Abstract

The paper describes the operational principles, the modeling foundations and some laboratory results of the gas-liquid separation process taking place within a cyclonic gas-oil separator. The centrifugal and the gravity forces, acting on the flow of the gas-liquid mixture, are the main driving mechanism to separate the phases. A research program, conducted by PETROBRAS and UNICAMP, was aimed to the hydrodynamic processes occurring within the equipment. Laboratory data were obtained from down size scale models operating with mixture of air and liquid with different viscosities. The basis for the modeling is launched and a discussion regarding the limitations and constraints of the operation is presented in light of the experimental results. Prospective field applications, based on the extension of the laboratory results to actual fluids and full dimension prototypes, are also presented.

Introduction

The cyclonic separator is designed to separate the free gas and oil at the well-head. Once the fluids are separate4 they can be transported to the platform through individual lines. The oil is pumped by a conventional ESP - Electrical Submersible Pump, installed in the lower part of the device. The gas is driven upward by the pressure difference that exists between the separator and the collecting vessel on the platform. This concept of separation has a number of advantages: the pressure at the well head is lowered thus increasing the reservoir production; the oil, separated from the gas, can be pumped by a centrifugal pump transporting gas and oil to the platform through distinct pipelines avoids, or at least reduces, some typical problem in two-phase flows; separating the phases at the well head makes feasibly measuring each stream, which results in a better inventory of the reservoir. Such benefits enable this technology as a &date to develop deep water or marginal oil fields.

This concept of separation system herein described is a variation of the Vertical Annular Separation and Pumping System - VASPS. VASPS is a UK patent application issued to the British Petroleum Company in 1988. Publications describing the operational principles of VASPS can be found in Refs, 1 through 3. The testing of VASPS is now a subject of the "VASPS Pre-Sub sea Phase 11"Project.which has been operated by AGLP on behalf of Mobil and Brasoil. At its present development stage, scale models of VASPS have been tested at AGIP's production and test site in Trecate.

The present work is a joint development between PETROBRAS and UNICAMP - The State University of Campinas, in Brazil. The contract pointed out to the development of a model expressing the two-phase hydrodynamic processes occurring within the separator. During the period of the work, down size prototypes were built and experimental data was taken to calibrate the model and support it. The purposes of the laboratory simulations were two-fold: to reveal the basic mechanisms of separation and to find the operational limits of the prototypes.

This content is only available via PDF.
You can access this article if you purchase or spend a download.