Fluid Migration and Accumulation within the Mississippian: Why 2% Oil Cut Here, 15% One Mile Away?
Kansas Geological Survey
Water cut is a big factor in gaging the success of horizontal drilling in the Mississippi Lime Play (MLP). The contributing factors are related in part to the spectrum of producing lithofacies and reservoir quality encountered that varies laterally and vertically, sometimes dramatically. As the extent of the play has increased, so have the types of reservoirs including conventional tripolite, spiculite, and dolomite reservoirs that may or may not be affected by Pennsylvanian karst. Conventional reservoirs are typically in transition when sufficient oil column is not present to lead to irreducible water saturation, inherently leading to variable water cuts based on height about free water and types of pores that are present.
Unconventional reservoir such as tight, dark organic-bearing dolomitic and silty lithofacies of the "Cowley" are often interbedded the spicultic and dolomitic conventional reservoirs. These rocks with sufficient oil prone organic matter and thermal maturity can locally become self- sourced reservoirs and possibly charge adjoining conventional reservoirs. Coupled with a thick thermally mature Woodford or Chattanooga Shale and fracturing, a hydrocarbon sweet spot is likely.
The structural history during and after the Mississippian with the development of the Arkoma and Anadarko basins and surrounding uplifts led to early thermal maturity of the Woodford Shale that goes back as far to the early Pennsylvanian. Evidence notable wrench faulting peaked in Atokan and Morrowan time in the Anadarko Basin extending well into Kansas. This dynamic setting lead to reactivation of basement weaknesses with both compressional strike-slip and transtensional faults that appear to closely tied to hydrocarbon migration fairways in the northern Midcontinent.
AAPG Search and Discovery Article #90201 © AAPG Education Directorate Mississippi Lime Forum, February 20, 2014, Oklahoma City, Oklahoma