In deepwater drilling, spacers are widely used between drilling fluids and cement to effectively remove the drilling fluids and improve cement bond. A variety of spacer systems have been applied over the past decades with biodegradable polymers. However, most of these biopolymers are thermally stable only below 200 to 300°F and lose viscosity above their degradation temperature. In this study, a new spacer system for HTHP wells has been developed with a novel biopolymer and lost circulation materials.
The performance of new spacer is compared with a previous spacer system, which has been successfully applied to wells on land and offshore, especially for preventing and remediating lost circulation issues while cementing. The rheological properties of unweighted and weighted spacers (12 to16 ppg) were measured from room temperature up to 400°F with a stabilizer. The new spacer exhibited a superior rheological profile at elevated temperatures. The compatibility tests were conducted between the spacers and various types of drilling fluids and cement slurries. The new spacer improved the compatibility with synthetic/diesel-based drilling fluid and cement with less or no viscosification. The sealing performance of the spacers was determined in a fluid loss cell with 20/40 proppant. The new spacer effectively prevented losses by sealing the proppant under pressure. To date, several land operations have been successfully completed and one case history is discussed in detail.
In summary, the new spacer system is stable at high temperature, improves compatibility with drilling fluid and cement, and maintains good sealing performance. The new spacer is applicable in any types of wells and cementing operations, especially where high-permeability, fragile, unconsolidated and low-fracture-gradient formations are present. The new spacer is biodegradable, forms a seal to minimize filtrate invasion into the formation, effectively reduces cement losses and formation damage from filtrate migration, and enhances hole cleaning prior to cement placement.