3D Modelling/Visualization Guides Horizontal Well Program In Wilmington Field
Authors: Phillips C. , Clarke D. 
Published: March 2010

Computerized mapping, modelling, and simulation programs used in conjunction with advanced geosteering technology have helped to successfully tap bypassed, heavy oil in California's mature Wilmington oil field. While THUMS (Long Beach Company) and Tidelands Oil Production Company-the two field contractors working separate portions of the field operated by the City of Long Beach-have taken different approaches to field optimization using horizontal drilling, each has been rewarded by significant additional production.

The following text specifically focusses on how 3D visualization tools have improved Tidelands Oil Production's recovery factor in the "Old Wilmington" or western portion of the field. Data from THUMS' Long Beach Unit, the eastern portion of the field, are included where needed to provide a thorough field overview.

The Challenge

The Wilmington oil field produces from Pliocene and Miocene clastic slope and basin turbidite sandstones. The individual reservoirs are defined by graded sequences of sandstone that are interlayered with siltstones and shales. The entire sequence is folded and faulted. Even the typically rhythmically deposited sequences have lenticular lobate shapes and are complicated by basal scour, onlapping, and channelling. The result is a sequence of rocks that often appears to be uniform but is not. These complexities also result in permeability variations that reduce the producibility of the sandstones, impact waterflooding, and result in a substantial amount of bypassed oil.

Wilmington Field's stratigraphic layers are divided into seven producing zones, 52 subzones, and locally into even finer subzones(1). The finer subdivisions are defined as hydrologic bodies or depositional sequences. Many techniques are applied todefine the thinner sand bodies into unique units, including core description combined with log-rock typing, detailed log correlation, production/injection history matching, bypassed pay saturation analysis on recent pass-through wells and reservoir simulation(2).

There is still much to be learned about the intricacies of Wilmington Field's reservoirs, although today's computerized visualization tools coupled with advanced while-drilling measurements have significantly contributed to the collective knowledgebase about this field. Meanwhile, its poorly drained sands remain ideal targets for horizontal drilling.

History in the Long Beach Unit

The eastern portion of Wilmington Field was originally produced with more than 1,000 wells drilled between 1965 and 1982. Even given the very long completion intervals used and water injection for pressure support, oil remained in pockets of tight, thin sands, as well in areas with poor injection support. Widely ranging permeabilities and faulting caused typically viscous oil (12.5 ° to 16 °API) to be left. behind in 20 to 50 ft. (6 to 15 m) thick sand units.

An additional 460 wells were drilled in the Long Beach Unit from 1982 to 1986 using a "sub-zone" approach to improve sweep efficiency and another 160 million barrels (bbl) or 25.4 million cubic meters (m3) were produced. Then, after 1986 bypassed sands were selectively perforated in even finer intervals.