Energy and Power Engineering, 2009, 44-49
doi:10.4236/epe.2009.11007 Published Online August 2009 (http://www.scirp.org/journal/epe)
Study of the Law about Water-Cut Variation for the
Fractured Metamorphic Reservoir of Buried Hill
with Bottom Water
——A Case study at Budate Reservoir in Beir Depression, Hailar Basin
Shenggao QIN 1, Yanling SUN 2, Zhenqi JIA 1, Dagang YANG 1
1Key Laboratory of Enhanced Oil and Gas Recovery of Education Ministry, Daqing Petroleum Institute, Daqing, China
2Information Center of No.1 Oil Recovery Company, Daqing Oilfield Co. Ltd., Daqing, China
Abstract: Aiming at the complex flowing environment including the buried hill of Metamorphite, the active
bottom water and the fracture at Budate Reservoir within Beir Depression of the Hailar Basin, combining the
laboratory studies and based on analysis of its drive mechanism, field wells’ parameters were used to analyze
the effects of different conditions of the fractured metamorphic reservoir with bottom water on its law of wa-
ter-cut variation and the waterflooding efficiency. The results show that for the Budate buried hill reservoir
with bottom water, the gravity should be taken into consideration to determine reasonable perforation ratio
and production pressure difference. And because of the acid sensitivity of the buried hill reservoir, application
of proper clay stabilizer will enhance the field oil recovery to a satisfactory extent.
Keywords: metamorphic reservoir, bottom water, buried hill reservoir, water-cut
1 Introduction
Currently majority of the discovered buried hill reser-
voirs home and abroad belong to the type of carbonate
reservoir [1][2], in which there are complex types of
pore canals always including solution crevice, fracture
and so on. Thereby the fluid flowing inside shows the
unique features. Many scholars home and abroad have
made progressive advance in this area with the reservoir
engineering method, numerical simulation and others
[3-5]. However, Budate Reservoir in the Beir depression
of the Hailar Basin is the buried hill reservoir with bot-
tom water, where it is very complicated of the fluid
flowing laws that have not been reported academically.
So it is a new topic to perform the study of the law of
fluid flowing in this kind of reservoir and the fruits ac-
quired will have positive reference value for the same
kind of reservoirs.
2 Reservoir Features of Budate Buried Hill
Budate Reservoir lies in the bottom of the Hailar sedi-
mentary basin. It developed from the Trias and was
composed mainly of the carbon siltpelite, a slightly met-
amorphite and the unequigranular feldspar rock-fragment
sandstone. Due to the dissection of many faults, each
faulted-block is a buried hill reservoir with its inde-
pendent oil-water interface.
Budate Reservoir has geological reserve about
1811×104t, but very poor physical properties such as the
average effective porosity of 5.3％, the average gas per-
meability of 0.14×10-3μm2 and water-sensitivity coeffi-
cient of 0.64 which shows a bit strong water sensitivity.
The fractures developed plus the pores make the forma-
tion a fracture-pore reservoir.
3 Drive Mechanism of the Buried Hill
Reservoir
3.1 Principle of Bottom Water Coning
Because of the active energy of bottom water, when an
oil well produces at a certain rate after perforation of an
oil well, a pressure drop funnel would form at the bottom

