A Completion Solution for the Paddy Reservoir in Northeast British Columbia: A Case Study

Abstract

Abstract The Paddy reservoir, located near the Foothills of the Rocky Mountains in northeast British Columbia, Canada, is a fluvioestuarine valley-filled sandstone that has moderate to high permeability. Evidence of tectonic stress has been observed during hydraulic fracture treatments in the form of excessive wellbore friction and net pressures. Historically, attempts to fracture-stimulate these wells has been difficult due to the inability to generate sufficient fracture width necessary for proppant placement. This paper presents a completion solution for the Paddy reservoir in northeast British Columbia that enabled successful placement of propped fracture treatments. Pressure response of past fracture treatments were analysed to understand the cause of past failures, and to quantify the influence of tectonicallyinduced stress. A recommended completion solution is presented which includes orientated perforating to reduce near-wellbore friction and a process for designing fracture treatments to enable successful placement of proppant. Field examples of the new completion technique are presented which show that near-wellbore friction was reduced by 50%, and that up to four times the amount of proppant was placed in the formation compared to previous treatments. Pressure match simulation results from the fracture treatments are also presented. Geologic Summary The Paddy Member forms the upper portion of the Peace River Formation and is distributed over the Peace River area of northwest Alberta and northeast British Columbia. It is underlain by dominantly coarse-grained shoreface deposits of the Cadotte Member and overlain by marine shales of the Shaftesbury Formation. The Paddy Member is made up of thinly bedded sandstones and shales with occasional thin coals. In the study area, the Paddy is approximately 40 m thick. Reservoir quality, incised valley sandstones located in the upper part of the unit are up to 18 m thick. They are dominantly fine to medium and occasionally coarse grained, fairly quartz-rich sandstones with 10 - 30% chert and other lithic grains. Beds are from centimetre to metre scale in thickness and show small to large-scale trough cross lamination. Where bedding thickness is reduced, millimetre scale wavy shale laminae are common and are often incorporated into stylolitic concentrations, which greatly reduce vertical permeability. The cleaner sandstones were probably deposited under fluvial conditions with some tidal influence where thin shale laminae are common. The dominant cement in these sandstones is quartz, which substantially occludes intergranular porosity in the study area. Small amounts of carbonate cements also occur but are rarely volumetrically important. In addition to intergranular porosity, a significant amount of microporosity has been generated through the dissolution of detrital grains, primarily chert. The abundance of microporosity in these sandstones, together with low water saturations indicated by wireline log analysis, may be the origin of the widely held concern that the Paddy reservoir is susceptible to formation damage through water blocking. Core from the study area indicates that porosity in the Paddy reservoir ranges up to 20%, with associated permeability to air at minimal confining pressure of several hundred millidarcies. A minimum porosity cutoff for pay is taken at approximately 8 - 9%, which is typically associated with 1 md permeability.