Simulations Comparing Different Initial Responses to Kicks Taken During Managed Pressure Drilling

Abstract

Abstract An industry-supported research project to investigate a practical basis for comprehensive well control procedures for managed pressure drilling (MPD) operations is in progress. This paper will describe the results of a simulation-based study comparing alternative initial responses to a range of kick scenarios. The primary responses considered were increasing casing pressure while continuing circulation, increasing the circulating rate without increasing casing pressure, and shutting in the well conventionally. These were investigated using a transient, multi-phase flow simulator. The purpose of the study was to provide a basis for determining the most effective initial response for controlling a kick taken during MPD. The results have helped to identify several important considerations. One important consideration was expected: the ability to minimize casing pressure and therefore the risk of lost returns by continuing to circulate rather than shutting in. There are significant complications if lost returns occur. Loss of returns is difficult to detect in a shut in well if a float is used. With an initial response based on increasing casing pressure until flow out is equal to flow in, it can be difficult to determine whether formation influx has stopped or partial lost returns are offsetting the influx. In cases with narrow margins between pore and fracture pressure, small differences in the drillpipe pressure being held constant during circulation with lost returns can potentially cause results ranging from total lost returns to uncontrolled flow at the surface. The location of the loss zone relative to the kick zone is particularly important in influencing these results. The need for a practical method of identifying lost returns during the initial response is evident, especially when working in a narrow window between formation and fracture pressure gradients. Simulation results are used to exemplify these considerations. A tentative result of this on-going study is that there may be no single best initial response to a kick taken during MPD. The best response may depend on well geometry, kick zone productivity, and likelihood of lost returns. Introduction MPD is an innovative technology that is especially applicable for drilling wells with a narrow margin between pore pressure (PP) and fracture pressure (FP). These wells are difficult to drill with a conventional design that requires high trip and kick margins. Drilling conventionally in a narrow PP-FP window may require more protective casing strings before the target depth is reached and the size of the production casing may have to be compromised. Consequently, the AFE (Authority for Expenditure) of the well may escalate to an extent that drilling may not be commercially viable. The constant bottom hole pressure (CBHP) method of MPD utilizes a pressurized drilling system similar to underbalanced drilling (UBD) with a rotating control head (RCH) and a surface drilling choke to precisely control the wellbore pressure. This style of MPD utilizes mud hydrostatic pressure, annulus frictional pressure and back pressure applied through choke to maintain a constant bottomhole pressure slightly above pore pressure at all times including during pipe connections. Conceptually, the well control procedures for MPD should be similar to those used for conventional drilling. However, industry standard procedures for MPD have not yet been developed, and there are differences in the procedures currently being proposed by MPD practitioners, especially for the initial reaction to an indicated kick. The objective of this research is to define, develop, document and demonstrate procedures for:Initial response to kickIdentifying a threatened underground blowoutControlling routine kickResponding to an underground blowout