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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fax 01-972-952-9435. AbstractDuring the last decade, wireline tractors have replaced coiled tubing or snubbing for the conveyance of wireline logging and intervention equipment into horizontal or highly deviated wells.Based on this trend towards lighter and more mobile intervention methods, new techniques and equipment have now been developed to enable PowerTrac Advance (PTA*) wireline tractor technology to deploy rotating equipment such as milling, honing and brushing.Wells suffering from scale buildup or seal bore damage have been successfully recovered, leading to considerable cost savings compared to conventional methods.The wireline conveyed rotation technology can be used equally well in vertical pipe sections, as well as in horizontal or highly deviated well bores.There are operational limitations as to what can be achieved and proper job planning is important to assure success.

Completion components integral to well design are selected for their required functionality. These components range from simple profiles used for securing retrievable plugs, to valves of varying complexity and design used during the completion or production phases. Often, remedial work is required to remove these components if they are no longer working or needed when they are a hinderance to well access or its productivity. This paper presents two case histories of completion component milling operations that were efficiently carried out by applying recent developments in combined tractor and mechanical application technologies. Electrohydraulic tractors were developed in the mid-1990s initially as means to convey electric line tools in highly deviated sections of wells. Applications were soon developed to include rotational capability run in conjunction with the tractor, enabling milling of well debris or completion components. For this, the tractor is used not only for payload conveyance, but also to provide weight on bit (WOB) during a milling operation. Recent technology developments are providing an increased level of control, enabling more complex component milling to be carried out efficiently and with greater degree of confidence. Such components, including flapper valves and nipple profiles, are made from a variety of steel alloys, shapes and dimensions. Efficient milling of these requires an optimal bit design, coupled with optimised milling parameters, for example, WOB, torque and RPM. The challenges of milling with limited available power are discussed, new milling solutions are disclosed, and the importance of real time feedback of milling parameters to ensure success are illustrated. This paper discusses new electronic and hydraulic developments applied to the tractor-milling platform. Case histories will demonstrate the hi-fidelity measurement, independent control and optimisation of all relevant milling parameters adjusted on the fly, delivering performance across all stages of the milling operation. They will show the high level of instrumentation now available which ensures the milling operation is conducted within prescribed and tested limits and allow performance parameters, designed and demonstrated in the lab, to be replicated one-to-one in the downhole environment. Improvements also include specific bit designs that have been developed though a rigorous testing program to minimise tool jamming and the metal debris created during the milling process, which could inadvertently cause other issues in the well. The technology enables switching between the tractors driven and rolling rotational anchor functionality whilst providing continual rotation and back-reaming capability to minimise the possibility of a stuck tool scenario. The case histories show that these developments have delivered unprecedented success in challenging cased hole milling operations.

Until recently, electric line tractor driving speeds have been lying significantly below their true potential, because of elements related to design, working principles and system dynamics. Several case histories from recent electric line tractor conveyance operations illustrate the number of operational benefits that have resulted from an engineering re-design, through applying the latest electronic and hydraulic technologies to electric tractor conveyance. Electrohydraulic tractors were developed in the mid 1990s as an alternative means to convey electric line deployed tools along the highly deviated or horizontal sections of wells. The application of this tractor technology has grown considerably over the years, having been applied to convey an increasing range of technology payloads (for example, logging tools, ballistic devices and powered mechanical applications) to an expanding stock of deviated wells with increasing length and tortuosity. The performance and capability of electric line tractor tools has always been a trade-off between numerous limiting factors including the electric line cable (strength, weight, length, voltage and current rating), the surface power supply, the tractor components (downhole motor power and drive train efficiency), and the completion size into which it is deployed. This has until now necessitated tractor pre-set requirements to successfully perform a job, resulting in limitations on performance criteria such as tractor pull force and speed. This paper discusses recent improvements to the tractor platform achieved through redesign and by applying new electronic and hydraulic developments which enable in-well, on-the-fly optimisation of the tractor components and parameters. The field operations demonstrate the transformation in tractor conveyance speeds achieved, in the order of three and a half times that previously delivered, representing a new standard in electric line tractor conveyance efficiency. These speeds, coupled with increased payload conveyance capability and the improved mission certainty which can be achieved, are even more relevant in wells of significant measured depth, lateral length and challenging well profiles and trajectory complexity. The technology presented will also allow well completion engineers to plan complex well intervention jobs in demanding wells with more confidence now that it is available to increase operational success.