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.
Cement plugs are a widely used well intervention method to achieve zonal isolation and well plug and abandonment. The current practice of cementing using wireline was reviewed on a system level to identify the primary challenges. Existing cement mix properties, such as compressive strength and wait-on-cement (WOC) time, were characterized using standard API RP 10B-2 (2013) tests. The sensitivity of these mixes to various wellbore temperature and pressure conditions was also studied. Based on the understanding of the current practice, modifications of the compositions, packaging, and mixing procedures in the field were proposed and tested accordingly. Based on the experimental results, the properties of the current cement mixes showed high sensitivity to temperature variations as small as 10°F. To achieve a cement plug as expected, accurate knowledge of the well temperature profile and precise selection of the best additives for such small temperature intervals are necessary. If crossflow occurs, then setting a plug itself can change the temperature profile. This makes cement plug operations even more challenging during actual field practice. The cement mixes were modified and tailored to reduce their sensitivity to temperature without affecting the dump time and strength development. This paper discusses the challenges associated with wireline-run cementing operations and presents a simple and streamlined process developed to help reduce operational time and minimize costs. The study also discusses cement mixes customized for dump bailer operations.
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