Layer Pulse Testing Using The Repeat Formation Tester
Authors: Saeedi J. 
Published: March 2010

A conventional pulse test provides estimates of average transmissibility and storage capacity between the pulsed and the observation wells. In a layered reservoir the pressure waves, instigated by pulsating the active well, travel at different velocities in individual layers. These velocities are functionsof layer transmissibilities and storage capacities. The measurement and recording of these complete pressure waves at the observation well will require pressure sensors lodged, in individual layers, behind the casing. This is not practical with current technology.

This measurement dilemma can be resolved if the observation well is newly drilled and still un cased. Instead of measuring the complete pressure wave for every layer, a sequence of discrete pressure points can be recorded for these layers, at known times, using a Repeat Formation Tester.

The Repeat Formation Tester (RFT) measures point pressures generally in an open-hole behind the mud-cake. A base RFT survey is done in the observation well prior toinitiating a pressure wave in the pulsed (active) well. After this time a rate change is implemented at the active well. Subsequently, at pre-designed time intervals one or more RFT surveys are done at the observation well. These discrete data from base and subsequent RFT surveys, together with the measured flow or injection profile in the pulsed well, are then amenable to conventional analytical interpretation for estimating layer permeabilities in non-communicating layers. If the layers are communicating, a numerical interpretation ethod is available based on vertical pressure profiles. The RFT data is plotted as vertical pressure profiles at different times. The differences between the base and subsequent RFT pressure profiles are history-matched using a three-dimensional numerical reservoir simulator. The history-match provides an estimate of layer horizontal and vertical permeabilities between the pulsed and observation wells.

This paper describes the measurement and the analysis methodology of a layer pulse test. The numerical simulator, necessary to analyze a layer pulse test in communicating layers, is validated using analytical methods. The description also includes the successful application of this technique in a pinnacle reef having communicating layers.

Introduction

Reservoir permeabilities over a scale which spans interwell distances, govern the performance of the reservoir in that interwell area. Single well pressure transient tests, if conducted long enough, help determine permeabilities over large scales but the permeabilities are not directional in nature. Conventional pulse and interference tests do give directional permeabilities in the interwell area but are limited to a single permeability in anyone direction. A layer pulse test which consists of suitable measurements in both the observation and pulsed wells together with simple but elegant interpretation techniques helps in estimating directional interwell permeabilities at different depths based on the lithological layering of the interwell area.

This paper will propose measurement and interpretation methodology for estimation of layer permeabilities in communicating and non-communicating layers. The utilization of the RFT ™ (1) Service in openhole in the observation well andproduction or injection logging(2) in the pulsed well are an integral part of this testing scheme.