Critical Factors for Optimum SAGD Well Placement and Liner Design in Lithic Sandstones

Abstract

The Osum Orion project in the Cold Lake oil sands region of Alberta uses Steam Assisted Gravity Drainage (SAGD) for bitumen production from the Albian Clearwater Formation. Commercial production since 2007 has revealed that production rates are dependent on two criteria: well placement, and completion design of the production liner. Each criterion when corrected doubles production rates and if both are optimized production rates quadruple. The Clearwater is a feldspathic litharenite with an upper clean sandy facies and a lower sandy heterolithic facies (SHS). Production wells from Pads 103, 105, and 107 placed in the sandy facies are double the rates from Pad 104 and 106 where the well pairs are within SHS. The lower vertical permeability in SHS impairs vertical communication between the production and injection wells. Repeat seismic supports this interpretation with Pads 104 and 106 having a patchy thermal response and poor conformance. The Clearwater sand is fine-grained and the slots were sized to minimize sand production and maximize flow. Rock fragments and feldspars comprise 70 to 85% of the sandstone and are reactive with the hot steam and as a result the produced water becomes enriched in calcium and carbonate ions. As fluid pressure drops at the narrow slots, CO₂ gas comes out of solution and a scale of calcium carbonate precipitates at the liner. The scale reduces flow at the slot further decreasing the open area in a positive feedback loop with the eventual result being cementation of sand near the wellbore. This issue was initially mitigated by chemical stimulations, but ultimately a long-term mechanical solution was implemented. Perforating the production liner decreased the pressure differential between the production and injection wells, doubling production, with minimal sand production. The initial pilot production wells of the project were completed with wire wrap screens and have been producing for 18 years without observing this scale issue. Wire wrap screens have a greater open area and metallurgy that inhibits scale precipitates. Future Orion SAGD production wells will target the sandy facies and be completed with wire wrap screens. Our study is in the Clearwater Formation, but the conclusions are applicable to SAGD development of other fine-grained lithic sandstones deposited in marginal marine settings.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016