Development of an Enhanced Two-Phase Production System at the Geysers Geothermal Field Page: 4 of 10
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well bore. In these cases the first indication at the surface of water breakthrough into the well
bore is an observed unusually sudden decrease in steam flow, because water has accumulated in
the deeper section of the well bore and has actually reduced in not eliminated any steam
production from the deeper steam entries. In these cases the two main factors for why the steam
has insufficient energy to lift the water is because of the relatively large well bore diameter, and
because of the existing operating backpressure at the well head is high compared to the reservoir
Simply put, the concept of how to overcome this problem is to necessarily alter either or both of
these two conditions. The inserting of smaller diameter tubing into the well will reduce the
effective well diameter, increasing the ability of the steam flow to lift the water to the surface.
Secondly, the surface equipment can be designed to minimize the backpressure at the well head,
by use of for example a cyclonic separator tank that can be operated at pressures as low as
One of the critical variables of this Project is to determine a workable tubing diameter. From
experience 2-7/8" and 4-1/2" tubing are common diameters for this type of application.
Additionally, these sizes are readily available.
A string of 2 7/8" drill pipe was inserted into the well and a flow test was conducted at three
depths: 5,025 ft, 6,025 ft. and 6,995 ft. The ability of the tubing to lift water at the various depths
was determined by a flow test. The well was allowed to flow through the drill pipe to a tank and
the volume of water was gauged over time. Figure 4 shows the results of that test.
TUBING AT 6995'
TUBING AT 6025'
TUBING AT 5025'
The test indicated that the deepest setting was the most successful at lifting fluids. Therefore, it
was determined that tubing should be set at the deepest depth possible, with sufficient
perforations to allow for water to enter the tubing, even if the bottom of the tubing is plugged.
Later, 4 " tubing showed that water could successfully be lifted with the larger diameter pipe
while allowing for increased steam flow. Therefore 4 "pipe was permanently installed in the
well to enhance geothermal steam production.
Wellhead Hanging Tool
To install the tubing in the wellhead, a special hanging tool needed to be fabricated that can
support the weight of 70,000 lbs. of tubing but without interfering with well control of both the
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Enedy, Steven. Development of an Enhanced Two-Phase Production System at the Geysers Geothermal Field, report, December 14, 2001; United States. (digital.library.unt.edu/ark:/67531/metadc719556/m1/4/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.