Geomechanical Properties of the Upper Ordovician Macasty Shale and its Caprock, Anticosti Islan: A Regional Evaluation for a Promising Tight Oil Play

Abstract

The geological integrity of the cap rock overlying targeted unconventional reservoirs is a theme that generates significant interest. On Anticosti Island (eastern Canada), the Upper Ordovician Macasty Shale is a current exploration target for its light oil and condensate potential with the first horizontal wells planned for summer 2016. The Geological Survey of Canada has recently carried out a regional evaluation of the geomechanical parameters (Young's modulus, Poisson ratio, Sh min) of the Macasty Shale and its Upper Ordovician – lower Silurian caprock on the island to better understand their spatial variability and their controls. This study is based on the available petrophysical logs from the oil and gas wells drilled between 1960 and 2010 for conventional targets on the island and through a calibration with data from the only reference well on the island for which a sonic log of the S wave is available. A series of calibration tests were conducted to determine the best method to generate a synthetic sonic log of the S wave for each of the wells considered. On the basis of the available regional data and the parameters required for the calibrations, eight wells were selected for the regional geomechanical study. At the scale of the well, the results highlight the presence of clear mechanical contrasts between the Macasty Shale and the overlying and underlying formations. These mechanical contrasts are reflected in the existence of barriers to the propagation of hydraulic fractures outside the Macasty Shale. Furthermore, the analysis of two wells located on both sides of a regional-scale fault, the Jupiter Fault, reveals that the vicinity of the fault does not affect significantly the mechanical properties of the caprock. The closer well was located in the footwall, about 300 m from the fault. At a regional scale the results demonstrate a remarkable homogeneity from a well to another, except in the south-central part of the island where a barrier to the hydraulic fractures is identified stratigraphically higher in the caprock rather than immediately above the Macasty Shale. This study demonstrates that it is possible to extract regional geomechanical parameters from a very limited set of data in a frontier basin.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016