Make Decision on the Fly: A New Method to Interpret Pressure-Time Data during Fracturing – Application to Frac Pack

摘要

Real time analysis of fracturing data is an invaluable tool for determining whether a fracturing job is progressing as planned. Therefore since the early days, understanding of fracturing pressure as a readily available diagnostic tool has been emphasized and practiced by the industry. Theories and techniques were developed for the interpretation of such data e.g. Nolte-Smith (1981). The well-known Nolte-Smith method (1981) analyzes the pressure response of a formation during pumping, in order to predict the fracture geometry being created. Although this technique provides a highly reliable tool in terms of interpreting fracturing events, but in real time practices, it can take this technique quite a long time to detect a change in fracture behavior. This is partly due to the data compression associated with the Nolte-Smith log-log plot. Also Nolte-Smith technique necessitates prior knowledge of closure pressure of the formation which is not always known. In this paper, we present a new method to analyze and interpret pressure-time data during fracturing. This method, which is based on a modification of Nolte-Smith technique, has proven effective in precisely interpreting fracturing behavior while the job is being carried out. Additionally it eliminates the short-comings of the original technique, as discussed above; meaning that the proposed method permits quick and accurate interpretation of fracturing data plus it needs no prior knowledge of formation in-situ stresses. This has been reached by a new innovative moving-reference-point concept assembled with a mathematical manipulation of the power-law fracture propagation theory. Application of the new technique in the analysis of a variety of field cases including several frac packs and regular fracturing treatments has proven quite successful. First accurate pressure-time matches were obtained and then using these matches, the Nolte-Smith parameters were determined which in part allowed detection of fracture behavior changes (e.g. propagation to width-gain) usually in less than a minute and sometimes even in a few seconds of the start of the event.