Microbial Assessment of Used Drilling Mud and Mix Cement Fluid for Production Well

Abstract

Drilling fluids and mud additives are generally acknowledged as potential sources of contamination in deep drilling programs, as they may contain high concentration of nutrients for subsurface microorganisms. Microorganisms introduced into drilling process cause a number of problems that can lead to significant costs for the industry. Numerous studies have shown that biogenic sulfide production in oil and natural gas fields have led to a number of problems, including reservoir plugging, reservoir souring, reduced product quality, and corrosion of metal-containing equipment. The aim of this study is to determine the microbial contamination of water drilling mud and cement Mix fluid at two Saudi Aramco well SA-10 & SA-12 and to adequately perform microbial assessment for the well both wells. Microbiological analyses were conducted to evaluate the level of contamination by TB (total bacterial) and SRB (sulfate reducing bacteria) using and q-PCR (quantitative poly chain reaction) technique. Microbial results for SA-10 indicated that total bacteria were 2.21  10 3 /mL for mix fluid sample and 1.22  10 5 /mL for drilling water sample. In addition, microbial results for total SRB were 1.65  10 2 /mL and 1.34  10 2 mL, respectively. Moreover, microbial results for SA-12 indicated 5.89  10 5 /mL of total bacteria and 98 /mL of SRB in the sample.