Abstract

Liner movement results in substantial improvements in cementing performance, principally by assisting mud displacement efficiencies. Rotation is more effective and safer than reciprocation. A number of plain (Astro) and taper roller bearings from different manufacturers were tested in a laboratory program. None of the bearings tested satisfied the original performance target of 24 hours life at a bearing load of 112,000 lbs and speed of rotation of 25 RPM. Taper roller bearings were found to give better performance than Astro bearings. One design of performance than Astro bearings. One design of taper roller bearing performed sufficiently well to satisfy most cementing jobs and would be selected for future use. It was thought, however, that all the bearings tested could be improved by better sealing and structural design. Documented field applications of liner rotation are discussed and found to be consistent with the test results in general.

Introduction

A liner is a casing string that does not reach the surface. It is hung on the previous casing string using a liner hanger device incorporating mechanically or hydraulically activated slips. Discussion of the various tools associated with a liner is beyond the scope of this paper, but this information is readily available from manufacturers. The liner is usually cemented from shoe to the top of the liner hanger. This is done to ensure zonal isolation and to provide a seal at the top and bottom of the liner provide a seal at the top and bottom of the liner and between the liner and the open hole.

In North Sea operations, the most common liner size is 7" and it is hung on the previous 9 5/8" casing string. The hole size drilled through the 9 5/8" casing is usually 8.5 inch. The annular clearance between the 7" liner and the 8.5" hole is 1.5 inch, giving a maximum standoff of 0.75" on each side of the 7" liner. Because of this small clearance, various methods are used to enhance mud displacement to ensure no mud channels or filter cake is left behind when the cement slurry is placed behind the liner. Mechanical aids such as placed behind the liner. Mechanical aids such as scratchers are also used to remove the filter cake, however their use is usually limited to the production zones and surrounding aquifers. production zones and surrounding aquifers. If a liner is not centralised or is lying on the low side of the hole then during cementing the cement slurry will seek a path of least resistance leaving mud channels behind. When the cement is set, these mud channels act as communication paths between adjacent water and hydrocarbon zones and between these zones and the top of the liner. To prevent these problems and to obtain a near 100% prevent these problems and to obtain a near 100% mud displacement the liner may be rotated or reciprocated. The need for these aids increases as hole angle increases. Reciprocation is easier and cheaper but may cause the liner to get stuck or cause lost circulation in weak zones due to the increased surge pressures caused by pipe movement. Also the liner can only be reciprocated as long as the liner setting tool is still attached to the liner. If the operator prefers to set the liner prior to cementing, then reciprocation is not prior to cementing, then reciprocation is not possible while pumping the cement slurry and possible while pumping the cement slurry and consequently mud displacement efficiency may be poor. poor. This paper will concentrate on one method of enhancing mud displacement; liner rotation using rotating liner hangers.

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