S. G. QIN, Y. L. SUN, Z. Q. JIA, D. G. YANG
45
Figure 1. Schematic of the water core
of the well (see in Figure 1). The original horizontal
oil-water interface before production transforms to the
shape of a core under the well by the oil-water potential
gradient. If the well produces at a certain stable rate the
formed water core would stay at an certain altitude; if the
production rate increases the core altitude grows until the
bottom water flows into the oil well which would pro-
duce water.
By the difference of the core’s advance speed there are
two types of bottom water drive: lifting and coning.
Lifting denotes that in the process of bottom water dis-
placement, the front edge of the displacing water
(oil-water interface) move upwards slowly, smoothly in a
big area; while coning indicates the displacing bottom
water rushes into oil wells along local zones of high
permeability. So lifting is favorable for oil displacement
by bottom water with good oil displacement efficiency,
long anhydrous production period and high ultimate field
recovery; while coning which happens always near
wellbores, would results in quick water breakthrough,
short anhydrous production period and low ultimate field
recovery. The flooding pattern of bottom water is de-
pendent on two types of factors. One type corresponds to
factors such as the geological features of the reservoir,
the relationship between oil layers and water layers, in-
terlayers’ development and distribution, physical proper-
ties of the subsurface oil and water and so on, and the
other corresponds to man-made development program,
perforation positions and ratio, production rate and so
on.
Hence, it is a key technological problem to control the
bottom water coning in the development process of this
kind of reservoirs. For the field, to control coning of the
bottom water to extend the anhydrous production period
a reasonable production rate should be adopted; for a
single well the output should not overcome a special
number which is called critical yield. Finally the detailed
regulatory measures for the yield, production pressure
difference and the perforation ratio should be used to
control the bottom water coning. And to control the yield
should be realized by the variables as perforation ratio
and production pressure difference, which are the major
measures to control bottom water coning to displace the
overall reservoir upwards in the type of lifting.
Because the displacement energy source underlies the
oil reservoir, at the oil-water interface below, the bottom
water should firstly overcome the gravity itself then to
displace crude oil bottom-up. In this process the action
of gravity should be taken into consideration.
3.2 Mathematical Model of the Water-Cut Varia-
tion
In the development program of bottom water reservoir,
perforation is always done at the top of the reservoir to
avoid early water breakthrough. In contrast with the total
reservoir thickness, the fluid flowing in the porous media
could be presumed as the combination of the horizontal
flowing at the top layers perforated and the vertical
flowing in the sub-layers [7][8]. Hen the equation about
the water-cut variation could be derived as following:
'
rw
ww
w
rw ro
ow
wo
K
Q
f
K
K
QQ






(1)



'
'
125
ln 0.5
wo
w
e
w
H
p
H
R
R




 

(2)
4 Analysis of Law on Water-Cut Variation at
Budate Buried Hill Reservoir
Now take well D112-227, D108-229 and B28-1 as exam-
ples for Budate Reservoir to appraise the laws of water
variation with different parameters that are listed at Table 1.

S. G. QIN, Y. L. SUN, Z. Q. JIA, D. G. YANG
46
Table 1. Parameters from three wells of Budate Reservoir
Well μw(mPa.s) μo(mPa.s) γw γo h(m)H(m)x Re(m) Rw(m) α
D112-227 0.65 4.68 1 0.7761176 155 0.1193300 0.1 0.97
D108-229 0.65 4.32 1 0.745 110.495.60.1341300 0.1 0.97
B28-1 0.65 4.32 1 0.745 64 8.4 0.8688300 0.1 0.97
4.1 Effects of Reservoir Thickness, Perforation
Ratio and Production Pressure Difference on
Water-Cut Curves
The Water-cut Variation curves under several produc-
tion pressure differences are shown in Figure 3 for well
D112-227. We could recognize that at the Block-faulted
reservoir of buried hill with bottom water, the gravity
would have great influence on the law of Water-cut
Variation as:
Considering strong water sensitivity of the Beir Depres-
sion, in the lab three groups of relative permeability
curves were measured as in Figure 2, one displacing
fluid is water, the others are two kinds of clay stabilizer
solutions(CS-05 and CS-07).
1) If gravity unconsidered (β=1), the calculated wa-
ter-cut will increase more quickly than that in the case of
gravity considered along with the change of water satu-
ration. That’s if gravity considered, during early period
of low water saturation, the curves are steeper with
slower rate of oil production and less oil recovery; dur-
ing the later period of high water saturation, more oil can
be produced and the residual oil retained by water dis-
placement should be developed by the tertiary oil recov-
ery technologies.
0
0.2
0.4
0.6
0.8
1
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Sw
Kr
Krw_w
Kro_w
Krw_5
Kro_5
Krw_7
Kro_7
2) If gravity considered, the water-cut increases along
the rise of water saturation slowly. This phenomenon
could be explained that the gravity of the bottom water
itself that are displacing oil upwards decreases the water
breakthrough or fingering, so as to slow the rising veloc-
ity of water-cut.
Figure 2. Relative permeability curves measured by different displ-
acing agent
0
0.2
0.4
0.6
0.8
1
0.3 0.4 0.5 0.6 0.7
Sw
fw
Δp=11
Δp=8
Δp=6
Δp=4
Δp=2
β=1
3) If gravity considered, the sizes of production pres-
sure differences have obvious influence on the law of
Water-cut Variation. The less production pressure differ-
ence, the slower rising velocity of water-cut along with
the increase of water saturation, so is its reduced extent.
This phenomenon could be explained that the action of
gravity becomes less along with the increase of produc-
tion pressure differences and at a certain big value of
production pressure differences the action of gravity
could be neglected.
Figure 3. Water-cut curves versus production pressure difference
(D112-227) For well D108-229 the Water-cut Variation curves un-

