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Geomechanics is a marginal subject combining mechanics and geology and thus can be regarded as a branch of mechanics. Geomechanics is a descipline invented by China, and has made outstanding contributions in both theoretical and practical fields fulfilling national key demands. However, under the new situation, it is also faced with both challenges theoretical and practical challenges in fulfilling national needs. In this article, the authors analysed the challenges, and pointed out strategies for develping Geomechanics in the new era: rebuilding confidence in the advantage of Geomechanics, refining and enhancing already existing progresses and deploying future research concertrated on providing Geomechanics solutions to key national needs.

The article describes an integrated approach to the development of solutions for the effective involvement of oil in the development of a thin-layered “hazel grouse” type reservoir. The principles of justification based on facies, geological-hydrodynamic and geomechanical modeling are analyzed. In the course of the work, new core data and a petrophysical model were obtained, which made it possible to substantiate the TRIZ status of the object. A conceptual geological model was built and an assessment of geological reserves was carried out to determine the priority zones for putting wells into operation.

A reservoir geomechanical modeling has been attempted in the hydrocarbon-bearing Miocene formations in the offshore Badri field, Gulf of Suez, Egypt. Pore pressure established from the direct downhole measurements indicated sub-hydrostatic condition in the depleted mid-Miocene Hammam Faraun and Kareem reservoirs. Vertical stress ( S v ) estimated using bulk density data yielded an average of 0.98 PSI/feet (22.17 MPa/km) gradient. Magnitudes of minimum ( S hmin ) and maximum ( S hmax ) horizontal stresses were deduced from the poro-elastic model. Relative stress magnitudes ( S v  ≥  S hmax  >  S hmin ) reflect a normal faulting tectonic stress in the Badri field. Pore pressure and stress perturbations (ΔPP and Δ S h ) in the depleted reservoirs investigated from actual measurements recognized ‘stress path’ values of 0.54 and 0.59 against the Hammam Faraun and Kareem Formations, respectively. These stress path values are far away from the normal faulting limit (0.68), indicating induced normal faulting or fault reactivation to be unlikely at the present depletion rate.

Underhand cut-and-fill mining has allowed for the safe extraction of ore in many mines operating in weak rock or highly stressed, rockburst-prone ground conditions. However, the design of safe backfill undercuts is typically based on historical experience at mine operations and on the strength requirements derived from analytical beam equations. In situ measurements in backfill are not commonplace, largely due to challenges associated with instrumenting harsh mining environments. In deep, narrow-vein mines, large deformations and induced stresses fracture the cemented fill, often damaging the instruments and preventing long-term measurements. Hecla Mining Company and the Spokane Mining Research Division of the National Institute for Occupational Safety and Health (NIOSH) have worked collaboratively for several years to better quantify the geomechanics of cemented paste backfill (CPB), thereby improving safety in underhand stopes. A significant focus of this work has been an extensive in situ backfill instrumentation program to monitor long-term stope closure and induced backfill stress. Rugged and durable custom-designed closure meters were developed, allowing measurements to be taken for up to five successive undercuts and measuring closures of more than 50 cm and horizontal fill pressures up to 5.5 MPa. These large stope closures require the stress–strain response of the fill to be considered in design, rather than to rely solely on traditional methods of backfill span design based on intact fill strength. Furthermore, long-term instrument response shows a change in behavior after 13–14% strain, indicating a transition from shear yielding of the intact, cemented material to compaction of the porosity between sand grains, typical of uncemented sand fills. This strain-hardening behavior is important for mine design purposes, particularly for the use of numerical models to simulate regional rock support and stress redistribution. These quantitative measurements help justify long-standing assumptions regarding the role of backfill in ground support and will be useful for other mines operating under similar conditions.

Mining operations play a crucial role in meeting global resource demands, emphasizing the importance of determining optimal stope dimensions for safe and efficient ore extraction. However, the complexity arising from multiple geomechanical factors affecting stope stability poses challenges in identifying ideal dimensions. Traditionally, engineers use an iterative process for stability analysis, but its limited scope and time-consuming nature call for more efficient algorithms. This research proposes a series of algorithms based on the brute force method using Potvin’s empirical stability criterion. The algorithm efficiently generates and evaluates stope dimension scenarios, enabling comprehensive stability analysis. Testing on case studies demonstrates its remarkable speed and effectiveness, making it a valuable tool for mine planning and optimization.

In this paper, we examine the coupled thermo-poromechanical behaviour of a fluid-saturated porous medium of infinite extent bounded internally by a fluid-filled cavity. The mechanical behaviour of the porous skeleton can either be Hookean elastic or elasto-plastic, with a constitutive response corresponding to a modified Cam Clay plasticity model. The fluid within the cavity can be subjected simultaneously to a temperature rise and a pressure pulse. The paper presents analytical results for the spherically symmetric thermo-poroelasticity problem and these are used to validate the thermo-poroelasticity module of a computational code. We proceed to examine the thermo-poroelasto-plasticity problem. Results presented in the paper illustrate the interaction between thermal and mechanical phenomena and their influence on the cavity fluid pressure and the skeletal stresses at the cavity boundary. The paper presents solutions that will be of value in benchmarking exercises.

