. The assessment included four production cases: from the Bakken formation only, from the Bakken and Three Forks formations with downside FP, from the Bakken and Lodgepole formations with upside FP, and simultaneously from the three layers. The simulated models were evaluated using monthly production rates and cumulative volumes. Producing from the Bakken and Lodgepole formations case resulted in a good match, whereas the other three scenarios requested an unreasonable range of parameters for history matching. The third model's tight match establishes fracture propagation through the Bakken and Lodgepole formations as the most likely source of produced water. Natural pressure depletion of the Bakken formation and downside fracture propagation are implausible due to the unrealistic values required to match the models. This study might be expanded to include more fields to gain a more comprehensive knowledge of the Bakken produced water sources, and the outcomes serve as a guide for future wells implementation and development.

INTRODUCTION

In 2021, the United States oil and gas industry generated 25.86 Bbbls of produced water (GWPC, 2022). Effective management of produced water is crucial for the industry's sustainability and cost efficiency.
A Novel MCMC-Based Hydraulic Fracture Diagnostics Approach Using Water Hammer Data
Authors: Liu Lijun , Liu Yongzan , Wang Xiaoguang
Published: September 2023

The water hammer signatures, which can be observed after pump shutdown at the end of a hydraulic fracture treatment, have proven to contain useful information about the geometry of generated hydraulic fractures. This paper presents a novel hydraulic fracture diagnostics approach using the water hammer data. A water hammer model that describes the pressure transient in hydraulically fractured horizontal well is established. In the model, a new multi-cluster hydraulic fracture boundary condition is derived by considering the perforation friction and leak-off in fractures. The method of characteristics is applied to efficiently solve the water hammer model. The water hammer signals can be effectively reproduced under different fracture characteristics. The MCMC method is applied to construct the posterior statistics of fracture parameters (e.g., width, length, height). The proposed approach is first verified by a series of synthetic models, and then applied to a real field case of a multi-stage hydraulic-fractured horizontal well in a shale gas reservoir to demonstrate its applicability and efficiency.

INTRODUCTION

Hydraulic fracturing has been the commonly used stimulation technique for the economic development of shale/tight gas and oil reservoirs. Although rapid progress has been made in fracturing technology, accurate characterization of hydraulic fracture is a great challenge which hinders the evaluation of fracturing efficiency and prediction of well productivity.

Various techniques have been developed to characterize hydraulic fractures, which can be divided into two categories, i.e., direct monitoring methods and indirect interpretation methods. Direct monitoring methods mainly include micro-seismic monitoring (Le Calvez et al. 2007; Zhu et al. 2017), fiber-optic sensing (Liu et al. 2020; Liu et al. 2023), coring observation (Maity et al. 2018), and downhole imaging (Roberts et al. 2018a; Roberts, et al. 2018b). These methods are usually characterized by their high accuracy, but limited by the high cost and limited observation range. Instead, indirect interpretation methods, including flowback analysis (Chen et al. 2018; Liu et al. 2019), pressure transient analysis (He et al. 2017; Wang et al. 2021), and water hammer analysis (Carey et al. 2015; Hu et al. 2022), are commonly used low-cost fracture diagnosis techniques. However, flowback analysis and pressure transient analysis usually require the production data after the well completion, which can hardly provide the real-time fracture information during hydraulic fracturing. The water hammer analysis has the advantages of short testing time, low-cost and real time.
Effect of Relative Humidity on Water Content and Volume Change in Buffer Blocks in Geological Repositories
Authors: Feng Yuan , Eun Jongwan , Kim Seunghee , Kim Yong-Rak
Published: September 2023

