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.
In recent years, the development of oil and gas from shale has proceeded quickly in the world due to the application of multi-stage fracturing technology in horizontal wells. It is imperative to study the poroelastic characteristics of the rock for modeling the performance of rock under in-situ conditions, thus ensuring the success of hydraulic fracturing. Biot's coefficient is one of the key poroelastic parameters for calculating the effective stress for creating artificial fractures in the shale formations. In this study, we propose anew method to measure the Biot's coefficient. Our method simplified the measuring procedures to obtain the Biot's coefficient by controlling the confining pressure, which isused to maintain the volume of the sample, while altering the pore pressure. Shales amples recovered form Bakken formation in Willistion Basin is tested using this method. The results of our experiments show that the Biot's coefficient of Bakken samples obtained from horizontal drilling and vertical drilling are significantly different from each other. This significant difference of Biot's coefficient with different drilling-direction provides scientists and engineers a solid base for in-situ stress analysis during multi stage hydraulic fracturing and reservoir depletion due to production.
Shale gas has become an increasingly important source of natural gas (CH4) in the United States over the last decade. Due to its unconventional characteristics, injecting carbondioxide (CO2) to enhance shale gas recovery (ESGR) is a potentially feasible method to increase gas-yield while both affording a sink for CO2 and in reducing the potential for induced seismicity. This study examines CO2 -ESGR to better understand its feasibility and effectiveness. We explore the roles of important coupled phenomena activated during gas substitution especially vigorous feedbacks between sorptive behavior and permeability evolution. Permeability and porosity evolution models developed for sorptive fractured coal are adapted to the component characteristics of gas shales. These adapted models are used to probe the optimization of CO2 -ESGR for injection of CO2 at overpressures of 0MPa, 4MPa and 8MPa to investigate magnitudes of elevated CH4 production, CO2 storage rate and capacity, and of CO2 early-breakthrough and permeability evolution in the reservoir. For the injection pressures selected, CH4 production was enhanced by 2.3%, 14.3%, 28.5%, respectively, over the case where CO2 is not injected. Distinctly different evolutions are noted for permeability in both fractures and matrix due to different dominating mechanisms. Fracture permeability increased by ~ ⅓ for the injection scenarios due to the dominant influence of CH4 de-sorption over CO2 sorption. CO2 sequestration capacity was only of the order of 104 m3 when supercritical for a net recovery of CO2 of 108 m3.
The occurrence of roof falls in underground mines has been reduced, largely to improvements in roof bolt technology, but continue to be a common source of mining-related injuries and fatalities. Particle flow modeling is an effective tool for simulating rock processes and behaviors related to mining activities. In this study, particle flow modeling is used to simulate the deformation of a roof layer in a room-and-pillar mine. Shale and sandstone models are compared, as are different roof bolt configuration scenarios. As input parameters would predict, the shale roof models deform more than the sandstone roof models. Greater bolt spacing is also associated with greater maximum deformation of the roof layer. Similar, more detailed studies of this nature could be used for predictive modeling to mitigate the risk of catastrophic roof falls in underground mines and to optimize the bolt configuration for unique mine factors.
Recent advances in high power plasma torch technology provide an apparatus to replace the conventional perforation methods in oil and gas wells. High power plasma torches are capable of cutting and removing rocks textures efficiently and they might be considered as one of the appropriate substitutions for current shaped charge perforation methods. According to its advantages the conventional shaped charge methods that one the important one is increasing permeability considerably and no need to have costly re-perforation operations to decreasing new formation damage named by perforation skin. Plasma torch perforation is gone along with heat flux generation. As the temperature increases during plasma torch operation, thermal energy accumulates the matrix expansion. This expansion generate thermal stresses induce the rock texture. Furthermore, thermal stresses exceeds the rock strength, thermal fractures will form in texture that mainly depend on rock thermal properties, pore size distribution, applied thermal stresses and confining and pore pressures. In this paper, the results of experimental studies on implementation of high power plasma torch in perforation and fracture initiation in oil and gas wells is presented. Also, numerically analyzing of generating these thermal fractures during plasma torch perforation will facilitate hydraulic fracturing operation.
