QUANTITATIVE RISK ASSESSMENT OF THE EFFECT OF SAND ON MULTIPHASE FLOW IN PIPELINE

The presence of sand particles flowing along with reservoir fluids in a pipeline increases the probability of pipeline failure. The risk of pipeline failure is either accentuated or abated by the flow conditions of the fluids in the pipeline. In this study, a quantitative risk analysis of the effect of sand on pipelines during multiphase flow, under the pipeline failure modes; sanding up, erosion, and encountering abnormal pressure gradient was conducted. Three piping components were considered: line pipe (nominal size 1.5 in [3.8 cm]), swing check valve (nominal size 12.007 in [30.5cm]) and 90 deg LR Elbow (nominal size 2.25 in [5.7cm]). Correlations that indicate the critical velocities and the critical sand concentrations above/below which these failures occur were employed and implemented in a Visual Basic program. The analysis was conducted at a temperature of 204 °C and pressure of 604 psi [4.2×106 Pa]. A probability distribution, simulating real-life scenario was developed using Monte Carlo simulation. This determines the probability of deriving critical sand concentration values that fall beyond the set statistical limits which indicates the probability of occurrence of the failure being investigated. For all three failures, the severity of occurrence (represented by CAPEX incurred in solving the failures) was multiplied with the probability of failure which gave rise to the risk indexes. Based on the histogram plot of average risk index and analysis, the study reveals that larger diameter components are prone to turbulence which lead to greater risk of erosion. The risk of abnormal pressure drop and sanding up were considerably lower than that for erosion (abrasion).