Abstract

The paper describes advanced inter-well pressure interference testing used for 3D model calibration accounting for formation layering and rock compressibility in a mature Siberian waterflood field.

The new interference test is based on pulse-code testing (PCT) and can scan inter-well zones without a longterm production shutdown, normally required for conventional pressure interference testing (PIT).

There are numerous applications of this technique but this paper shows only two of them:

  • Calibration of a geological model with respect to shale breaks by determining effective formation thickness by PCT and then its correlation with a production flow profile determined by Spectral Noise Logging and temperature modelling

  • Determination of rock compressibility distribution throughout a 3D simulation grid by estimating formation compressibility from PCT and correlating it with formation porosity from open-hole logs

The importance of compressibility calibration cannot be overestimated because it defines the formation pressure response to the non-compensated or over-compensated withdrawals across the field and different pay zones.

Conventional PIT can assess formation transmissibility and hydraulic diffusivity between wells. These two properties can be further converted to some basic 3D model inputs, for example effective formation thickness and compressibility, if permeability, SCAL, PVT and formation saturation are known. The main limitation of the conventional PIT is that it requires a receiving well to be shut-in to avoid contamination from production and that the pressure signal should not be contaminated by interference with other wells except the selected pulsing one. This limitation makes conventional PIT impractical for quantitative reservoir characterisation.

PCT generates coded flow-rate pulses in one well and provides a mathematical technique to decode a pressure signal in receiving wells into components from each pulsing well. This allows running PCT in multiple working wells with pre-set rate variation without shutting down production and assessing several inter-well intervals in parallel. A one-month PCT described in this paper resulted in 5% production loss, while conventional PIT would need three months with 60% production loss and a high risk of failure due to pressure contamination from remote processes.

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