Effective detrending methodology for harmonic transient pressure response

Harmonic Pulse Testing (HPT) is an unconventional well testing methodology in which the injection or production rate is varied in a periodic way following, in common practice, a square pulsing scheme. HPT was developed with the aim of characterizing and monitoring well performance and reservoir behavior without interrupting ongoing field production activities and without resorting to dedicated well testing surface equipment. Interpretation of HPT requires pressure response and associated rate history to be analyzed in the frequency domain through the application of Fourier transform. However, detrending of pressure pulsing data is necessary because signal decomposition into multiple frequency components is affected by the upward trend of the first transient and possibly by other phenomena associated to reservoir operation. In this paper a detrending methodology is considered as an algorithm aimed at isolating the pure periodic component of a pressure signal generated by harmonic rate history, from any other effect. An interesting heuristic algorithm for pressure data detrending was proposed by Ahn and Horne in 2011 but it’s reliable application is limited to particular cases associated to simple production/injection schemes. Based on Ahn and Horne’s previous work, a new heuristic algorithm is proposed by the author with the goal of overcoming the limitation of the previous one.