Detectable Radius of Investigation for One Flow Period with Bourdet Derivative

A new definition of the radius of investigation (ROI) is proposed to overcome the ambiguity present in the results from conventional ROI quantification methods. The term ROI is commonly used to quantify the minimum reservoir size or the distance to a potential boundary evaluated through pressure transient testing. However, the various methods available in the literature to quantify ROI often provide different answers stemming from varying assumptions and thus often lead to confusion in terms of the appropriate definition to choose. Although the ROI method developed by Van Poolen is well recognized in the industry, there is still debate about its general applicability because it is limited to a constant-rate flow period and is insensitive to flow rate, flow sequence, gauge resolution, and measurement noise level. This contrasts with operational experience, where a higher flow rate, higher gauge precision, and lower level of measurement noise lead to higher quality pressure transient testing data from which reservoir boundaries, or other features, can be identified farther away from the wellbore. In other words, higher flow rates, better gauges, and lower noise levels can lead to a larger achievable ROI. We propose a new definition of ROI, which is the detectable ROI for each drawdown or buildup flow period. The detectable ROI is derived from the actual pressure derivative response and not from a generic model assumption. By defining a derivative noise envelope, the new method clearly identifies the time when the derivative deviates from an unbounded model due to the presence of a boundary and thus provides an estimate of the detectable ROI for the analyzed period. This method overcomes the limitations of most conventional methods and provides ROI predictions that depend on flow rate and gauge noise while maintaining a consistent result with the current pressure transient interpretation. While detectable ROI is applicable for general drawdown/buildup pressure transient tests, the concept was developed with deep transient testing (DTT) in mind.