Determining Durations of Transient, Transition, and Boundary-dominated Flow Regimes for Rectangular-Shaped Drainage Areas

Abstract

The primary objective of this work is to investigate the times at the end of transient flow period and the start of boundary dominated flow using Bourdet pressure derivative for various combinations of well types and reservoir geometries and compare them with existing definitions of the radius and depth on investigation for constant rate production and constant pressure production cases. Empirical methods are applied on synthetic production data obtained from numerical simulator to estimate these times. The scope of this work includes vertical wells and horizontal wells with vertical fractures in various rectangular shaped drainage areas. This work also presents analytically derived shape factors which are used in pseudo steady state equation for horizontal wells with vertical fractures in rectangular-shaped drainage areas. Shape factors previously presented by other authors were used to validate the method and apply it to some new drainage area configurations. To account for noisy production data which leads to uninterpretable pressure derivatives, an outlier’s detection method i.e. Angle Based Outlier Detection (or ABOD) has been evaluated. Although this method was proposed by Kriegel et al. (2008) for outliers’ detection in high-dimensional data, it has been found to be equally useful in our case of two-dimensional production data. This method has the advantage of having no user-defined parameters i.e. it is unaffected by the personal bias and it provides justification for objective identification and removal of outliers from production data based on divergence of angles that a point makes with other surrounding points in the data. Synthetic production data with random addition of gaussian noise is used to evaluate this method based on mean absolute error (MAE) and true negative, true positive, false positive and false negative responses.