XRF Chemostratigraphy for Characterizing a Shale Reservoir Along a Horizontal Well Track

Abstract

Chemostratigraphic correlations have been shown to be a reliable means of correlation within unconventional reservoirs. However, these analyses have focused on vertical wells rather than lateral wells. Tracing lateral chemostratigraphic variability back to a vertical section with a chemostratigraphic profile provides a means of targeting intervals of interest along the lateral well for subsequent hydraulic fracturing. Chemostratigraphic analysis uses elemental proxies for changing conditions within the environment of deposition. The principal elements used in this study to indicate detrital sedimentation are aluminum (Al), potassium (K), silicon (Si), titanium (Ti), zirconium (Zr). Declining trends in the detrital proxies indicate transgression while increasing trends indicate regression. The amount of quartz, both biogenic and detrital, is inferred using a Si/Al ratio. Biogenic quartz is inferred when detrital influx cannot account for the amount of quartz observed. Molybdenum (Mo) and vanadium (V) are indicators of basin restriction. The presence of V indicates anoxic conditions and Mo indicates euxinic conditions. This study utilizes Hand-Held XRF (HHXRF) data from cuttings within one horizontal well targeting the Woodford Shale in the Anadarko Basin. The cuttings were collected every 20-40 feet, revealing broad trends in lateral variability, brittleness; three potential high TOC concentration zone were identified for fracturing through from lower brittle zone within the Woodford Shale. These zones are located in the basal Woodford Shale during the onset of a transgressive systems tract (TST). The three separate targets along the lateral well appear to have been deposited in isolated mini-basins, resulting in euxinic conditions that allow for the preservation of organic matter. Chemostratigraphic analysis of the vertical section reveals the middle and lower portions of the Woodford record a declining trend in the detrital elemental proxies. This indicates a majority of the Woodford Shale in this area was deposited during a rise in stratigraphic base-level associated with a TST. The maximum flooding surface (MFS) occurs at MD: 6884ft based on minimal detrital input. High Si/Al ratio section below the maximum flooding surface indicates the existence of biogenic quartz at the top of the TST and is part of the condensed section (CS). Above the MFS the detrital proxies indicate a regression and are interpreted as the subsequent highstand systems tract (HST).

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