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Summary Asphalt nanoparticles (ANs) were developed by synthesizing asphalt powders with chloroacetic acid (ClCH2COOH). The objective of this synthesis was to develop engineered ANs with a cationic point capable of adsorbing on the net negatively charged clay platelets, thereby improving drilling fluid functionality and pore-plugging performance, reducing shale dispersion, and ultimately enhancing shale stability. Tests carried out to study the performance of the synthesized ANs include particle size analysis, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy, drilling fluid rheology, and filtration rate and shale dispersion tests. FT-IR spectrum results confirming the occurrence of a chemical reaction between asphalt and ClCH2COOH showed a shift in NH vibration from 3,439.95 cm−1 (before synthesis) to 3,435.05 cm−1 (after synthesis). Based on particle size analysis, an average particle size diameter of 92.9 nm was observed, suggesting the tendency of ANs to invade and seal nanopore spaces. The shape of ANs ranged from spherical to irregular, because intercalated structures were observed from the scanning electron microscopic analysis on the interaction between ANs and sodium bentonite (Na-Bent). An increase in attracting force between the Na-Bent particles caused by the adsorption of ANs cationic point on bentonite clay particles led to an increase in drilling fluid rheological properties as the ANs %w/v increased. The drilling fluid filtration rate was, however, not significantly affected by the %w/v increase in ANs because results indicated slight decrease in fluid loss when compared with the base mud (BM). According to the shale dispersion test, the shale cuttings percentage recovery of the 2%w/v ANs sample was 76.5%, owing to the decrease in fluid-rock interaction caused by ionic adsorption and encapsulation of shale surfaces by the ANs. Experimental results from this investigation indicate that the likely mechanisms of the effect of ANs on shale formations would be sealing off nanopore spaces in formations because of its ultratiny particle size; adsorption of the net negatively charged shale cuttings by the ANs cationic point, thereby reducing drilling cuttings dispersion; and improving hole-cleaning performance due to its effect on the drilling fluid rheological properties.

ABSTRACT: The generation of H2S (hydrogen sulfide) in formation and wellbore is a significant cause that results in natural disasters, wellbore corrosion, and personal safety. It is essential to study the generation causes and precautions of H2S to avoid harmful gas damage. BSR (bacterial sulfate reduction) and TSR (thermochemical sulfate reduction) experiments have been discussed based on different reaction environments and conditions of H2S. It has been demonstrated that BSR is the primary cause and TSR is the secondary cause of the H2S generation in the studied fractured wells. The existence of SRB provides a premise for the occurrence of BSR. The pH value of solutions will affect SRB activity and H2S generation quantity. The reaction temperature will affect whether TSR occurs and the amount of H2S generation. The reaction pressure only affects the occurrence time of H2S in TSR, but hardly affects the generation quantity. Furthermore, the replacement of fracturing fluid formula, NaOH, bactericides and high temperature steam can be used to inhibit the generation of H2S in the formation and wellbore. This study has a certain reference value and suggestions on the causes, influencing factors, laws and prevention methods of H2S in oil reservoir. 1. INTRODUCTION Hydraulic fracturing is one of the most significant technical issues to improve underground flow environment and increase the well production in petroleum engineering. It has made great achievements in the field of rock mechanics in recent decades(Atkinson, 2015; Hubbert & Willis, 1957). In the process of hydraulic fracturing, fracturing fluid needs to be injected to extend fractures and transport proppant into the fractures, so that more fluid channels can be kept open for a long time(Gandossi & Von Estorff, 2013). However, use of fracturing fluid with certain composition in some oil and gas fields may generate toxic gas and endanger personal safety(Michalski & Ficek, 2016). Taking Daqing Oilfield in China as an example, hydrogen sulfide (H2S) has been detected from some fractured wells, and the value has greatly exceeded the allowable safety range (150 mg/m3 for H2S). Furthermore, the presence of H2S will also corrode wellbore and bring environmental risk because of its sour corrosivity(Hedges, Chen, Bieri, & Sprague, 2006; Holubnyak et al., 2011). Hence, the generation source, influencing factors and elimination measures of H2S generated from the formation or the wellbore ought to be found out immediately.

The effect of corrosion inhibitor Benzotriazole on synthetic-based mud system was studied. Rheological performance of the benzotriazole enhanced synthetic-based fluid system was studied and compared against the base mud. To study its effect on dynamic wellbore conditions, different drilling fluid compositions were placed in a hot rolling oven for 16 hours at temperatures 150 °C and 170°C and the effect of temperature on mud properties were studied. Tests carried out include rheological test (before and after hot rolling), filtrate pH, lubricity test, and fluid loss test. The corrosion penetration rate was studied using the weight loss method. Based on experiment results, the synthetic-based mud system which comprised of benzotriazole displayed a reduction in coefficient of friction up to 95.93%. At ambient condition, optimal ratio of mineral oil:benzotriazole (M:B) which gives best lubricity performance on synthetic-based mud system is 80:20. This leads to improved corrosion inhibition and lubricity of the synthetic-based fluid by reducing the coefficient of friction up to 90.13%. Increased temperature led to further decrease in coefficient of friction with a % torque reduction of 95.93 displayed by the 80:20 ratio M:B mud composition at 170 °C. Significant alterations of the mud composition rheological and fluid loss parameters before and after exposure to high temperature in hot rolling oven were not observed. pH values were maintained ≥7 at the dynamic conditions highlighting solubility of the formulated fluid composition and absence of contaminants which can pose significant threats to the rates of corrosion in drill pipes. Increasing the concentration of Benzotriazole led to a reduction in corrosion rate. However, as the temperature effect increased, the corrosion rate elevated. Based on results from this investigation, it was concluded that Benzotriazole can be applied as a corrosion inhibitor in a synthetic-based drilling fluid system as an alternative corrosion inhibitor without significant alteration of the base mud properties. Benefits of this will be the optimization of extended reach well drilling operations due to excellent lubricity performance, corrosion rate reduction, compatibility with HPHT wellbore condition and fluid loss control.