Automation of Gas Lift Operation in Bombay Offshore Fields.

Abstract

The material difference between a conventional gas lift system and an automated gas lift system is that the later helps to improve the efficiency and smoothen the gas injection to each and individual wells for maximised oil production. It is an acknowledged fact worldwide that wherever the automation in continuous gas lift system has been introduced, the oil production has increased from 5 to even 35%.

In Bombay offshore fields, all the artificial lift wells are on continuous gas lift and it is appropriate at this stage to introduce the automation of gas lift in phase wise for the area where the gas lift system have been contemplated.

On introduction of gas lift automation, the benefits like automatic control of quantity of gas injection in individual well as per the well requirement, optimum gas allocation to each well, easy and quick monitoring, troubleshooting of gas lift operation on individual well basis, and the last but not the least overall increase of oil production, can be derived. The other additional benefits like conservation of energy in terms of utilisation of high pressure gas can also be accrued in gas lift operation.

The present paper has dealt with the simplified methodology of gas lift automation for surface injection system. To achieve the objective, hardware and software are the major heads and dimensions of these have been dealt in detail.

Introduction

Continuous gas lift is presently operating in about 300 wells of Bombay High field, 30 wells of Heera field, and 10 wells of Neelam (by temporary means) of Bombay offshore. This mode of lift is planned to be installed on regular basis in Neelam Field, South Heera and Heera Phase-III development wells in the near future covering about 110 wells on 15 well platforms using 2 central process platforms.

73% of wells of Bombay high field presently operate on continuous gas lift and contribute about 65% of total oil production from the field. There are 5 process platforms, to receive well fluid from 77 well platforms. On process platforms, oil and gas are separated, associated gas after compression is supplied for gas lift purposes and for sales at onshore terminal via sub-sea gas trunk-line. In Heera field, 75% of wells operate on continuous gas lift and contribute about 73% of total oil production from this field. The field is having one central process platform and receives well fluid from 9 well platforms.

The details of gas lift operation in Bombay high has been elaborated by Verma et al. The conventional multi-mandrel gas lift system along with fixed orifice as operating valve in most of the cases have been used. The gas injection at well platform consists of 2"/3" injection line with PCV, restricted orifice (injection choke), pressure & flow recorders, pressure & temperature indicators, as well as proper safety systems. The compressed gas at about 1150 psi is supplied to well platforms via sub-sea line network of 4-12" dia from 5 process platforms. The different troubleshooting operations carried out on these wells have been described for some cases in Reference [8]. Similar systems are available in Heera field also.

To monitor & control offshore oil wells, SCADA system has been installed at 63 well platforms of Bombay high field with central stations at process complexes which are provided with a PDP 11/44 computer, a Master Telemetry Unit (MTU) and Master Radio with Omni directional antenna. The schematic layout of this system is given in figure-1. The computer system is being upgraded in phases.

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