Seismic events induced by the depletion of hydrocarbon reservoirs can cause damage to housing and cause societal and economic unrest. However, the factors controlling the nucleation and size of production-induced seismic events are not well understood. Here we used geomechanical modeling of production-induced stresses and dynamic rupture modeling to assess the conditions controlling down-dip rupture size. A generic model of (offset) depleting reservoir compartments separated by a fault was modeled in 2-D using the Finite Element package DIANA FEA. Linear slip-weakening was used to control fault friction behavior. Fault reactivation was computed in a quasi-static analysis simulating stresses during reservoir depletion, followed by a fully dynamic analysis simulating seismic rupture. The sensitivity of reactivation and rupture size to in situ stress, dynamic friction, critical slip distance, and reservoir offset was evaluated. After reactivation, a critical fault length was required to slip before seismic instability could occur. In a subsequent fully dynamic analysis the propagation and arrest of dynamic rupture was simulated. Rupture remained mostly confined to the reservoir interval but could also propagate into the overburden and underburden or sometimes transition into a run-away rupture. Propagation outside the reservoir interval was promoted by a critical in situ stress, a large stress drop, a small fracture energy, and no or little reservoir offset. With increasing offset (up to the reservoir thickness), reactivation was promoted but dynamic rupture size decreased.Plain Language Summary Gas production can cause earthquakes, which can be felt at the Earth's surface. Even though these earthquakes are relatively small, they can sometimes cause damage to housing and infrastructure which may have large societal and economic impact. An example of this problem are the earthquakes in the Groningen gas field in the north of the Netherlands, where the damages due to induced earthquakes have led to a production cap and early phase-out of gas production. An important question is how the earthquakes are made, and how large the earthquakes may become. Here we modeled the production-induced earthquakes with geomechanical modeling, which calculates the effect of gas production (pressure changes) on the forces (stresses) in the subsurface. These altered stresses can exceed the strength of preexisting faults in the subsurface, causing the fault to break and generate an earthquake. The modeling results showed that earthquake size depended on many factors such as the initial stress in the reservoir and the fault behavior. The earthquakes often remained confined within the gas producing interval. The geometry of the gas reservoir and faults played a large role in generating the earthquake. Results are consistent with field observations and help to understand the timing, location, and size of seismic events.

In this work, fracture behavior of multilayered unidirectional graphite/epoxy composite (T800/3900-2) materials is investigated. Rectangular coupons with a single-edged notch are studied under geometrically symmetric loading configurations and impact loading conditions. The notch orientation parallel to or at an angle to the fiber orientation is considered to produce mode-I or mixed-mode (mode-I and -II) fracture. Feasibility of studying stress-wave induced crack initiation and rapid crack growth in fiber-reinforced composites using the digital image correlation method and high-speed photography is demonstrated. Analysis of photographed random speckles on specimen surface provides information pertaining to crack growth history as well as surface deformations in the crack-tip vicinity. Measured deformation fields are used to estimate mixed-mode fracture parameters and examine the effect of fiber orientation (β) on crack initiation and growth behaviors. The samples show differences in fracture responses depending upon the orientation of fibers. The maximum crack speed observed is the highest for mode-I dominant conditions and it decreases with fiber orientation angle. With increasing fiber orientation angle, crack takes longer to attain the maximum speed upon initiation. Continuous reduction of dynamic stress intensity factors after crack initiation under mode-I conditions is attributed to crack bridging. The crack initiation toughness values decrease with the degree-of-anisotropy or increase with fiber orientation angle. A rather good agreement between crack initiation toughness values and the ones from previous investigations is observed. There is also a good experimental correlation between dynamic stress intensity factor and crack-tip velocity histories for shallow fiber orientations of β = 0, 15, and 30°.

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The main operational parameters controlling borehole stability in drilling shales are the density and the chemical composition of the drilling fluid. The density of the drilling fluid provides support of the borehole wall, while the chemical composition of the drilling fluid can be adopted to reduce the infiltration rate and to maintain hole stability for prolonged exposure time of the drilling fluid to the shale. To describe the interaction between the drilling fluid composition and the mechanical behaviour of shales, an electro-chemo-mechanical formulation of quasi-static finite deformation of swelling compressible porous media has been derived from the theory of mixtures. The model presented in this paper, which is applicable to biological tissues and synthetic hydrogels also, consists of an electrically charged porous solid, saturated with an ionic solution. The mixture as a whole is assumed electro-neutral. Four phases following different kinematic paths are defined: solid, fluid, anions and cations. Balance laws have been derived for each constituent and for the mixture as a whole. A Lagrangian form of the second law of thermodynamics has been derived to formulate the constitutive relations for the swelling behaviour of shales as well as the transport equations for the fluid and the ions. P. 127