Microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight Bakken reservoir

To improve the accuracy of microseismic event locations, we developed a new inversion method with double-difference constraints for determining the hypocenters and the anisotropic velocity model for unconventional reservoirs. We applied this method to a microseismic data set monitoring a Middle Bakken completion in the Beaver Lodge area of North Dakota. Geophone arrays in four observation wells improved the ray coverage for the velocity inversion. Using an accurate anisotropic velocity model is important to correctly assess the height growth of the hydraulically induced fractures in the Middle Bakken. Our results showed that (1) moderate-to-strong anisotropy exists in all studied sedimentary layers, especially in the Upper and Lower Bakken shale formations, where the Thomsen parameters (ϵ and γ) can be greater than 0.4, (2) all the events selected for high signal-to-noise ratio and used for the joint velocity inversion are located in the Bakken and overlying Lodgepole formations, i.e., no events are detected in the Three Forks formation below the Bakken, and (3) more than half of the strong events are in two clusters at approximately 100 and 150 m above the Middle Bakken. Reoccurrence of strong, closely clustered events suggested activation of natural fractures or faults in the Lodgepole formation. The sensitivity analysis for the inversion results showed that the relative uncertainty in parameter δ is larger than other anisotropy parameters. The microseismic event locations and the anisotropic velocity model are validated by comparing synthetic and observed seismic waveforms and by S-wave splitting.Shell Oil Compan

Pressure dependence of the elastic moduli of body-centered-cubic transition metals

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1977.Bibliography: leaves 134-143.Microfiche.viii, 143 leaves illThe single-crystal elastic moduli, Cij, and their pressure derivatives, dCij/dP, have been measured ultrasonically at 25°C for body-centered-cubic Ti-V-Cr, Nb-Mo, and Ta-W solid solutions. The rigid-band model for the alloy electronic structure is known to work fairly well for these metals in predicting the density of states at the Fermi energy and related properties. The results of this study show that changes in the composition dependence of the Cij and, particularly, the dCij/dP appear to be related to topological changes in the Fermi surface which occur as the electron population varies in the rigid-band model. The relationship between the band structure and the Cij is discussed and a qualitative explanation is given for the correlations between the moduli and the Fermi surface. Sources of error in the ultrasonic measurements are considered in detail. It is found that compression of the pressure medium can cause significant errors in the dCij/dP values under certain experimental conditions, and methods for minimizing these errors are suggested. The results are also compared to other ultrasonic measurements and to X-ray and shock-wave compression experiments. Possible sources of disagreement, where it exists, are discussed