A weighted central difference, on the other hand, uses a constant index step size, e.g. It is different from a weighted central difference in the way that it uses a constant log-cycle window size, L, on both sides of the point of derivation. Image courtesy of Samaneh Moghadam (April, 2020). 2: Illustration of a derivative calculating using the Bourdet method. 2 and is a way to calculate and smooth the derivative based on a log-cycle window size, L.įig. The Bourdet approach is illustrated in Fig. To calculate the Bourdet derivative (Bourdet et al., 1989) at any given point, one point before (left) and one point after (right) is used. The Bourdet derivative is commonly used in well-test analysis (PTA) for identifying flow regimes (Lee et al., 2003) and has similarly found utility in RTA. The Bourdet Derivative (Bourdet et al., 1989).There are three different ways to compute this derivative in whitson +: The logarithmic derivative used in RTA applied directly on the rate normalized pressure (RNP) data is given by, i.e., It is defined as the rate divided by flowing pressure drop.ĭerivatives assists with flow regime identification and can be calculated for both pressure (p), rate normalized pressure (RNP) and pressure normalized rate (PNR).ĭerivative analysis amplifies the reservoir signal, but also amplfies the noise. Pressure normalized rate is very useful for production analysis where flowing pressures and rates change through time. Pressure normalized rate is the inverse of rate normalized pressure. It is defined as the flowing pressure drop divided by rate. Rate Normalized Pressure (RNP) is very useful for production analysis where flowing pressures and rates change through time. The purpose of conducting this analysis is to determine the linear flow parameters (LFP=\(A\sqrt\), every given day to calculate total rates. On the other hand, there is an option to use constant pressure solution by selecting "Real Time" as a function of time as presented here. In the whitson+ classical RTA module, material balance time is the default time function, hence the theory for the constant rate solution is emphasized in this part of the manual.
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