Balol field is located in the heavy oil belt of North Cambay Basin in the state of Gujarat, India. The API gravity and oil viscosity is 15° and 300 cp respectively. Low primary recovery of 13% necessitated the application of ISC (In situ Combustion). The success of ISC in the southern part of Balol field has led to more than four-fold increase in oil production. Oil rate increased from a level of 60 m3/d to about 260 m3/d together with decline in Water cut from 82 % to 40% with injection of air @ 0.18 MMSm3/d. The ISC process was first implemented on commercial scale in October 1997 and has been instrumental in achieving the recovery of about 50 % of STOIIP from southern sector.

In ISC process in Balol, air is injected through injection well which is ignited artificially, to initiate the process in high temperature oxidation mode. The combustion takes place when oxygen, crude oil react to generate heat alongwith water and combustion gases. Oil is displaced by the vaporizing action of the thermal front and sweep provided by the combustion gases, hot water and steam. Nitrogen does not take part in the reaction and makes a free trip to the producers.

The produced fluids like flue gas, oil and water were collected at regular intervals, their composition were measured for monitoring the In-situ combustion process. The increase in CO2 concentration to the level of 15 %, reduction in oil viscosity and water salinity by half, increase in Well Head temperature and SO4 ion concentration in produced water enabled in understanding of various aspects of combustion process like confirmation of ignition, front movement and burn efficiency.

This paper elaborates how monitoring has helped in re-orientation and optimisation of air injection leading to manifold increase in oil production. Currently, oil recovery is close to the envisaged recovery factor.

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