AI-based real-time multi-model framework for groundwater-responsive pile behaviour

ABSTRACT: The interaction between reservoir Biot's effective stress and pore pressure change is significant in stress-sensitive reservoirs. Consequently, coupling geomechanics and fluid flow to analyze pressure transient problems for stress-sensitive reservoirs may be necessary. Effective permeability loss monitoring in fractured oil wells is essential in maintaining economic reservoir productivity. This paper proposes a new analytical solution for the nonlinear hydraulic diffusivity equation (NHDE) in Biot's effective stress-sensitive reservoir fully penetrated by a fractured oil well. The proposed modeling considers the hydraulic fracture infinite and crosses the whole reservoir net pay. A new permeability stress-sensitive pseudo-pressure m(σ′) is presented, and the solution of the NHDE is derived in terms of this function. NHDE is expanded in a first-order asymptotic series, and an integro-differential solution coupled to a Green's function (GF) is used to represent the source/sink term. A set of pressure and permeability data from geomechanical literature is used and transformed into effective stress through Biot's equation. The effects of overburden, source/sink term, deviation factor, and Biot's coefficient are investigated to prevent severe permeability losses. Model calibration is performed using a numerical oil flow simulator named IMEX®, widely used in formation evaluation literature. The accuracy, ease of implementation, and low computational costs constitute the main advantages of the model addressed in this paper. Hence, it may be a valuable and attractive mathematical tool to identify flow regimes, providing permeability loss control and supporting well-reservoir management. 1 INTRODUCTION The production of petroleum reservoirs results in a decrease fluid pressure and an increase in effective overburden stress (Fernandes, 2022). As fluid production proceeds, the progressive increase in effective overburden load will, in turn, compact the reservoir rock and change its stress state (Soares and Ferreira, 2002; Soares et al., 2003). For reservoir rocks that are mechanically stable with fluid-flow properties e.g. the ones that permeability are not influenced by effective stress changes or are solely dependent upon fluid pressure change under a constant overburden load, pressure transient problems can be properly analyzed by conventional methods. Nonetheless, for stress-sensitive formations, coupling geomechanics with flow equations become the modeling more realistic. The economic production of either wells completed in low permeability reservoirs, e.g. shales or damaged wells has been possible because of hydraulic fracturing. In this scenario, estimating hydraulic fracture's geometric parameters and flow characteristics represents useful information for the calibration of fracture design methods and permits forecasting well flow behavior (Miskimins and Barree, 2003; Miskimins, 2019).

Effects of effective stress changes on permeability of latrobe valley brown coal

Effective Stress Change and Post-Earthquake Settlement Properties of Granular Materials Subjected to Multi-Directional Cyclic Simple Shear

Thermally activated deformation in age-hardenable ferritic FeNiAlTi alloys

Hydrocarbon leakage through faults and fractures commonly limits in-place hydrocarbon reserves. Faulting and fracturing are controlled by effective stress changes, and such changes may therefore alter hydrocarbon column heights. The predictive power of stress history analyses in seal evaluation depends on how accurately the stress history and relationships between effective stress changes and hydrocarbon leakage can be determined. Stress history and hydrocarbon occurrence were examined in four different overpressured provinces of offshore Norway in the search for such relationships. These provinces have experienced different geological histories and variable amounts of hydrocarbon leakage. Because all these areas received fairly recent hydrocarbon charge, the work focused on the identification of recent geological events that may subsequently have influenced recent stress history, including the present-day stresses. Areas of recent structuring were found to be characterized by more extensive hydrocarbon leakage than areas with less such structuring. This increased frequency of hydrocarbon leakage was interpreted to be the result of shear failure at the trap crests, induced by the combined effects of elevated pore pressures, stress anisotropy, and recent stress changes. These results suggest that identification of recent stress changes based on the geological history of the study area could aid the prediction of hydrocarbon occurrence. It is inferred that stress history analyses can also reduce the uncertainty involved in seal analyses elsewhere.