Efficient and accurate modeling of rock deformation and well production in weakly consolidated reservoirs requires reliable and accurate reservoir modeling techniques. During hydrocarbon production, the reservoir pressure is dropped, and rock compaction is induced. In such depletion-induced reservoir rock deformation, both elastic and plastic deformation can be generated. The numerical investigation of depletion-induced plasticity in shale oil reservoirs and its impact on coupled reservoir modeling helps provide insights into the optimization of horizontal well productivity. This study introduces a coupled flow and geomechanical model that considers porous media flow, elastoplastic deformation, horizontal well production, and the coupling between the flow and geomechanical processes. Simulation results are then provided along with numerical modeling parameters. Effects of relevant parameters, including depletion magnitude, rock mechanical properties, and hydraulic fracture parameters, jointly affect rock deformation, rock skeleton damage, and horizontal well productivity. Depletion-induced plasticity, stress, pressure, and subsidence are all characterized by the solution strategy. In addition, the implementation of direct and iterative solvers and the usage of full coupling and sequential coupling strategies are investigated, and the associated solver performance is quantified. It helps evaluate the numerical efficiency in the highly nonlinear numerical system. This study provides an efficient coupled flow and elastoplastic model for the simulation of depletion in weakly consolidated reservoirs.

In the Sichuan Basin, seismic activity has been low historically, but in the past few decades, a series of moderate to strong earthquakes have occurred. Especially since 2015, earthquake activity has seen an unprecedented continuous growth trend, and the magnitude of events is increasing. Following the M 5.7 Xingwen earthquake on 18 Dec. 2018, which was suggested to be induced by shale gas hydraulic fracturing, a swarm of earthquakes with a maximum magnitude up to M6.0 struck Changning and the surrounding counties. Questions arose about the possible involvement of industrial actions in these destructive events. In fact, underground fluid injection in salt mine fields has been occurring in the Sichuan Basin for more than 70 years. Disposal of wastewater in natural gas fields has also continued for about 40 years. Since 2008, injection for shale gas development in the southern Sichuan Basin has increased rapidly. The possible link between the increasing seismicity and increasing injection activity is an important issue. Although surrounded by seismically active zones to the southwest and northwest, the Sichuan Basin is a rather stable region with a wide range of geological settings. First, we present a brief review of earthquakes of magnitude 5 or higher since 1600 to obtain the long-term event rate and explore the possible link between the rapidly increasing trend of seismic activity and industrial injection activities in recent decades. Second, based on a review of previous research results, combined with the latest data, we describe a comprehensive analysis of the characteristics and occurrence conditions of natural and injection-induced major seismic clusters in the Sichuan Basin since 1700. Finally, we list some conclusions and insights, which provide a better understanding of why damaging events occur so that they can either be avoided or mitigated, point out scientific questions that need urgent research, and propose a general framework based on geomechanics for assessment and management of earthquake-related risks.

Solid organic matter (OM) plays an essential role in the generation, migration, storage, and production of hydrocarbons from economically important shale rock formations. Electron microscopy images have documented spatial heterogeneity in the porosity of OM at nanoscale, and bulk spectroscopy measurements have documented large variation in the chemical composition of OM during petroleum generation. However, information regarding the heterogeneity of OM chemical composition at the nanoscale has been lacking. Here we demonstrate the first application of atomic force microscopy-based infrared spectroscopy (AFM-IR) to measure the chemical and mechanical heterogeneity of OM in shale at the nanoscale, orders of magnitude finer than achievable by traditional chemical imaging tools such as infrared microscopy. We present a combination of optical microscopy and AFM-IR imaging to characterize OM heterogeneity in an artificially matured series of New Albany Shales. The results document the evolution of individual organic macerals with maturation, providing a microscopic picture of the heterogeneous process of petroleum generation. Solid organic matter (OM) plays a key role in the production of hydrocarbons in shale formations, yet information on OM heterogeneity at a nanoscale is lacking. Here, the authors use atomic force microscopy-based infrared spectroscopy to document the evolution of individual organic macerals with maturation.

A new explicit sequentially coupled technique for chemo-thermo-poromechanical problems in shale formations is developed. Simultaneously solving the flow and geomechanics equations in a single step is computationally expensive with consequent limitations on the computations involving well or reservoir-scale geometries. The newly developed solution sequence involves solving the temperature field within the porous system. This is followed by the computation of the chemical activity constrained by the previously computed temperature field. The pore pressure is then computed by coupling the pore thermal and chemical effects but without consideration of the volumetric strains. The geomechanical effect of the volumetric strain, stress tensors, and associated displacement vectors on the pore fluid is subsequently computed explicitly in a single-step post-processing operation. By increasing the borehole pressure to 20 MPa, it is observed that the rock displacement and velocities concurrently increase by 50%. However, increasing the wellbore temperature and chemical activities shows only a slight effect on the rock and pore fluid. In the chemo-thermo-poroelasticity steady-state simulation, the maximum displacements recorded in the Hmin and Hmax are 0.00633 m and 0.0035 m, respectively, for 2D and 0.21 for the 3D simulation. In the transient simulation, the displacement values are observed to increase gradually over time with a corresponding decrease in the maximum pore-fluid velocity. A comparison of this work and the partial two-way coupling scheme in a commercial simulator for the 2D test cases was carried out. The maximum differences between the computed temperatures, displacement values, and fluid velocities are 0.33%, 0.7%, and 0%, respectively. The analysed results, therefore, indicate that this technique is comparatively accurate and more computationally efficient than running a full or partial two-way coupling scheme.