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Abstract

Multiphase, flow is widely encountered in the petroleum industry. It is expected that a petroleum industry. It is expected that a significant part of the future production of oil and gas in Offshore will come from deeper, water and in many cases from marginal fields. Rigid fixed platform system with production and processing facility located in the same field may not be economical in such cases.

Many oil companies are investing heavily to develop multiphase technology with the ultimate goal to transport unprocessed multiphase well fluid for a long distance. Initial efforts for development of multiphase pumping and metering have been successful. The R and D backup for flow modelling is being provided by the research centres.

In the present study, a review of present state of multiphase long distance transportation, multiphase pumping, metering and flow modelling distance multiphase flow from Indian Onshore and Offshore fields have been presented. Four new field developments with multiphase well fluid transportation have been presented which are currently under execution.

Introduction

Multiphase well fluid transportation is quite common in oil industry. The produced fluid of every oil and gas well becomes multiphase (oil water and gas together) or two phase (oil and gas) mixture on reaching at well head.

Single phase liquid or gas flow at well head is a very a case. Transportation of this multiphase fluid from well to the seperation/processing facility (platform/gathering station) is accomplished through pipe lines.

Idealy, the separation facility should be located at the wellhead to get optimum production from any oil/gas well. However it is the costliest alternative since this system requires too many seperation and processing facilities. Similarly, locating, centralised separation facility or a field having many oil/gas wells spread over large surface area, requires large multiphase pipeline network. This system creates excess back pressure at wellhead resulting in reduced self flow life and lower production from the well. Therefore, in most cases, a compromise based on economic analysis, is adopted in locating the process facility for any field.

In recent years many discoveries have been made in Indian Offshore and in some cases the water depth is, beyond 100 metres. Some of the marginal fields discovered recently are given at Table-1. It is predicted that more and more new discoveries will come from Offshore and mainly from deeper water.

Most of the new discoveries in India, have been marginal in nature and more complex technologies are required to produce and a transport the fluid mainly because of presence of H2S, CO2, sand and paraffin in the well fluid and fast depletion of reservoir pressure. The production systems for these marginal fields require subsea well completion in many cases. The economics for these marginal fields development, therefore, call for transportation of multiphase fluid from wellheads to long distance located process platforms where spare processing capacity is platforms where spare processing capacity is available or to a land based process facility. It is, therefore, multiphase long distance transportation is emerging as a major technology of the future. It is expected, to dominate on technological options for exploitation of Offshore, deep sea completions and marginal field developments.

Multiphase technology has been applied in almost all producing fields ranging from smaller to bigger. Almost 60-70 percent of all Offshore and Onshore pipelines are having multiphase flow since all the well flow lines/production flowlines to process platform/process facility are in multiphase flow mode. However most of the flowlines are of smaller diameter and length.

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