ABSTRACT: Dos Cuadras Field: Shallow Horizontal Wells Breathe New Life Into an Oil Field
GOODHUE, CHIP, and DUANE CAVIT, Unocal Corporation, Ventura, CA
The Dos Cuadras field is located in the Santa Barbara Channel, 7 mi southeast of Santa Barbara, California. Discovered in 1969, the field was developed from four platforms and has produced over 220 MMBO from Pliocene turbidite sands.
The Dos Cuadras structure is a 4-mi-long, doubly-plunging, east-west-trending anticline cut by a major south-dipping reverse fault and numerous down-to-the-southeast normal faults. The shallowest oil sands, the C-P interval of the Repetto Formation, range in depth from 460 to 1200 ft and at the apex of the structure occur less than 300 ft below the sea floor. These sandstones average 35% porosity and 70% oil saturation. Because conventional drilling was unable to reach these shallow sandstones except at close proximity to the platforms, less than 8% recovery was achieved during the initial field development.
Various plans were considered to develop the shallow reservoirs, including installation of slant conductors, drilling multiple subsea completions, and setting satellite platforms. All of these ideas were either unsuccessful, deemed uneconomic, or were environmentally unsound.
In 1990, Unocal began a four-well pilot program to tap additional Brown zone reserves using horizontal wells. All four wells were successfully drilled and are now on production. Completion intervals range from 1000 to 3100 ft and IPs varied from 200 BOPD to 1000 BOPD. The success of these wells confirms that long-reach horizontal drilling has come of age and can be used to limit the amount of onshore surface area or the number of platforms needed for oil and gas development.
AAPG Search and Discovery Article #91016©1992 AAPG-SEPM-SEG-EMD Pacific Section Meeting, Sacramento, California, April 27-May 1, 1992 (2009)