This paper analyzes the effect of stress on the rock properties fracture and matrix compressibilities, fracture and matrix porosities, and permeability in naturally fractured reservoirs (NFRs). In NFRs, fluids are stored inside the matrix pore space and inside the fractures of the rock. The reservoir characterization parameter indicating the volumetric fraction of fluids deposited inside the fractures is the storage capacity ratio, which is function of the fracture and matrix porosity, and fracture and matrix total compressibilities. Due to the difficulty to obtain these values, in reservoir engineering computations such as pressure transient analysis and reservoir simulation, among others, it is generally assumed that the matrix and the fracture total compressibilities are equal. This induces a big uncertainty in the estimation of the storage capacity ratio and leads to a wrong estimation of the volume of fluids inside the fractured rock. Changes in pore pressure due to production or injection of fluids affect the effective reservoir in-situ stress. The mechanical behavior of the fractured rock and its effects on the rock properties permeability, porosity and compressibility in the matrix and fracture frames are analyzed using the elastic properties bulk modulus and normal compliance of the fracture. These properties can be obtained from petrophysical core analysis or multi-component seismic interpretation, and linked to pressure transient analysis through the storage capacity ratio equation. A step-by-step procedure of the analysis is presented and illustrated with an example for quantifying the effects of changes in effective stress on the fracture and matrix compressibilities.

We studied the 24 year record of water level responses in Devils Hole, Death Valley National Park, NV, to dynamic crustal stresses from earthquakes. The continuous water level record exhibited 219 responses from earthquakes around the world, displaying hydroseismogram and coseismic offset types of response. We found that the water level in Devils Hole is extremely sensitive to earthquakes, and the seismic energy density required to initiate both hydroseismogram and coseismic offset responses is e ~ 10−6 J/m3, 2 orders of magnitude smaller than previously documented. Multiple mechanisms at Devils Hole may be responsible for observed water level responses to distant earthquakes. The hydroseismogram‐type responses are best explained by poroelastic deformation, while coseismic offset responses are likely the result of localized permeability changes. This study could have implication to studying dynamic triggering of earthquakes, as remote earthquakes can lead to pore pressure changes and consequently effective stress changes in fluid‐filled fault zones.

A numerical study on the long term thermo-poroelastic effects of cold water injection into naturally fractured geothermal reservoirs

In this work we use VSP data to help solve practical exploration problems. In particular, we show how VSP data can be used to quickly assess the response of various seismic attributes. Specifically, we use downgoing energy to evaluate and relate anomalous behaviour of seismic attributes to changes in effective stress. Selected attributes are then computed on up-going VSP energy using later arrival times and, if sensitivity with respect to changes in effective stress is retained, they are subsequently computed on surface seismic data. Such simplified VSP-based analysis enables quick and efficient qualitative assessment of variations in lithology, geo-pressure, or other rock properties under investigation. We also discuss how multi-offset VSP data can be used to speed up pre-stack depth migration (PSDM) of surface seismic data in areas where anisotropy is non-negligible and typically not fully defined.

Fabrication and verification of novel 3D FBG-based transducer for directly measuring vertical and lateral effective stresses

