Detectable Radius of Investigation for One Flow Period with Bourdet Derivative

Abstract

Abstract 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 that exist in the literature to quantify ROI 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 a debate about its general applicability because it is limited to a constant-rate flow period and is insensitive to flowrate and flow sequence, to gauge resolution or measurement noise level. This contrasts with operational experience, where a higher flowrate, higher gauge precision, and a lower level of measurement noise generates 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 flowrates, better gauges, and lower noise levels can lead to larger achievable ROI. We propose a new definition of ROI, that is the detectable ROI for each drawdown or build-up flow period and 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 flowrate and gauge noise while maintaining a consistent result with current pressure transient interpretation.