Improved Primary Cement Jobs Through the Use of Unique Spacer Design Technology: Gulf of Mexico Case History Study
Authors: Schumacher J.P. , Bell R.W. , Morrison S.E. , Chan A.F. , Wydrinski R. 
Published: December 2007

Abstract
The primary cement job is critical to the success of a well completion. In many instances, the use of present spacer technology has resulted in mud contaminated cement. This paper discusses how the ARCO designed spacer system exhibits exceptional performance to clean out the wellbore and improve the quality of the cement job.
Field examples from Offshore Gulf of Mexico show that this cleanout technology, together with pipe centralization and proper job execution, has resulted in good downhole placement of the cement slurry with minimal mud contamination. This success not only has drastically reduced the need for remedial cement work, but also has made the cement bond evaluation straight forward.
This spacer technology has been successfully applied in water-based, oil-based and synthetic-based mud systems. Furthermore, the use of this spacer technology is now being expanded to other ARCO operations around the world.

Introduction
Past Experience. A good primary cement job across a productive horizon has been considered by many to be important and considered by others to be one of the most critical points at the end of drilling and the beginning of the completion stage in an oil well construction. In the U.S. Gulf of Mexico (GOM) offshore and Gulf Coast (GC) onshore, poor cement jobs have been shown to be very costly especially in areas where formations have a distinct oil-gas-water contact and isolation is desired completely across a pay interval. Poor cement and the lack of zonal isolation has resulted in expensive squeeze repair operations, reduced production rates, premature watering out, failure of stimulation treatments and other problems that has ultimately increased operating costs and cause loss of reserves.
Past experience concerning unsatisfactory cement quality or a cement evaluation log that is not straight forward has caused many problems on new completions. The normal flow of the completion operation is forced to halt or is slowed down to a crawl with expensive services and equipment put on standby while the cement evaluation log is evaluated and reserves and chance factors are examined by the completion team. Often times the cement evaluation log is played back using revised parameters to enhance the quality of the log. Still other times, a decision is made using the best information available at the time risk weighting reserves versus cost to repair.
Later in the life of a well, increased water production due to poor zonal isolation has caused wells to load up, cease natural flow and is placed on artificial lift resulting in additional facility cost and often requiring a rig recompletion to install gas lift valves. Excessive water production puts more pressure on the surface facility capacity and increases water disposal costs and the environmental effects. Squeeze operations in older dual and selective gravel packed completions in high cost areas like offshore GOM, have been shown to provide short lived success with premature failure or are too expensive to even attempt, resulting in zonal abandonment and lost reserves.
Identifying Contaminated Cement. Cement Bond Logs (CBL) are used to determine the quality of the cement. The standard interpretation for CBLs are based on the compressive strength of the cement. If the cement becomes contaminated, the compressive strength is lowered. This decrease in strength will cause the amplitude from the CBL to be higher than expected. This increase in amplitude is usually confused with a cement channel. To avoid this confusion, a Cement Evaluation Log is necessary to look at 5 to 60 degree segments around the casing. If the cement around the casing has uniform quality and the compressive strength is above 200 psi then this indicates cement contamination with adequate cement strength for zonal isolation.
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