S. G. QIN, Y. L. SUN, Z. Q. JIA, D. G. YANG
47
der several production pressure differences are shown in
Figure 4 which shows same law as discussed above.
For well B28-1 the Water-cut Variation curves under
several production pressure differences are shown in
Figure 3. From table 1 while other parameters are nearly
the same, the perforation ratios for well D112-227,
D108-229 and B28-1 are x=0.1193, x=0.1341 and
x=0.8688, respectively. Such conclusions could be drawn
as:
1) Along with the increase of perforation ratio, the ef-
fect of gravity on reducing the rising velocity of wa-
ter-cut becomes less. This case will be the nearly the
same as that while gravity unconsidered.
2) Along with the increase of perforation ratio, the ef-
fect of production pressure difference on the increase of
water-cut becomes less, even disappears.
When the oil layers are completely perforated, that’s
x=1, the fluid in the whole reservoir flows in the radial
direction. Then the bottom water will drive the oil at the
least efficiency and its energy will make the oil well
drought.
Such laws discussed above are in accordance with the
actual development cases for block-faulted reservoir
with bottom water.
4.2 Effect of the Clay Stabilizers
The water sensitivity index of the core samples from
Budate Reservoir fall into the range of 0.60～0.67 (a bit
strong water sensitivity). Besides the oil and water rela-
tive permeability curve measured, in the lab other two
relative permeability curves were also measured with
clay stabilizer CS-5 and CS-7 (see in Table 2). Then the
effects of clay stabilizers on relative permeability curves
and on the law of Water-cut Variation are analyzed to
provide reference for the optimization of clay stabilizers
at Budate Reservoir.
Based on the parameters from well D108-229 (see in
Table 1), three curves of Water-cut Variation of water,
CS-5 and CS-7 are shown in Figure 5 for gravity uncon-
sidered and in Figure 6 for gravity considered in Figure 7.
0.0
0.2
0.4
0.6
0.8
1.0
0.3 0.4 0.5 0.6 0.7
Sw
fw
Δp=11
Δp=8
Δp=6
Δp=4
Δp=2
β=1
Figure 4. Water-cut curves versus production pressure differences
(D108-229)
0
0.2
0.4
0.6
0.8
1
0.3 0.5 0.7
Sw
fw
Δp=11
Δp=8
Δp=6
Δp=4
Δp=2
β=1
Figure 5. Water-cut curves versus production pressure differences
(B28-1)
0
0.2
0.4
0.6
0.8
1
0.3 0.5 0.7 0.9
Sw
fw
water
CS-5
CS-7
Figure 6. Water-cut curves versus different clay stabilizers (gravity
unconsidered)
0
0.2
0.4
0.6
0.8
1
0.30.50.70
Sw
fw
.9
water
CS-5
CS-7
Figure 7. Water-cut curves versus different clay stabilizers (gravity
considered)

