Kyushu University Global COE Program
Journal of Novel Carbon Resource Sciences, Vol. 4, pp. 27-31, Sep. 2011

Technical Report

History Matching of Gas Production Performance inNishikanbara Water-dissolved Gas Field
Tomofumi Higuma*1, Hikari Fujii*2, Ryuichi Itoi*2, Katsunori Horikawa*3*1

Graduate School of Engineering, Kyushu University*2
Faculty of Engineering, Kyushu University*3
Toho Earthtech, Inc.
(Received May 27, 2011; accepted August 16, 2011)

In Nishikanbara Gas Field of Niigata prefecture, Japan, water-dissolved gas has been produced since the 1950s.
To establish an optimum development plan, numerical reservoir simulation models were constructed for the first timein this field using a black oil reservoir simulation software. For validating the model, history-matching of production
gas water ratio (GWR) and reservoir pressure was carried out treating the absolute permeability of reservoir rocks
and initial distribution of solution GWR as matching parameters. After several trial and errors, the models weresuccessfully validated through the history-matching with actual data.

1. Introduction

In the Nishikanbara gas field of Niigata prefecture,
Japan, water-dissolved gas, whose major component ismethane, has been produced since the 1950s. Because
the water-dissolved gas is dissolved in the groundwater,
large amount of the water needs to be pumped up forgas production. As a result of producing groundwater,
significant land subsidence was induced at the early stageof production in this area. To prevent the land subsidence,
all produced water has been re-injected to the reservoir
since October, 1973 and no land subsidence has been
observed since then. On the other hand, production gas
water ratio steeply dropped in some wells due to themixing of original groundwater with the re-injectedwater.
Various approaches have been proposed for thedevelopment of water-dissolved gas field. Marsden(1993) reported the development of water-dissolved
gas around the world1). Akibayashi, Karube and Hara(1986) estimated the transmissibility in the waterdissolved gas field 2). Nishida and Aoki (1980) simulated
the subsidence behavior in water-dissolved gas field3).
However, water-dissolved gas fields are not commonly
known on a global scale and its simulation method havenot been established yet though it is important to create
an optimum development plan.
This study aims to develop numerical reservoir
simulation models that reproduce the gas production
performance from the water-dissolved gas reservoirs byusing a black oil reservoir simulation software.

2. Geology

The Nishikanbara water-dissolved gas field is locatedin the western part of Niigata city of Niigata prefecture,
Japan. (Fig. 1, Fig. 2) The number of production andinjection wells is 130 and about 33 million sm3 ofmethane gas has been produced from the gas field peryear. In this study, numerical models were developed forthe main reservoirs, G4, G5 and G6 in this field.

Fig. 1 The location of Nishikanbara area.

Fig. 2 The locations of the bases.
The Nishikanbara gas field is located in the southeasternpart of a synclinal structure. From south to north, thetop depth of the reservoirs gradually becomes deeper inthe production area. Fig. 3 shows the top depth of thereservoir G4. The trend of the structure of each reservoir
is similar to that of the reservoir G4.

Journal of Novel Carbon Resource Sciences, Vol.4, Sep. 2011

3. Numerical ModelingmmFig. 3 The top depth of the reservoir G4.
Table 1NameG4(b)G4G4(c)G4-1
G5G6

Parameters of each reservoir

Lithology Depth(m)coarse
sand
coase
sand,
gravelcoase
sand,gravelcoase
sand,gravelgravelThickness Permeability(m)(darcy)420-510

30-35

15-20

485-580

25-30

20-25

555-640

20-25

10-15

640-840

80-12015-20

855-1025

60-70

20-25

The parameters of each reservoir are shown in theTable 1. The reservoirs lie at the depth from 400 m toover 1000 m. These reservoirs are consisted of coarse
sand or gravel, whose permeability ranges 10-30 darcy
and the porosity is averaged as 28 %. G4 is separated
into G4(b), G4(c) and G4-1 by mud layers. Similarly, thereservoir G5 is divided into G5 and G5-1 and there is
an impermeable layer between them. Furthermore, theextent of this impermeable layer is not clarified yet. G5-1
and the reservoir G6 disappear at the north part of theproduction area.
Since the reservoir pressure is higher than the saturationpressure, a gas cap is not formed in these reservoirs.
The value of the initial solution gas water ratio (SGWR)
ranges from 1.0 SCM/SCM to 1.7 SCM/SCM. From south
to north, initial SGWR gradually increases as the top
depth of the reservoirs become deeper. As the productionof natural gas continued, the SGWR gradually dropped
due to the mixing the groundwater with the re-injectedwater in some part of production area.

