The particle size of Class G oilwell cement has been responsible for limiting its use in specific remedial cementing operations since the largest particles in a typical Class G cement are in the 100–150 micron range, cement slurries will not penetrate fractures narrower than about 0.4 millimeters (400 microns) or sand packs finer than about 10/20 mesh.
Simply reducing the particle size of conventional Class G cement was initially attempted to solve this problem. The chemical and physical properties of Class G clinker made it impossible to significantly lower the particle size of the cement. However, by modifying the clinker chemistry and the resultant physical characteristics of the material, a new small particle size cement (SPSC) has been produced. The SPSC material has particle sizes many times smaller than Class G cement, which allow it to penetrate into areas inaccessible to conventionally sized cements.
Some of the new applications areas which can now be specifically addressed are:
Sealing off vertical communication in a gravel packed completion by penetrating the pack sand up to the formation face. If placed properly, steam migration, unwanted water flow and low pressured, desaturated zones can be isolated or eliminated.
Squeeze cementing into narrow channels, micro-annuli, or narrow mud channels.
Depending on formation permeability actual penetration into the formation itself.
Laboratory development, slurry design, placement techniques, and field case histories are presented to illustrate the practical nature of SPSC.
References and illustrations at end of paper.
Squeeze cementing consists of many job types; squeezing off perforations, slotted liners or wire wrapped screens, liner laps or holes in casing. Usually, conventional cements can be designed to attain a successful squeeze, however, the squeezing of liners or wire wrapped screens has proven difficult. The primary reason for this difficulty has been that conventional oilwell cements will not penetrate out into the gravel pack and significantly reduce either vertical or horizontal permeability. Because of this, problems such as unwanted water production, desaturated intervals, and steam breakthrough have gone largely untreated.
Conventional oilwell cements can not penetrate into gravel packs because of the size distribution of the cement particles. Since the largest particles are in the 100–150 micron range, bridging and cement dehydration will occur when the slurry attempts to penetrate fractures narrower than about 0.4 mm (400 microns) or sand packs finer than about 10/20 mesh.
Since cement penetration using conventional cements was so difficult previous attempts to squeeze liners or screens required perforating the liner or screen and squeezing cement out the holes. Although this method proved acceptable, it required not only perforating, but placement of viscous polymer pills prior to the treatment.
SPSC was developed to solve the problem of inadequate cement penetration by combining small particle size and proper dispersion. This combination allows the cement to penetrate the pack by either placement of a plug (using a dump bailer) or by squeezing through a tool.
As a slurry design was being developed, the following tests were conducted.