ABSTRACT: A formation failure analysis was performed considering the anisotropic mechanical properties, time-dependent behavior, and failure process caused by mud invasion into the formation. To investigate the complex interactions between the mud pressure penetration and weak bedding planes, a fully coupled hydromechanical model was implemented and the crack tensor approach was used to consider the non-linear elastic properties of rock containing discontinuities. The numerical analysis results for the pressure transmission test showed that the hydromechanical model properly simulated the pore pressure changes experienced during the experiment and could be used to evaluate the permeability of the shale samples. In addition, the field case study results suggested that the effects of the pore fluid flow and the existence of bedding planes are significant for time-dependent wellbore instability phenomena: as the inclination angles of the bedding planes increased, the deformation of the borehole surface increased under the investigated stress conditions. The study results also suggest that mud invasion accelerates rock yielding and plastic deformation on the wellbore surface, leading to progressive wellbore failure over time in shale formations. 1. INTRODUCTION Wellbore instability is one of the key factors that need to be considered in drilling engineering and requires technical measures to reduce drilling costs (Zeynali, 2012) and nonproductive time (Zhang, 2013). Most wellbore instability problems occur in shale formations (Steiger and Leung, 1992). These problems can be triggered by borehole failure owing to variations in strength properties along and across bedding planes (Tsusaka et al., 2021) and pore pressure changes (van Oort et al., 2019). Understanding the factors affecting wellbore instability is essential for improving drilling efficiency and safety. Borehole failure occurs when the disturbed rock cannot support the load previously burdened by the removed rock, leading to a stress concentration around the wellbore (Abbasi et al., 2018). The magnitude and orientation of the increased stress region are affected by the anisotropic mechanical properties of rock containing discontinuities, whereas a change in the stress condition is often triggered by a pressure change caused by the penetration of drilling fluids into the formation (Asaka and Holt, 2023). Bedding planes are thought to be weaker than the intact rock and, thus, have a higher likelihood of shear failure (Shaver et al., 2020). Mud invasion of low-permeability shale formations induces effective stress changes (Albooyeh et al., 2018). Furthermore, when fluid pressure in the borehole penetrates the bedding planes, the apparent shear strength of the bedding planes is reduced because of the reduced normal stress. As the inclination of the well increases under a normal stress faulting regime, a high shear stress acts on the borehole surface and possibly causes formation failure (Yamamoto et al., 2004). Thus, designing the optimum mud weight and well trajectories is crucial for securing wellbore stability during drilling.

Summary Accounting for poro-mechanical effects in full-field reservoir simulation studies and uncertainty quantification workflows is still limited, mainly because of their high computational cost. We introduce a new approach that couples hydrodynamics and poro-mechanics with dual-porosity flow diagnostics to analyze how poro-mechanics could affect reservoir dynamics in naturally fractured reservoirs without significantly increasing computational overhead. Our new poro-mechanically informed dual-porosity flow diagnostics account for steady-state and single-phase flow conditions in the fractured medium while the fracture-matrix fluid exchange is approximated using a physics-based transfer rate coefficient, which models two-phase flow using an analytical solution for spontaneous imbibition or gravity drainage. The deformation of the system is described by the dual-porosity poro-elastic theory, which is based on mixture theory and micromechanics to compute the effective stresses and strains of the rock matrix and fractures. The solutions to the fluid flow and rock deformation equations are coupled sequentially. The governing equations for fluid flow are discretized using a finite-volume method with two-point flux-approximation while the governing equations for poro-mechanics are discretized using the virtual element method. The solution of the coupled system considers stress-dependent permeabilities for fractures and matrix. Our framework is implemented in the open-source MATLAB Reservoir Simulation Toolbox (MRST). We present a case study using a fractured carbonate reservoir analog to illustrate the integration of poro-mechanics within the dual-porosity flow diagnostics framework. The extended flow diagnostics calculations enable us to quickly screen how the dynamics in fractured reservoirs (e.g., reservoir connectivity, sweep efficiency, and fracture-matrix transfer rates) are affected by the complex interactions between poro-mechanics and fluid flow where changes in pore pressure and effective stress modify petrophysical properties and hence affect reservoir dynamics. Because of the steady-state nature of the calculations and the effective coupling strategy, these calculations do not incur significant computational overheads. They provide an efficient complement to traditional reservoir simulation and uncertainty quantification workflows because they enable us to assess a broader range of reservoir uncertainties (e.g., geological, petrophysical, and hydromechanical uncertainties). The capability of studying a much broader range of uncertainties allows the comparison and ranking from a large ensemble of reservoir models and select individual candidates for more detailed full-physics reservoir simulation studies without compromising on assessing the range of uncertainties inherent to fractured reservoirs.

