Steam Chamber Development In Diatomites: The Role of Microseismic Monitoring in Identifying Conformance and Out-of-Zone Fracture Growth
- Adam Baig (ESG Engineering Seismology Group) | Theodore I. Urbancic (ESG) | Margaret Seibel (Engineering Seismology Group Canada Inc. ESG)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 3 Production and Well Operations, 5.1.7 Seismic Processing and Interpretation, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.4.6 Thermal Methods, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
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The treatment of diatomite reservoirs with cyclic steam is intended to enhance the mobility of the oil in reservoir, thereby stimulating hydrocarbon production. With optimized array geometries, the advanced analysis of the microseismicity resulting from these treatments can yield much more information on these events, such as their failure mechanisms through the process of moment tensor inversion. When these mechanisms suggest that the strain induced by the events is occurring
on natural or newly created fractures, their orientations may be gleaned from the moment tensor.
In this study, we monitor microseismic events observed during the injection and production stages of a ‘Huff and Puff' steaming operation in a diatomite. Our focus is on analyzing the growth of two event clusters that occurred during production cycles after steaming. Since the events are located using three downhole, we can invert for the components of failure.
One cluster showed significant vertical growth and the mechanisms of the microseisms were consistent with dilatational opening of fractures, closures of the fractures, or double-couple (shear) events. While the trend of the cluster of events is reflected in the fracture orientations of some of the events, many of the events have fractures occurring at defined angles to the overall trend. This observation allowed us to infer that the stress regime under which most of the events were responding is dynamically changing as the strain induced by surrounding events evolves in the reservoir. The second grouping of events was spatially contained and consisted of inflationary or deflationary failure mechanisms, suggesting containment that reflects steam chamber development; further exemplified by the variability in fracture azimuths, suggesting that the local stress conditions played a more significant role in the observed failures.
Based on this study, we suggest that advanced microseismic analysis has the potential to outline when steam chamber development occurs within design specifications and when the regional/local stress conditions influence steam chamber development, such as observed in the example of poor containment. In both examples, the occurrence of events during production suggests that failures occur as a result primarily as a result of stress unloading and stress re-distribution locally.
Microseismic monitoring of steam injections has been used to infer the growth of steam chambers, ensure containment of the steam, and distinguish induced seismicity from events due to injections and from moderate tectonic seismicity in the vicinity of reservoirs. The mapping of event hypocenters is a primary tool used to translate the microseismic waveforms into useful data, as these data are assumed to be either directly responding to the injection of steam or the production of the hydrocarbons. The geometry of the microseismic "cloud?? gives a first-order approximation on the size of the process zone and is used to optimize the performance of the stimulations.
Injection of steam in diatomite reservoirs during Huff and Puff operations is beneficial to reduce the viscosity of the hydrocarbon allowing for better production. The process of this injection creates a growing process zone with elevated temperatures and pressures that can result in a moderate amount of deformation that is rapid enough to initiate seismic wave propagation. Relieving this pressure during production can also generate microseismicity as the reservoir is deflated and
fluid hydrocarbon is mobilized towards the treatment well. The goal of such stimulations is to create a large region of low viscosity oil, however, out-of-zone growth is undesirable and, in extreme circumstances, can lead to a breach of the reservoir
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