HAZOP of Well Control Procedures Provides Assurance of the Safety of the SubSea MudLift Drilling System
Authors: Schubert J.J. , Juvkam-Wold H.C. , Weddle C.E. 
Published: December 2007

To meet the challenges of drilling in intermediate to ultra-deep waters (depth greater than 5000'), a drilling technique referred to as dual gradient drilling, DGD, is being developed and tested by four industry projects. These projects are being conducted by the SubSea MudLift Drilling (SMD) JIP, the DeepVision JIP, Shell Oil Company, and Maurer Technology. The first three achieve dual gradient by placing pumps at or near the seafloor to lift the drilling fluid and cuttings from the well annulus to the surface via a return line. The fourth project proposes the injection of hollow glass spheres into the riser near the mudline.

All four DGD projects must address well control issues affected by the dual pressure gradient imposed by the drilling fluid, the possible u-tube that is associated with the dual gradient systems, and the equipment that is being designed for each individual project. Very early in the SMD JIP well control techniques for dual gradient drilling were identified as a key success factor in the project. The members of the SMD JIP Well Control Team were given the task to study the current state of the art in floating drilling well control, determine which procedures need to be modified for SMD, and make such modifications. The goal of the team was to develop a well control program that was at least as safe, if not safer, than the current practices.

One tool that was utilized to assure that the Well Control Team met it goal was the Hazard and Operability Analysis, HAZOP. Here we describe the HAZOP process in application and how it was utilized to provide assurance that the well control procedures written by the team members are as safe or safer than the current state of the art in floating drilling well control.

Introduction

Risk Analysis can be performed by utilizing one or more of the several risk assessment tools that have been developed1. These techniques range from the very simple to the elaborate. Some of the techniques that could be applicable to the SMD JIP will be briefly discussed below.

Change analysis looks risks effects and risk management strategies for changing situations. Changes can be in equipment utilized, system layout, operational procedures or different activities are performed. This can be used in any situation in which the "normal" procedure or setup is not utilized or has been modified1. For the SMD system, a change analysis could have been used when comparing the Driller's method of well control (assuming it is considered the base case for well kill in deepwater) to the Wait and Weight method.

A What-if analysis is most often used when more precise methods (e. g. FMEA or HAZOP) are not practical. It is a loosely structured problem solving approach. 1 This approach attempts to provide answers to questions such as "what if the MLP stops working in a kill situation". From these questions and answers possible solutions can be identified. In the case of the well control procedures, a What-if approach was utilized in conjunction with the HAZOP to identify possible hazards.

Failure Modes and Effects, FMEA analysis is used in risk assessment in equipment design. In an FMEA the questions asked are what can fail, and what are the effects of the failure on the rest of the system. 1

Fault Tree Analysis is a graphical technique which compares and links the relationships between equipment failure, human error, and external events can combine to cause hazards to occur. Probabilities and frequencies are often added to quantify risks. 1It is very often used in analyzing complex systems.