Accounting for poro-mechanical effects in full-field reservoir simulation studies and uncertainty quantification workflows using complex reservoir models is challenging, mainly because of the high computational cost. We hence introduce an alternative approach that couples hydrodynamics through existing flow diagnostics simulations with poro-mechanics to screen the impact of coupled poro-mechanical processes on reservoir performance without significantly increasing computational overheads. In flow diagnostics, time-of-flight distributions and influence regions can be used to characterise the flow field in the reservoir, which depends on the distribution of petrophysical properties that are altered due to production-induced changes in pore pressure and effective stress. These extended flow diagnostics calculations hence enable us to quickly screen how the dynamics in the reservoirs (e.g. reservoir connectivity, displacement efficiency, and well allocation factors) are affected by the complex interactions between poro-mechanics and hydrodynamics. Our poro-mechanically informed flow diagnostics account for steady-state and single-phase flow conditions based on the poro-elastic theory and assume that the reservoir does not contain fractures. Fluid flow and rock deformation calculations are coupled sequentially. The equations are discretised using a finite-volume method with two-point flux-approximation and the virtual element method, respectively. The solution of the coupled system considers stress-dependent permeabilities. Due to the steady-state nature of the calculations and the effective proposed coupling strategy, these calculations remain computationally efficient while providing first-order approximations of the interplay between poro-mechanics and hydrodynamics, as we demonstrate through a series of case studies. The extended flow diagnostic approach hence provides an efficient complement to traditional reservoir simulation and uncertainty quantification workflows and enable us to assess a broader range of reservoir uncertainties.

In critical state soil mechanics, the critical state refers to the combination of effective stress and void ratio (e) at which a soil continues to shear with no change in effective stress, shear stress, and e. The phenomena can be visualized using the critical state line (CSL). The CSL represents the locus of e at critical state with effective mean stress (σ′mean). To define the CSL, the CSL slope (λ), termed “compressibility,” and CSL y-axis intercept at 1 kPa (Γ), termed “altitude,” are required. The CSL in e – σ′mean space provides a simple model of complex soil behavior that allows engineers to construct constitutive models using the state parameter (ψ), which is the mathematical difference between the in-situ e of the soil and the e of the soil at critical state. Currently, Γ can be obtained only through laboratory testing, while λ and ψ can be obtained via laboratory testing or correlation. This paper presents forthcoming correlations based on the ΔQ soil behavior index (which is obtained via the cone penetration test, CPT) to forecast Γ, λ, and ψ, and compares the ΔQ-based correlations’ performance to other CPT-based correlations as well as to data obtained from literature. To compare the correlations, the authors used data from a site investigation performed in Fraser River sand as part of the Canadian Liquefaction Experiment.

A deep insight into tight gas transient flow behavior is important for understanding the production behavior of tight gas reservoirs. In this work, we constructed a two-dimensional model to illustrate one methodology of evaluating effective permeability of fractured flow media. Pulse-decay experiments on one fractured core to study porosity and permeability for both matrix and the fracture, under a series of pore pressure and effective stress. Based on the results, the approach proposed in this study has the advantage over the steady-state method that can capture the character of transient flow if the fracture network penetrates the core. The transient gas propagation in the matrix, fractured cored with the fracture width of 1 μm and 1 cm are in shapes of piston-like, arrow-like, and dumbbell-like, respectively. Though the fracture width is only 1 μm, it reduces the time to reach pressure equilibrium to about one-fourth and the effective permeably ratio is 3.98. Totally 59 pulse-decay experiments were performed on one fractured core. We successfully history matched all the pulse-decay experiments on a fractured core by a commercial simulator with the Global Match Error (GME) less than 0.2%, that the readers can readily adopt this approach. Based on the history matching of upstream and downstream pressure curves, the fracture permeability and porosity are 6 orders’ and 1 order's magnitude higher than the matrix. The matrix permeability is the most sensitive to the pore pressure and effective stress, and no consistent trend is observed for the fracture permeability and porosity as the pore pressure and effective stress change.