Addition of Surfactant-Modified Graphene Improves Water-Based Drilling Mud
This paper reports the effect of sodium dodecyl sulfate modified graphene (SDS-Gr) on the rheological features, fluid loss, and swelling inhibition mechanism of clay.
This paper reports the effect of sodium dodecyl sulfate modified graphene (SDS-Gr) on the rheological features, fluid loss, and swelling inhibition mechanism of clay. The outcomes revealed that the addition of SDS-Gr to traditional drilling mud clearly affects the rheological properties, increasing its suitability for drilling. Moreover, SDS-Gr additive reduces fluid loss by 20% compared with the mud without SDS-Gr.
Graphene is a widely investigated material that possesses an atom-thick 2D conjugated structure, large surface area, and high conductivity. Graphene displays better fluid-loss control than polymer-based materials. The literature has reported the utility of graphene in controlling shale swelling. Graphene features plugging capacity with regard to shale surface because of a flexible nanosheet-like structure that prevents the interaction of water with shale and hinders shale swelling. In the present study, the authors investigated the performance of SDS-Gr as a fluid-loss control agent and swelling inhibitor for shale. To combine the features of SDS and graphene, the graphene surface was factionalized with SDS. The inhibitive effect of SDS-Gr also was inspected through a variety of inhibition-evaluation methods. Finally, Fourier transform infrared spectroscopy (FTIR) analysis was conducted to establish the adsorption of SDS on clay.
The swelling-inhibition features of modified water-based mud (WBM) have been demonstrated by extensive experimental evidence. The characteristics of the WBM used in this study are detailed in the complete paper.
For the dispersion-recovery test, the shale was crushed and sorted by sieve shaker between Mesh 10 and Mesh 5. To measure the dispersion of shale, 20 g of shale cuttings were added to 350 mL of WBM with and without shale inhibitor. The aging cell was hot-rolled at 25 rev/min and at 66°C for 16 hours in the rolling oven to mimic a borehole environment. Afterward, the cell was cooled to room temperature. The shale cuttings were sieved with Mesh 35 and then washed thoroughly with running water to eliminate small shale particles. The shale cuttings on the sieve were desiccated at 105°C for 24 hours in the oven. Finally, the cuttings were weighed and the recovery percentage was calculated.
Material Characterization. The scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDX) data demonstrated the significant difference in the shale surface before and after treatment with SDS-Gr. Once the surface of shale was treated with SDS-Gr, the unseamed surface appeared in the SEM micrograph. The EDX confirmed that the composition of the shale is similar to that reported in the literature. The EDX of SDS-Gr shows a higher content of carbon with sodium, oxygen, and sulfur. The SDS-Gr-modified shale demonstrates that the percentage of the carbon content prominently increased compared with that of the shale.
Fig. 1 shows the FTIR spectra of graphene, SDS-Gr, shale, and SDS-Gr-modified shale, measured to confirm structural characteristics. In the FTIR spectra of graphene, two prominent bands appearing at 2846 and 2916 cm−1 are attributed to symmetric and asymmetric stretching of methylene groups. The FTIR spectra of SDS-Gr revealed that the SDS modified the surface of graphene and that variations were observed. The figure demonstrates that the broad peak caused by stretching vibrations disappears because of functionalization by SDS. The study of FTIR spectra of the shale material indicates a match with that of kaolinite, suggesting, along with other observations, that shale is formed by kaolinite. When SDS-Gr was added to the shale sample, the shale inhibitor interacted with shale surface and plugged the nanopores. The FTIR spectra of SDS-Gr-modified shale demonstrated all the characteristics of the clay. However, the broad peak caused by stretching at 3416 cm−1 was prominently reduced. The peak caused by adsorbed and hydration water at 1640 cm−1 was also reduced, confirming that the attachment of SDS‑Gr to shale induces hydrophobicity.
