Lu, Chuan (Department of Civil and Environmental Engineering, University of Alberta) | Brandl, Jakob (Department of Civil and Environmental Engineering, University of Alberta) | Deisman, Nathan (Department of Civil and Environmental Engineering, University of Alberta) | Chalaturnyk, Richard (Department of Civil and Environmental Engineering, University of Alberta)
In this study, a novel experimental system has been developed for static and dynamic elastic properties measurements at seismic frequencies under anisotropic stress and shear deformation conditions. This system focuses on static and seismic range frequencies dynamic (0.1 Hz to 20 Hz) elastic deformation properties of poorly consolidated oil sands and highly overconsolidated (clay) shales. The main body of the experimental system is a computer control servo-hydraulic system. A pair of laser displacement sensors measure nanometer scale displacement during the dynamic tests. A coarse scale and fine scale load cell system was developed for measuring force with high precision during dynamic testing. A novel triaxial cell for use with the loading system was also developed to simulate the reservoir stress and pore pressure condition during static and dynamic testing and allows permeability to be measured during testing. The loading system, dual load cell calibration procedure and results, and results for acrylic and 3D printed sand specimens are presented. The stable and reasonable results demonstrate the capacity of the new experimental system.
Numerous questions surround stimulation and depletion in unconventional reservoirs with many important implications. Understanding depletion-induced stress changes is critical for designing in-fill drilling and avoiding phenomenon such as hydraulic fracture growth into depleted areas and hydraulic fractures from in fill wells affecting pre-existing wells (the frac-hit or parent well/child well phenomenon). In this paper, we utilize a fully coupled fracture-poro-mechanical computational model described by Jin & Zoback (
This study examines which is the margin of usability for Artificial Intelligence (AI) algorithms related to the rock properties distribution in static modeling. This novel method shows a forward modeling approach using neural networks and genetic algorithms to optimize correlation patterns among seismic traces of stack volumes and well rock properties. Once a set of nonlinear functions is optimized in the well locations, to correlate seismic traces and rock properties, spatial response is estimated using the seismic volume. This seismic characterization process is directly dependent on the error minimization during the structural seismic interpretation process, as well as, honoring the structural complexity while modeling. Previous points are key elements to obtain an adequate correlation between well data and seismic traces. The joint mechanism of neural networks and genetic algorithms globally optimize the nonlinear functions and its parameters to minimize the cost function. Estimated objective function correlates well rock properties with seismic stack data. This mechanism is applied to real data, within a high structural complexity and several wells. As an output, calibrated petrophysical time volumes in the interval of interest are obtained. Properties are used initially to generate a geological facies model. Subsequently, facies and seismic properties are used for the three-dimensional distribution of petrophysical properties such as: rock type, porosity, clay volume and permeability. Therefore, artificial intelligence algorithms can be widely exploited for uncertainty reduction within the rock property spatial estimation.
This paper investigates novel approaches to sour-gas treatment for use in the Middle East that are outside the common oil and gas market and compares them with traditional techniques. In the complete paper, a new, fully coupled implicit tool was used to model an onshore Omani asset with multiple reservoirs, each featuring different fluids and multiple networks. Processing sour natural gas is a challenge. If mercaptans are present in the sour gas, the limited mercaptan-absorption capacity of the well-known alkanolamine solvents can be a problem. An Excel-based tool was developed that uses cubic-equation-of-state (EOS) and thermodynamic electrolyte-chemistry modeling to assess sour-production streams.
Corrosion inhibitors are often the first line of defense against internal corrosion, and effective mitigation relies on proactive monitoring and management of these inhibitors to allow for regular feedback and dose adjustment. This paper describes a novel method of chemical dosage based on time-resolved fluorescence (TRF) that allows a simple, accurate, and efficient quantification of chemicals below parts-per-million ranges, even for double (scale/scale, scale/corrosion) quantification. A study done to find the root cause of coiled tubing string failures in Montney indicated microbial-induced corrosion, leading the CT service provider to create a biocide treatment program. Rigless coiled-tubing-unit (CTU) interventions can be effective in returning to production wells that have lost electrical-submersible-pump (ESP) efficiency because of organic, inorganic, or mixed scale deposits. Sour gas is being produced from a number of carbon-steel-completed wells in the US, Canada, France, and Saudi Arabia.
Downhole magnetic surveys have been most commonly applied in highly magnetized igneous rocks, which have usually been studied within pure geoscience, especially beneath the ocean floor. These rocks preserve the direction of the Earth's field at the time of their formation (i.e., the prevailing magnetic field is "frozen" in the rocks as they solidify, giving them a strong natural remnant magnetization). A primary application has been to identify points in time at which the Earth's magnetic field has undergone a polarity reversal. These reversals have been dated globally (e.g., isotopically in the case of volcanic series or by correlation with biostratigraphy in the case of volcaniclastics) and have given rise to a geomagnetic polarity time scale (GPTS) that is based on laboratory measurements. It has been possible to recognize these reversals through downhole measurements and, therefore, to date the rocks accordingly.
Little is known about the nature and origin of microcrystalline quartz in sandstone reservoirs or mudstone reservoirs. We have utilized advanced analytical capabilities to improve our understanding of controls on microcrystalline quartz development in several examples where porosity is preserved in deeply buried sandstone reservoirs to understand the development in siliceous mudstones.
