Offshore Riser Slug Flow Avoidance: Mathematical Models for Design and Optimization

Abstract

Yocum, B.T., Member AIME, Yocum International Asso. Abstract Losses in capacity of up to 50% in offshore oilfield production systems have been caused by poor design of two phase flow risers. Operators often do not realize the reduced capacity and additional costs caused by slug flow formation in risers, because the total system has been adjusted for slug flow avoidance, to a non optimum operating point. This paper (1) proposes a riser point. This paper (1) proposes a riser slug flow prediction chart with accept able slug and stratified flow range (2) develops a mathematical model for the elevation pressure drop and frictional pressure loss in the riser as a function pressure loss in the riser as a function of flow capacity (3) discusses the influence and characteristics of entering conditions (4) proposes several alternative designs to eliminate slug flow at minimum pressure loss and cost (5) recommends a inter company data gathering and testing program on risers, and, other vertical sections, in order to formulate more exact design models for optimization. Introduction During the 1960's progress was made in advancing the technology, and, rapid computer calculation, of two phase flow oilfield production systems. These utilize the flashing of the two phase mixture of oil and gas, to produce flow with pressure drop. Several large scale oilfield installations have been made both onshore and offshore. An example of a multiwell-flowline-trunkline system is shown in Figure 1. Such configurations of interdependent wells, branchlines, junctions, main trunklines, and gas/oil separators, often prove to be optimum cost solution in many fields; especially offshore fields. Large capital savings often are possible, both for initial and future facilities, as well as operating cost savings, when compared with the single well, single or looped flowline concept, producing to a centrally located gas/oil separator plant. Separate gas lines may be avoided by us of the trunk lines.