Eastern Section Meeting

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Support for a Deep Fault Related Hydrothermal Dolomite Model for Some Michigan Basin Dundee Formation Reservoirs


The Dundee Formation is the most prolific oil producing formation in the Michigan Basin. Oil reservoirs in this middle Devonian carbonate are either facies-controlled or fracture-controlled and both can be diagenetically modified (Luczaq et al., 2006). Even though fracture-controlled reservoirs are more common than facies-controlled reservoirs (Luczaq et al., 2006) and maximum production is from the coarser grained diagenetically modified portions (Montgomery et al., 1998), not much is known about how fracture-controlled diagenetically modified Dundee reservoirs formed (Luczaq et al., 2006). To help answer this, Luczaq et al. (2006) studied chemical analysis results from aqueous inclusions and concluded that the diagenetic modification of many fracture-controlled reservoirs is best explained by the short-duration migration of high temperature fluids through faults connected to Pre-Cambrian basement, rather than through fluid migration related to long term basin burial. Although Luczaq et al. (2006) presented a convincing argument for a deep fault related hydrothermal dolomite (HTD) model, some workers doubt reactivated basement faults could propagate upward and act as hydraulic conduits through the thick salt sections present in the Late Silurian Salina Group underlying the Dundee Formation. To study the appropriateness of the model for some Dundee reservoirs, we examined gravity and magnetic data over several known reservoirs. Our analysis shows that interpreted Pre-Cambrian and overlying shallower faults coincide with several fracture-controlled diagenetically modified Dundee reservoirs. An additional finding was that gravity data indicates faults associated with some eastern Basin fracture-controlled diagenetically modified fields propagate upward through the late Mississippian section (the subcrop with glacial drift), indicating the faults were active through at least that time. This recognition offers hints as to the tectonic event(s) that reactivated these faults. Furthermore, the existence of the faults in the shallow section offers a means to detect them using detailed gravity. If the deep fault related HTD model is correct for many Dundee reservoirs, it provides new strategies for exploration. Given the limited areal extent of many deep fault related HTD reservoirs, it is likely several Dundee reservoirs remain undiscovered. Additionally, these methods appear to be applicable to the discovery of fields in other formations and areas.