The Lateral Entry Guidance System technology is an intelligent method of navigating through the junctions of a multilateral well using Coiled Tubing.
The technology works equally well in cased and open-hole junctions without the need of sophisticated and expensive selective entry jewellery. The tool is slender enough to pass through production tubing and most completion restrictions and functions in all typical casing/liner diameters.
As LEGS technology itself has been presented in different forums before, the sole purpose of this paper is to present the particular conditions encountered in the Western Kazakhstan oilfields and methods used to make this technology work at depths over 5000 m.
The reasons behind the unsuccessful attempt to stimulate one well followed by a very successful stimulation of another well using LEGS bottom hole assembly will be showcased.
The result was a verification of a well design and operating philosophy against the alternative techniques of completion based selective entry. The outcome was the best producing well of the Karachaganak oilfield to date.
The paper will help potential users understand the challenges they may encounter and eventually, determine them to tailor their field development strategy in order to eliminate these problems and facilitate the use of LEGS.
LEGS technology has been used in different oilfields in Canada, USA and Venezuela for the last few years.
It only started to be used in Kazakhstan at the end of 2005.
Since then, two LEGS jobs were performed in Karachaganak oilfield, in the Western part of the country. The Karachaganak field is a large carbonate reservoir and field experience has lead to acid washing of the production interval to give optimum results.
The first well presented a series of challenges that led to an initial attempt that did not gain lateral entry. The challenges are presented here. Many lessons were learnt and were applied when the second well was stimulated, resulting in the best producing well in the field.
More and more oil companies use the multi-lateral type wells to increase the contact area of the hole with the producing formation, thus increasing production.
However, the gain in hydrocarbon recovery cost is often offset by the cost of re-entering the laterals for cleaning, stimulations, data acquisition etc.
In cased holes, special re-entry completion components can be installed but they are technically challenging and expensive.
Furthermore, these special junctions cannot be installed in open hole multi-laterals ¹.
The obvious need for an affordable way of accessing the laterals in a multi-lateral well led to the development of the LEGS technology.
LEGS BHA is conveyed in the well using coiled tubing. Once the BHA is placed at the junction between the main bore and the lateral, it relies on the pressure supplied through coiled tubing to independently search for the lateral window.
When the lateral is found, a pressure signal is transmited to surface and the operator is prompted to run the coiled tubing in the lateral.
Tagging the toe of the lateral is the ultimate confirmation of the successful entry and the treatment of the lateral begins.
A basic understanding of the way the tool works is necessary, in order to better understand the material presented in this paper.
LEGS BHA ¹ comprises three main sections (see Fig. 1):
Control Section (or Valving) - is the upper section and it controls the sequence of events in the tool. One of the valves in this section is a detent type valve and it puts the tool in one of the two possible modes. When the detent valve is closed, which is its normal position, the tool is in navigating or "search" mode.