Abstract

Shell is a major player in the Global deployment of Managed Pressure Drilling (MPD) technology to reduce drilling prob-lems, minimize formation damage and improve reservoir management techniques.

The impetus is a recognition that most of the world's mature hydrocarbon reservoirs are in the lower end of the depletion cycle and an increasing number of horizontal wells are left with un-cemented completions. In addition, to access new untapped reserves, requires venturing into deeper water depths and the exploitation of deeper tight gas reservoirs, each with its own challenges.

This paper describes the process involving rigorous pre-screening, planning, execution and feedback of learning de-veloped that enables fast implementation of underbalanced drilling (UBD) and integrated technologies into "Brown Field" areas and new business opportunities in "Green Field" devel-opment.

This begs the question; what is Managed Pressure Drilling technology and what is the relationship with underbalanced drilling?

The International Association of Drilling Contractors (IADC) defines Managed Pressure Drilling as "an adaptive drilling process used to precisely control the annular pressure profile throughout the well bore. The objectives are to establish the down-hole pressure environment limits and to manage the annular hydraulic pressure profile accordingly".

In a sense managed pressure drilling, covers all drilling, since management of pressure is the goal of all drilling activities. However, there is general industry agreement that Managed Pressure Drilling is an umbrella term that refers to drilling activities conducted in a closed loop system. Conventional overbalanced drilling sits at one end of the Managed Pressure Drilling spectrum and underbalanced drilling at the other end.

In conventional drilling, bottom hole pressure is managed by controlling the density of the drilling fluid to maintain well bore pressure profile above the pore-pressure throughout the well bore. Underbalanced drilling on the other hand, the well bore pressure profile is intentionally kept below the pore-pressure of all the exposed formations in the well bore. In be-tween these two extremes are various techniques used to con-trol the annular pressure profile and overcome constraints im-posed as a result of the equivalent circulating density of the mud system. Seen from Shell's perspective, Managed Pressure Drilling is a basket of drilling techniques that can be adapted to solve drilling related problems, reduce formation damage and or dynamically characterize production reservoirs (while drilling) to enable improved reservoir management. It is also worthy to note that not all Managed Pressure Drilling tech-niques require a closed loop system.

Introduction

Shell has deployed underbalanced drilling in oil and gas reser-voirs since the early 1990's. The introduction of horizontal drilling in the reservoir in the 1980's resulted in many new challenges. It created the need for a different approach to en-able drilling in depleted and fractured reservoirs. Shell initi-ated underbalanced drilling operations with foam1 in 1992 and in 1993 and 1994 the company conducted trials using multi-phase drilling fluids and the closed loop 4-phase separation system. In 1995, Shell successfully drilled the first horizontal underbalanced well using coiled tubing in Canada2. In 1997, Shell introduced underbalanced drilling in the offshore envi-ronment3. In the late 1990's, our Research and Development staff also developed and introduced expandable tubulars to the industry. A global approach to deploy these technologies was initiated in year 2000, when underbalanced drilling and ex-pandable tubulars were launched as two of four key technolo-gies (the others being 4D Seismic and Smart Wells) to be taken up within the Shell Group. Early on, the synergy be-tween underbalanced drilling and expandables was recognised as was the synergy between these two technologies and swel-lable elastomers and research and development work in these areas was supported.

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