Well Stimulation by Downhole Gas-Air Burner
Authors: Depriester C.L. , Pantaleo A.J. 
Published: December 2007

A successful gas-air burner has been developed to stimulate production by downhole in the producing interval, and heat losses.In field trials production increased with burner rate, up to maximum rates tested, directionally in agreement with theory. Production increases of 8 to 46 BOPD were observed for burner heat-release rates from 55,000 to 120,000 Btu/hour in wells producing 12 to 17 degrees API crude, cutting 5 to 75 per cent brine. The highest production increase measured was in a 3,500 ft. well with 140F formation temperature.In the longest test to date, the burner operated 300 days, including 240 days at rates of 100,000 Btu/hour or above. The test was stopped to examine the burner, and inspection indicated operating life would be at least two years, adequate for commercial use. Burner design, auxiliary equipment, operating procedure and range of economic application are discussed.

Introduction

Use of wellbore heating to increase oil production has been practiced extensively the last 15 years using both continuous and batch methods. Batch methods vary from simply dumping a few barrels of hot crude down the well annulus to large volume injection of crude or fuel oil heated to high temperature and pumped down the tubing at high surface pressures. Continuous wellbore heating has been practiced with hot water- or oil- circulating heaters, and to a lesser extent with downhole electric heaters. According to a supply company estimate, there are 3,500 circulating heaters operating in California alone.

Valuable as these stimulation methods are, there remains an extensive range of conditions outside their capabilities. Batch heating requires periodic repetition, and costs increase when large volume, high-temperature treatments are used. Hot water circulating heaters are excellent performers in shallow wells, but the wellbore temperature attainable at reasonable cost falls off rapidly with depth because of high heat losses to strata above the producing formation. Electric heaters work well in some areas, but cable problems and burnout from coking are frequent problems. Power losses increase with depth, and capacity of electric heaters usually is not above 70,000 Btu/hour.It was concluded that significant improvement in the economics of viscous crude production would result from a new, high performance downhole heating method. Preferably the new method would be capable of high heat-release rates at depths to at least 5,000 ft. in wells with typical casing programs. Capital and operating costs should be minimized, consistent with dependable performance and minimum operating attention.

This paper reports results of successful field trials with downhole gas-air burners and briefly describes burner design, installation and operation. Field test results are reported for an early model capable of 50,000 Btu/hour and for a new design proven satisfactory up to 120,000 Btu/hour and possibly capable of higher heat-release rates. The early model demonstrated feasibility of downhole burner operation, economic production increases, and the need for higher continuous heating rates to obtain additional production stimulation.

Gas-Air Burner System

The gas-air burner system includes the donwnhole burner, surface equipment to supply a combustible mixture of gas with air at elevated pressure, and downhole tubing to deliver the gas-air mixture to the burner. The burner is ignited by a small electric glow plug powered by cable run through the burner gas-air supply tubing. Equipment installation is straightforward and operation is trouble-free as demonstrated by field tests.

Gas-Air Burner

The burner shown in Fig. 1 has a tapered combustion chamber, cast from a specially formulated ceramic in the upper portion of a 15 ft, 3 1/2 in. diameter steel tube. A thermocouple, electric resistance igniter and flame arrestors are mounted in a machined steel igniter block located above the combustion chamber. The thermocouple indicates a temperature rise when the burner is operating; the igniter is used only to start the burner flame. Flame arrestors prevent flame propagation from the combustion chamber into the upper section of the burner and gas-air supply string. Gas-air mixture enters the combustion chamber through inlet tubes from the igniter block.

JPT

P. 1297^