The Testing of KA28 - Pressure Analysis in a Two-Phase Reservoir Page: 4 of 11
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THE TESTING OF KA28 - PRESSURE ANALYSIS IN A TWO-PHASE RESERVOIR
Malcolm A. Grant
Applied Math. Div., DSIR, Box 1335 Wellington N.Z.
Examples of two-phase pressure transient analysis are given,
for injection and discharge. Transients measured in KA28 are used
to identify the fluid feeding the well and to measure permeability.
Kawerau geothermal field in New Zealand has been exploited at
a low level (20 MWe) since 1956. Separated steam is used by a pulp
mill. The field has an area of 10 sq. km. (1). Investigatory
drilling has continued
consists of fractured
volcanics over a
greywacke basement (4).
Base temperature is
over 290 C. Permeabil-
ity is on average very
good, and also very
erratic. KA21 found
permeability in the
gregwacke at 1100m, in
286 water. Its flow of
600 t/h makes it the
equivalent). KA30 at the
other end of the field is nearly as good. Between
are some duds and some good wells.
KA28 was drilled as a stepout, 300m from KA21.
It was a surprise and a disappointment, as it found
lower temperature and permeability. Temperature
increases to 2660 at 770m (Fig.2), similar to the
adjacent wells. Beneath there is cooler water.
Detailed measurements with a surface-recording
spinner and temperature tool identify zones of fluid
loss or gain at 674m, 778m and around 1080m. (M. Sym
pers. comm.) The two upper feeds are very similar in
character and are hereafter lumped together as a
single upper feed, represented by values at 700m.
Stable downhole temperature at 700m is 264 , and
reservoir pressure 62 bars gauge. Temperature at
1080m is about 230 , and reservoir pressure 93 bars
gauge (5). The quoted reservoir pressures are the
measured downhole pressures at which no fluid enters
or leaves the well at that depth. They are not the
same as stable downhole pressures (6), as a well
cannot in general reach equilibrium at two depths.
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Grant, Malcolm A. The Testing of KA28 - Pressure Analysis in a Two-Phase Reservoir, article, December 16, 1980; United States. (digital.library.unt.edu/ark:/67531/metadc884565/m1/4/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.