Advances in Ma terials Physics and Che mist ry, 2012, 2, 173-176
doi:10.4236/ampc.2012.24B045 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc)
Study on Rational Well Spacing Optimization of Low
Permeability Gas Reservoir
Jian-guo Zhang , Yong Wu, Fang Ai
Nationl Engineering Laboratory for Low-permeability Oil/Gas Exploration and Development, Researc h Inst itute of Petrol eum
Explora tion and Development of Petrochina Changqing Oilfield Company, Shanxi Xia n, China
Received 2012
ABSTRACT
The Shanggu gas field is the low porosity and low permeability. Single well controlled reserves, economic limit well spacing and
econo mic ratio nal spacing t hrough different methods are cal culated. With the development experien ce of Su Lige gas field as guid-
ance, the rational spacing of Shanggu gas reservoir is 700m×900m by calculating daily gas production rate an d cumulat ive gas pro-
duction with different well spacing using numerical simulation method.
Keywords: Low Permeability; Rational Well Spacing; Well Pattern Density; Reservoir Numerical Simulation
1. Introduction
With th e enhancement of development technique of oil and gas
field, many lo w permeability fields, which couldn’t yield oil or
gas economically in the past, are becoming more and more
valuable[1]. We must demonstrate well spacing before or after
the development of field [2-4]. Well spacing is o f vital i mportance
for ultimate recovery and economic benefit of oil and gas field,
especially for low permeability gas reservoir, which is widely
reported both at home and abroad[5-15]. Currently, there are
two basic methods in papers, which research the rational well
spacin g of gas field, they are singl e well controlled reserves and
numerical simulation. The well pattern density of low
permeability area in Jingbian gas field is low and the control
degree of production wells is also low, which are the main
reasons why the degree of reserve recovery is low. In order to
enhance the producing degree and recovery ratio, well spacing
is needed to be changed. Based on the basic principal of well
pattern density optimization, rational spacing is economic, should
avoid well interference and meet the standard of maximum
recovery ratio and producing degree. How can we calculate the
ration al spacing, which means maximum economic ben efit and
recovery ration can be achieved with minimum wells? This
paper calculates the rational spacing, which is suitable to
Shan ggu lo w permeab ili ty gas fiel d, and reco mmen ds a r atio n al
spacin g ar r angement.
1) Relationship between Well Spacing And Sand Scal e
The main factors affecting the rational spacing are single
sand body scale, superposed features of sand body, pattern of
composite sand body and sand body’s control action of porosity
and permeabilit y.
From the results of geologic research, we know that channel
width is 60-250 m and channel belt width is 600-2000 m. Ac-
cording to channel belt width, horizontal spacing is 600-1500m.
For the same sand body, well spacing is less than channel width
(Table 1).
2. Methods of Determining Well Spacing
2.1. Single Well Controlled Reserves
Assuming that gas well controlled reserves is known, the sands
are uniform throughout the controlled extent of the reservoir,
and drainage area is cylinder radial flow area, according to
parameters and evaluation result of developed Shanggu gas
field, the sin gl e well contr olled area can b e written as
gor
gk
k
hsp
BN
A100 =
(1)
Table 1. Developmental Scale of Neopaleozoic Channe l i n Gaoqiao.
Zone Thickness of sand body
（
m
）
Channel width
（
m
）
Channel belt width
（
m
）
Min Max Var iation change Min Max Var iation change Min Max Var iation c hange
H8u 0.78 9 4-6 8.66 374.3 80-200 38.3 3126.54 750-1600
H8l 1 12.2 5-7 12.7 597.98 150-250 59.9 5405.98 1000-2000
S1 0 .58 8.06 3-5 5.49 315.82 60-150 22.47 2563.48 600-1200
S2 0 .54 8.7 4-5 4.92 355.26 70-180 19.76 2941.45 700-1500

J. -G. ZHANG ET AL.
174
where
Ak-single well controlled area, Km2; Nk-geologic reserve
controlled by single well, 108m3; Bg-gas volume factor,
dimensionless; h-Thickness controlled by single well, m; sg-skin
factor, dimensionless.
Single well controlled area is about 0.45Km2 by using this
method to evaluate 43 gas wells. The well spacing is 0.67Km
calculat ed by square area.
2.2. Economic Li mit Spa c ing
Economic limit spacing is the minimum spacing in terms of
economic benefit. Economic limit spacing is in direct
correlation with economic limit reserve. Under the condition of
without considering the risk of drilling and considering the cost
of drilling engineering and surface construction, the operation
cost of gas production, the selling price of gas and the loan
interest rate, etc, the equation of production well spacing using
economic limit spacing method can be written as
Gross input of certain pattern density:
2/)( 321
)1)((
TTT
BFDin
RIIISAC
++
+++⋅=
(2)
Gross output of this pattern density:
10 ()
outR gax
CN ECPOT= ⋅⋅⋅−−
(3)
Gross profit:
in out
GC C= −
(4)
When gross profit equals to zero, the pattern density is limit
pattern density:
0
in out
GC C=−=
(5)
Then, economic limit pattern density S is
12
( )/2
10 ()
()(1 )
R gax
TT
DFB
N ECPOT
SAIIIR +
⋅⋅ ⋅−−
=
++ +
(6)
min
1
LS =
(7)
According to the development experience of Jingbian gas
field, we know that when average reserves abundance is larger
than 1.1×108m3d/km2, the economic limit spacing is smaller
than 0.7 00km.
