THE SUCCESSFUL RECOVERY OF WELL PRODUCTIVITY IN THE BODALLA SOUTH OILFIELD

Abstract

The Bodalla South oilfield is located in the Cooper-Eromanga Basin, south-west Queensland. The field consists of two main oil reservoirs, the Hutton and basal Jurassic sandstones of the Eromanga Basin sequence. Several of the development wells drilled into these reservoirs exhibited high skin factors which resulted in reduced well productivities. These skin factors were also seen to increase with production from these wells. Core studies on samples from the Hutton and basal Jurassic reservoirs revealed the presence of migrating fines and showed that the fines were predominantly kaolinite clay particles. A formation damage study showed that the initial formation damage, created by drilling and completion operations, acted as a barrier to these mobile fines and resulted in the increasing formation damage. The study concluded that the damage can be removed by the underbalance re-perforation of the particular intervals.

A four well workover program was undertaken at Bodalla South with the aim of the underbalance re-perforation of producing intervals with substantial formation damage. These complex workovers involved dual string tubing-conveyed perforation operations along with appropriate completion techniques. A mixed KCl/NaCl brine containing a clay stabiliser was used and was filtered through a filter cartridge system to remove all particles greater than 10 microns. Compressed nitrogen from standard gas bottles was used along with crude oil to achieve the 1 000 psi underbalance required for the re-perforation of the reservoir intervals.

The workovers were very successful in restoring the productivity of the damaged intervals; in one case, oil production increased from 160 b/d to around 1 600 b/d. This improved production performance has been sustained. The workovers were complex and expensive, costing in total around A$800 000. However, payback was achieved, in one instance, within one month.