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

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA freshwater silicate based drilling fluid, containing 20-30% sodium silicate by volume, was successfully used to drill a gas well in northeastern British Columbia. Major drilling issues in the area include borehole instability in 500 plus meters of highly dispersible Ft. Simpson shale, high pressure gas zones and potential moderate-severe lost circulation.Despite problems of severe lost circulation and high mud weights, the caliper log on the silicate well showed <1% hole enlargement over the Ft. Simpson shale and 12% enlargement over the entire intermediate section. Typical offset calipers with other water-based muds average 48% and 31% enlargement over the Ft. Simpson and entire well section, respectively.Rates of penetration with silicate mud were generally better than offset wells. Uphole formations drilled to 1060 meters with a low solids, lower density silicate fluid (1195 kg/m 3 mud density) drilled at an average of 19.2 m/hr. Offsets drilled with gel-chemical or gel-PHPA systems over the same interval normally averaged 12.6 m/hr. This paper describes the planning and drilling of the first well with a drilling fluid containing silicates up to 30% concentration. Topics discussed include borehole stability, rates-of-penetration, motor performance, drilling fluid stability and properties, and environmental aspects of silicate disposal.

Importance of Shale Anisotropy in Estimating In-Situ Stresses and Wellbore Stability Analysis in Horn River Basin

“…Organic-lean Fort Simpson shales are clay rich, with almost equal concentrations of illite, kaolinite, and chlorite [Ross and Bustin, 2008]. It is Devonian age, weak, brittle shale and calcareous silty laminated with high quartzitic content [Stewart et al 2000]. Shale is formed of platy type of grains when it is compacted, the grains are usually distorted and elongated in one or more directions, and aligned in parallel to sub-parallel orientation, making it a layered material.…”

“…One of the most troublesome formations is Fort Simpson shale which is about 800-1000m thick [Ross and Bustin, 2008] reactive high clay content shale which swells when contacted by fresh water and usually consist of high pressure zones. To avoid these types of wellbore instabilities, an intermediate casing string is typically set right after passing through the Fort Simpson shale [Stewart et al 2000] or before entering Muskwa. In this paper, the authors analyzed some of the wellbore instability problems encountered in the HRB and identify possible causes of these problems.…”

Inhibition of the Hydration Expansion of Sichuan Gas Shale by Adsorption of Compounded Surfactants

“…Organic cations can narrow the diffusion pathway and decrease the diffusive transport of water by adsorbing onto the external surfaces of clay minerals . Silicates, which were first introduced in the 1930s to solve shale instability issues, have also been shown to enhance the stability of shale. , Potassium chloride and sodium chloride are commonly added to water-based drilling fluids to minimize clay hydration. In addition, polymers and polyamines are widely used to control clay swelling.…”

“…17 Silicates, which were first introduced in the 1930s to solve shale instability issues, have also been shown to enhance the stability of shale. 18,19 Potassium chloride 20 and sodium chloride 21 are commonly added to water-based drilling fluids to minimize clay hydration. In addition, polymers 22 and polyamines 23 are widely used to control clay swelling.…”