Modification Of A Downhole Gas Burner For Successful Ignition In A Low-Pressure Heavy Oil Reservoir
Authors: D&apos;souza M.V. , Tsang P.W. 
Published: March 2010

Ignition problems were encountered with a downhole gas burner for initiating a fireflood in a low-pressure depleted heavy oil reservoir. The gas burner design was modified and tested for two air injection rates at the National Research Council of Canada. A better split of the air flow and mixing with the fuel gas, as well as improved flame stabilization were provided in the modified burners. Successful ignitions were achieved in the Husky Tangle fags Fireflood Project in the Lloydminster area.

Introduction

Husky Oil Operations Ltd. has been conducting thermal recovery pilots in the Lloydminster heavy oil pools for some twenty years. Cyclic steam stimulation and steamflood pilots have been more successful than fireflood pilots, but the latter is a potential recovery process for the extensive heavy oil resources in thinner formations. Development of fireflood recovery technology is continuing in the Tangleflags Fireflood Pilot in Saskatchewan, northeast of Lloydminster (Fig. 1). The pilot was initiated in 1984 with three 12.1 ha, inverted seven-spot patterns and six offset wells, as shown in Figure 2. The wells were completed in the General Petroleum (GP) Formation (a type-log is shown in Fig. 3).

In 1985. the injection well 4C7-13 was auto-ignited by steam and air injection. This pattern has been performing well with extremely good oxygen utilization. The other two injection wells, A6-13 and A7-13, were ignited successfully in 1985 with downhole natural gas burners, but poor oxygen utilization in both patterns forced their shut-down in October 1985 and August 1986, respectively.

The performance of the gas burner ignitions and the producers were examined. Poor burner ignition in a low-pressure depleted reservoir was cited as a major reason for the poor oxygen utilization. Similar ignition problems were encountered in the low-pressure depleted reservoir at the Husky Golden Lake Sparky Fireflood Project. It was concluded that the gas burner design should be modified for re-ignition in the Tangleflags pilot and to meet the commitment of continuing development of the fireflood technology.

The operation of the existing gas burner was reviewed at the Gas Dynamics Laboratory of the National Research Council of Canada (NRC) in Ottawa. A design program was initiated to modify the burner for operation at the 500 and 1000 kPa reservoir pressures in the Tanglefiags Pilot. A modified burner was built and evaluated at NRC. Using the modified burner, injection well A6-13 was ignited in June 1986. The burner was further modified at NRC for a lower air injection rate in A7-13, which was also successfully ignited in November 1986. Good oxygen utilization was subsequently achieved in both patterns.

Burner Design Flame Stability and Ignition Considerations

A flame is secured in a stream of combustible gases when the burning velocity SL of the mixture equals the local gas velocity U. When either one of these quantities exceeds the other, instabilities due to blow off or flashback of the flame are experienced. The burning velocity depends on the initial pressure, temperature, and composition of the combustible mixture, and its maximum value is usually realized close to the stoichiometric mixture ratio.