Thermogravimetric analysis of SDS-Gr, shale, and SDS-Gr-modified shale was also performed. From ambient temperature to 200°C, the mass loss in the shale sample was 11% of its initial weight. However, SDS-Gr-modified shale demonstrated only a 3.8% weight loss, much lower than that seen in unmodified shale material. The difference in the percentage water loss confirms the intercalation of the SDS-Gr with shale that makes the surface hydrophobic and reduces the water content. Up to 800°C, the shale and SDS-Gr-modified shale display 36 and 17% weight loss, respectively.
Mud-Making Test. The measurement of the apparent viscosity (AV), plastic viscosity (PV), yield point (YP), and fluid loss are presented in Table 2 of the complete paper. These rheological features can provide crucial information about the drilling mud. When SDS-Gr is applied to traditional drilling mud, a prominent decrease in AV of pre- and post-hot-rolled drilling mud was observed. PV should be kept low in a drilling mud. The PV of the drilling mud decreases significantly after addition of SDS-Gr (0.85 wt%) and during an increase in temperature. The rheological study of the drilling mud established that the introduction of SDS-Gr to the drilling mud before and after hot rolling increased the YP value. The traditional inhibitive mud seems to be more affected by the temperature and pressure than SDS-Gr-modified WBM.
To evaluate the plugging capacity of the SDS-Gr, the filter-loss method was used. The SDS-Gr-modified mud displayed a considerable decrease in fluid loss because of the SDS-Gr film formation on the surface of the filter paper that plugs the pores and hinders the water flow from the filter paper. The formation of a less-permeable film can be confirmed from the formation of the filter cake. The gel strength quantifies the attractive forces within the drilling-mud system under no-flow conditions. The outcomes revealed that the addition of the SDS-Gr reduces the gel strength of traditional drilling mud.
Dispersion and Swelling Test. The dispersion test assesses the fragmentation and attrition of the shale material when exposed to the drilling fluid. The quantity of shale cuttings recovered after hot rolling indicates the quality of inhibition against dispersion. The SDS-Gr-modified mud demonstrates higher shale-cutting recovery that can be ascribed to adsorption of the SDS-Gr to the surface of shale, hindering the interaction of water with shale surfaces and increasing the resistance of shale materials to the effects of the aqueous medium.
The linear swelling-rate measurement demonstrates the inhibition capacity of the SDS-Gr shale inhibitors. For this purpose, the linear swelling of the clay materials was also observed in the water and potassium chloride (KCl) and the SDS-Gr shale inhibitor. The 0.85 wt% of the inhibition matrix was used to form an aqueous solution. The outcomes demonstrate that water displays the highest percentage of linear swelling. However, an aqueous solution of KCl and SDS-Gr decreases the swelling rate. The swelling test also confirms the better performance of SDS-Gr as compared with KCl.
Swelling and Inhibition Mechanism. The clay consists of layers of negatively charged aluminosilicates that are held together by the electrostatic forces caused by positive ions. Sodium, calcium, and magnesium act as intercalating ions and make the clay surface hydrophilic. Once the water molecules approached the cations, because of their interaction, the interlayer d-spacing increased and clay swelling commenced. Consequently, the volume, number, and the surface area of particles of wet clay increased severalfold compared with the dry clay. The SDS-Gr can limit swelling by interaction with clay. In addition to the SDS, the graphene plugs the pores of clay to eliminate the chances of osmotic swelling of clay particles. The SDS-Gr thus hinders the water molecules in reaching the surface of the clay by making it hydrophobic and changes its rheological properties. The description of the mechanism is in good agreement with the outcomes obtained in SEM, FTIR, rheological, and dispersion studies.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 197774, “Improvement in Rheological Features, Fluid Loss, and Swelling Inhibition of Water-Based Drilling Mud by Use of Surfactant-Modified Graphene,” by Azeem Rana and Tawfik A. Saleh, King Fahd University of Petroleum and Minerals, and Mohammad K. Arfaj, Saudi Aramco, prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11–14 November. The paper has not been peer reviewed.