Numerical models were developed for the reservoir
G4, G5 and G6 respectively using a black oil reservoir
simulation
software,
ECLIPSE100ver.2008.2(Schlumberger co., Ltd). Since the dissolution of methanegas into water can not be modeled in this simulation
software, the water was regarded as oil and the propertiesof groundwater were given to the oil.
For the first stage of model development, the reservoirs
were discretized to numerous cells. The size of one cellin the production area was decided as 200 m × 200 m forG4 and G6 and as 150 m × 150 m for G5. This production
area was configured as 8.4 km × 15 km in the model ofG4, 9 km × 13.5 km in G5 and 9 km × 11 km in G6.
As approaching the outer boundary, the size of cells isincreased to shorten the computation time. Finally thesize of each model was decided as 58.8 km × 65.4 km
in the model of G4, as 85.2 km × 89.7 km in G5 and as
59.2 km × 61.4 km in G6 (Fig. 4). The grid of verticaldirection was configured for each model individually.
Each reservoir in G4 is divided into two layers and theimpermeable layers between the reservoirs are regarded
as one layer (Fig. 5). Though there are a lot of multiple
completed wells among G4(b), G4(c) and G4-1, the ratioof the production rates from individual reservoir has notbeen measured. Hence, the product of permeability andthickness (k-h) of G4(b), G4(c) and G4-1 were used toallocate the production rate to each reservoir.

yProduction
area
89.7km

13.5km9km

85.2kmxFig. 4 The grid of the numerical model of the reservoir G5.

x

G4(b)

z

Impermeable
layer
G4(c)

x

Impermeable
layer
G4-1

Fig. 5 The separation of depth direction in G4.

Reservoir G5 is separated into 10 layers of same
thickness. Top four layers are regarded as G5 and thefifth layer from the top was regarded as impermeable
layer. Bottom five layers are regarded as G5-1 (Fig. 6).
Reservoir G6 is separated into 5 equal parts.

xz

G5

Reservoir pressure (bar)History Matching of Gas Production Performance in Nishikanbara Water-dissolved Gas Field

Simulated
Observed

Impermeable
layerG5-1Fig. 7 The result of history matching of reservoirpressure in a well (Reservoir G4).

After defining the gird systems, the petrophysicalproperties obtained from the field were input to themodels4). Then, production and injection history of eachwell were input to caluclate the production performance.
The calculation was continued until the calculated
production GWR and reservoir pressure at each wellmatched the observed ones. The absolute permeability of
the rocks and initial distribution of solution GWR weremainly adjusted for history matching. In addition, theporosity of outermost grids was also adjusted because
the water-dissolved gas reservoirs have large lateralextent but the models have limited extent.

Production GWR (㎥/㎥)

Fig. 6 The separation of depth direction in G5.

Simulated
Observed

Fig. 8 The result of history matching of production
GWR in a well (Reservoir G4).

4. Result4.1. Reservoir G4Fig. 7 and Fig. 8 show the results of history matchingof reservoir pressure and production GWR in a well.
The decrease and recovery of the reservoir pressure
is reproduced well as shown Fig. 7. The decreasing
production GWR is also reproduced in other wells. A
example is shown in Fig. 8. Since there are a lot of multiple
completion wells in the reservoir G4, it is important toreflect not only the thickness but also the permeabilityof the reservoir for allocating the production rate. In thisstudy, horizontal permeability values, were 23 darcy, 22darcy and 8 darcy for G4(b), G4(c) and G4-1 respectively.
The vertical permeability was assumed as 20 % ofhorizontal permeability. The ratios of the thickness of
the reservoirs to whole thickness of G4 are 17.0 %, 15.5
% and 19.0 % for G4(b), G4(c) and G4-1 respectively.

4.2. Reservoir G5

The reservoir G5 is divided into G5 and G5-1. G5 is
the upper part of the layer and G5-1 is the lower part ofthe layer. Because it is not obvious whether there is aconnection between the two layers, the numerical model
was initially configured without connection between thetwo layers. However, the numerical simulation model
could not be reproduced with reasonable accuracy.