Wher e
S-economic limit pattern density, wells/Km2; ID-drilling
cost of single well(includes perforation, test, logging and so on),
104 yuan/well; IF-fracturing cost of single well, 104 yuan/well;
IB-surface construction cost of single well(includes system
engineering, field construction, etc), 104 yuan/well; Pg-selling
price of gas, yuan/103m3; C-commodity rate of gas, ratio; O-
operation cost of gas, yuan/103m3; Ta x-toll of gas, yuan/103m3;
A-gas bearing area, km2; R-yearly loan interest rate, ratio;
N-gas in place, 108m3; ER-recovery ratio with pattern density
being S, ratio; Cm-gross input,104 yuan; Co ut-gross output ,104
yuan; G-gross profit, 104 yuan; T1-years of stable production,
year; T2-decr easing year s with d ecline fractio n bein g 20%, year;
Lmin-economic limit spacing, km.
2.3. Rational Spacing
Economic limit spacing is rational pattern density with certain
profit. If considering the profit is 0.2 times of selling price, then
12
( )/2
10(0.2 )
()(1)
R gaxg
TT
DF B
N ECPOTP
SAI I IR
+
⋅⋅ ⋅−−−
=
++ +
(8)
Superimposed with Shanggu reserves, we know that average
reserves abundance is larger than 1.1 × 108m3d/km2. The eco-
nomic limit spacing is smaller than 0.834km.
3. Rational Spacing Determined by Numerical
Simulation
On the basis of geologic model, we found mechanism model of
Shan 135 well and G61-11 well. Basic paramet ers of mechan is m
model are length and width: 5000×6000m, grid spacing: 100 ×
100 m, reserves abundance: 1×108m3/km2, five zo nes in vertical ,
which corresponds to subzone, namely, H8, S1, S2, Benxi,
without considering Xiagu reservoir.
We consider 8 combinations of well spacing/horizontal range,
as shown in Table 2. Results are listed in Figure 2, Figure 3
and Table 3. When i nd ivi d ual well pro ducin g rate i s 1×104m3/d
and comparing calculation results of different well spacing and
horizontal range, we conclude that the shorter the well spacing
is, the more the well number is and the higher the gas produc-
tion rate is, the shorter the years of stable production is. When
well spacing/horizontal range is 700×900m, years of stable
production is 3 years and both the gas production rate and re-
covery ratio is relatively high.
Figure 1. Relationship Graph between Economic Rational Spacing
and Reserves Abundance of Ancient Gas Field.
Tabl e 2. Design Table with Well Spacing/Horizontal Range.
Well S pacing
（
m
）
1100 1000 900 800 700 600 600
Horizontal Range
（
m) 1300 1200 1100 1000 900 800 750

J. -G. ZHANG ET AL.
175
Table 3. S tatistical List of Optimum Spacing and Horizontal Range of Ancient Gas Field.
Project No. 1 2 3 4 5 6 7
Well Spacing（m） 1100 1000 900 800 700 600 600
Horizontal Range（m） 1300 1200 1100 1000 900 800 750
Number of wells（well） 20 25 30 36 50 56 64
Years of Stable Production（year） 9.4 6.2 4 .8 4.2 3.2 2.4 2.2
Daily Gas Production（104m3/d） 20 25 30 36 50 56 64
Gas Pr o duction Rat e（%） 2 2.6 3.1 3 .7 5.1 5.7 6.5
Cumulative Producti on at the end of Stable Production（108m3） 5.41 5.53 5.64 5 .8 2 5.94 6.10 6 .3 4
Degree of Reserv e Reco v ery at the end of Stable Production（%） 16.72 17.08 17.44 17.99 18.36 18.85 19.58
Cumulative Production aft er 20 Years（108m3） 10.86 11.35 12.09 13.04 14.18 14.56 14.97
Degree of Reserve Recovery after 20 Years（%） 33.55 35.08 37.37 40.30 43.83 44.98 46.25
Figure 2. Cumulative Production Comparison Graph with Differ-
ent Spacing and Horizo ntal Range.
Fig ure 3. Daily Gas Production Comparison Graph with Different
Spacing and Horizontal Range .
4. Determination of Rational Spacing In Shang
Gu Gas Reservoir
Reserves abundance of Su Lige gas field is 1.2×108m3/km2 and
rational spacing and horizontal range is 600m×800m. Reserves
abundances of project area which is lar ger th an 0.5×108m3/km2
are 2612.07km2, which accounts for 60% of total area. Average
reserves abundance is 1.16×108m3/ km2 and geologic reserve is
3030×108m3, which accounts for 79.77% of Shanggu gas
reserve, whose reserves is 3798.62×108m3. So rational spacing
and horizontal range of project area is larger than 600m×800m.
Shanggu Gas reserves abundance of project area which is
larger than 0.5×10 8m3/km2 accounts for 79.77% of gas reserve.
So the rational spacing and horizon tal range is 700m×900m.
5. Conclusions
1) Rational pattern density not only meets the requirement of
development of gas field but should ensure maximum economic
benefit. Rational pattern density is determined by geologic
characteristic of g as field.
2) This paper determines th e ratio nal sp acing of low per mea-
bility area in ancient gas field is 700m×900m by using eco-
nomic limit spacing, economic rational spacing and numerical
simulation. And this paper demonstrates an effective way of
determining rational spacing and spacing arrangement of low
permeability gas reservoir.
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