The Haynesville shale presents special challenges when designing cement systems. Extended-reach, horizontal wellbores create a high-pressure/high-temperature (HP/HT) environment not conducive to conventional cement slurries. Tight annular clearances and a narrow pore-pressure/fracture-gradient window have forced the industry to push the boundaries of cementing theory. Cement designs with a latex additive have improved rheological characteristics that yield lower equivalent circulating densities (ECDs) and reduce the frictional coefficient necessary for manageable surface pressures. The latex-based designs are thermally stable up to 400°F and provide excellent fluid-loss control, while still improving surface mixability. Most of the desired properties are observed when the cement is liquid; the set cement sheath can also provide corrosion resistance, annular bonding, and elasticity for well cycling.
The development, testing, and case histories of latex-based cement slurries are discussed in this paper and compared to conventional cement designs for horizontal applications. By improving the physical properties of the cement while it is still in a fluid state, the cement can be properly placed, thus decreasing the potential for job failures. With the fluid viscosities enhanced, the pump rates can be optimized using hydraulic modeling to obtain increased mud-displacement efficiency. Laboratory testing has shown the latex additive to be effective from 1 to 2.5 gal per sack of cement. The latex additive enhances several cementing properties and reduces the need for additional fluid modifiers. By reducing the additives in the blend, the testing variability is decreased and repeatability is increased. Similar designs have been used in the past, but failure to maintain system stability created limitations. With new technology and theory, a heavyweight, thermally stable cement can be pumped during the most adverse well conditions.