This paper introduces the statistical method for diagnosing flow regimes for flowing and shut-in conditions. The method utilise the second differencing of pressure change and time that are stationary; then integrate the residual pressure differences using simple statistical tools such as sum of square error SSE, moving average MA and covariance of data to formulate the statistical derivative models. These models are tested with constant pressure, constant rate conditions and in well with high water production. Results from three scenarios investigated demonstrated that the statistical derivatives yielded much clearer reservoir radial flow regimes as the conventional pressure derivatives without data smoothing; therefore give more confident formation permeability estimation. It demonstrated that for high water production well, a good radial stabilisation can be identified. It also showed that in all three scenarios, the drawdown radial fingerprint can be replicated in the build-up pressure responses, hence a good match of the data.

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