Multiphase Flow and Drilling Fluid Filtrate Effects on the Onset of Production

Abstract

Abstract Formation damage from the drilling process must be overcome to initiate production in wells that are neither cased nor perforated. The drawdown to initiate production can be limited by low reservoir pressure, sanding potential and water coning concerns. In these cases the required drawdown to initiate flow becomes important. Published results of laboratory experiments indicate that the flow initiation pressure (FIP) increases significantly when the permeability of the producing formation is below 50mD and that it is lower for oil based drilling fluids than water based fluids1. This study presents possible explanations. The dependence of FIP on formation permeability and drilling fluid type was evaluated both experimentally (using small cores) and theoretically. The results suggest that the relatively large FIP in low permeability cores could be a consequence of conditions influencing multiphase fluid in the experiment, e.g., core length, or whether or not the experiments were run under constant flow or constant pressure-drop conditions. Under such circumstance, the onset of production in a well may not have the same dependence on formation permeability as does the laboratory measured FIP. In addition, at least some of the drilling fluid filtrate must be removed before any of the oil can be produced. When the filtrate is aqueous, capillary forces are present. The importance of these forces could explain why the FIP is higher for water- than oil-based drilling fluids. Both experimental and theoretical results are presented consistent with this explanation.