Abstract

Mumbai High located about 160 km West-North-West of Mumbai city in the Arabian sea on the continental shelf of Western India , is the largest and most prolific oil field in India. It is divided into two blocks i.e. North and South. Two important carbonate reservoirs in Mumbai High are L-II & LIII. In between these two blocks L-III reservoir becomes shaly , which acts as a barrier between these two blocks facilitating independent exploitation of the reserves of Mumbai High North and South fields. The clastic reservoir S-1 sand is free gas bearing and it lies in between L-II & L-III reservoirs. L-III reservoir which is present through out the field while L-II reservoir is hydrocarbon bearing only in the Northern block of Mumbai High. The L-III reservoir is multilayered accumulation with 10 main sub layers. The sub layers are designated from top to bottom as A1, A2-I to A2-VII, B & C. Crude oil in A1 layer in western flank is highly paraffinic in nature having high pour point , wax content & asphaltenes. The wells producing waxy crude oil from A1 layer in western flank have shown gradual decline in production due to precipitation and deposition of paraffins & asphaltenes causing impairment of permeability. Deposition of asphaltene in the reservoir makes the formation oil wet there by reducing the relative permeability to oil. Asphaltenes are not soluble in straight chain hydrocarbons such as Kerosene, Diesel oil and Condensate. A new chemical formulation was developed which was field implemented.

The treatment has improved the well productivity of number of wells . The best part of the technique is the sustained production. Case studies of number of wells has been discussed in the paper.

Introduction

Mumbai high is producing oil mainly from L-II & L-III limestone reservoir. L-II is hydrocarbon bearing in Mumbai high north, where as L-III is hydrocarbon bearing in north & south. The L-III reservoir is multi layered accumulation with 10 main sub layers. The sub layers are designated from the Top to bottom as A1, A2-I, A2 VII, B & C. The structural features control the fluid distribution such that the main oil producer sections are located in lower zone in the Eastern up dip area & in the upperzones in the middle & on the western flank of the field. The sub layer reservoir properties vary both laterally & vertically and this causes complex up fluid flow behavior & pressure communication within the layers under dynamic condition.

The A1 layer in the western flank area is a single layer & the most potential for additional production & recovery improvement. A1 layer holds about 230 MMT oil (IOIP) in Mumbai high north and south with only 7% recovery so far.

Technology for optimal exploitation has been established through successful drilling of number of horizontal wells in the area.

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