Fluid flow modeling of naturally fractured reservoirs remains a challenge because of the complex nature of fracture systems controlled by various chemical and physical phenomena. A discrete fracture network (DFN) model represents an approach to capturing the relationship of fractures in a fracture system. Topology represents the connectivity aspect of the fracture planes, which have a fundamental role in flow simulation in geomaterials involving fractures and the rock matrix. Therefore, one of the most-used methods to treat fractured reservoirs is the double porosity-double permeability model. This approach requires the shape factor calculation, a key parameter used to determine the effects of coupled fracture-matrix fluid flow on the mass transfer between different domains. This paper presents a numerical investigation that aimed to evaluate the impact of fracture topology on the shape factor and equivalent permeability through hydraulic connectivity (f). This study was based on numerical simulations of flow performed in discrete fracture network (DFN) models embedded in finite element meshes (FEM). Modeled cases represent four hypothetical examples of fractured media and three real scenarios extracted from a Brazilian pre-salt carbonate reservoir model. We have compared the results of the numerical simulations with data obtained using Oda’s analytical model and Oda’s correction approach, considering the hydraulic connectivity f. The simulations showed that the equivalent permeability and the shape factor are strongly influenced by the hydraulic connectivity (f) in synthetic scenarios for X and Y-node topological patterns, which showed the higher value for f (0.81) and more expressive values for upscaled permeability (kx-node = 0.1151 and ky-node = 0.1153) and shape factor (25.6 and 14.5), respectively. We have shown that the analytical methods are not efficient for estimating the equivalent permeability of the fractured medium, including when these methods were corrected using topological aspects.

Historically, the geomechanical behavior of a hydrocarbon reservoir has been modeled based on the classical theory of poro-elasticity, which considers absolute reversibility of deformation, which is liable to a porous medium when the mechanical state of the rock is altered. The sands associated with heavy oil formations are generally characterized by low levels of cohesion and density, which is viewed in an increased sensitivity of the rock to permanent deformation and hysteresis; hence it is not suitable to model these formations as if their rheological behavior is elastic. This set the need to construct a model, which describes the permanent plastic deformation that rocks from this kind of reservoir have.The modeling of the stress-strain behavior of plastic porous media aims to evaluate the permanent deformation that the rock suffers and to study the impact of this phenomenon on the behavior of the reservoir permeability porosity and mechanical stability of the layers overlying (compaction, subsidence). Several theoretical research and experimental surveys have defined that most heavy oil reservoirs can be studied as elasto-plastic materials.The purpose of this paper is to show the couple model of constitutive equations (stress-strain model) and fluid flow equations that describe the dynamic behavior of a heavy oil reservoir during an isothermal process, which deforms elasto-plastically, and thereby, to predict several geomechanical phenomena or consequence as productivity drop due to changes in the permeability, pore collapse, cap rock integrity, subsidence, among others, that allow an approach to the behavior of these kind of reservoirs in order to improve production processes and simulation.

In the summer of 2011, we used three geotechnical instruments to assess the ground conditions in planetary analog sites on the Devon Island, Canadian High Arctic. The instruments included Percussive Cone Penetrometer (PCP) developed by Honeybee Robotics, and the two off the shelf instruments: Dynamic Cone Penetrometer (DCP), and the Static Cone Penetrometer (SCP). The three systems differed by the methods the rod was driven into the soil. SCP used a reaction force provided by the operator to drive the rod into the ground, the DCP used a drop hammer, and PCP used a high frequency hammer (percussive) system.The three instruments were evaluated based on their ability to be used by astronauts and be deployed autonomously on planetary robotic platforms (e.g. rovers, hoppers). The SCP, although simple to operate, was limited to soft soils and its data was unreliable. DCP required two people to operate, was heavy, and though the data was reliable, it took a few minutes to obtain it. The PCP has proven to be very reliable, fast, and the data was obtained and plotted in real time. Hence, PCP is recommended as the optimum geotechnical tool for planetary exploration for either a robotic system or an astronaut.The tests were performed at the Drill Hill site within the Haughton Crater. The site was covered by the polygonal features, the telltale signs of water activity (freeze-thaw cycle) beneath the surface. The measurements were taken at the polygons junctions, sides, and the center. It was found the polygon junctions are the weakest, followed by polygon sides, and finally polygon centers (the strongest). The depth to ground ice at these three locations was 65 cm in each case.

Nowadays, a large percentage of oil daily production in some Latin American countries comes from heavy oil reservoirs. The oilfield development and reservoir exploitation strategy for this kind of reservoirs must take into account the impact of geomechanical issues on modelling any reservoir production scenario, either for a single well or sector model simulator. The modelling or simulation tools used to represent the performance and behavior of heavy oil reservoirs present some limitations such as they are not fully coupled and they only use a nonlinear elastic constitutive model to represent the mechanical behavior of the reservoir. Both examples show major limitations to figure out a closer analysis to the true behavior of heavy oil reservoirs. The geological formations related with mentioned reservoirs usually present a mechanical behavior similar to materials with very low capacity to support changes in the stress-state and to present permanent and unrecoverable deformations after loading and unloading processes. Therefore, to analyze the behavior of heavy oil reservoir is mandatory to use modelling tools that incorporate a coupled analysis between fluid-flow process and strain-stress using an elasto-plastic constitutive model. The elasto-plastic constitutive model defines the plastic and elastic phenomenon caused by loading and unloading that occurs in the heavy oil-reservoir. Several research centers have been focused to design experimental tests to learn more thoroughly the results provided by this model, and the results have been satisfactory. However, laboratory tests are not easy to access in most of cases, so it is necessary to have a numerical simulation model that allows knowing the mechanical behavior of the reservoir associated for any production scenario or strategy. This paper presents the results from a coupled model, which integrates both the geomechanics and fluid-flow equations for a single-well case using different constitutive models. This model could provide an overall result of the mechanical behavior of unconsolidated sand under production of high viscosity oil. The results comparison for the three considered cases, just fluid flow, an elastic lineal behavior of the rock and finally an elasto-plastic behavior, provides a great difference between the stress-state among cases with a dramatic change in the formation permeability, and therefore in the reservoir pressure. This numerical model is a useful approximation to improve the characterization of heavy oil reservoirs. As a result, heavy oil reservoirs will have a more successful production intervention or recovery process.

Modelling the process of induced fracture initiation, propagation and interaction with natural fractures is a very challenged task. Significant progress has been made in recent years in the development of complex fracture models to address the needs for more suitable design tools than the conventional planar fracture models. However, some aspects of this complex process are not still fully understood in terms of their impact or importance to the overall fracture geometry, or the complexity of simulating them is beyond the current modelling capabilities or requires computation effort that is not practical for engineering purpose. A technique that has been developed to represent the process of fracture propagation is the Continuous Approximation of Strong Discontinuities, which introduces a special kinematics, capable of representing the process of degradation of the material. One way to implement this approximation is to introduce the effects of a very narrow band of localized deformations within the existing finite elements. In this paper was used a finite element procedure that performs numerical analysis of fluid flow in a deformable porous media in a fully coupled scheme. In this analysis the propagation of the hydraulic fracture occurs specially along the pathway of the natural fractures, due to their lower tensile strength and greater permeability.