Fig. 9 The map of the production area (Reservoir G5).
The disagreement in the model was found in theproduction GWR near the reservoir boundary (Fig. 9).
Because sand was produced from the reservoir to some of
the injection wells through the open intervals, the lower
part of the injection wells were plugged by sand. Becauseof this sand trouble, groundwater is mainly injected intothe layer G5. If there is a connection between G5 andJournal of Novel Carbon Resource Sciences, Vol.4, Sep. 2011

G5-1, the groundwater of the G5 could have invaded tothe G5-1. Therefore, it is important to estimate where theconnection exists. Because the production GWR steeply
dropped in the wells near the reservoir boundary, it wasinfered that the connection between G5 and G5-1 exists
near the reservoir boundary.
After some trial and errors of history matching, theshape and the width of connection was decided as shownin Fig. 10 and Fig. 11. In southern part of the production
area, upper four layers were regarded as G5, and lower
five layers were regarded as G5-1. However, only theupper five layers of G5 exist in the northern part.

yFig. 12 The result of history matching of production
GWR (Reservoir G5).

xFig. 10

Conceptual model of G5 which has a connection.

Reservoir pressure (bar)z

Simulated
Observed

Fig. 13 The result of calculation of reservoir pressure(Reservoir G5).

4.3. Reservoir G6

Fig. 11

Plain view of the conceptual model of G5.

Fig. 12 shows the result of history matching ofproduction GWR in a well, one without connection(CASE1) and the other with connection (CASE2). In
CASE1, production GWR did not drop in the 1990 though
the ovserved data showed a decrease. On the other hand,produced GWR showed good matching in CASE2.
This results show that there would be a connection
between G5 and G5-1 in the northern part of prodcution
area. Because the injected water moved into G5-1
through the connection, the groundwater of G5-1 has
been gradually diluted by the groundwater of G5. Sincethe reservoir pressure was also matched, the numericalsimuration model is considered to have reasonableaccuracy (Fig. 13).

In the history matching, the production GWR dropped
too fast in some wells. This problem occured because
the production and injection depth changed due to thesand production in each well. A field survey showed that
almost all of injection wells were partly plugged by sand.
In particular, some injection wells were plugged morethan 30 % of the open intervals. To reproduce this trend,
the layer 3 was defined as an impermeable layer.
The results of history matching in a well were shownin Fig. 14 and Fig. 15. The SGWR in the lower part ofthe reservoir showed no decrease because the upper
part of the reservoir was selected as the injected zone
due to the sand trouble. In the process of production, thegroundwater in upper and lower zone was mixed and theproduction GWR was kept about 0.5 SCM/SCM from the1980 as shown in Fig. 15.
Because both reservoir pressure and production GWR
matched well for G6, the validity of the G6 model wasconfirmed.

History Matching of Gas Production Performance in Nishikanbara Water-dissolved Gas Field

Reservoir pressure (bar)

5. Conclusion

Simulated
Observed

Production GWR (㎥/㎥)

Fig. 14 The result of history matching of reservoirpressure in a well (Reservoir G6).

Using a black oil reservoir simulation soft,
ECLIPSE100, numerical simulation models weredeveloped for the main reservoirs, G4, G5 and G6 in
Nishikanbara water-dissolved gas field, Niigata, Japan.
For developing these simulation models, petrophysicalproperties and geological information were input tothe models. To obtain good matching results, absolutepermeability of the rocks, initial distribution of solution
GWR and the porosity of outermost grids were treated as
the matching parameters.
In the history matching, the trend of decreasing
solution GWR and the change of reservoir pressure werereproduced with good accuracy. Through the history
matching, it is estimated that there is a connection
between the layers G5 and G5-1, and also there is animpermeable barrier between the upper and lower zoneof G6.
References
1)

Simulated
Observed

2)
3)
4)

Fig. 15 The result of history matching of production
GWR in a well (Reservoir G6).

S. Marsden, in the Future of Energy Gases, U. S.
Geological Survey Professional Paper 1570, ed. by
D. G. Howell, United States Government Printing
Office, Whashington, p. 383 (1993).
S. Akibayashi, K. Karube and J. Hara, Journal of theJapanese Association for Petroleum Technology, 51(3),42 (1986).
T. Nishida and K. Aoki, Journal of the Mining Instituteof Japan, 97(1115), 13 (1981).
Japan Natural Gas Association, Handbook of WaterDissolved Gas (Suiyousei tennengasu souran), p. 101(1980). (in Japanese)