![]() ![]() The third section will discuss the fault damage zone or fault gouge as interpreted from the horizontal well strip logs. The second section will delve into the stress state implied by the faulting. ![]() The first section will discuss the observations and interpretation of the 3D seismic. et al., 2017), but it is meant to show how the integration of straightforward 3D seismic interpretation and well site strip logs can explain the unique distribution of two different oils in the same reservoir. This article is not meant to be an in-depth discussion of 3D seismic attributes for fault identification, nor is it a treatise on strike-slip faults (Liao, Z. The horizontal wells target the CLLK A Sand member shown in yellow. Both the Nordegg and the Doig Phosphate are considered source rocks in NW Alberta. The Charlie Lake Formation (CLLK) is sandwiched between the Nordegg Member (highlighted in red) and the Doig Phosphate unit (highlighted in purple). Above the Charlie Lake (highlighted in brown in Figure 4) is the Jurassic-age Nordegg Member, also a potential source rock in NW Alberta (Riediger, C.L., 1990). The Doig Phosphate is a well-known source rock in NW Alberta. Below the Charlie Lake is the organically rich Doig Phosphate Formation highlighted in purple. Because the wells were hydraulically fractured, production was also expected to come from tighter intervals of the Charlie Lake above and below the yellow sand. The horizontal wells in the NW end of the pool targeted the thin sand interval highlighted in yellow in Figure 4. The Charlie Lake (CLLK) Formation is a bioturbated, dolomitic sandstone of about 55 m thickness (Mossop, G. Well base map showing the well control and the outline of the proprietary 3Ds in green. Map of Alberta with the red star showing the location of the Worsley Field. A number of horizontal wells were drilled before the acquisition of the 3Ds with mixed results. Even though the 3D seismic was not expected to resolve the thin sweet spot of the reservoir, an economic case was made justifying the acquisition of the 3Ds by aiding and improving the ability of the horizontal well bores to stay in zone. The merged outline of the two 3Ds is shown in the green outline in Figure 3. This article will focus on the NW end of the pool, where two proprietary 3Ds were acquired by Birchcliff Energy in 20. In 2007, Birchcliff Energy purchased the pool and focussed their drilling on pool extensions with multi-stage, hydraulically fractured horizontal wells both in the SE end and in the NW end of the existing pool. All wells require hydraulic fracturing to produce, and the pool is considered a tight oil play. The pool was discovered in 1996 and was initially developed with vertical wells. ![]() Oil production comes from the Triassic-aged Charlie Lake Formation. This case study is located in the Worsley area of NW Alberta, about 100 km north of Grand Prairie (see Figure 2). Overview map showing strike-slip faults and the distribution of two different oils. Perhaps in your career you have come across examples of unexplainable reservoir fluid differences maybe this article will suggest an alternative explanation. Figure 1 provides an overview of the discussion to follow. This concept is an interesting example of the integration of 3D seismic, well site geology, geomechanics, and oil chemistry to confirm the existence of a strike-slip fault that created the unusual juxtaposition of two radically different oils. We often think of faults and fault damage zones as conduits for fluid flow, but in this case the strike-slip fault is a barrier. The oils produced on either side of the fault were radically different, suggesting that the strike-slip fault acted as a permeability barrier to fluid migration. Wells drilled through the fault face showed evidence, on strip logs, of the fault gouge. ![]() A number of horizontal wells were drilled on both sides of a strike-slip fault, and some were drilled through the fault face. This article discusses a case study where strike-slip faults are identified on 3D seismic and play an important role in hydrocarbon entrapment. Strike-slip faults with no vertical displacement, on the other hand, are notoriously difficult to detect on seismic data. Faults with associated vertical displacement or folding are often visible on seismic data. Faults have always played a major role in the trapping of hydrocarbons, usually by creating structural traps. ![]()
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