Preparation and Application of a Novel Anti-Contamination Agent for Use in Drilling Fluids.

An anti-contamination agent (Zn/Al-ATMP-LDH) was synthesized by intercalation and used to correct the abnormal thickening and related operational risks caused by contact contamination between drilling fluids and cement slurries during high-temperature/high-pressure cementing. The experimental results show that the agent is chemically stable and exhibits good compatibility with conventional spacer fluid additives. When compared with the direct addition of amino tris(methylenephosphonic acid) (ATMP), confining ATMP within a layered double hydroxide (LDH) markedly mitigates the retarding effect. At a dosage exceeding 0.3 wt%, the compressive strength of cement stone increased from 0 to 32.84 MPa following curing at 90 °C for 1 day and continued to develop steadily after 7 days. Following conditioning at 187 °C and 145 MPa for 120 min, the spacer system formulated using the proposed agent as the core component served to enhance the rheology of the mixed slurry via synergistic adsorption-regulation-dispersion stabilization-controlled release. The mixed slurry maintained stable rheological properties before and after aging with no uncontrolled thickening. When mixing the cement slurry and drilling fluid at a 7:3 volume ratio, the slurry consistency exceeded 60 Bc within 1 h, failing to meet operational requirements. In contrast, the mixed slurry containing the anti-contamination spacer (cement slurry-drilling fluid-spacer = 7:2:1) exhibited a thickening time greater than 300 min and was successfully applied in field-cementing operations in a well in the Gaomo area.