Oklahoma’s Anadarko Basin, one of the world’s super basins, is currently known for horizontal drilling in the Woodford Shale, the principal source rock in the basin. However, above the Woodford, many attractive oil and gas reservoirs have been pursued with vertical technology over the past 100 years. As one of the deepest basins in the United States, with horizontal Woodford wells routinely drilled between 14,000 to 17,000 FT TVD, there is a lot of rock above the source in which hydrocarbons have accumulated.
Lynx Oklahoma Operating is focused on developing targets for horizontal drilling within and adjacent to existing legacy fields in the Anadarko Basin, specifically Caddo County, Oklahoma. After analyzing multiple targets in Caddo County, including the deep Woodford, Meramec, Springer, Red Fork and multiple Hoxbar reservoirs, Lynx decided to initiate its horizontal program targeting crude oil in the Hoxbar Marchand. The Hoxbar Marchand is a sandstone oil reservoir with a typical gravity of 42 to 48 degrees API at 9,500 FT to 10,500 FT TVD, historically developed utilizing conventional vertical technology since the mid-1960s.
Legacy vertical Hoxbar Marchand wells vary in performance. Many are marginal vertical producers and vertical wells drilled but never completed for various reasons, including reservoir properties deemed commercially unproductive, commodity prices and operator challenges. Lynx’s Chief Executive Officer Nelson Bolen states, “These variables provide an attractive dynamic when analyzing conventional reservoirs for modern horizontal unconventional development, as the vertical penetrations provide a detailed subsurface database, showcase producibility, but leave most of the oil behind.” Although vertical Hoxbar Marchand development was in thicker, clean sandstones and thinner, dirtier sandstones, prospects in the thinner, dirtier rock were often not developed beyond the first few wells. This provides an opportunity to add value utilizing modern unconventional technology on legacy conventional rock.
According to Al Warner, senior vice president of geology, “Lynx’s geological approach was to first construct a series of detailed cross sections wherein individual sandstone benches, generally 5’ to 25’ but, in some instances, up to 50’ were correlated. These individual benches were then mapped over their entire extent, providing targets that, in many cases, extend beyond the known limits of a given field or play. In a number of instances, this detailed ‘splitting’ of the sandstones included mapping and extending the shalier sandstones over broader areas which have proven commercially productive.”
When targeting sandstones, like the Hoxbar Marchand, the gamma ray log is not the gospel when identifying productive or nonproductive rock. Other factors must be considered during drilling to stay in the optimum interval. Hydrocarbon shows both gas and oil provide excellent evidence of potentially productive rock, but are not always easily identified, especially when drilling with weighted oil-based mud. Rate of penetration is another excellent leading indicator that is utilized during geosteering and for target changes.