The nonmarine Pliocene and Pleistocene Tulare Formation forms the stratigraphically highest subsurface reservoir in the Midway-Sunset Oil Field (Pl.1) It crops out extensively within and along the western flank of the field in the east-central Temblor Range, where it has been remapped recently by Nilsen (1995; P1.1). In outcrop it generally forms a gently northeast-dipping succession of beds that truncates with angular unconformity all older strata; locally, however, it has been folded and faulted by younger deformation (P1.1). At the northern end of the field and in the McKittrick area, it has been deformed into a series of closely spaced northwest-trending anticlines and synclines associated with the McKittrick fault, a young southwest- dipping thrust; in this area, Farley (1990) has mapped the "Tulare fold belt" in outcrop and subsurface.
Santa Fe Energy Resources (SFER) produces significant quantities of heavy oil from the Tulare Formation in the Midway-Sunset Oil Field (Campbell, this volume). This production has been made possible by various enhanced oil recovery (EOR) techniques, including steamflooding and fireflooding. However, because the largely unconsolidated coarse clastic deposits that make up the Tulare Formation include lithologic units and facies that complicate typical EOR techniques, SFER has collected a number of long, continuous cores through the productive intervals of the Tulare Formation. These cores provide a suitable framework for the field trip core workshop.
In the late 1980’s, three long conventional cores were taken from SFER Wells 121-25, 363-25, and 443-25 in sec. 25, T. 31S., R. 22E. These cored wells were from a SFER steamflood pilot of the Tulare Formation in the SW/4 sec. 25. These cores were described in detail by Applied Earth Technology, Inc. (AET, 1988) as part of a regional stratigraphic and sedimentologic study of the Tulare Formation. The core descriptions and interpretations presented here in are from the AET report. AET also conducted a supplemental study of the matrix composition and character of the reservoir conglomerates, using scanning-electron microscope techniques; some of these results are also reported herein.
In the 1990’s, SFER obtained additional conventional core from the Tulare Formation in five Midway-Sunset wells. Two of these wells were cored across the basal contact of the Tulare Formation into the underlying San Joaquin Formation; core from one of these wells will be shown at the Core Workshop to represent the uppermost San Joaquin Formation (Nilsen, this volume).
