Abstract

Through close co-operation between Statoil MWS and Welltec, a working Well Tractor has been successfully introduced into operation in the North Sea.

The Well Tractor technology has been extensively field proven and has demonstrated significant cost savings for operating companies when compared to previous methods of performing well intervention operations in horizontal wells. In some cases, use of the Well Tractor technology can mean the difference between whether or not required well intervention operations can be carried out.

Careful prejob planning is necessary to ensure success, since the Well Tractor technology adds a new dimension to the techniques required in normal wireline logging and well intervention.

Introduction

Drilling and completing horizontal, ERD and Designer wells are common operations world wide. These types of well will play a major role in the coming decades along with multilateral horizontal wells.

It is possible to drill and complete such wells with little greater difficulty than conventional wells. However, intervention in these types of well and in particular live well intervention, presents far more of a challenge. Until recently coiled tubing or snubbing has been the only option.

Coiled tubing and snubbing interventions are costly, logistically complex due to the number of people and amount of equipment involved, and require a fairly long operational time window. The logistical problems, especially for coiled tubing work, are often enough to prevent the operation taking place; for example on ERD type wells as the required coiled tubing reel weight often exceeds the platform crane capacity.

Cost analyses performed in Statoil have revealed considerable savings when utilising wireline tractors for electric line type operations versus coiled tubing for the same type of operation.

Further, it is expected that the market for production logging in ERD- and horizontal wells will increase due to the reduced intervention cost and simplified logistics when utilising well tractors as the method of conveyance versus coiled tubing or snubbing.

The idea of using a down hole tractor for pulling wireline into highly deviated or horizontal wells is not new. However most concepts have not left the drawing board or reached the prototype stage.

In 1996 the first offshore testing world wide of wireline driven downhole tractors took place through the combined efforts of Statoil Maritime Well Service (MWS) and Welltec.

Well TractorR Description

The Well Tractor system is designed to be run with standard wireline equipment and tools available in the field. The Well Tractor tool is the size, shape (3 1/8" OD, 21' long) and weight of an average-sized logging tool and can be transported in the same manner as normal logging tools.

The system comprises five main sections (Fig. 1): surface communications and motor control panels, downhole electronics section, hydraulic section, drive sections and hydraulic compensator.

The surface communications and motor control panels are used to communicate with the tractor, to change from logging mode to tractor mode and to power the Well Tractor in tractor mode. Displays show electrical current consumption and the surface voltage.

The downhole electronics section can be switched between either tractor mode or logging mode. The signal which controls this is transmitted from the control panel on the surface. P. 95

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