New Insight into the Mechanisms of Shale Inhibition Using Water Based Silicate Drilling Fluids

Abstract

There has recently been a resurgence in the use of water based muds containing sodium silicate for drilling reactive shale sections, particularly in the North Sea. The performance of these silicate water-based muds (SWBM) has been mixed: they are extremely effective in inhibiting swelling and dispersion of claystone and chalk, however some concerns exist over the stability of the system in terms of fluid properties, long term wellbore stabilisation and lubricity. This paper details new results, previously unreported, which give a better insight into the mechanism of clay stabilisation using SWBM. Recent literature has suggested that silicate fluids are as effective as oil-based muds (OBM) in wellbore stabilisation. This paper describes research and development indicating that silicate precipitation occurs within shales to form a barrier or membrane that hinders ion movement. However, there are distinct differences between the efficiency of membranes produced by oil based and silicate water based muds. Results are included which demonstrate that the ion- exclusion membrane is not as effective with Silicate systems as it is in OBM. New core flow experiments demonstrate that a permeability reduction with silicates and a slow rate of ionic equilibration are the principal causes for the osmotic barrier seen in swelling tests. Further results indicate a change in the physicochemical nature of clays after exposure to high pH silicate fluids. It appears that redistribution of alumino-silicate occurs which may play an important role in the inhibitive nature of these fluids. These evaluations are placed in context with well data in which primary considerations are the nature of any lost time incidents and overall SWBM performance. P. 897

A review of the shale wellbore stability mechanism based on mechanical–chemical coupling theories

“…9). According to this model, this mechanism can generally be divided into four parts: the water activity affecting the stability of shale wellbore, the membrane efficiency affecting water entrance, the clay content influencing rock properties, and the drilling fluid influencing rock strength (Bailey et al, 1998).…”

An Inhibition Properties Comparison of Potassium Chloride and Polyoxypropylene Diamine in Water-based Drilling Fluid

“…And since the 1960s, KCl/polymer system has been applied in many shale formations drilling extensively (Mondshine, 1973). For example, in glycol systems and silicate systems, proper addition of KCl will improve the inhibition dramatically with a synergic effect (Bailey et al, 1998;Qiu et al, 2006). However, to minimize clay swelling and hydration, relatively high concentrations of KCl ranging from 2% to 37% are required (Patel, 2009).…”

Use of Silicate Mud to Control Borehole Stability and Overpressured Gas Formations in Northeastern British Columbia

“…A number of excellent papers have been written further detailing possible mechanisms for shale inhibition. (2,5) Although the gelation and precipitation of silicate is a desirable process on the shale surface, if the entire mud begins to experience gelation or precipitation then mud problems will result. Potential mud problems include excessive rheology and a decrease in the silicates ability to inhibit shale.…”