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Updated June 2024

The AER has limited its reserves evaluation of low permeability and shale resources to horizontal multistage fractured wells that are licensed for production in the Cardium, Montney, and Duvernay Formations.

The producing wells were evaluated based on nonconfidential wells on stream in 2023. Forecasts extend 30 years to September 1, 2053. Some wells were not included in this analysis because of their limited extent of production. 

Flow Regimes and Reserves for Low Permeability and Shale Resources

Dominant flow: In vertical wells, this kind of flow regime is radial. The pressure drawdown is localized at sandface, and the drainage area is unrelated to completions or horizontal multistage fracturing. In low permeability and shale resource wells, dominant flow regime is linear. The pressure drawdown is throughout the fracture and the drainage area is effectively created by completion or horizontal multistage fracturing. 

Transient flow: Transient flow happens during the first few-to-several months after a well goes on production and while a pressure “pulse” is moving out into an infinite or semi-infinite acting reservoir. 

Boundary-dominated flow: Boundary-dominated flow is a late-time flow behaviour. It typically dominates long-term production data. The reservoir is also in a state of pseudoequilibrium during this kind of flow. Some major factors affecting the time that it takes for a well to reach boundary-dominated flow include well spacing, fracture spacing, fracture propagation, fracture permeability, and matrix permeability. 

Flow Regimes and Reserves Estimates

Based on the expectation of long-duration linear flow periods in these wells, traditional forecasting methods used for more conventional reservoirs are not appropriate for the Cardium, Montney, and Duvernay Formations.

Developed producing reserves were derived using a transient flow model. This helped characterize long-duration linear flow and validate production data points. Flow regime diagnostic plots were used to identify linear flow patterns and define the decline parameters for traditional decline equations. The diagnostic plots help

  • assess production history by eliminating early-time data (where the well may have had insufficient time to establish a defined flow regime) and
  • identify whether a well is still in transient flow or has transitioned to boundary-dominated flow. 
Undeveloped Reserves

Undeveloped reserves were assigned based on the reasonable assumption that undeveloped locations will be drilled in the next five years and that there are no physical restrictions to drilling the proposed locations. 

Formation Evaluation Methods

Cardium Formation:
  • Decline method (modified Arps) for well-by-well reserves

Some early production data was affected by operator practices and early linear flow was followed by a long transition period. Linear flow was not observed in some wells because of varying bottomhole pressure and operating practices.

The AER has changed the methodology for assigning condensate reserves for the Cardium Formation. Previously, condensate volumes were determined using a condensate-gas ratio that erroneously included gas volumes from oil wells in the calculation. The 2023 condensate data is from Petrinex, and well-by-well reserves were assigned using the decline method (modified Arps).

Montney and Duvernay Formations
  • Decline method (modified Arps) for well-by-well reserves
  • Yu (20141) method to determine liquids yields
  • Oil wells (high gas yields) (a separate methodology developed by) Yu

Some gas wells in this formation also have a high liquids yield. Yu developed two methods: one for gas with high liquids yields (condensate), and a method for oil with high gas yields (volatile oil). Both Yu methods were used for these formations.

1 Yu, Shaoyong “A New Methodology to Forecast Solution Gas Production in Tight Oil Reservoirs” Paper presented at the SPE/CSUR Unconventional Resources Conference – Canada, Calgary, Alberta, Canada, September 2014.