Abstract

HEERA, one of the most promising hydrocarbon producing fields in Mumbai offshore; produces oil and gas from multilayered pay zones ranging from depth of 700 meters to 1500 meters. Bandra Formation, the uppermost strata of reservoir is a Miocene structure. This is the youngest pay zone in the Cenozoic carbonates of Mumbai Offshore basin comprising of limestone with shale bands at a depth of about 700 meters sub-sea bearing lean gas with 96+ percent of C1. Heera Offshore Processing Complex presently uses 2, 50,000 SCMD of rich gas for internal consumption mainly in turbine generators and Process Gas Compressor drivers. Process complex delivers gas to three users i.e. Gas Lift Wells at 80 kg/cm2, End Consumer at 56 kg/cm2 and Internal Consumption at 27 kg/cm2. Presently, fuel gas is tapped from Process Gas Compressor discharge at 80 kg/cm2. This gas has about 28% of C2+ component and good source for Value Added Products like C2/C3, LPG, Naphtha, etc. Study reveals that Bandra gas shall be ideally suited as fuel gas. Rich gas when replaced by lean Bandra gas as fuel gas will in turn add in to the Value Added Products (VAP) extraction. Around 1.0 MMSCMD gas production is expected thru upcoming three gas producers on HG platform in Bandra formation lasting for a period of 15 years.

The study suggests maximum utilization of Bandra gas as fuel gas in phased manner depending on the available formation pressure. Study also infers a) Optimization of the compressor utilization depending on the end pressure requirement by way of dedicating one compressor exclusively for compressing lean Bandra Gas at 56 kg/cm2, b) Split the two trains of Gas Dehydration Unit and operate them at 80 kg/cm2 and 56 kg/cm2 pressures respectively. Thus saving in compression energy of 960 KW per compressor, c) Sourcing fuel gas from Bandra formation shall reduce collective emissions of Green House Gases (GHG), mainly CO2, by an average of 7.28 percent compared to the present emission using rich gas, d) Rich gas thus added in the gas to consumers will add quantities of VAP (C2/C3: 50 TPD, LPG: 50 TPD and Naphtha: 8 TPD) extracted at downstream end.

The above study has optimized compression, dehydration facilities in terms of energy conservation, reduction of GHG emission and generation of VAP. Recommendations of the study are currently in the process of implementation.

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