In the absence of field rules to the contrary, the open flow
capacity of a gas well shall be determined by flowing the well into a pipeline
for a period of 24 to 72 hours, as required to attain stabilization through
approved metering equipment. This procedure shall be known as a one point
stabilized flow test. The rate of flow shall be recorded on a standard orifice
meter chart, either graphically or mathematically, or recorded electronically
in a flow computer connected to a metering device. The rate of flow at the end
of the period shall be extrapolated to atmospheric pressure by using the
characteristic well slope as determined from a multipoint back-pressure test.
(a) Multipoint back-pressure test. A
multipoint backpressure test shall be taken for determination of characteristic
well slope, "n," as determined from the equation
Q = C(Pc2 - Pw2) n
where:
Q = the rate of flow, using MCF per day at 14.65 pounds per
square inch absolute and 60°F;
C = the performance coefficient of the well;
Pc = wellhead shut-in pressure, expressed in pounds per square
inch absolute and using the casing or tubing pressure, whichever is higher;
Pw = static wellhead working pressure, expressed in pounds per
square inch absolute, at the termination of each flow period. Except as
otherwise provided, the casing pressure shall be used if the annulus is open to
the formation. If the annulus is not open to the formation so that the pressure
cannot be measured on a static column, the tubing pressure shall be used if the
flowing pressure is corrected for friction. All squared pressures shall be
expressed in thousands; and
n = a numerical exponent characteristic of the particular well,
referred to as "slope."
Multipoint back-pressure tests shall be limited to one per
commercial gas well. A second test shall be permitted for a commercial gas well
only if the well is recompleted into a separate common source of supply or for
good cause shown.
The basic procedures for taking a multipoint back-pressure test
shall be as follows:
(1) The well
shall be shut in for 72 hours, plus or minus six hours, and the shut-in
pressure shall be taken. This shut-in pressure shall be considered stabilized
unless readings taken with commission-approved equipment at a shorter period
are higher. In this event, the highest recorded pressure during the test shall
be used as the shutin pressure. If the shut-in period appreciably affects the
surface pressure, appropriate correction of the surface pressure shall be made
in order to account for the pressure due to the liquid column.
(2) If the well being tested has a pipeline
connection, it shall be flowed for at least 24 hours before the shut-in period
at a rate high enough to clear the well of liquids.
(3) A series of at least four flow tests
shall be taken. The tests shall be run in an increasing flow rate sequence. In
the case of high liquid-to-gas ratio wells, a decreasing flow rate sequence may
be used if the increasing sequence method will not give point alignment. If the
decreasing sequence method is used, a statement giving the reasons why the use
of this method is necessary, with a copy of the data taken on increasing
sequence, shall be furnished to the commission.
(4) Each flow test shall extend for not more
than two hours. If the wellhead working pressure does not decline more than 0.1
percent of the wellhead shut-in pressure during any 15-minute period before the
end of the twohour flow period, the pressure may be recorded and the next flow
test started. All subsequent flow periods shall be of the same duration.
(5) If the back-pressure curve
cannot be drawn through at least three of the plotted points, the well shall be
retested. If upon retest a curve cannot be drawn through at least three of the
plotted points, an average curve shall be drawn through the points of the test
if the slope of the curve will be not more than 1.0 and not less than 0.5.
(6) If the curve drawn through at
least three points of the back-pressure test has a slope greater than 1.0 or
less than 0.5, the well shall be retested. If upon retest the slope of the
curve is greater than 1.0, a curve with a slope of 1.0 shall be drawn through
the data point corresponding to the highest rate of flow. If upon retest the
slope of the curve is less than 0.5, a curve with a slope of 0.5 shall be drawn
through the data point corresponding to the lowest rate of flow.
(7) All tests shall be subject to review and
approval by a representative of the state corporation commission.
(8) The lowest rate of flow on the test shall
be at a rate high enough to keep the well clear of liquids.
(9) If possible, the working wellhead
pressure at the lowest rate of flow shall be drawn down at least five percent
of the well's shut-in pressure and, if possible, 25 percent of the well's
shut-in pressure at the highest rate of flow. If data cannot be obtained in
accordance with this paragraph, a written explanation shall be furnished to the
commission.
