Application of Hybrid Silicate as a Film-Forming Agent in High-Temperature Water-Based Drilling Fluids

Abstract

Effective control of shale swelling and lost circulation using drilling fluid is considered the dominant strategy for maintaining borehole stability, especially drilling operations in deep oil and gas wells. In this work, a hybrid silicate that contains lithium silicate and potassium methyl silicate (PMS) was employed as a film-forming additive to reduce shale hydration and filtration loss in the high-temperature drilling fluid. Scanning electron microscopy (SEM) results revealed that a dense quartz crystal film coating on the shale can be formed in a hybrid silicate solution when the temperature exceeds 150 °C. The in situ-formed film on the shale surface with a thickness of 60–130 μm was composed of fibrous crystalline silica. Furthermore, the aqueous hybrid silicate exhibited enhanced hydration inhibition ability by preventing water invasion of the formation. Aqueous hybrid silicate with a concentration of 0.5–3 wt % lithium silicate and 0.1–0.2 mol/L PMS was first chosen to obtain the optimum concentration according to the hydration inhibition ability and film formation characteristics. The hybrid silicate was added into a drilling fluid formulation applicable in high-pressure and high-temperature conditions, and the rheological characteristics and filtration properties were investigated. The results confirmed that drilling fluids with the addition of hybrid silicate can mitigate variation of viscosity and yield point before and after aging at 180 and 220 °C. Besides, the filtration behavior was also improved by adding hybrid silicate into the drilling fluid. A lower filtration loss was observed at the concentration of 1.0 wt % lithium silicate and 0.2 mol/L potassium methyl silicate, which showed 63 and 50% HPHT fluid loss reduction for unweighted and weighted formulations at 205 °C and 3.5 MPa, respectively. In addition, the drilling fluid featured stable rheological and filtration properties and excellent shale hydration inhibition characteristics when exposed to high temperatures, making it a promising candidate for drilling in deep oil and gas wells.

In Situ Shale Wettability Regulation Using Sophisticated Nanoemulsion to Maintain Wellbore Stability in Deep Well Drilling

“…Based on our previous work on the film-forming high-temperature drilling fluid, a hybrid silicate solution of 0.2 mol/L PMS and 0.5 wt % lithium silicate was used as the aqueous phase of the nanoemulsion. 23 The preparation of nanoemulsions was accomplished according to the following procedure. First, 20 g of PMS and 7.5 g of lithium silicate were added to 280 mL of distilled water to form the aqueous phase and then the aqueous phase in conjunction with the anionic surfactant SDBS were mixed vigorously to form a mixture.…”

“…81-1665), which was consistent with the previous report. 23 And 22°and 30.5°were assigned to crystalline SiO 2 (PDF No. 82-1563).…”

“…Compared to our previous report on crystalline silica film formed on the shale surface by hybrid silicate, the hydrophobic film formed by nanoemulsion is of more interest. 23 Figure 12a,b presents the schematic of film formation processes and mechanism to illustrate hydrophobic film formation on shale surfaces in the nanoemulsion. It is speculated that the inorganic silicate in the water phase of the nanoemulsion is preferentially hydrolyzed to form nanofibrous silica due to the confinement effect of methyl.…”

“…19,20 Inorganic silicates, including sodium silicate, potassium silicate, and lithium silicate, have been of great interest since 1940 21,22 and might be a promising option due to their physical plugging of pore throats, film-forming, and high-temperature resistance properties. 23 Nevertheless, wellbore instability induced by water invasion into shale still elicits significant challenges toward deep complex formations. 24 Inspired by the hydrophobic phenomena observed from lotus leaves and water striders, the artificial hydrophobic surfaces have been applied to many fields, 25,26 such as antifouling, 27 oil and water separation, 28 anticorrosion, and ice suppression.…”

“…Herein, we report a highly stable oil-in-water (o/w) nanoemulsion containing organosilanes and soluble hybrid silicate based on the previous study, 23 which possesses excellent inhibition properties via forming a hydrophobic film on shale surfaces in situ at elevated temperature. We have investigated the storage stability toward the time interval of the o/w nanoemulsion, as well as its inhibition properties and mechanism.…”