Application of Sequence Stratigraphic Re-Interpretation of Lower Lagunillas Member to Further Development of Bloque IV, Lake Maracaibo, Venezuela

Helena Gamero De Villarroel, Roger Higgs, Ian Bryant, Bulent Baygun, Michael Herron

The Lower Lagunillas Member of the Miocene Lagunillas Formation of Bloque IV of the Bachaquero field was discovered in 1957 and was originally estimated to contain 2 billion barrels of oil. This reservoir interval has traditionally been interpreted to have been deposited in a delta plain setting and to comprise 3 reservoir sub-divisions that were developed as a single drainage unit. Sedimentological interpretation of four cored wells has led to the development of a new model of deposition in tidally influenced lower delta plain and delta front settings. This model is supported by FTIR measurement of illite concentrations and prompt neutron capture boron measurements that are indicative of a brackish water depositional setting.

The conceptual geological model has been used to guide correlation of wireline logs from 46 wells in the central part of Bloque IV and to provide a high resolution sequence stratigraphic model of the Lower Lagunillas reservoirs. Twelve genetic layers are identified that are separated by locally developed intra-formational seals into up to eight drainage units. High permeability, tidally influenced channel-fill sands have acted as preferential conduits for gas influx, leaving bypassed oil in lower quality sands that were deposited as lagoonal deltas and bars.

This reservoir model has been supported by re-examination of production data and by openhole measurements in a recent infill well and cased-hole logging of two other wells in the study area. The new model will form the basis for redevelopment of this reservoir to further increase recovery from this mature field.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995