Abstract

The changing economics of oilfield development has resulted in operators, and therefore, service companies, being challenged to produce greater quantities of oil at reduced costs. Deeper and more corrosive environments are being produced to increase production capacities, and new technology is being encouraged in the attempt to generate as much "value" from a well as possible. This pursuit and the resulting development of new techniques have been major factors in allowing not only projects that traditionally would not have been viewed as economically feasible to be attempted but also the lives of existing fields in which production has been declining to be extended.

This paper will discuss the specific techniques used to drill and complete several multilateral horizontal wellbores in the Middle East. The discussion will focus on how the latest developments in drilling technology were employed to successfully drill the horizontal wellbores in the subject wells. Additionally, the completion systems used to permit control and access of the multiple wellbores in these wells will be presented. The paper will also review other developments in drilling technology that can facilitate success in applying this technology.

This paper draws upon specific field case histories in the Middle East to demonstrate the techniques discussed and their economic benefits.

Introduction

The multilateral concept is a prime example of innovative technology that has been used to support current economic needs, and operators in the Middle-East have been among the pacesetters in the use of this new concept. In this type of completion, a unique system mechanically connects horizontal laterals to a parent wellbore and allows production from the individual laterals to be commingled or selective. In 1996, it was estimated that over 35 multilaterals of various descriptions were drilled in the Middle-East. Actually, the multilateral well concept is not new, with the first recorded multilateral dating back to 1953 to a field in Russia, but it has only been since the early 1990's that the conceptual techniques have progressed sufficiently for it to be considered as fully developed.

The values of the multilateral concept have always been recognized, but traditionally, the drawback to its use has been the completion techniques available and their capability to allow remedial work to be conducted. To date, approximately 85% of multilaterals have been openhole sidetracks with no liners or completion equipment, but as can be seen in the recent revisiting of this concept, these limitations have been overcome for the most part.

In looking at the financial drivers of a multilateral well, the unproductive (or vertical) part of the well is considered as "cost-driven," while the productive part of the well (the deviated or horizontal sections) would be considered as "value-driven." By definition, therefore, a multilateral well, especially if it is a re-entry, can be considered almost entirely as a "value-driven" process. Thus, the technology and processes that are available must be carefully evaluated to ensure that a multilateral is the correct option for the scenario under evaluation. As with all new and developing technologies, it must also be recognized that in addition to the advantages to be gained, there may be additional technical and economic risks that should be carefully evaluated.

Multilateral technology can be used in a variety of scenarios such as infill field development where available slots are limited, field life extension by accessing newly defined reserves, or deepwater developments. Generally, multilaterals can be broadly divided into two categories:

  1. Re-entries - where an existing well is re-entered, and multiple branches drilled off the existing wellbore.

  2. New developments - where a new well is drilled with the intention of completing as a multilateral of some type.

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