Abstract

A study is made of the effectiveness of some of the wellsite and "quick-look" applicatons of wireline formation testing tools, with emphasis on "quick-look" permeability indicators in clastic formations.

Approximate values of the "in situ" formation permeability can be calculated from wireline formation tester information. The methods proposed are to (a) analyse the pressure build-up curve (as the primary method) and (b) average the two permeability values obtained from the pressure draw-down analyses of the two pre-tests (as the secondary method). The objective is to sample a representative cross-section of the sands in the reservoir unit, and to project the permeability data derived to cover the entire reservoir.

It may be more critical to obtain an estimate of permeability deeper into the reservoir, away from the formation which has possibly been altered by the drilling process. For this purpose, it can be better to use the pressure build-up data from the wireline formation tester. Whereas this technique makes more attempt to indicate the virgin formation permeability, it is, perhaps, the harder of the two techniques to rigorously apply. It is often difficult to locate the relevant section of the build-up curve to analyse.

A case study shows examples of the effectiveness, as well as the limitations and inaccuracies, of techniques for wellsite or "quicklook" estimates of these analyses of wireline formation tester information to determine "in situ" formation permeability.

In spite of the obvious limitations on permeability determinations described, this application is seen as a useful supplement to some of the powerful roles of the tool, such as: establishing formation pressures, pressure gradients and fluid contact determination; formation sampling; reservoir depletion monitoring.

A useful application of the technique is envisaged as a wellsite or "quick-look" "net pay" indicator. It is often essential to try to estimate semi-quantitatively the effective permeability throughout the reservoir towards the end of the drilling process.