Impacts of Transient Analysis on Kuito Production Operations
Authors: Song S. , Peoples K. 
Published: October 2008

The Kuito FPSO and subsea production system offshore Block 14, Angola, was recently expanded to handle additional production from another area of the field.

As part of the detailed design of the new production system, transient simulations using OLGA were performed to study the system's thermo-hydraulics behavior. This paper presents how OLGA, a transient multiphase flow simulator, was benchmarked using extensive production data from the existing Kuito production system and how the benchmarked OLGA models were used to perform the operability analysis of the new subsea production system. Transient operations, like planned shut-in and startup, unplanned shut-in and startup, blowdown, and pigging, were studied including issues associated with hydrodynamic and severe slugging. Particular attention was paid to how the new production system would interact with the existing production system during the transient operations.

This paper will also present details on actual start-up of the new production system and the benefits transient simulation offered.

Introduction

Transient simulations were used as part of the operability studies for the ChevronTexaco Kuito production system. The Kuito field, located in Angola Block 14, West Africa, is being developed in several phases. The A production center is the initial development of the field. The A subsea production center consists of 12 production wells around a 12-slot production manifold. The manifold is linked to an FPSO via two production flowlines and a test line. An umbilical system consisting of two gas lift/methanol umbilicals and one control umbilical supports production from the manifold.

A new set of wells (the C center) was planned to be clustered in a manifold configuration similar to the A center. The manifold and the associated subsea distribution units will be tied back with an umbilical/flowline system to the existing Kuito FPSO. A tie-in module dedicated to the C center with all the necessary associated facilities such as pigging system, chemical injection, gas lift control and umbilical termination units will be installed on the FPSO.

The Kuito fluids are semi-heavy with relatively low GORs. The A center flowline system is inclined downwards followed by a flexible riser. Thus, it is favorable for severe slugging to form in the system. The C center is located so that the flowlines will be inclined upwards to help mitigate slugs. To properly tie the C center into the existing FPSO, quite a few operational issues needed to be addressed. How will the C center production system interact with the A center? If one system is shutdown, will it adversely affect the other system? If slugging occurs with the C center system at early field life due to low production, will the A center production system be stable or unstable? All these operational issues were intended to be studied by using transient simulations.

Transient multiphase flow simulators can simulate how the flow parameters, like pressure, temperature, liquid holdup and flowrates change with time. Thus, transient simulations are often performed to analyze system shutdown, re-startup, and blowdown, flowrate ramping, pigging, and other transient operations. OLGA is one of the most widely used multiphase flow simulators in the industry and OLGA 2000 was used for this work.