Re-using old Formation MicroScanner logs to help understand reservoir and fracture development at the Dover East Field, SW Ontario, Canada

摘要

Schlumberger ran three FMS (Formation MicroScanner) logs in 1988 over the Black River oil bearing reservoir section in the Dover East 7-5-VE field. Microresistivity variations recorded by the FMS tool were converted into digital color images using standard processing parameters. At the instruction of Liberty Oil & Gas the main objective was to provide a continuous log of interpreted dip results and near-wellbore images and to answer the following: 1. Do we see systematic trend(s) to the fracture orientation? 2. Can we determine fracture distribution and orientation (single and multi-wells)? Is there a relationship between fractures orientation/density and production? Several dip categories were identified on the images: bed boundaries, natural fractures (open, partially open and healed) and drilling induced fracture and faults. A cumulative rose diagram of bed boundaries reveals bimodal distribution of dip azimuths. The subhorizontal bed boundaries dip toward "NNE" and "S" either indicating a gentle undulating surface or faulted block surfaces. The bedding data confirms the location of Dover on the crest of the Algonquin Arch. The analysis of fractures in three Dover East wells shows that the Black River oil bearing reservoir is heavily fractured. A total population of 92 structures (open/healed fractures and fault) was identified showing two dominant populations indicating a complex tectonic history of the area. The most dominant set is "E-W", with two minor subsets, and the secondary maximum is along a "N-S" trend. Both of these trends fall into Sanford's conceptual fracture framework of SW Ontario. The FMS study shows a direct correlation between fracture orientation and well productivity and helps predict which fractures are likely to be open (enhancing reservoir and production) or closed (creating a barrier to flow). This fracture/fault and reservoir information in the Black River hydrothermal dolomite reservoir at Dover will also be directly applicable to the overlying Trenton reservoir. As such, it will be very valuable for the recently approved Jacob Gas storage pool development by Union Gas. This study is of distinct operational value and could be applied to other Ordovician pools in SW Ontario.