FRANKLIN, STAN P., STEVE S. GLICK, and CLEMENT K. CHOU, Chevron Overseas Petroleum Inc., San Ramon, CA, and MIGUEL DEARMAS, Chevron Colombia, Inc., Bogota, Colombia

ABSTRACT: Geological-Engineering Evaluation: Castilla and Chichimene Fields, Cubarral Association Contract, Colombia

A multidisciplinary geological and engineering evaluation project was undertaken for fields within the Chevron Colombia operated Cubarral Association Contract. The goal of the project was to combine geological and engineering evaluations to form a strategy for maximizing the efficiency of ongoing field development, recompletion, and production procedures. The Association Contract is located in the Llanos basin about 100 km southeast of Bogota. The fields: Castilla, Chichimene NE and Chichimene SW contain approximately 2200, 100, and 65 MMBO in place, respectively. The Guadalupe sandstone produces 14 to 21 degrees API oil.

The geological evaluation consisted of three phases: (1) revision of the structural interpretations, (2) detailed stratigraphic analyses, and (3) delineation of tilted fluid contacts and determination of original-oil-in-place. Structural interpretations show that the traps are formed by northeast-southwest trending asymmetric, hanging-wall anticlines. Stratigraphic analyses show that reservoir properties and continuity are strongly affected by depositional environment which varies between the fields. A major facies change between massive, braided-stream sandstones at Castilla and deltaic to shallow marine sandstones at Chichimene northeast is reflected in production characteristics. The fields show strongly tilted oil-water contacts due to regional hydrodynamic gradients. Geometrical nd hydrodynamic calculations were used to delineate the direction and magnitude of the tilts to assess original oil-in-place.

The engineering evaluation consisted of three phases: (1) forward modeling of water cone formation as a function of drainage radius and net pay column, (2) production history matching to determine the sensitivity of water-oil ratio to perforation height, and drainage radius, and (3) use of the models to determine most efficient well spacing and completion procedures. Water coning is a significant problem due to the high oil viscosity and high vertical permeability. Simulations show that greater standoff from the oil-water contact reduces coning and exceeds the detrimental effects of higher bottomhole drawdown associated with shorter perforated intervals.

The result of the multidisciplinary evaluation was a detailed plan for field development, which included optimization of well spacing, completion practices, and recovery efficiency for the fields.

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