Abstract

In-situ combustion process was initiated in March, 1990 on a pilot scale in heavy oil field of Balol. Based on the success of the Pilot in terms of stabilised combustion and additional oil gain, the process was extended to a near by larger pattern in January, 1992. The main objectives were to observe the process performance in a larger area and to see the effect of placing the injector closer to downdip producers. The overall combustion performance of the project indicates that combustion can be initiated, sustained and propagated in reservoir like Balol and substantial oil gain can be achieved through proper monitoring of the process. The success of the project and the experienced gained through operating it, led to the decision of commercialisation of the process in the entire field. This paper deals with the performance of the in-situ combustion process at Pilot and extended scale, operational problems faced during implementation and the future strategy of commercialisation of the process.

Introduction

Oil and Natural Gas Corporation Limited (ONGC) initiated Pilot testing of in-situ combustion process in March, 1990 in the heavy oil field of Balol in North Gujarat, India.

Interest in application of in-situ combustion process as an Enhanced Oil Recovery (EOR) tool was stimulated mostly due to the existence of large heavy oil reserves with low expected primary recovery. The encouraging results of the Pilot led to the extension of the process to an adjoining 9-hectare pattern in January, 1992. Presently combustion is in progress in both the patterns.

Pilot

Based on the laboratory findings, an inverted 5-spot pattern of 2.2 hectare was initiated on March 16, 1990. The Pilot has four producers (IC-2, IC-3, IC-4 & IC-5), one injector (IC-1) and one observation well (IC-6), 20 m away from injector and in line with IC-5. Figs. 1 & 2 show configuration of Pilot and location map of Balol field respectively. Table 1 shows petrophysical parameters of the Pilot area.

The main objectives of the Pilot were:

  • To test whether combustion can be sustained and propagated.

  • To assess incremental oil recovery and Air-Oil Ratio.

  • To build-up and absorb the technology.

Pilot Operation

Ignition. Sand-face ignition was initiated by means of a gas burner. A total of 6.64 MM kcal (26.34 MM Btu) of heat was injected in a span of seven days during ignition operation.

Air and water injection performance. Air & water injection profiles of the Pilot are shown in Figs. 3 & 4 respectively. Dry combustion phase lasted for 110 days after ignition period. Thereafter, the process was switched over to wet combustion phase. Air injection was increased in steps from 10,000 Nm3/d to 35,000 Nm3/d during dry combustion period. But due to subsequent rise in gas-liquid ratio in updip wells, air rate was reduced to 20,000 Nm3/d. Initially, during wet combustion phase, air and water were injected simultaneously at water-air ratio (WAR) of 0.002 m3/Nm3. It was switched over to cyclic injection in January, 1992. WAR was maintained, thereafter, at 0.001 m3/Nm3. A cycle consists of 6 days of air injection followed by one day of water injection. Since last week of February '96 water injection is being carried out through updip well IC-5 and air injection is being continued through IC-1.

As on March 31, 1996 cumulative air and water injected were 32.81 MM Nm3 and 34,250 m3 respectively.

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