(10) Correction for
the compressibility of flowing gas shall be made in accordance with approved
commission methods.
(11) If the
static wellhead working pressure reading cannot be obtained due to packer or
dual completion, the pressure shall be calculated by using appendix A in the
document adopted by reference in paragraph (b)(4).
(12) If a satisfactory test cannot be
obtained on wells whose indicated open flow is 500 mcf or less, an exception to
the foregoing procedure may be granted by the commission and a slope of 0.85
may be assigned to the well.
(13)
Upon completion of the test, all the calculations shall be shown on any
approved form and shall be accompanied by a back-pressure curve neatly plotted
on equal scale log paper of at least three-inch cycles.
(b) One-point stabilized flow test.
(1) An initial one-point stabilized flow test
shall be made within 30 days from the date of first production of gas into a
pipeline and additional tests shall be taken yearly or as ordered by the
commission. Upon the completion of all flow tests, a copy of the flow
calculations shall be submitted to the commission.
(2) Immediately after the shut-in wellhead
pressure is taken, the well shall be opened into the pipeline and gas shall be
produced for the subsequent 24 to 72 hours at the test rate as required to
reach stabilization. During this time, the working pressure at the wellhead
shall be maintained as nearly as possible at 85 percent of the wellhead shut-in
pressure, expressed in pounds per square inch gauge, or as close to 85 percent
as operating conditions in the field will permit.
(3) The wellhead working pressure shall never
be more than 95 percent or less than 75 percent of the wellhead shut-in
pressure of the well being tested unless, in the judgment of the commission's
representative, it is impractical to maintain the pressure within these limits.
In this case, the well shall be produced at maximum capacity through either the
tubing or the annulus, whichever will give the greater drawdown.
(4) The open flow shall be calculated by use
of the formula specified in this paragraph. Flow shall be measured by an
approved meter throughout the test period, and the wellhead and meter pressures
shall be measured at the close of the test period by gauges approved for use in
the state corporation commission's "manual of back pressure testing of gas
wells," written pursuant to commission order dated May 15, 1957, docket number
34,780-C (C-1825), which is hereby adopted by reference, including the
appendices.
The rate at which the well is producing at the end of the flow
period shall be considered the stabilized producing rate corresponding to the
wellhead working pressure existing at that time, if the rate is not greater
than the average producing rate for the entire flow period. The observed
stabilized producing rate shall be converted to open flow by use of the
following formula:
See Formula at
http://www.kssos.org/pubs/register%5C2007%5CVol_26_No_20_May_17_2007_p_801-864.pdf
where:
OF = Open flow, expressed in MCF/D.
R = Stabilized producing rate, expressed in MCF per day at
14.65 pounds per square inch absolute and 60°F.
Pa = Atmospheric pressure, expressed in pounds per square inch
absolute.
Pc = Wellhead shut-in pressure of the well, expressed in pounds
per square inch absolute.
Pw = Stabilized wellhead working pressure at rate R, expressed
in pounds per square inch absolute.
n = Characteristic well slope as determined by the multipoint
back-pressure test.
(5)
Shut-in wellhead pressure shall be measured after the well has been shut in for
approximately 72 hours. The well shall have been shut in for not less than 66
hours and not more than 78 hours when the shut-in pressure is taken. If the
representative of the commission believes that the shut-in pressure taken upon
a well is incorrect, the representative may require that the well be blown to
clean fluids from the well bore or may take any other reasonable steps that may
be necessary to get a true pressure reading upon the well. If more than one
shut-in pressure is taken upon a well during the test period, the highest
shut-in pressure obtained shall be used in calculating the open flow of the
well.
(c) Metering
devices. An orifice meter, a critical flow prover, or a turbine meter in good
operating condition and properly calibrated in accordance with the
manufacturer's recommendation shall be the only acceptable metering devices.
The owner of the metering device shall have documentation of any recalibration
or refurbishment of the metering device and shall furnish the documentation to
the conservation division upon request.
(d) Gas venting. Gas shall not be vented
except when absolutely necessary.
