JARVIS, HARRY A., and VICTOR LAY, Occidental International Exploration and Production Company, and CESAR OROSCO, Occidental Petroleum Corporation of Peru, Lima, Peru

ABSTRACT: The 1-AB Block Fields: A Giant Oil Accumulation in Eastern Peru

The 1-AB block fields are located in the northeastern part of Peru. Geologically, the area is the sub-Andean Maranon Basin, a continuation of the Napo Basin from eastern Ecuador. During the 20 years that Occidental has operated Block 1-AB, approximately 11,500 km of seismic data has been recorded and 34 exploratory wells have been drilled, resulting in the discovery of 18 fields, or 53% exploration success. The 1-AB oil accumulation discovered in 1972 is a group of medium to small asymmetric anticlines distributed along six northwest-southeast trending structural alignments: North Capahuari-South Capahuari-Tambo, Carmen-North Huayari-South Huayari-Dorissa, Forestal-Shiviyacu, Jibaro-Jibarito, San Jaacinto and Bartra. This concentration of productive structures in a relative small area is unique within the Maranon basin. The controlling factors include exceptional pre-Cretaceous uplifting and the presence of very good to excellent Cretaceous sandstones reservoirs.

The two major Cretaceous producing zones, the Chonta and Vivian sandstones, have been defined within the Coniacian and Campanian ages respectively. The Chonta sands are related to shelfal deposition across Block l-AB, represented by strand plain and barrier island sediments. The Vivian formation is a massive fluvial sandstone covering all of the Maranon basin and ranging in thickness between 40 and 200 feet. After oil was accumulated, fresh water influxes into the reservoirs of the northern and eastern fields caused oil biodegradation and salinity variation of the reservoir waters, depending upon the intensity of biodegradation. Oil remigration also has been documented for the South Huayari field.

Before January 1, 1992 the l-AB fields had produced 418 million barrels of oil. An estimated additional 198 million barrels will be recovered by future development drilling and production of existing wells. Although the wells initially produced by natural flow, hydraulic pumping, gas lifting and pumping unit methods, today most of them use electrical submersible pumps. Even though the total water cut presently is about 90%, oil production in 1991 averaged 53,356 BPD; in March, 1992 it was increased to 57,980 BOPD because of two successful additional development wells. A significant increase of oil production is anticipated as a result of a twenty-well drilling program that is in progress during 1992 and 1993.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.