(163g) Bacterial Nanocellulose as an Eco-Friendly Additive in Water-Based Drilling Fluids Applied to Shale Formations

Drilling fluids are mixtures of natural and synthetic chemical components used to cool and lubricate the bit and the drill string, clean the hole bottom, carry cuttings to the surface, control formation pressures, among others. An efficient drilling fluid must also present several characteristics, such as desirable rheological properties, fluid loss prevention, stability under high-temperature and high-pressure conditions, as well as stability against contaminating fluids such as salt water, calcium sulfate, cement, and potassium. According to the nature of the continuous phase, fluids are classified into two main groups, water-based drilling fluids (WBMs) and oil-based drilling fluids (OBMs). OBMs are known to provide unequalled performance but they are subject to environmental regulations. WBMs present low environmental impact but exhibit some disadvantages associated with shale inhibition, lubricity, and thermal stability. To avoid these drawbacks, specific additives can be added to deliver properties close to OBMs performance while minimizing the environmental impact.

As nanotechnology has gained in popularity, lignocellulosic materials have been fractionated to the nanoscale where their components can be separated and utilized in drilling applications. The nanoscale dimension of cellulose, as well as its morphology, aspect ratio, surface chemistry and surface energy impart very distinctive properties when compared to cellulose fibers, such as improved mechanical performance and thermal stability.

Different raw materials and processes to isolate nanocellulose have been widely studied. From lignocellulose materials such as wood, cotton, linen, sugar cane, and agricultural wastes to even bacteria and tunicates, nanocellulose has been effectively produced. Sources and choice of processing for nanocellulose production will directly impact specific characteristics, such as morphology, aspect ratio, rheological and optical properties, among others. The three main groups of nanocelluloses are cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), and bacterial nanocellulose (BNC).

In this work, a sustainable alternative for the design of WBMs with environmental and economic advantages for use in shale formations is sudied. In particular, the replacement of XGD, a natural polymer with viscosifying and viscoelastic properties that is stable over a wide range of temperature, salinity and pH, is investigated. Due to its chemical structure, low cost and environmentally friendly characteristics, BNC from glucose-sweetened black tea is proposed as an alternative for such replacement and their performance in WBMs are evaluated. The effects of WBMs components on their structural, rheological, filtration, and thermal properties are investigated. Additionally, the rheological properties of WBMs are also theoretically described using the Sisko model.

The NCB was purified in alkaline solution and characterized. The NCB suspension in the form of nanoribbons (1.40% m/m) exhibited a Z potential (at pH 7) of -9.79±1.68 mV. On the other hand, a high percentage of crystallinity (about 90%) was measured. The average viscosimetric degree of polymerization was 8181±1583, characteristic of bacterial celluloses. In addition, the thermal stability was good, with its maximum degradation temperature close to 370 °C. The micrographs revealed that the nanoribbons have an average width of 76 nm.

Subsequently, WBM systems containing polyanionic cellulose (PAC) [0.50%], sodium bentonite (BT) [1.5%] and NCB or xanthan gum (XGD) [1-0.00; 2- 0.10; 3- 0.25; and 4-0.50%]. XGD-based WBMs were used for comparison purposes. Their rheology and thermal stability were evaluated. NCB-containing WBMs exhibited higher viscosities than those containing XGD while thermal stability is similar for both fluids.

The results indicate that NCB is an interesting and possible replacement candidate for XGD in the formulation of WBMs.