Buffer materials are critical for engineered barrier systems (EBS) to handle high-level radioactive waste (HLW) in geological repositories. The water content and volume change of the buffer block during storage and installation are affected by environmental conditions, such as relative humidity and the initial water content of blocks. This paper investigated the drying process of bentonite buffer blocks by using a water transport model coupled with the capillary liquid flow and vapor diffusion, and the process was experimentally verified by desiccation tests. The model represents vapor-liquid equilibrium as the driving force for vapor diffusion, considering the effect of pore capillaries on thermodynamic activity. The theoretical relationship between relative humidity and water saturation is basically consistent with experimental measurements, and the established model can predict the drying rate under different relative humidity conditions. At the same time, the volume change of the buffer block during the drying process was analyzed. Based on the results, the effect of different environmental relative humidity and initial moisture content on block drying was evaluated. The results show that the block with lower initial saturation is less affected by the relative humidity of the environment than the block with higher initial saturation, and the environment with lower relative humidity is more likely to change the moisture content and volume of the block. This study can be used to predict the effect of different environmental conditions on the distribution and deformation of soil interior saturation.

INTRODUCTION

The disposal of spent fuel from nuclear power plants is a global concern, and the deep geological repository is widely considered to be the solution for the long-term storage of nuclear waste, as shown in Fig. 1 (Choi et al., 1999; Fukuda et al., 2003; Cho and Kim, 2016; Salonen et al., 2021). Spent fuel is stored in specially designed containers and placed in tunnels dug deep in stable geological formations (Hedin & Olsson, 2016). The buffer material between the canister and the bedrock prevents groundwater from flowing into the deposition holes and keeps the canister centered in the hole, the buffer material also prevents the diffusion of radioactive material into the bedrock in the event of a canister rupture (Salo & Kukkola, 1989; Lee et al., 2007; Yoon et al., 2018; Larson et al., 2020). Bentonite or its modified soil is often used as a buffer material because of its extremely low permeability in the saturated state (Suzuki et al., 2013; Choi et al., 2022).
Stability Evaluation of the Constructed Salt Cavities of Jintan Gas Storage in China
Authors: Jianan Wu , Dewen Zheng , Guosheng Ding , Qiqi Wanyan , Kang Li , Lina Ran , Yanxia Kou , Song Bai , Haitao Li
Published: September 2023

Learning from the operation experience of built salt cavern gas storages is necessary for new cavity construction. Jintan Gas Storage is the first salt cavern underground gas storage in China and Asia. Since the pilot experiment in 2003, it has been put into operation for about 20 years, with over 29 caverns built and a working gas volume of 800 million cubic meters formed. Due to the complexity of geological conditions and lack of building experience, the shape of some constructed salt cavities is irregular or even deformed, facing stability risks. Based on the geological information and sonar data, the geomechanical model of every constructed cavity is established to evaluate its stability and the possibility of expanding the operating pressure. According to the cavern shape from sonar measurement, all built cavities are divided into three types of trapezoidal roof, large flat roof and abnormal roof. The simulation results and sonar measuring data of different time show that the cavity with a large flat top is the most unstable, and this kind of cavity has a roof collapse with a displacement of 2-8m. The trapezoidal roof cavity is the most stable and has the largest volume, while the abnormal roof cavity has a larger range of plastic damage around the cavity, and the most serious waste in the use of salt rock resources. In addition, based on the stability assessment, the operating pressure of trapezoidal cavity can be appropriately expanded by 1-2MPa, while the minimum pressure of large flat roof cavity should be appropriately enhanced, and the gas production rate should be reduced to maintain the stability of the gas storage. This study can provide guidance for the construction of other salt cavern gas storages.

INTRODUCTION

With the rapid development of economy and the fast growth of natural gas demand, underground gas storage (UGS), as one of the five links including production, transportation, storage, sale and use in the natural gas chain, is becoming increasingly important (Ding, 2015; Zhang, 2017). As a cost-effective, safe and stable gas storage model at present, salt cavern storage is not only an important facility for natural gas supply, but also a significant guarantee for national energy security (Gabrielli, 2020; Yang, 2022). Most of North America's strategic oil reserves are stored in salt caverns. In recent years, natural gas demand in China has rapidly developed, and salt cavern UGS have entered a golden period of development (Ding, 2023; Gao, 2022).