Dilation factor [Formula: see text] is the ratio of relative change in velocity to relative change in deformation (strain). It has significant implications for 4D seismic studies where it can be used to infer reservoir or overburden thickness changes from seismic changes, but the effect of stress on [Formula: see text] and its components is not well understood. We conduct static strain and ultrasonic velocity measurements to study the effect of stress on [Formula: see text] and its components. Measured absolute [Formula: see text] values (6–91 in sandstones and 6–11 in shale) depend on the deformation mechanisms causing the strain. The dynamic (low-amplitude) Young’s modulus generally is higher than the static (high-amplitude) Young’s modulus. Hence, theoretical models that use the same mechanism to describe wave propagation and macroscopic deformation are invalid. The ratio of dynamic to static modulus depends on the direction of stress applied with respect to the density and placement of cracks. Values of [Formula: see text] differ for P- and S-waves, especially in the presence of fluids. The values also depend strongly on the stress states; hence, using a constant value of [Formula: see text] from the surface to reservoir depth should be avoided. Absolute [Formula: see text] values increase for sandstones and decrease for shales with decreasing confining pressure, which explains the low [Formula: see text] values from 4D seismic data. Our data offer insight into the behavior of [Formula: see text] values with different rock types, stress, and fluid, and they can be used to constrain model calculations.

Clay minerals are present in most sedimentary rocks. They find applicability in a wide range of disciplines, such as material, soil, earth, environmental, and biological sciences. Despite their abundance and use, swelling of clays under stress has not received enough scientific attention. We used a two-method approach, consisting of molecular simulation and nanoindentation measurements on montmorillonite. Our analyses of the molecular structure of montmorillonite at various stresses and hydration states showed that swelling behaves in a nonlinear way with stress. Nanoindentation results of Young’s modulus agree with our simulation results, showing the importance of the interlayer in composite clay properties.

Lost circulation material (LCM) is known to enhance the breakdown limit of wellbores. However, the related gain in the wellbore circulation density remains a weak link in the literature. A design scheme for the LCM blend is developed in this work that allows for quantification of the maximum enhancement in fracture gradient of wellbores. An analytical solution is developed for this purpose that accounts for wellbore inclination and azimuth. The LCM blend is selected by applying appropriate criteria for the particle size distribution (PSD) to the estimated width of near-wellbore fractures. A constitutive model for stress-strain behavior of the LCM is developed from in-house laboratory data of axial compression test on LCMs. The test is intended to simulate compression of the LCM plug upon partial closure of the fracture faces. The obtained constitutive model is used along with the presented analytical solution to estimate the fracture width, tip stress intensity and the wellbore stress redistribution after fluid filtrate leakoff and closure of fracture faces on the LCM agglomerate. The LCM blend composition is selected by optimizing the resulting variations in the fracture tip stress intensity and wellbore stress enhancement between the pre-leakoff (suspended particle) and post-leakoff (solid agglomerate) states of the deposited particles inside of the fracture. The compromise between fracture tip stress intensity factor and compressional stress redistribution around wellbore wall is shown to determine the extent of enhancement in the wellbore fracture gradient, i.e., the maximum circulation density that would not cause wellbore breakdown. Case studies with fracture gradient gains as large as one lbm/gal are presented.

The seismic data set is a fundamental requirement for producing oil and gas fields. It provides understanding of the structure and stratigraphy of the reservoirs, and it is now routinely employed in reservoir modeling for advancing insights into how fields are being produced. Modern 3D seismic data were first developed in the 1960s, but it wasn't until the 1980s that seismic interpretation software enabled the building of gridded reservoir models from seismic interpretations. Reservoir modeling utilizing seismic interpretations drove insights into reservoir quality and performance, helping to understand the communication between reservoir units and wells, particularly in fields with many wells. But key challenges such as the cost of building or updating reservoir models and scale variance created barriers for early industry-wide adoption. Data integration required calibration to correct and account for the difference in measurement scales of seismic data and well data, as well as to create robust relationships between seismic properties and petrophysical properties in the model. Over time, technological advancements led to a reduction in the cost of reservoir modeling, while increased acquisition, processing, and utility of seismic data provided the means to drive innovation toward incorporating seismic. Today, 3D and 4D seismic data play pivotal roles in defining and updating reservoir models where hundreds to thousands of simulations can be realized in a reservoir model to explore history matching and model uncertainties.

The use of particulate lost circulation material (LCM) is common in treating lost circulation events of subterranean drilling. LCM isolates the wellbore pressure from fracture tip by forming an impermeable agglomerate inside the wellbore fractures. Fracture width estimation is the center piece of designing the particle size distribution (PSD) of LCM blends. State-of-the-art practice for width estimation of wellbore fractures has been predominantly associated with assumption of axial fracture development from wellbores. However, this assumption is not valid for all wellbore orientations. Shallow vertical wellbores and highly inclined or horizontal wellbores in a normal faulting regime are example configurations where axisymmetric wellbore fractures develop transverse to the wellbore axis. The change in fracture geometry yields a substantially different width estimate for transverse fractures compared to the axial ones. This study aims at demonstrating this disparity and the impact that it would have on the LCM blend design. For this purpose, a linear elastic fracture mechanics solution is applied to the fractured wellbore to estimate the fracture width. Results indicate that an axial model of the fracture could substantially overestimate the fracture width depending on the wellbore inclination and in-situ stress magnitudes. Application of the solution in selecting the composition of a three-component blend from selected LCMs via a blend particle size criterion is shown. The discrepancy between the LCM blends PSDs obtained from the axial and transverse models of the wellbore fracture are thoroughly discussed.