Abstract: Successful Drilling of the First Horizontal Well in a Mature Field

Ilsis Marruffo, Claudio Achong

This paper discusses how the decision to drill the first horizontal well of a reservoir was taken, based on production acceleration and the incremental economy of cash flow.

The reservoir is located in the Guafita-Norto Field in Western Venezuela, contiguous to the La Yuca-Cano Limon Fields in Colombia.

Guafita-Norte has 183 million stb of remaining oil reserves with 26 production wells on electrical submergible pumps.

The STOIP of this under saturated reservoir (bubble point pressure is 36 psi) is 160 million stb with an initial GOR of 10 stf/stb, having a permeability between 1.5-12 darcies with a strong water drive, water coning and sanding problems due to fines migration.

During 1995, it was decided to drill the first horizontal well in the reservoir based on a 3-D numerical simulation with radial flow (for water coning) and local grid refinement (for horizontal wells) coupled to an economic analysis.

The simulation predetermines an initial production rate for a horizontal well 2.5 times greater than for a vertical one, and the incremental cash flow for the horizontal well is 4.5 MM$ larger for the the vertical one in four (4) years, with a ROR of 200%.

The horizontal well was drilled with oil-based mud to avoid hole collapse, and it was completed open hole with a single screen pack.

The well is currently producing between 2000 and 3500 stb/d, clean, on natural flow.

This study has clearly shown that the ultimate and decisive parameter to be weighed before undertaking this type of project, is the economic analysis, which must be performed as extensively as the technical analysis.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela