(178ab) On the use of bacterial nanocellulose as an additive of drilling fluids

Drilling fluids play a crucial role in oil and gas extraction, aiding in cuttings transportation, wellbore stabilization, and equipment lubrication. Among these fluids, water-based formulations (WBMs) are favored for their environmental safety and cost-effectiveness (Guo et al., 2023). Bentonite clay (BT), a fundamental constituent of WBMs, offers exceptional rheological properties that are crucial for wellbore stability and fluid performance (Guo et al., 2023). While traditional additives like xanthan gum (XGD) have been utilized to improve WBMs, there is an interest in the use of bio-based nanomaterials such as nanocelluloses (Song et al., 2016).

The nanocelluloses emerges as a promising candidate, demonstrating favorable rheological behavior and thermal stability in drilling fluids (Song et al., 2016). Some investigations have explored its potential as a replacement of XGD in WBMs, scrutinizing its effects on various aspects including rheology, and filtration processes (Villada et al., 2018). Additionally, enzymatic treatments utilizing cellulase enzymes have been contemplated to mitigate the viscosifier effect and improve cement adhesion on the formation, offering a novel strategy for fluid optimization in drilling and cementing operations (Barría et al., 2022).

In this work, drilling fluids based on bacterial nanocellulose (BNC) were designed. The performance of BNC in WBMs was assessed and compared with the corresponding XGD. The rheological properties of WBMs were determined by steady shear assays using a viscometer. The Power-Law model was used to predict the rheological behavior of fluids. The thermal stability of the WBMs was evaluated through the aging test in an electric oven at 90°C for 24 hours. An inhibition assay was carried out by preparing BT pellets and submerging them in 0.1% wt BNC, and 0.1% wt XGD suspensions, respectively. In addition, the drilling fluids with BNC were treated with enzymatic agents to evaluate their reutilization in the cementing operation. The enzymatic treatment was performed by the incorporation of several cellulase concentrations and the changes in viscosity of WBMs were determined under different conditions of temperature, pH, and time.

Materials and Methods

Bentonite (BT), polyanionic cellulose (PAC) and xanthan gum (XGD) were supplied by MARBAR S.R.L, M-I SWACO (a Schlumberger company), and Química Oeste S.A., respectively. Regarding BT, it primarily consists of smectite, with impurities such as quartz, feldspar, and gypsum (Villada et al., 2018). Bacterial nanocellulose (BNC) was produced from Kombucha tea pellicles and characterized for morphology, thermal stability, crystallinity, and viscometric degree of polymerization.

Inhibition tests were conducted for XGD and BNC suspensions by gravimetric analysis.

Additionally, 16 WBMs were prepared with varying compositions of BT, PAC, and either BNC or XGD, followed by characterization of rheological, structural, and filtration properties. Enzymatic treatments using cellulase enzyme were evaluated for their impact on WBMs rheological properties under several conditions, employing a factorial design to assess key factors.

Results and Discussion

Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis revealed nanofibers of BNC with an average thickness of 76 nm and lengths exceeding 1 μm. Optical microscopy showcased nanofiber agglomeration, a common characteristic in this type of nanocellulose. Additionally, the zeta potential of BNC was measured at -9.79±1.68 mV (pH=7), indicating a negative charge, consistent with similar previous studies (Liu et al., 2023). BNC exhibited exceptional thermal stability, with a maximum degradation temperature of approximately 370 °C and a char content of 13%, aligning with previous findings (Peng et al., 2013). Fourier-transform infrared spectroscopy (FTIR) analysis revealed characteristic peaks corresponding to O-H stretching, C-H stretching, and O-H bending, confirming the composition of BNC. X-ray diffraction (XRD) patterns indicated a cellulose type I structure with a crystallinity index of 89.71%, reflecting BNCs high crystallinity.

WBMs containing BNC and XGD were rheologically characterized, showcasing increased viscosity with higher concentrations of additives. SEM micrographs highlighted particle agglomeration in fluids with elevated bentonite content, while fluids with BNC displayed fiber presence. Rheological behavior exhibited non-Newtonian, pseudoplastic characteristics, with BNC-containing fluids demonstrating increased viscosity compared to XGD-containing fluids. Figure 1a illustrates the rheological properties and the adjusted Power-Law model for BNC fluids containing varying concentrations of BNC (0%, 0.1%, 0.25%, and 0.5% BNC, denoted as 1-BNC, 2-BNC, 3-BNC, and 4-BNC, respectively). Fluids containing BNC exhibited superior performance in aging and thermal tests compared to those without BNC.

Enzymatic treatment studies revealed significant effects of pH and enzyme concentration on viscosity reduction in WBMs. The response surface analysis depicted interactions between these variables, suggesting pH-dependent enzyme selection for polymer decomposition (Fig. 1b).

Conclusions

NCB was evaluated as a possible additive to replace XGD in WBMs. The effect of NCB on the rheological, filtration, and thermal properties of WBMs was studied. The high crystallinity of BNC could explain the differences between XGD and BNC results.

The obtained results suggest that BNC constitutes a potential additive as a replacement of XGD in the design of WMBs. In addition, the possible reuse of the WBMs after modification with enzymes for the cement stage promotes a hydrocarbon exploitation more sustainable avoiding the use of additional chemical products.

References

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