Abstract

A multidisciplinary study addressed the unconventional Montney reservoir with new or modified tools invoking geochemical data. More than 1100 metres of cores from the Altares and Cypress fields in northeast British Columbia gave a solid stratigraphic framework to test reservoir parameters such as rock fabric, pore throat sizes, brittleness and hydrocarbon fill, integrating petrophysical data with XRF, XRD, brittleness core measurements and mercury injection capillary pressures.

Organic geochemistry was key to understand and calibrate pore throat sizes using a phase envelope comparison of isotube and isojar gas compositions; larger differences being linked to smaller pore throats. This was combined with Pittman R30 pore throat calculations from logs and with bitumen content calculated from NMR indicating that some Upper Montney units with larger pore throats are filled with bitumen that corresponds to an early migration of liquid hydrocarbon. Bitumen rich zones have been associated with enrichment in sulfur and samarium. Pore size restriction in the Lower Montney is linked to high clay content and to quartz cement as determined by XRF analysis.

Brittleness prediction (Young’s modulus) using XRD has been achieved with a new formula specific to the Altares Field in which only Feldspars have a positive relationship with brittleness; all published XRD base formula gave much poorer results. Brittleness prediction was also achieved using one single XRF element: chromium which is proxy to clay content and as such has a negative relationship. The reason for the poor predictability using other single XRF elements is the difference in lithological content and textures of the Upper and Lower Montney.

Isotope compositions gave supporting evidence for high reservoir pressure gradients associated with secondary gas cracking overpressure, allowing recognition of fault bounded reservoir compartments. Isotope data also revealed the presence of horizontal detachments confirmed by increased bed dips seen on image logs.

Open fractures filled with dry gas found associated with compressive structures have been identified using gas chromatography; no microseismic events have been found associated with the identified zones of open fractures and, in one well with production logs, 92% of the production came from unstimulated intervals.

Among the novelties of the present work are the analyses of data in 3–D and even 4–D (time) whereas previous work had remained static or studied in a 2–D context; thus, carbon isotopes and DFIT data were analyzed in 3–D or against TVDss.