Experimental Study on the Causes and Protective Measures of Hydrogen Sulfide in Formation and Wellbore

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.