April Luncheon

PLEASE NOTE DIFFERENT DATE AND VENUE FOR APRIL MEETING

THANK YOU TO OUR APRIL LUNCHEON SPONSOR!

Please RSVP by 3:00pm on Friday, April 11, 2025.

Reservations made after the deadline will incur an additional fee of $10.

LOCATION: In-Person luncheon meeting will be held on Wednesday, April 16th, at Midland Shared Spaces. Virtual meeting on Zoom. 

TOPIC: Outcrop “pseudo well” logs reveal high-resolution stratigraphy in the Ordovician Montoya Group and Silurian Fusselman Formation, ramp carbonate reservoirs of the Permian Basin

ABSTRACT: Historically, the Silurian Fusselman Formation, a widespread oil, gas, and saltwater disposal reservoir in the Permian Basin, has lacked a consistent, outcrop-based internal stratigraphic framework.  This formation and the underlying Montoya Group are notoriously difficult to interpret in the subsurface due to their homogeneous wireline log responses.  Months of field work conducted in the Franklin, Organ, and Sacramento Mountains have revealed consistent relationships between outcrop proxies for wireline and cuttings analyses and the established internal sequence boundaries (M1-M4) of the Montoya.  It is likely that these boundaries can be interpreted confidently in wells with cuttings samples and/or modern advanced logging suites.  These analyses have further revealed previously undocumented stratigraphic surfaces and lateral facies changes within the Fusselman Formation.

            At its type section in the northern Franklin Mountains, the Fusselman contains portions of 6 third-order sequences, deemed FT (Fusselman Type Section Sequence) 1-6.  Depositional environments within these cycles range from medial ramp to tidal flat.  FT6 corresponds to the Crazycat Member of the Fusselman, equivalent to the subsurface Wristen Group.  FT1-5 correspond to the Flag Hill and Chamberino Members, equivalent to the subsurface Fusselman Formation.  FT1-3 show consistent geometries with well-defined transgressive systems tracts, maximum flooding zones, and highstand systems tracts.  FT4-5 are missing portions of this ideal succession.  Cyclicity within FT6 is unclear.  Moving north of the type section, the cycles become less-pronounced and more incomplete due to a dominance of proximal facies and greater post-depositional erosion.  All cycle boundaries correspond to well log signatures, particularly the dolomite crystal size log which highlights changes in the early diagenetic environment.  The number of cycles in the Flag Hill/Chamberino (5) corresponds closely to the number of global sea level rise-fall episodes during the Llandovery stage (4-7).  The decline in cycle distinctiveness in the upper cycles and in the Crazycat may reflect changes to polar ice volumes moving from the Early Silurian to Middle-Late Silurian.  This work represents the first documentation of high-frequency stratigraphic cyclicity in the Fusselman outcrop and sets a foundation for future efforts to predict reservoir quality in the subsurface.

BIO: Andy Roark is a development geologist at Chevron with 10 years of experience working exploration and development in shale and

tight plays and associated saltwater disposal assets across the Rockies, Anadarko-Ardmore, Permian, and Gulf Coast basins. He currently

supports fields in Lea and Eddy Counties of southeastern New Mexico. He received a bachelor's degree in geology from the University of

Alabama and a Master of Science in Geology at Texas A&M University. For the past five years, he has led multiple recurring geologic field

trips to the Permian Basin and surrounding areas for Chevron and regional professional societies.

PLEASE NOTE DIFFERENT DATE AND VENUE FOR APRIL MEETING