Increased Reserves through Horizontal Drilling in a Mature Waterflood, Long Beach Unit, Wilmington Oil Field, California

Brigitte H. Berman

Ranger Zone development started in 1965. A waterflood was initiated from the start using a staggered line-drive pattern. Infill drilling in the early 1980s and again in the 1990s revealed bypassed oil in the upper Ranger Fo sand. Detailed studies of the aerial extent of the remaining oil resulted in drilling 17 horizontal wells to recover these reserves.

The Fo target sand thickness is 20 to 50 feet. Well courses are between 10 and 15 feet below the top of the Fo with lengths varying from 800 to 1,000 feet. The success of the Fo drilling program has prompted expansion of horizontal drilling into thin-bedded sand units. Well lengths have increased to between 1,500 and 1,800 feet with structural trend used to advantage. Where needed, probes are designed to penetrate the target sand before setting intermediate casing. The drilling program has been extended into bilateral horizontal completions.

Geosteering with MWD/GR and a 2 MHz dual propagation resistivity tool is used to the casing point. In the completion interval, only the MWD/GR tool is used and a drillpipe conveyed E-log is run afterward to confirm expected resistivities. Despite the many well penetrations in the Ranger Zone, structural control is only fair. Accuracy of MWD data generally low and geosteering is done by TVD log correlation.

With a recovery factor of over 30 percent in Ranger West, from approximately 800 wells drilled in the last 30 years, the horizontal drilling program targeting bypassed reserves has brought new life to this mature reservoir.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California