The most commonly used method of bottom hole heating is the circulation of hot water through a heat exchange system. This involves heating water by the use of circulating coils or conventional low pressure steam boiler equipment with its relatively inefficient use of fuel and the need for a power and pumping unit for circulation.
This method, although having some merit at shallow depths is expensive on operation and limited in application because of the inability to provide adequate temperatures at lower depths.
The application of heat by the use of electricity also has been tried extensively and found useful to a limited extent in some situations, but because of the cost of operation and secondary problems of cable maintenance it has not proven to be a satisfactory answer under the conditions of pressure, chemical action, depth, and other conditions found in these problem wells.
The Lawler system of bottom hole heating uses high pressure, high temperature steam as a source of heat and utilizes simple principles of physics to obtain the transfer and application of required temperatures at depth.
The system not only solves the problems of heating of wells effectively but does so with a high degree of operating economy as well.
This fact of operating economy takes on added significance when it is noted that the cost of recovery has in many cases of well stimulation by electrical heating or circulation of hot water been greater than the value of the added production obtained.
From an economic point of view the figures relating to production increase are the most important of the above data.
A sub-marginal producing well was chosen intentionally for the testing because of the greater problem involved in returning this type of well to profitable production.
Other experience with bottom hole heating indicates it is easier to increase substantially the production of a 20-bbl. well, for instance, than to bring a sub-marginal producer into profitable production.
The average daily increase of production obtained in this test was 6.5 bbls. per day. This was an increase from the daily average of 2.5 bbls. before heating to an average production of 9 bbls. per day after heating. This is a 360% increase, and when projected to a yearly basis would be an increase of 2,340 bbls.
The second most important factor established by these tests is the outstanding economy of the operation as shown by the low gas consumption of 100 cubic feet per hour in bottom hole heating test. Field sources of gas are often available for these purposes.
The depth of this test was 2200 feet which was a typical depth for the wells in this field.
The maximum depth at which the equipment will operate is not known as further testing is required to establish this fact.
However, in consideration of the large reserve of working pressure available during the test at 2200 feet it can be assumed that the generator will produce sufficient steam pressure and temperature to introduce the heat required to reach formations much deeper than this test.
LAWLER MODEL NO. 100- A DRY STEAM GENERATOR
TYPE.....WATER TUBE DESIGN
TUBE SURFACE -100 sq.ft. Heating
MATERIAL . . Molybdenum Seamless Steel Tubing
MAXIMUM PRESSURE . . .500 P.S.I.
3000 P.S.I. Hydrostatic Test SUSTAINED EVAPORATION 300 lbs.
B. T. U. INPUT - 105,000 to 210,000
B.T.U. per Hour
OVERALL DIMENSIONS Height 30'
Length 52', Width 21'
WATER CAPACITY ... 10 gal. Full
5 Gallons at Operating Level
STARTING TIME - 200 P.S.I. within
FEED WATER PUMPS Walking Beam
or Lifting Unit Operated
WATER CONTROLS . . . Pressure
Regulator, Electro Magnetic and
Sight Water Level
FUEL .... Natural Gas, or Butane
FUEL CONSUMPTION . . 100,000 -
200,000 Cu.Ft. per Hour Natural Gas
BURNER . . . Bryant Industrial Type
ELECTRIC CONTROL 6 or 12 Volt
D.C.; 110 Volt A.C.
FEED WATER MAKE-UP ....
... by Condensation Return