Wellbore instability in chalk formations poses significant challenges during drilling and production due to low rock strength, fluid sensitivity, and creep. This study investigates the efficacy of diammonium phosphate (DAP) as a chemical consolidating agent to enhance chalk mechanical properties under simulated reservoir conditions. Austin Chalk core samples were treated with a 1M DAP solution at 75°C and 1,000 psi confining pressure for 72 hours to promote hydroxyapatite precipitation. Triaxial loading tests compared the treated and untreated specimens. Results demonstrated that the DAP treatment improved the confined compressive strength by 16-81% across confining pressures (400–1,600 psi). Mohr-Coulomb failure envelopes revealed a cohesion increase from 600 psi (untreated) to 1350 psi (treated), with unconfined compressive strength doubling to 3200 psi. These enhancements, attributed to hydroxyapatite cementation, indicate DAP’s potential to mitigate wellbore failure by strengthening the formation itself. The findings advance chemical stabilization strategies for chalk, offering a novel solution to reduce non-productive time and improve long-term well integrity in carbonate reservoirs.
Desouky et al. (Sun,) studied this question.
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