Flow Assurance Analysis on a Subsea Network Offshore Peru: Lobitos Asset - Case Study

Abstract

Producing from shallow waters offshore Peru, Lobitos is a mature Light Oil asset operated by SAVIA Peru S.A. The operator undertook the task of building a network model that included production platforms, pipelines and processing facilities. Given the operating conditions and produced fluids composition, paraffin formation was identified as a primary flow assurance issue in the system. This paper describes the flow assurance analysis on the transfer lines, and discusses the findings and recommendations.

The production system comprises twenty offshore platforms interconnected via four subsea pipeline networks: high pressure gas-lift gas, low pressure gas, liquids, and sales gas. Compression occurs at selected key platforms. The twenty platforms and the four pipeline networks are combined into a single complex model able to reproduce the hydraulic behavior and the flow trajectories under any conditions imposed on the system. The model enables the operator to predict the onset of hydrates, wax, and asphalthenes. With the help of specialized software, a pressure-temperature (P-T) diagram, along with solid-liquid phase envelopes, were plotted for each of the liquid transfer lines.

Analysis of the system revealed that among the organic scales, paraffin was creating an observable impairment to flow. Given the volume of liquids transported and the fluid composition, the sea-shore transfer lines were identified as critical points for paraffin deposition. With wax content as low as 0.6 % m/m, the line connecting the CC-ZZ-PRIMAVERA facilities is the most paraffin-affected pipe, given that wax will precipitate at temperatures as high as 105° F (41° C). The hottest point in the line only reaches 77° F (25° C). The pipe connecting the LO10-PRIMAVERA facility is also subject to paraffin precipitation. In this case, the paraffin would become unstable at 90° F (32° C), but given that the fluids only reach 63° F (17° C) and the line transports about 40% of the produced liquids, it was identified as another critical point in the system. The line from the H-PRIMAVERA facility is the least affected, given that all fluid comes from shallow, warmer waters, and the volume transported is only 1% of the production.

Because the infrastructure is old, pigging operations are ruled out; however, since most of the wells are gas lifted, it is recommended that hot gas be injected wherever possible to increase the wellhead temperatures. Additionally, two extra-points of paraffin solvents have been implemented.

The use of an integrated model that rigorously accounted for mass and heat transfer phenomena along with proper fluid characterization and a specialized flow assurance algorithm enabled the accurate prediction of paraffin deposition and identification of key points for implementing remedial measures.