Micro-Flux Control: The Next Generation in Drilling Process for Ultra-deepwater
Authors: Santos Helio , Leuchtenberg Christian , Shayegi Sara 
Published: October 2008

Drilling wells for oil/gas in ultra-deepwater has been increasingly challenging. The major problem faced in these locations is the very narrow margin between the pore (or collapse) and fracture pressures, which leads to numerous casing strings needed and, in many cases, the wells end up uneconomical. Wells drilled in these scenarios using the conventional drilling method are extremely risky, and in order to overcome these difficulties several initiatives are under way to develop a dual-gradient method, which are extremely expensive.

A new drilling method has been developed to tackle these problems, allowing a much safer operation, reducing the risks, and also permitting the wells to be drilled to TD (Total Depth) much cheaper. Drilling is taken to the limit in a safe manner, extending each phase as much as possible, using the entire available mud weight window for that well. This new method uses much simpler equipment than the mud lift ones, with very quick field implementation.

Previous works1,2 presented this method in detail; this paper will focus specifically on the method's application for deepwater3. The method brings clear benefits to environments with normal to slightly above normal pore pressure. However, in high pore pressure scenarios, it can also bring significant improvement in safety and minimizing downtime compared to the traditional way of drilling wells.

Introduction

More and more the industry has been facing challenges to drill wells in difficult areas. Some of the exploration frontiers that have posed more problems to the drilling industry are deep and ultradeep water (UDW). Conventional drilling has been recognized for some time to be inadequate in being able to reach TD for various prospects. In some cases, due to technical limitations; in others, due to economical reasons. The list of problems faced while drilling in UDW is not small, but the following major ones can summarize them:–Shallow geotechnical hazards, such as water and/or gas flow, and hydrates–Environmental concerns due to well control Situations4–8–Cost and environmental issues relative to loss of circulation9–Wellbore instability9–Narrow margins between pore pressure and fracture gradient9–Drilling downtime associated with limited ability to control and manage Equivalent Circulating Density (ECD) without interruptions10

All the hurdles to drill in UDW with the conventional drilling method led the industry to pursue some alternatives in the last decade11–13. The dual gradient drilling (DGD) has been developed for some time with different concepts being attempted14-18. Low Head Drilling (LHD), Near Balance Drilling (NBD), and even Underbalanced Drilling (UBD) have all being sought as alternatives to improve the economics of UDW prospects. Each has advantages, but, in some cases, the disadvantages of the alternative method are so many that it becomes not feasible to be implemented19–21.

This paper describes the application of a new drilling method that has been recently presented in another paper1 for UDW drilling. The method is based on simple principles and it allows drilling to be taken to the possible limit.