Seismic Characterization Of Niobrara Fluid And Rock Properties PDF Download

Unconventional reservoirs are becoming increasingly important on the world energy stage. Such reservoirs are hydrocarbon sources that need stimulation of some kind in order to be produced in an economically viable way, unlike conventional sources, where oil or gas readily flows into producing wells through more permeable strata. In recent years, unconventional reservoirs have proven to be highly important in North America and have, despite some setbacks and shutdowns, survived reductions in oil and gas prices. A big part of this can be attributed to exploration companies' ability to extract unconventional hydrocarbons with good efficiency, which is in turn attributed to enhanced understanding of the physical dynamics of such reservoirs due to a large body of work done by researchers. Nevertheless, unconventional recovery factors are still considerably low, and further research contributions are needed to better understand how these reservoirs work and interact with stimulation. In this thesis, I focus on the role that faults and fractures play in low permeability reservoirs' response to stimulation, particularly hydraulic fracturing. I analyzed three data sets acquired from and around injection and monitoring wells in the Barnett Shale in Texas. In two of these data sets, I identified small-scale faults and integrated faulting information with other data from wells (e.g. microseismic recordings) to understand how the presence of faults affects injected fluid flow. Results showed that even small-scale faults can have significant effects on hydraulic fracturing progress by providing corridors for fluid flow along them (a high permeability path due to fractures surrounding faults) or by dissipating fluid pressure across them, preventing fluids from effectively crossing to the other side of the fault. For one data set with different seismic surveys acquired before and after stimulation and gas production, I used 3D seismic attribute analysis to identify fractures in and around injection wells to evaluate the methods used, namely azimuth-dependent Amplitude Vs. Offset (AzAVO) and Velocity Vs. Azimuth (VVAz), and to understand how stimulation and production affected fractures in this area of the Barnett. Results showed that fracture density, rather than orientation, is more affected by the pressure introduced during stimulation and by pressure reduction with injected fluid removal and production. I also used well logs to determine the effects of mineral and organic matter content on important rock properties such as porosity. I compared results obtained on small samples (cores) in the laboratory with my results obtained from well logs which are significantly dimensionally larger than cores analyzed in labs. I concluded from analyzing well logs that porosity, for example, is proportional to organic content. This conclusion is similar to that derived from laboratory findings: porosity in many shales resides in organic material such as Kerogen.