Abstract

Reservoir management objectives for the Arun field include the enhancement of deliverability and optimization of liquid productivity. Horizontal wells offer a means of increasing the deliverability from the lower permeability zones while maximizing liquid production from zones which are expected to be relatively rich in condensate.

The Arun reservoir is characterized by higher permeability in the upper section. This causes the lean injection gas to sweep preferentially the upper zones leaving substantial volumes of the reservoir in the lower zones unswept. In an attempt to optimize liquid production, many wells were completed only in the lower zones and have proved to have relatively high condensate-gas ratios (CGR). However, their deliverabilities are low because of the lower permeability. All means of increasing the lower zones' deliverability are being evaluated and horizontal completions became one of the options.

The objective of the horizontal well is to obtain higher producing rates of both gas and liquid from the lower permeability, higher CGR, portion of the reservoir. The horizontal wells are completed open hole in the lower zones (the horizontal section) with a partial liner set across the upper, higher permeability zones, to delay breakthrough of lean injection gas. Three horizontal wells were successfully drilled during 1990 and 1991. The length of the horizontal sections drilled varied from 1000 to 1500 feet. An average production rate of 90 MMSCFPD of gas at 1800 psig wellhead pressure with an average CGR of 60 bbls/MMSCF was achieved. The deliverability results are approximately 50% higher than other lower zone wells and the CGR results are significantly higher than the conventional wells in the field.

Performance of the horizontal wells is helping MOI meet the Arun Reservoir Management objectives, and more horizontal/high angle wells are planned for the future.