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.
A better understanding of the energy budget has important implications for enhancing the efficiency of hydraulic fracturing treatments. In particular, what percentage of the input treatment energy is released as radiated energy? What characterizes the deformation of the failure?
We use a bonded-particle modeling approach to investigate both the radiated energy release and the amount of brittle failure. To test our model, we simulate triaxial compression tests on calibrated sandstone samples. Our results show that much of the failure is marked by a tensile component, despite the development of one or two large shear planes crosscutting the samples. Additionally, only 2.5% of the input energy is radiated as seismic waves. We propose an updated empirical energy-magnitude relation: log ER = 1.9MW +8.5, where ER is the radiated energy and MW is the event moment magnitude. This relation is an alternative to the commonly used Kanamori relationship and more applicable for the small-magnitude acoustic emissions in triaxial tests and likely microseismic events in hydraulic fracturing experiments, which are both marked by strong tensile deformation. Close examination of the source mechanisms of the induced acoustic emissions reinforce the complex nature of the micromechanics behind rock fracturing in general, due to strong deviations of the local stress field from the applied external field.
The complex fracture network or stimulated reservoir volume (SRV) can be induced by hydraulic fracturing of the unconventional reservoirs. The SRV dimension is one of the main drivers in a horizontal well performance after the hydraulic fracturing operation. It is of great importance to simulate the SRV dimensions to identify the optimum hydraulic fracturing treatment parameters. In this research, a new analytical model is proposed to accurately simulate the SRV dimension created from hydraulically fractured horizontal wells in unconventional reservoirs. More specifically, a SRV dimensional model is developed to simulate SRV dimensions using effective stresses, injected slurry volume and other reservoir and pumping data during the generation of the hydraulic fracture network. The SRV dimensional model is calibrated using microseismic data from 6 stages of a hydraulic fracturing job in a horizontal well penetrating the Glauconite formation in Hoadley field, Alberta, Canada. The calibrated SRV dimensional model can serve as an optimal fracture spacing estimator for future hydraulic fracture job designs. The average simulated SRV width is smaller than the average fracture port spacing and therefore for this study it is suggested to have the fracture port spacing tighter and equal with the simulated SRV width for optimum production.
We present a numerical model for the simultaneous initiation and subsequent propagation of multiple transverse hydraulic fractures from a horizontal wellbore. In particular, we investigate the efficiency and robustness of the multistage hydraulic fracturing technique. We restrict the created hydraulic fractures to remain radial and planar but fully account for the stress interaction between fractures, the fluid flow in the wellbore and across the different perforation clusters which are modeled via a classical relation between the friction pressure drop and the flow rate entering a given fracture. The initiation is modeled from a radial notch of given initial length using linear elastic fracture mechanics. The solver models the complete pressurization of the wellbore, the initiation of the different fractures and their propagation and interactions. The split of the fluid between the different clusters is part of the solution at each time-step. We present some validations and a case study investigating the effect of a number of heterogeneities (in-situ stress etc.) on the robustness of the limited entry technique.
Underground storage is currently being considered by numerous countries as a long term solution for the disposal of high level nuclear waste. Research and design within each national program is generally tailored to a specific rock type, such as stable granitic plutons, bedded salt formations, clay, and sedimentary rocks ranging from limestone to shale. One important technical aspect of these designs is the accommodation of the mechanical impacts of thermal inputs (heating) from the fuel as it goes through the remainder of its life cycle. The results of experiments completed in a variety of different geological settings, including FEBEX by ENRESA in Grimsel, Switzerland, the Drift Scale Test (DST) at Yucca Mountain, the Äspö Pillar Stability Experiment (ASPE) from the Hard Rock Laboratory (HRL) in Sweden, and the Mine-By Experiment (MBE) by Atomic Energy Canada Limited’s (AECL) Underground Research Laboratory (URL), are analysed and compared to examine how thermal loading and the modelling process varies between different rock types.
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.
Enhancing formation permeability through hydraulic fracturing (HF) has become a proven tool for hydrocarbon extraction in shale (i.e., a resource rock formation) as well as geothermal heat extraction from hot, dry rock reservoirs. Permeability in the nanodarcy range is possible in many such unconventional oil and gas reservoirs, thus requiring production to greatly depend on the existence of natural fractures and the additional surface area generated by hydraulic fracturing. Mapping and characterizing the structure of a hydraulic fracture network can be performed using acoustic emission analysis techniques. Many techniques exist to obtain an estimated stimulated reservoir volume (SRV), which is used as a correlation metric for expected well performance. Most of these techniques use the discrete acoustic emission events as boundary points and determine the volume of rock inside the three-dimensional cloud of data that was acquired. While some of these methods for determining rock volumes affected throughout the fracturing process are sophisticated, understanding of the cumulative fracture opening volume from acoustic emission data is not well understood. Laboratory hydraulic fracturing tests were performed while monitoring acoustic emissions continuously. Sample sizes were approximately 15×15×25 cm3. Granite was used as the reservoir material due to the high brittleness, very low permeability, and relative homogeneity. Acoustic emission data recorded throughout the fracturing process was analyzed for three-dimensional event source locations, source mechanisms, orientations and directions of crack movement, and volumetric deformations. A cumulative volumetric deformation was calculated for a specific area near the openhole wellbore where fracture initiation occurred. This volumetric deformation was then compared to micron scale CT scan data for the same region. The fracturing pattern and the geometrical properties of fracturing (e.g., volume, fracture width, etc.) can be measured and analyzed from the 3D CT images. The resolution of the micro-CT images is sufficient to resolve most tiny fractures. By direct observation through micron CT imaging, the acoustic emission data is compared. The consistence of volumetric contributions of these two sets of data is investigated.
We report a field study on solution mining of magnesium chloride from bischofite layers in the Netherlands at depths between 1500 and 1850 m. Subsidence that was observed in the area is due to part of the brine production being realized by cavern squeeze; some of which were connected. We used an earlier developed inversion scheme to quantify the distribution of the squeeze volumes from the subsidence measurements. We incorporated in it the creep behavior of the rock salt as a convolution between the time-dependent response of a squeeze event and the actual production history. With a Maxwell viscoelastic behavior in the salt with realistic time constant, we achieved a good result for the subsidence values and for the observed ratio between subsidence bowl volume and squeeze volume. With the new understanding we created physics-based forecasts for different production scenarios and provided an estimate for the remaining time and the producible volumes before the maximum allowed amount of subsidence is reached. After completely stopping production, our model predicted a rebound of the subsidence.
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.
This laboratory investigation involved evaluating the potential to enhance drilling Rate of Penetration (ROP) and drilling efficiency by applying axial vibrations on the bit using a pulse cavitation drilling tool in combination with varying levels of axial compliance. The pulse cavitation tool generates cavitation bubbles in the drilling fluid by flowing through a venturi. When the cavitation bubbles produced within the tool are collapsed, pressure pulses are generated which produce pressure pulsations and oscillatory forces on the bit. Drilling results were evaluated on the basis of ROP, Mechanical Specific Energy (MSE), bit loads and bit displacements. The tool was tested both with and without compliance to evaluate the effects of the compliant element. Experimental results show that the pulse cavitation tool starts to cavitate and produce vibrations when a critical flow rate is reached. When the drilling system was rigid (i.e. no compliance was used), the vibration produced did not have any significant effect on the ROP. However, when the drilling system was compliant the vibrations produced by the tool intensified the natural displacement vibration of the compliant element and the ROP was increased and MSE was decreased.