THE DETECTION AND SIGNIFICANCE OF FRACTURES IN THE PALM VALLEY GAS FIELD

Abstract

The Palm Valley Gas Field was discovered in March 1965 when the Palm Valley 1 well flowed up to 11.7 million cubic feet of gas/day from Ordovician sandstones and carbonates. Since then, a further five wells have been drilled, with a wide variation in gas flow rate, from less than one million, to over 130 million cubic feet/day.

Matrix porosities and permeabilities are generally very poor to poor; however, cores, log analysis, and interference tests confirm the presence of an extensive fracture network providing the main permeability conduit for gas production.

Recent drilling (Palm Valley 4, 5 and 6) has enabled a comprehensive suite of modern wire-line logs to be run with the specific aim of identifying the location and orientation of fractures. From analysis of the resultant data, it can be demonstrated that both fracture direction and concentration vary significantly from well to well, giving rise to corresponding differences in productivity. Fracture occurrence also varies from fractured zones that parallel bedding planes and may be correlatable from one well to another, to vertical or semi-vertical fractures that intersect the borehole diagonally.

High well productivity can be correlated with greater fracture density, which in the Palm Valley Field has so far been proven to occur along the axis of the anticline, as well as with the intersection of major fractured 'zones' displaying a dominant fracture orientation sub-parallel to parallel to that of the principal residual stress.