This paper presents a comprehensive numerical modeling framework integrating macroscopic continuum and microscopic discontinuum numerical modeling methodologies. The continuum model is formulated on the poro-elastic-plastic theory in combination of erosion law. The discontinuum model couples discrete element method with pore-scale fluid flow model (e.g., lattice Boltzmann method). The microscopic discontinuum model can capture most primary hydromechanical physics occurring in the sand production process but its computation cost is very expensive, so it is used to develop erosion laws through performing extensive parametric study in modeling small-sized problems. The developed erosion laws are integrated into the continuum model to investigate real-sized problems. The theoretical formulations of the poromechanics and erosion laws are briefly reviewed. The discrete element – lattice Boltzmann coupling scheme is described with a couple of examples demonstrating its suitability in serving as a virtual laboratory for erosion law improvement or calibration.
The Numerical Manifold Method (NMM) with a two-cover-meshing system is an ideal method to handle boundaries, considering its flexibility with no need to adjust mathematical nodes onto boundaries, the meshing efficiency and its integration precision. In this study, we derived different forms of Lagrange multiplier methods (LMMs) and jump function methods (JFMs) for boundary constraints in the frame of NMM. These approaches for boundary constraints make full use of the aforementioned advantages of NMM and are established based on a clear physical meaning of water flow by an energy-work seepage model. The LMM approaches are discontinuous approaches in which Lagrange Multipliers provide links between discontinuous physical covers cut by material interfaces, whereas the JFM approaches are continuous, in which the discontinuities of material interfaces are realized by introducing jump terms across a continuous medium. The boundary constraint approaches developed in this study were coded into an NMM water flow model. We compared simulation results involving Dirichlet boundary conditions and idealized faulted rock using LMM and JFM with analytical solutions, and prove that both methods provide accurate results, with additional degrees of freedom introduced (or eliminated by special physical meaning). Based on these results, we recommend the LMM considering its accuracy and efficiency, flexibility, especially when involving intense geometric change or fracture intersections. Last, we apply and demonstrate the LMM approach in a simplified model of flow through porous rock with a major fault and a tunnel and arrived at convincing results.
: A fully implicit method for coupled fluid flow and geomechanical deformation in fractured porous media is presented. Finite-volume and finite-element discretization schemes are used, respectively, for the flow and mechanics problems. The discrete flow and mechanics problems share the same conformal unstructured mesh. The network of natural fractures is represented explicitly in the mesh. The behavior of the fractured medium due to changes in the fluid pressure, stress, and strain fields is investigated. The methodology is validated using simple cases for which analytical solutions are available, and also using more complex "realistic" test cases.
Hydraulic fracturing is a well stimulation technique that makes the recoveries from the vast unconventional hydrocarbon resources in US economically feasible. Proppants are granular materials that are injected into hydraulic fractures to keep them open following a fracturing treatment. Hence, the proppant selection is of particular significance in petroleum industry. Due to recent advances in imaging technologies and high-performance computing, estimation of the elastic and transport properties of proppant packs at different closure stresses using imaged-based simulations is a credible alternative to direct experiments. In this study, transport properties (permeability and inertial flow parameter) of a ceramic proppant pack exposed to varying loading stresses are calculated using Lattice Boltzmann (LB) model simulations. The images of this packing shows rearrangement of the packing structure, embedding of the grains at the rock wall, and crushing of individual proppants. LB simulation results of this packing show that the permeability and inertial flow parameter are less sensitive to stress variations before crushing of the grains occurs.
In naturally fractured shale oil and gas reservoirs, it is expected that the hydraulic fracture behavior is significantly influenced by the interaction with pre-existing natural fractures. However, the relationship between fracture behaviors and natural fractures has not been sufficiently clarified because direct observation of all the fractures or microcracks generated during the field or laboratory scale hydraulic fracturing is difficult. In this paper, a series of flow-coupled DEM simulations varying the properties of natural fracture, such as the permeability of natural fractures and the angle between created hydraulic fracture and natural fracture (approach angle), is presented. As a results, different fracture growth patterns were observed with different combination of approach angle and permeability of natural fracture. When the approach angle is high and the permeability is low, the hydraulic fracture ignores the existence of natural fracture and it propagated straight to the direction of maximum compressive principal stress. On the other hand, when the approach angle is low and the permeability is high, hydraulic fracture propagated along with a natural fracture. After that, it branched or curved to the direction of maximum principal stress.