Targeting Mechanical Facies in the Green River Basin to Improve Completions Strategies

Abstract

Drilling vibration monitoring has been used in the Green River Basin to estimate the elastic properties along a series of vertical wells to improve targeting of pay sands and increase perforation efficiency. The mechanical properties provide an assessment of pay sands independent of the traditional Gamma Ray pay determination for each individual well. In many cases hotter Gamma Ray zones have shown low Poisson’s ratios in line with the expected response of reservoir sands and when produced, demonstrate high reservoir quality.

The standard operating procedure field-wide is to use Gamma Ray and mud gas to pick producible multi-stage completion units within each formation and target these areas with hydraulic fracturing. However, due to radioactive minerals and clays in some of the formations, Gamma Ray and even other log curves, are not always a reliable indicator of reservoir sands. Without the independent mechanical information pay zones would have been bypassed during completions. Sidewall core measurements confirm the higher Gamma Ray readings with favorable mechanical properties are target worthy facies.

Determining vertical, multi-stage frac boundaries is difficult in fluvial dominated systems. Traditionally stage boundaries are picked geometrically based on a gross stage height of 200-250’ with minimal effort placed on identifying frac barriers between stages in the relatively homogenous looking log character of the overbank mudstones. Using the down-hole, drilling-derived mechanical properties, we are able to identify barriers to frac height growth and more properly determine appropriate stage placement and distribution within the vertical well.

By isolating zones based on mechanical facies rather than the Gamma Ray response, the perforation efficiency has been increased when compared to standard well performance in the area. Production is still in the early stages, but initial readings indicate the wells completed based on mechanical facies are within the upper quartile of the field. With more initiated perforation clusters the well should have better contact with the reservoir, and produce higher yields over time. With the industry focused on completions strategies in unconventionals, this study may serve as an endmember showing the uplift that is possible when fracture stages are adjusted to target mechanical facies rather than applying geometric completions or using radioactivity as a proxy for mechanical variability.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018