Abstract
The northern part of the Cambay Basin located in Mehsana, Gujarat (India), is fenced by a number of heavy oil fields reserving about 140 MMT OOIP. Balol and Santhal fields form a part of this heavy oil belt with API gravity 15-18. The oil viscosity ranging from 50 to 450 cps at reservoir pressure of 100 kg/cm2 and 700C temperature. High mobility contrast between viscous oil and water has resulted into low primary recovery. Subsequent Artificial lift methods resulted into high water production rather than oil. Thus, it necessitated for in-situ combustion technique.
In-situ combustion is a thermal enhanced oil recovery process. The technique is based on the principle of reducing viscosity by heating of oil in the reservoir itself. It involves ignition in the well and injection of air to sustain flame front. In this process a small quantity of in-place oil burns, producing CO2, water vapours and heat. It helps in lowering the viscosity of oil, which increases the oil mobility and displace it towards the surrounding producers.
It is a matter of pride that ONGC, Mehsana has successfully implemented this technology. The project was initiated at Balol field on pilot scale in 1991. Based on encouraging results, in-situ combustion technique was implemented on commercial scale in 1997 at Balol and Santhal fields. It has not only given a new lease of life to these fields but has also increased the oil recovery factor from 6-12% to 39-45%.
Production engineering for in situ combustion involves careful planning and monitoring for successful implementation. Based on field experience, some of the major issues which came up during implementation are summarized in this paper. It can be helpful for successful planning and implementation of new projects
