Statistics of cementing highly deviated wells in the Niger Delta (50 deg or more) show that only about 33% are successful and do not require an elaborate squeeze cementing operation. Two out of every six wells drilled in the past had good primary cement bond logs less than an average of 15mv.
The remedial squeeze operations are expensive requiring such operations as perforation of casing which often times reduces the intergrity of this pressure vessels, putting the existing bond at risk and finally the drill out testing of the squeezed casinf intervals. This entire remedial operation is non-productive rig time resulting in increased well cost.
Analysis has traced this poor primary casing cementation history to a number of deficiences (1) Improperly designed cement recipes (2) Poor hole geometry (3) Bad cementing or placement techniques (4) poor casing string centralisation resulting in channelling.
The effect of each of this factor is amplified due to the fact that the Niger delta is characterised by sand /shale sequence which contributes to hole washouts or even caving resulting in hole sizes that are much larger than the bit size.
In the Niger delta, poor casing centralization contributes over 50% of the poor primary cement job. Even good cement recipes and good cementing practices are jeopardised by flow pattern resulting from poor casing centralization.
Operator experience had indicated that the use of conventional spring / rigid type centralizers for casing centralisation in the Niger Delta had not been successful in correcting this deficiency in highly deviated wells.
A new centralizing package has been introduced and successfully used in the cementing of horizontal and multilateral wells.
To authenticate the result from the use of this new package, a study was implemented in the Imo River field of the Niger Delta. The results obtained so far from the cementation of three horizontal wells and the two multilateral wells in the Niger Delta totaling seven horizontal wells, indicates that there is a 100% improvement in primary cementing and zonal isolation. CBL/VDL was logged on all wells, giving excellent results in the profile of 5millivolt with no need for expensive remedial squeeze cementing. (Fig 2).
Actual well candidate selection criteria, technical and economic performance evaluations on the application of this new centralizer package are included in this paper.