Abstract

As cased hole multilateral oil and gas wells gain favor in the oil industry, the early methods of creating windows by milling in-situ are being replaced by the use of pre-milled window joints inserted into the casing program. The major benefit of these pre-milled windows is the fast and easy drill-out to create the lateral branch, lateral re-entry because of the difficulties of milling a window with precisely controlled and predetermined geometry and the easing of the debris management.1 However there are certain shortcomings, such as the higher costs and the increased risks associated with premilled systems placed at high angles (more than 60 degrees), the danger of applying excess torque to the casing string to correctly orient the window and the frequent surveys required to verify that orientation.

As the use of pre-milled windows increases in popularity, so the industry is striving to make improvements in the technology in order to address these shortcomings and create a safer, more economic and reliable system. This paper will discuss the development of a guidance system that utilizes natural gravity to self orient a pre-milled window in order to overcome some of these shortcomings. This simple but novel counter weighted cross section tool, placed in close proximity to the pre-milled window is designed to:

  • Eliminate the need to rotate the casing to orient the window and avoid the danger of excess torque.

  • Accurately orient the window to the high side within acceptable limits.

  • Negate the need to make repeated surveys as the casing is installed.

This paper will detail the basic design of this patent pending guidance component, discuss its first commercial application and analyze the results achieved. It will conclude that, though further refinement is needed, this device can be a viable alternative to the window orientation methods currently in use.

Introduction

Multilateral oil and gas wells have been in existence in some form for over 40 years. Only in the last ten years or so, with the advances in horizontal drilling and completion systems has their full potential been more fully recognized. It has been well documented that Multilateral technology can have a dramatic impact on reservoir development economics in several ways:

  • Increasing the net present value of reserves.

  • Minimizing surface "footprint" of field operations while lowering development costs.

  • Maximizing the productivity per well slot while reducing the size and cost of platforms in offshore applications.

  • Reducing total footage drilled per foot of zone exposed, thereby reducing drilling time and expense. 2

This technology is generally believed to offer the maximum reservoir exposure to the well-bore at minimum cost per foot. For these reasons multilateral systems are expected to undergo continual and significant technical advances and to become increasingly popular over the coming decade. One of the major advances that must be made in the technology of pre-milled windows involves the methods used to properly orient the window outlet with respect to the high side of the well-bore during casing installation, in order to facilitate ease of access to the selected lateral.

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