S. G. QIN, Y. L. SUN, Z. Q. JIA, D. G. YANG
48
Table 2. Feature values of relative permeability curves measured at lab
Core
No.
Kg
(10-3μm2)
φ
(%)
Swi
(%)
Sor
(%)
Krw at
Sor
(%)
Anhydrous
Recovery
(%)
Ultimate
Recovery
(%)
Range of oil-water
phases
(%)
Sw at point of two
curves’s intersection
(%)
Clay
stabilizer
C166-1 119.21 23.19 39.21 33.43 29.3018.31 45.01 27.36 49.20 水
C166-2 114.01 22.92 40.17 28.72 30.0025.71 52.00 31.11 53.80 5
C166-4 186.56 23.05 34.30 30.88 28.5032.47 53.00 34.82 50.75 7
Conclusions could be drawn as:
1) Using clay stabilizers can reduce the rising velocity
of water-cut at the stage of low water saturation, that’s
oilfield can recovery more oil at the stage of low water
saturation than that in the case of water flooding.
2) Using clay stabilizer CS-5 makes the point of water
breakthrough later than that the case of water flooding.
3) Using clay stabilizer CS-7 makes the rising velocity
of water-cut smooth and makes the oil recovery at the
low water saturation the biggest number but with earlier
point of water breakthrough.
4) Using clay stabilizers makes the flowing range of
two phases wider. The anhydrous oil recovery efficiency
and the ultimate number both obviously larger than that
of the case of water flooding.
5 Conclusions
1) Gravity has great influence on the law of Water-cut
Variation for the Block-faulted reservoir of buried hill
with bottom water: if gravity considered, the water-cut
increases along with the rise of water saturation slowly at
the stage of low water saturation. The less production
pressure difference, the slower rising velocity of wa-
ter-cut along with the increase of water saturation, so is
its reduced extent. At a certain big value of production
pressure differences the action of gravity could be ne-
glected.
2) Both the perforation ratio and the production pres-
sure difference have great influence on the law of Wa-
ter-cut Variation for the Block-faulted reservoir of buried
hill with bottom water. Along with the increase of perfo-
ration ratio, the effect of gravity on reducing the rising
velocity of water-cut becomes less. This water-cut curve
will be the nearly the same as that while gravity uncon-
sidered. Along with the increase of perforation ratio, the
effect of production pressure difference on the increase
of water-cut becomes less, even disappears.
3) Clay stabilizers can reduce the rising velocity of
water-cut at the stage of low water saturation and make
the anhydrous oil recovery efficiency and the ultimate
number both obviously larger than that of the case of
water flooding.
6 Nomenclature
Krw — relative permeability water, dimensionless;
Kro — relative permeability oil, dimensionless;
μw — water viscosity, mPa•s;
μo — oil viscosity, mPa•s, mPa•s;
γw — relative density of water, dimensionless;
γo — relative density of oil, dimensionless;
H — thickness to avoid water in a oil well, m;
α' — Reservoir pressure coefficient, dimensionless;
Re — well spacing, m;
Rw — wellbore radius, m;
Sw — water saturation;
Kg — gas permeability, 10-3μm2;
φ — porosity, dimensionless;
Swi— irreducible water saturation, dimensionless;
Sor — residual oil saturation, dimensionless.

S. G. QIN, Y. L. SUN, Z. Q. JIA, D. G. YANG
49
REFERENCES
[1] BO Song-zhang, “Development of carbonate buried hill reservoir,”
Petroleum Industry Press, Beijing, Vol. 5, pp.2-8, 1996.
[2] S. Ullah, Tse Yone Shen, S. A. Mobarak, et al., “Development
feasibility study: Dongshengpu buried hill reservoir,” SPE 17577,
Vol. 11, pp. 273-284, 1988.
[3] M. G. Starcher, J. R. Murphy, P. D. Alexander, et al., “Video
camera log used for water isolation in the main body ‘B’ pool,
Elk hills field, Kern Co., California-water and oil identification,”
SPE29654, Vol. 3, pp. 384-394, 1995.
[4] K. A. Edwards, B. Anderson, and B. Reavie, “Horizontal injec-
tors rejuvenate mature miscible flood-south swan hills field,”
SPE77302, Vol. 2, pp.174-182, 2002.
[5] CHEN Shao-sheng, XU Kun, Han Yun, et al., “Study on charac-
teristics and development law of fractured basement reservoirs:
A case study of fractured basement reservoirs in Damintun de-
pression of Liaohe basin,” SPE80541, Vol. 4, pp. 1-9, 2003.
[6] ZHANG Ji-guang, WANG Jin-kui, QIN Long-pu, et al., “Char-
acteristics of metamorphic buried hill reservoir in Sude’erte of
Beir fault depression in Hailar basin,” ACTA PETROLEI SINIC,
Vol. 28, No. 4, pp. 21-30, 2007.
[7] LU Ai-min andYAO Jun, “Change of water cut and oil produc-
tion in fractured reservoir with bottom water,” Special Oil and
Gas Reservoir, Vol. 13, No. 5, pp. 56-61, 2006.
[8] LU Ai-min and YAO Jun, “Rational perforating level and well
spacing for fractured carbonate reservoirs with bottom water,”
Vol. 35, No. 1, pp. 97-100, 2008.