Reservoir Description is Key to Steamflood Planning and Implementation, Webster Reservoir, Midway-Sunset Field, Kern County, California

B. R. Hall, M. H. Link

The Webster reservoir at Midway-Sunset field, Kern County, California, is an unconsolidated sand reservoir of Miocene age ("Stevens equivalent," Monterey Formation). The Webster was discovered in 1910 but, due to poor heavy oil (14° API) economics, development for primary production and subsequent enhanced recovery were sporadic.

Currently, the reservoir produces by cyclic steam stimulation in approximately 35 wells. Cumulative oil production for the Webster since 1910 is about 13 million bbl.

The Webster is subdivided into two reservoirs--the Webster Intermediate and Webster Main. The Webster Intermediate directly overlies the Webster Main in one area but is separated by up to 300 ft of shale elsewhere. The combined thickness of both Webster reservoirs averages 250 ft and is located at a drilling depth of 1,100-1,800 ft. From evaluation of modern core data and sand distribution maps, the Webster sands are interpreted to have been deposited by turbidity currents that flowed from southwest to northeast in this area. Oil is trapped in the Webster reservoir where these turbidites were subsequently folded on a northwest-southeast-trending anticline.

Detailed recorrelation on wireline logs, stratigraphic zonation, detailed reservoir description by zone, and sedimentary facies identification in modern cores has led to development of a geologic model for the Webster. This model indicates that the Webster Intermediate was deposited predominately by strongly channelized turbidity currents, resulting in channel-fill sands, and that the Webster Main was deposited by less restricted flows, resulting in more lobate deposits.

In anticipation of future steamflood development of the Webster reservoir, a 4-pattern, inverted 9-spot, pilot project is planned. The geologic description of the Webster reservoir, in combination with planned simulation studies, is critical for predicting vertical and lateral sweep efficiency and for steamflood design and well placement.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.