Lavrov, A. (SINTEF Petroleum Research) | Torsæter, M. (SINTEF Petroleum Research) | Albawi, A. (Norwegian University of Science and Technology) | Todorovic, J. (SINTEF Petroleum Research) | Opedal, N. (SINTEF Petroleum Research) | Cerasi, P. (SINTEF Petroleum Research)
Integrity of the near-well area is crucial for preventing leakage between geological horizons and towards the surface during CO2 storage, hydrocarbon production and well stimulation. The paper consists of two parts. In the first part, a finite-element model of earlier laboratory tests on thermal cycling of a casing/cement/rock assemblage is set up. It is demonstrated that radial tensile stresses contributing to annular cement debonding are likely to develop during cooling of such an assemblage. The results of the modeling are in agreement with the results of the earlier laboratory experiments, with regard to the temperature histories, CT data, and location of acoustic emission sources. In the second part of the paper, a computational procedure is developed for upscaling of data about rock damage obtained from CT, to a finite-element model of flow in porous media around a well. The damaged zone is shown to dominate the flow along the axis of a compound specimen (a hollow cylinder of sandstone filled with cement). Implications for leakage along an interface between cement and rock in-situ are discussed.
Upfront predictions of hydraulic fracturing and gas production of potential shale gas targets in Europe are important as often large potential resources are deduced without detailed knowledge on the potential for successful stimulation. Such predictions are challenging as they need to be based on limited available data, i.e. without well tests or proper case studies. In this study, a geological model was constructed for a representative area in the South of the Netherlands (Noord-Brabant province) where a potential shale gas target (the Posidonia Shale Formation) is present in the subsurface. Petrophysical analysis of rock properties and geomechanical analysis of the stress field are performed. The sensitivity of hydraulic fracturing to rock properties, stress state and treatment schedules was studied using a commercially available hydraulic fracturing simulator. A systematic series of simulations was performed for a range of input parameters to address geological uncertainty and optimum stimulation treatment. The results show that uncertainty in leakoff coefficient and minimum horizontal stress are most important in predicting fracture dimensions and conductivity. Minor upward growth of fractures is observed for all scenarios. Analysis of Coulomb stress changes due to hydraulic fracturing shows that opening of fractures alone is unlikely to cause fault reactivation.
A new technique has been developed to estimate how seismicity evolves through the mine, making the technique an interesting addition to defining areas with high, medium, and low damage potential due to their embedded seismic history. The use of solid triangulations in representing the areas of interest makes the developed methodology a simple and powerful addition to the study of seismicity in mines. The research illustrates a new technique to model seismic events and combine them into block models, providing the user with the ability to analyze these data as a function of time (4-D) model, with the possibility of combining different analysis criteria to display the data, create sections of the information in any direction needed, cut the data at any elevation to see what has happened through the life and development of the mine. The seismic history of the mine can be displayed and analyzed using the developed technique, defining areas of progressive deterioration associated to the energy levels released by the seismic events.
Robust and reliable hydraulic fracturing models that appropriately account for random initiation of fractures, strongly nonlinear coupling among deformation, fracturing and fluid flow in fracture apertures and leakage into porous rock matrix, would be a key step toward developing a better understanding of physics associated with hydraulic fracturing process. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. The coupled DEM-network flow model reproduces a variety of realistic growth patterns of hydraulic fractures. The effects of in situ stress, fluid viscosity, heterogeneity of rock mechanical properties and injection rate on the fracture patterns will be presented and discussed. In particular, simulation results of multistage horizontal wellbore with multiple perforations clearly demonstrate that elastic interactions among multiple propagating fractures, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicating fracturing patterns.
Because of relatively recent decisions by the current administration and its renewed assessment of the nuclear life-cycle, the various deep geologic disposal medium options are once again open for consideration. This paper focuses on addressing the favorable creep properties and behavior of rock salt, from the computational modeling perspective, as it relates to its potential use as a disposal medium for a deep geologic repository. The various components that make up a computational modeling capability to address the thermo-mechanical behavior of rock salt over a wide range of time and space are presented here. Several example rock salt calculations are also presented to demonstrate the applicability and validity of the modeling capability described herein to address repository-scale problems. The evidence shown points to a mature computational capability that can generate results relevant to the design and assessment of a potential rock salt HLW repository. The computational capability described here can be used to help enable fuel cycle sustainability by appropriately vetting the use of geologic rock salt for use as a deep geologic disposal medium.
Rock masses are inherently variable in their nature owing to the complex interrelationship between discontinuities and intact rock. The simplest way to account for this uncertainty is through the explicit modelling of the spatial heterogeneity. This is commonly conducted through stochastic simulation, where multiple realizations of studied attributes are produced. Within this paper a geostatistics-based approach to modelling spatial uncertainty which is new to the field of open pit mine design is presented. The method is based on the use of sequential Gaussian simulation to reproduce the spatial heterogeneity observed in studied attributes. The paper presents the formal methodology used for stochastic simulation and the results obtained from the modelling process. Models were constructed by stochastically varying the geological strength index and uniaxial compressive strength within a geomechanical simulation model of the Ok Tedi mine site in Papua New Guinea. Simulations demonstrate the importance of understanding the scale dependent characteristics of sample variance and the effects of spatial heterogeneity on both the critical SRF and projected failure size.
Roberts, D.T. (Cardiff University) | Crook, A.J.L. (Three Cliffs Geomechanical Analysis) | Cartwright, J.A. (University of Oxford) | Profit, M.L. (Rockfield Software Limited,) | Rance, J.M. (Rockfield Software Limited,)
Polygonal Fault Systems (PFS) are increasingly observed in seismic data of the subsurface. These unusual networks of normal faults are known to develop over vast areas in fine-grained sequences which in many cases may form the regional caprock. Consequently, there is the potential for PFS to compromise the integrity of these sequences with obvious implications for subsurface fluid migration. The processes leading to the formation of PFS remain poorly understood, although their confinement to particular sediment packages and spatial extent are powerful arguments for a constitutive control. The work presented here attempts to progress recent efforts examining a diagenetic trigger for polygonal fault genesis. More specifically, investigations of diagenetically sourced structure development in mudstones have been undertaken in order to formulate a geomechanical argument to explain their formation. This argument is tested in finite strain computational models using the geomechanical code ELFEN, so that the formation over geological time can be studied. Prediction of PFS in both two and three dimensions are presented that demonstrate that this modelling approach can predict realistic PFS geometries including the observed transition from random to preferential fault alignment with increasing degree of stress anisotropy.