Exploiting Natural Fracture and Fault Fairways in the Jean Marie Carbonate Platform, N.E. British Columbia

Abstract

This presentation will review the nature of fractures in the Jean Marie from thin section to the seismic scale and focus on the seismic methods used to detect and exploit these high permeability fairways. Drilling results and production indicators of fracture flow will be reviewed, and the controls on fracturing discussed. The Jean Marie carbonate is an Upper Devonian aged carbonate platform that developed on the western margin of North America. Gas is regionally trapped in moderate porosity and low permeability stromatoporoid-renalcid limestone reef mounds and limestone intermound sediments. The pool has been developed using underbalanced horizontal drilling to minimize damage to the fine pore system in this underpressured reservoir. Advanced seismic techniques are being used to detect porosity zones and high permeability fairways which increase deliverability and recovery of gas from the Jean Marie carbonate. Variable well productivity has been observed in similar facies, as has high productivity in low porosity rock. In the last five years, in the Kotcho area, Encana has been targeting natural fracture/fault networks in the Jean Marie. These zones of fracture enhanced and diagenetically altered carbonates have better permeability, and often better porosity. The fracture networks appear to have controlled the distribution of hydrothermal fluids which enhance the porosity and permeability of the carbonate via dissolution and recrystalization. Horizontal wells that encounter fractures generally have better deliverability and greater associated reserves. The use of seismically derived porosity and fracture detection techniques has improved the well planning and the frequency of discovery of higher permeability/deliverability zones. Fracture detection is an important component in the development of the understanding of the permeability system in a reservoir. Fractures and faults can be high permeability production zones, or thief zones for fracturing programs, or barriers to flow if they are cemented shut. The techniques used by Encana in the Jean Marie can be applied to other reservoirs and other lithologies.