Workflow to Evaluate Wax Deposition Risk Along Subsea Production Systems

Abstract

Abstract The potential for wax formation and deposition along subsea production systems pose a severe flow assurance risk. During early stages of a field development (when information is limited), the risk needs to be quantified in order to develop preliminary mitigation strategies. This paper presents a workflow that can be used to evaluate the wax deposition risk for any field development by integrating the available wax laboratory data with simulation tools. The proposed workflow consists of tuning fluids models, benchmarking the wax deposition models (using the measured wax deposition rates), and conducting wax deposition simulations with the benchmarked models. Deposition mechanisms such as diffusion and shear stripping can be adjusted during the benchmarking step. The wax deposition predictions can be used to evaluate various design options during development stage and for devising operating strategies throughout the life of the field (such as insulation requirements, injection of paraffin inhibitor, pigging operations, etc.). In field developments where thermal management is a challenge and wax deposition cannot be avoided, a structured approach toward wax modeling is crucial to make the right engineering decisions. Wax laboratory measurements alone are not sufficient to quantify the wax deposition risk because of the uncertainties associated with the laboratory results and the difficulties to reproduce the actual field production conditions. When comparing the results obtained with the default wax model coefficients (no benchmarking) and the benchmarked models, the predictions are significantly different. Similar deviations are observed with the predictions based on wax data reported by different laboratories (for the same fluid sample). The overall design and operating strategy are highly dependent on wax deposition rates. Therefore, the discrepancies between the wax data measured by different laboratories suggest the need to standardize the test protocols. The main objective of the proposed workflow is to try to bridge the gap between the laboratory wax test measurements and transient flow assurance modeling. The ultimate goal is to reflect the wax characteristics in the large scale field operations. This workflow is intended to facilitate the communications between engineering design teams and flow assurance laboratories; because more representative data are needed to better predict the wax problem throughout the field life.