Structural recovery behavior of barite-loaded bentonite drilling muds

Abstract

Freshly prepared barite-loaded bentonite suspensions take more than a day to reach surface chemical equilibrium. These suspensions prepared 24 h earlier also display structural recovery with time of rest after structural breakdown by stirring, where the yield stress increased with time of rest. The Nguyen–Boger model and the so-called Leong model were quite accurate in predicting the structural recovery behavior of these suspensions. The time scale of structural recovery of barite–bentonite suspensions in the mass ratio 1:1 (13.1 wt.% solids), 2:1 (18.4 wt.%) and 3:1 (23.1 wt.%) based on the Leong model is ~ 4 h. In the presence 0.2 dwb% pyrophosphate and triphosphate, this time scale was increased to more than 20 h and ~ 10 h respectively. Both these additives also reduced the yield stress. The loading of barite on a 7 wt.% bentonite slurry up to 5 wt.% produced a weakened flocculated network structure. Then the resultant structure began to gain strength but very gradually until barite loading of 30 wt.% was achieved. Above 30 wt.% barite, the yield stress increased exponentially. The large increase in the particle concentration by the added barite now produces a much stronger network structure with the bentonite particles.