Performance of cationic asphalt particles synthesized through (CH3O)2SO2 displacement reaction on water-based drilling fluid properties and evaluation of their impact on wellbore stability in shale formation drilling

• (CH 3 O) 2 SO 2 synthesized cationic asphalt particles are capable of invading the internal pore spaces of clay particles, providing effective plugging performance. • (CH 3 O) 2 SO 2 synthesized cationic asphalt particles cations displace the exchangeable cations in the bentonite clay unit layers thereby intercalating and forming electrostatic attractive bonding with the bentonite clay surface to increase water based drilling fluid viscosity. • Due to adsorption of (CH 3 O) 2 SO 2 synthesized cationic asphalt particles cations and the net negatively charged shale cutting surfaces, shale dispersion and clay swelling can be reduced. • Incorporating CMC polymer into the (CH 3 O) 2 SO 2 synthesized cationic asphalt particles water-based drilling fluid system can reduce fluid loss and improve wellbore stability. To solve the problem of wellbore instability, cationic asphalt particles obtained through synthesis of asphalt and dimethyl sulphate (CH 3 O) 2 SO 2 at molar ratio of 1:1 were incorporated into water-based mud. After chemical synthesis, various characterization techniques were performed to confirm suitability of the synthesized cationic asphalt particles for enhancing wellbore stability and water-based mud properties. These tests include: particle size analysis, Zeta Potential test, Fourier-Transform Infrared Spectroscopy (FT-IR), low-pressure/low-temperature (LPLT) and High-pressure/High-temperature (HPHT) rheology evaluation, LPLT/HPHT fluid loss test, shale dispersion tests, and clay swelling tests. Owing to the displacement of hydrogen present in the asphalt amine group (N H) by the (CH 3 ) 2 during chemical synthesis, asphalt particle size changed from an initial 50 µm to 356.2 nm. FT-IR spectroscopy indicated formation of new C N covalent bond at wavenumber 1200cm −1 (90 % Transmittance) highlighting the occurrence of chemical reaction. The cationic asphalt particles zeta potential values ranged between -39 mV to -65 mV, thereby highlighting the synthesized asphalt particles excellent colloid stability in aqueous media. The asphalt particles induced fluid loss reduction when incorporated with CMC into the base mud. Due to encapsulation, electrochemical attractive and bridging forces between the (CH 3 O) 2 SO 2 cationic asphalt and net negatively charged clay surface, a shale recovery percentage of 77.7 % was achieved while clay swelling test results highlighted clay swelling index of 0.73 mm. These indicate that the synthesized cationic asphalt particles can reduce clay swelling and shale dispersion thereby improving wellbore stability.