Field Use Of Full Opening Cementers
Authors: Fritzel M.J. , Baker E.E. 
Published: December 2007

Abstract
Multiple-stage cementing of long casing strings and weak formations in the past has been at the mercy of the one-shot plug system.
With the introduction of the full opening (FO) cementer to the field in 1971, it is possible now to cement multiple stages or weak formations whenever necessary without interfering with normal drilling operations.
The FO cementer is placed in the casing string at the desired depth, and after completion of a normal bottom cement job, the FO cementer can be operated at another time by a set of opening and closing sleeve positioners that are run in conjunction with an RTTS positioners that are run in conjunction with an RTTS packer or an isolation packer for positive fluid packer or an isolation packer for positive fluid displacement and pipe pack-off.
The FO cementer can be used for operations other than cementing providing it is located in uncemented casing and enough weight is available to operate the FO cementer. The weight required for opening and closing the FO cementer varies with the different casing sizes. It is recommended that at least 20,000 lb of pull be available for opening and 10,000 lb of weight be available for closing 7-in. and larger FO cementers, with 10,000-lb pull and 5,000-lb force available to operate the 4 1/2-in. to 5 1/2-in. FO cementers.
The FO cementers have taken the guesswork out of multiple-stage cement jobs and they have made it much easier to recover casing from an unproductive well.

Introduction
The problems that are encountered when designing casing programs are not based entirely on well depth and hole size. Often times the casing programs are designed around low-pressure zones, weak formations, and the availability of floating equipment that can be used effectively to aid in overcoming these problems. problems. The standard of the oil industry has been the multiple-stage cementer(s) that can be placed in the casing string above or below a weak zone(s). The multiple-stage cementers are operated with either the displacement type or the freefall-type plug sets. Normally only one multiple-stage cementer is run, thus enabling a two-stage cement job to be performed; however, if a three-stage job is needed, then two multiple-stage cementers can be run.
Although the multiple-stage cementers will continue to be a needed and a valuable part of the casing program, they do have disadvantages, one being that, once incorporated in the casing string, they have to be operated prior to any further drilling. The other is that, once they have been used, the plugs and the working internal portion have to drilled out.
This paper discusses the full opening cementer (the FO cementer) that can be used in place of or in conjunction with the multiple-stage cementer. It also discusses an addition to the FO cementer called the FO packer collar.
In the early stages of development of the Prudhoe Bay Field, it was discovered that in order Prudhoe Bay Field, it was discovered that in order to keep the casing from collapsing through the permafrost region, it was necessary to limit the permafrost region, it was necessary to limit the number of casings to cement annuli. This was accomplished by running a 20-in. conductor to approximately 100 ft, cementing it to the surface with the proper cement slurry and then setting a string of 13-3/8-in. casing through and to approximately 500 ft below the permafrost and cementing it to surface (Fig. 1). The 9-5/8-in. casing then is run to either T.D., or to a point where a liner could be set to T.D.
In order to limit the number of casing to cement annulus, it was necessary to place a nonfreezing fluid between the 13-3/8- and 9-5/8-in. casing. This was accomplished by incorporating two multiple-stage cementers in the 9-5/8-in. casing string. The bottom multiple-stage cementer was placed near the shoe of the 13-3/8-in., and the top multiple-stage cementer was placed at the base of the permafrost.