ABSTRACT

Fine-scale correlation of sixty-two well penetrations of Sparta B sandstones (Middle Eocene) in Fordoche Field, Pointe Coupee Parish, Louisiana, shows the unit is compartmentalized into an upper and lower sandstone by a thin "shale" body that is resolvable on standard (1= 100 ft) E-logs. Sedimentary structures and trace fossils preserved in conventional core of this thin "shale" indicate that it consists of interbedded fine to medium-grained sandstones and carbonaceous mudstones deposited as storm washover lobes, and tidal-inlet channels associated with a barrier-island complex. The bulk of Sparta B production (estimated at 5.3 MM STB OIP and 2.6 BCF GIP) is from upper shoreface and storm-washover sandstones whose pore spaces contain diagenetic chlorite, kaolinite, and calcite. Enhanced oil recovery (EOR) techniques involving SHF (sequential hydrofluoric acid stimulation) have eliminated declining production rates caused by these diagenetic minerals. Remaining in-place oil and gas is 4,195,960 STB and 1,812 MMCF respectively. Sparta mudstone samples bear a pyrolysis signature confirming a barrier-island depositional regime. T_max values indicate Sparta rocks are immature to marginally mature in south-central Louisiana. Combination of reservoir engineering and petrophysical techniques permits resolution of extremely thin, unconventional oil and gas reservoirs that contain large reserves of "by-passed" hydrocarbons.