A Practical Study of the Influence of Drill Solids on the Corrosion of Downhole Tubulars When Using Brine Based Drilling Fluids
Abstract The proliferation of highly concentrated brine drilling fluids systems due to their enhanced performance benefits has instigated a plethora of technical studies on the mechanisms and control of their induced corrosion on downhole drilling tools and tubulars. The majority of these studies often overlook the effect of drill solids on corrosion rates. Therefore, a pragmatic and experimental study was conducted to investigate the effects of various factors on the corrosion rates of downhole tubulars with a streamlined focus on the obscure role of the understudied drill solids; which have not been fully elucidated. Drill pipe corrosion coupons and drilling fluids/solids obtained from 5 similar wells (located in Grande Prairie, Alberta, Canada) were utilized for experimental analysis. Wells 1 to 4 were on the same pad (surface drilling location) drilling the same formation with the same fluid properties, while the 5th well was on a different pad but drilled the same formation with the same fluid properties to exclude disparity. Industry-standard measurement was carried out on the live used corrosion coupon rings, drilling fluids and solids obtained from these wells to determine selected properties. The total solids content analysis was carried out using an OFITE API (American Petroleum Institute) filter press. Weight loss tests on drill pipe corrosion coupons were used to determine field corrosion rates which were bolstered with the Parr Hastelloy autoclave test in the Laboratory. The oxygen content was monitored using Hach 2100Q dissolved oxygen meter. Field data, images and experimental results showed that a rapid and minuscule increase of drill solids (as little as 1% v/v) in the active system can impact corrosion rates greater than chemical additives and even oxygen content. It was discovered that low concentration of solids can produce significant damage and a high corrosion potential in non-viscosified fluids thereby making live monitoring of drilling fluids’ properties a priority to mitigate corrosion. This study fills an important technical gap in corrosion study that is indispensable for the optimization of corrosion control in drilling operations. By carrying out a controlled and investigative study backed up with drilling field data and images, the effects of the less understood drill solids have been partially demystified.