Complex Well Control Events Accurately Represented by an Advanced Kick Simulator
Authors: Rezmer-Cooper I.M. , James J. , Fitzgerald P. , Johnson A.B. , Davies D.H. , Frigaard I.A. , Cooper S. , Luo Y. , Bern P. 
Published: December 2007

I.M. Rezmer-Cooper, SPE, and J. James, Anadrill, P. Fitzgerald, Schlumberger Wireline and Testing, A.B. Johnson, SPE, D.H. Davies, SPE, and I.A. Frigaard, Schlumberger Cambridge Research, S. Cooper, Schlumberger Retail Petroleum Services, Y. Luo, SPE, and P. Bern, SPE, BP Exploration.

Abstract
New functionality has been added to an advanced kick simulator to provide a more versatile and robust tool in well planning and well control. New physical models are described that enable the simulator to represent accurately, for a range drilling and formation fluids, the dynamic conditions in slimhole wells, multiple producing zones in highly deviated/horizontal sections, underbalanced drilling, losses to permeable zones, and compliant wellbores.
The slimhole pressure drop model highlights the importance of accurate prediction of the annular flow regime when assessing the effects of high speed pipe rotation. Current industry misconceptions concerning slimhole annular pressure drop are discussed, along with the implications for early kick detection in slimholes.
A new gas migration algorithm, validated for kicks in wells deviated up to 90 is now included. We show that gas can move significantly faster in deviated wells than in an equivalent vertical wellbore, and highlight how the simulator can be used to give improved estimates of surface gas flowrates for worst case kicks for use in mud-gas separator sizing.
The inclusion of models for wellbore compliance, fluid loss and gas suspension characteristics enable a more realistic representation of shut-in pressure. We also discuss the important differences between gas kicks and mixed oil/gas kicks in terms of important well control parameters, such as peak choke pressures, arrival times of gas at surface, and early kick detectors.
Modelling multiple zone influxes and different influx types allows for the versatility required for the dynamic simulation of controlled underbalanced drilling and well control arising from such practices.
The results from the simulation of a field kick in a highly deviated well (that included an extended shut-in phase and fragmented kill procedure) have been used to demonstrate the importance of accurately modelling such non-standard kills, and the consequences of not adhering to standard well control techniques.

Introduction
Drilling environments and the techniques employed to cope with them are becoming increasingly complex. Elaborate tools are also being used to understand the physics involved in these complex scenarios. Practical planning for well control events and related problems (postevent analysis and day-to-day kick tolerance calculations) has been carried out with advanced simulation tools.
These models were initially developed as planning and training tools to improve drilling safety. Such simulators are the results of extensive theoretical and experimental research. The first phase of the simulator described here was developed with the collaboration of the UK Department of Energy (then the UK Health and Safety Executive), and BP International. The second phase, and the focus of this paper, was funded in part by the European Union Thermie programme and BP Exploration. The objective of such tools is to develop a deep understanding of the physical processes that occur when gas enters the wellbore during drilling. Although the primary applications have been in improved safety of operations, the simulator described in [3] has also been used to reduce overall well costs.
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