In this study, several advanced analytical techniques were used to evaluate the crystallographic and compositional controls on the formation of microcrystalline quartz. SEM/Cathodoluminescence (CL) imaging confirms that quartz overgrowths have a complex growth history. Previous workers (Kraishan et al. 2000) suggested that CL patterns in quartz cement are largely due to trace elements rather than defects and that aluminum varies consistently between each cement phase. Electron Backscatter Diffraction (EBSD) combined with Wavelength Dispersive Spectrometry (WDS) confirms that the complex banding visible in CL is not due to changes in crystallographic orientation but more likely variations in quartz composition associated with changes in pore fluid composition and/or reservoir conditions. Secondary Ion Mass Spectrometry (SIMS) analysis provides maps of ultra-trace element distribution that confirm that trace amounts of iron, manganese, and titanium can be used as proxies for defect density and temperature. Additionally, SIMS analysis provides oxygen isotope data providing insight into the initial reservoir conditions and temperature of formation of microcrystalline quartz in several formations.
Microcrystalline quartz in the form of replacement, micropore, and overgrowth cements is present in the Wolfcamp A in the southern Delaware Basin. The amount of cementation has an effect on the reservoir quality and appears to have an impact on the petrophysical properties. The siliceous mudstones are comprised predominantly of biogenic silica (sponge spicules, radiolarians, which are the silica sources for the authigenic microcrystalline quartz), detrital grains (quartz and feldspars), pyrite framboids, and organic matter.
Integrating the results from these advanced analytical techniques has helped us develop our understanding of the processes controlling the formation of quartz cement and improved our ability to reconstruct the reservoir diagenetic history of quartz growth leading to a proposed model for predicting porosity preservation in deep, hot sandstone reservoirs and the formation of microcrystalline quartz in siliceous mudstones. This is the first research to report on spatially resolved isotopic analysis of silica cements integrated into a petrographic framework and a proposed mechanism for microcrystalline quartz growth.
Gas production from shale formations is growing, especially in the USA. However, the origin of shale gases remains poorly understood. The objective of this study is to interpret the origin of shale gases from around the world using recently revised gas genetic diagrams. We collected a large dataset of gas samples recovered from shale formations around the world and interpreted the origin of shale gases using recently revised gas genetic diagrams. The dataset includes >2000 gas samples from the USA, China, Canada, Saudi Arabia, Australia, Sweden, Poland, Argentina, United Kingdom and France. Both free gases collected at wellheads and desorbed gases from cores are included in the dataset. Shale gas samples come from >34 sedimentary basins and >65 different shale formations (plays) ranging in age from Proterozoic (Kyalla and Velkerri Formations, Australia) to Miocene (Monterey Formation, USA). The original data were presented in >80 publications and reports. We plotted molecular and isotopic properties of shale gases on the revised genetic diagrams and determined the origin of shale gases. Based on the distribution of shale gases within the genetic diagram of δ13C of methane (C1) versus C1/(C2+C3), most shale gases appear to have thermogenic origin. The majority of these thermogenic gases are late-mature (e.g., Marcellus Formation, USA and Wufeng-Longmaxi Formation, China) and mid-mature (associated with oil generation, e.g., Eagle Ford Formation, USA). Importantly, shales may contain early-mature thermogenic gases rarely found in conventional accumulations (e.g., T⊘yen Formation, Sweden and Colorado Formation, Canada). Some shale gases have secondary microbial origin, i.e., they originated from anaerobic biodegradation of oils. For example, gases from New Albany Formation and Antrim Formation (USA) have secondary microbial origin. Relatively few shale gases have primary microbial origin, and they often have some minor admixture of thermogenic gas (e.g., Nicolet Formation, Canada and Alum Formation, Sweden). Two other revised gas genetic plots based on δ2H and δ13C of methane and δ13C of CO2 support and enhance the above interpretation. Although shales that contain secondary microbial gas can be productive (e.g., New Albany Formation, USA), the resource-rich, highly productive and commercially successful shale plays contain thermogenic gas. Plays with late-mature thermogenic gas (e.g., Marcellus Formation, USA and Wufeng-Longmaxi Formation, China) appear to be most productive.
Jin, Yan (China University of Petroleum at Beijing) | Jin, Guodong (Baker Hughes, a GE Company) | Syed, Shujath Ali (Baker Hughes, a GE Company) | Jin, Miao (China University of Petroleum at Beijing) | Hussaini, Syed Rizwanullah (King Fahd University of Petroleum and Minerals)
Subsurface unconventional shale samples are always scarce. Outcrop analogs are often used as an alternative to enhance the understanding of the corresponding reservoir formation. One assumption is usually made that rock composition and properties between the outcrop and subsurface samples remain the same or similar, despite differences in their burial and diagenetic histories. This paper presents a comparative case study to investigate the similarities and differences in rock properties between outcrop and subsurface samples from the same formation.
Two subsurface and two outcrop samples from the Lower Silurian Longmaxi formation in Sichuan Basin of China were characterized to determine their mineralogical, geochemical, petrophysical, elastic and mechanical properties. Micro-CT images showed that one subsurface sample was drilled normal to the bedding, while other three samples were parallel to the bedding. Two subsurface samples differ in their mineralogy – the horizontal sample is clay-dominant, while the other one is predominantly comprise of quartz, dolomite and calcite minerals, very similar to two outcrop samples. All four samples are thermally immature and their Tmax is less than 435 °C. Subsurface samples have the highest TOC of 3.75% but relatively lower HI and OI. Other pyrolysis parameters are very similar between subsurface and outcrop samples. All samples have very low porosity of less than 2.5% and permeability of less than 9 nD, although subsurface samples have a relatively higher value.
The discrepancy in mineralogical composition, especially the clay content, results in different elastic and mechanical behavior of outcrop and subsurface samples. The subsurface sample is highly anisotropic in both compressional and shear wave anisotropy due to the large amount of clay minerals, while one outcrop sample exhibits the strong shear wave anisotropy only and the other one is almost isotropic. Subsurface samples have lower values of Young's modulus, peak stress, Mohr-Coulomb failure parameters and unconfined compressive strength than outcrop samples.