ABSTRACT: Reservoir Geology and Performance of Turbidite Producing Sands, South Timbalier 295 Field, Offshore Louisiana, Gulf of Mexico

MASON, E. P., Shell Offshore Inc., New Orleans, LA

Uncertainty exists concerning the range of production performances to expect from different deep water reservoir facies. South Timbalier 295 is one of a select few Gulf of Mexico fields with production history data available from several different turbidite depositional settings. The depositional environment and production performance of the three main pay sands will be discussed.

Since its discovery in 1984, 27 wells have been drilled at South Timbalier 295 Field. Reserves are 25 million bbl of oil and 125 billion cubic feet of gas. A very successful six-well drilling program just concluded was based on a fully integrated (3-D seismic, well and production data) field study completed in 1991. Cross sections and detailed field maps were constructed for every pay sand. Additionally, a series of subregional interval and net sand isopachs were built and then used to reconstruct the tectonic history of the area. The reconstruction helped define how paleostructure influenced sand deposition.

The "K8," interpreted to be a series of mid-fan turbidite sheet sands which lapped onto a paleohigh, is characterized by good lateral continuity. Over 1,000,000 barrels of oil have been produced from Well A-12 at a sustained 1,500 barrel daily rate with only a small pressure change. A large downdip aquifer providing good pressure support is likely.

The "K16" consists of amalgamated channel sands characterized by rapid lateral variation. Interval and net sand isopachs also indicate thinning onto a paleohigh. Despite the channelized architecture of the "K16", connectivity of channels across amalgamation surfaces appears to be common. High sustained production rates with little pressure change indicate connection to a large aquifer.

The "K40" consists of two separate turbidite ponded basin sheet sands which, lapping onto a paleohigh, pinch-out updip. Over 800,000 bbl of oil have been produced from the A-5 well at a sustained rate of 1,200 barrels daily. Good recoveries, little pressure

change and noticeable movement of the oil/water contact suggests good lateral connectivity and support by a large downdip aquifer.

All three sands are fine grained, moderately well sorted, subarkosic sandstones. Porosity and permeability average approximately 31% and 500 MD, respectively, for all three reservoirs.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)