Cementing Considerations for Casing While Drilling: Case History

Abstract

Casing while drilling (CWD) is an emerging technology being introduced in different areas around the world This new configuration, where the casing is used as a drillstring, presents new challenges for primary casing cementing operations compared to the conventional cementing operations. A full understanding of the required changes of the cementing methodology from conventional drillpipe drilling operations can contribute to the success of any CWD campaign. CWD cementing differs from conventional cementing practices because it is impossible to use standard centralizers attached to the casing while drilling because of extended and faster casing rotation. When more than one bit is required to reach the next casing point, CWD requires full-bore casing access to pull and run bottomhole assemblies (BHA) through the casing. In these instances, conventional floating equipment cannot be used. Wireline logging is normally conducted in cased hole after the cementing job. The cement volumes are calculated with a cement excess factor instead of a caliper log. This paper describes the methodology developed to successfully cement surface, intermediate, and production casings in more than 125 wells in south Texas where CWD was used. These same techniques can be applied in CWD operations elsewhere. Introduction CWD differs from conventional cementing practices in several ways. Centralization for Casing while Drilling In CWD operations, standard bowspring or welded-body centralizers are not recommended. The casing string will be subjected to longer and faster rotation while drilling the entire openhole section, and standard centralizers are not suitable for these conditions. They may cause severe wear damage and may lose their original placement, decreasing pipe centralization. In addition, these standard centralizers attached to the casing can be lost in the hole, causing additional problems when drilling ahead. In CWD, there is no option to place any type of centralizers with an OD larger than the gauge hole size. Bow-type centralizers are desirable where washouts are expected because they provide restoring force to centralize the casing in the hole. The bows on this type of centralizer have lower resistance to casing rotation. A good mud system is essential to minimize the hole washouts. If washouts are unavoidable, the reduced pipe standoff should be compensated by enforcing other best cementing practices, such as providing good mud properties, pumping rates, spacer design, etc.1

The Application of High-Density Elastic Cements to Solve HPHT Challenges in South Texas: The Success Story

“…Operators in south Texas are now implementing many new technologies as they strive to effectively exploit HPHT reservoirs. These include underbalanced drilling and drilling with casing (Strickler and Solano 2007) to avoid associated problems with the intermingling of high pressure and depleted zones, novel lost circulation curing techniques, and mechanically modified cements.…”