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Research Article Determine the Inflow Performance Relationship of Water Producing Gas Well Using Multiobjective Optimization Method Xiao-Hua Tan, 1 Jian-Yi Liu, 1 Jia-Hui Zhao, 1 Xiao-Ping Li, 1 Guang-Dong Zhang, 1 Chuan Tang, 2 and Li Li 3 1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Xindu Road 8, Chengdu 610500, China 2 Shell China Exploration & Production Co. Ltd., 8F Yanlord Landmark Office Building, No. 1, Section 2, Renmin South Road, Chengdu 610500, China 3 Oil & Gas Technology Research Institute, PetroChina Changqing Oilfield Company, Xi’an 710018, China Correspondence should be addressed to Xiao-Hua Tan; [email protected] Received 12 December 2013; Accepted 26 May 2014; Published 16 June 2014 Academic Editor: Nachamada Blamah Copyright © 2014 Xiao-Hua Tan et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. During the development of water drive gas reservoirs, the phenomena of gas escaping from water and water separating out from gas will change the seepage characteristics of formation fluid. erefore, the traditional gas-water two-phase inflow performance relationship (IPR) models are not suitable for calculating the water producing gas well inflow performance relationship in water drive gas reservoirs. Based on the basic theory of fluid mechanics in porous medium, using the principle of mass conservation, and considering the process of dissolution and volatilization of gas and water formation, this paper establishes a new mathematical model of gas-water two-phase flow. Multiobjective optimization method is used to automatically match the sample well production data in water drive gas reservoirs and then we can achieve the sample well’s productivity equation, relative permeability curve, water influx intensity, and single well controlled reserves. In addition, the influence of different production gas water ratios (GWR) and gas-soluble water coefficients on absolute open flow rate ( AOF ) is discussed. is method remedied the limitation of well testing on site and was considered to be a new way to analyze the production behaviors in water producing gas well. 1. Introduction Well productivity is one of primary concerns in field devel- opment and provides the basis for field development strategy [1]. Xiaoping and Birong [2] put forward a method to deduce the binomial productivity equation which could calculate the inflow performance relationship (IPR) curve of water producing gas well and presented the application of the IPR curve in determining gas and water production rate from water producing gas well. Zhu et al. [3] proposed three new formation evaluation parameters for low perme- ability gas reservoir, On the basis of the rate controlled mercury injection, nuclear magnetic resonance and physical simulation technologies. Wang et al. [4] analyzed gas and water phase relative permeability through cores with three different permeability leaves by the establishment of physical simulation experiment system and experimental process of water-gas mutual flooding. Park et al. [5] proposed a fuzzy nonlinear programming approach to design production systems of gas fields. e synthetic optimization method could find a globally com- promise solution and offer a new alternative with significant improvement over the existing conventional techniques. Cardoso [6] found that reduced-order model is well suited for reservoir simulation. Han et al. [7] presented a multi- objective evolutionary algorithm applied to history matching of water flooding projects, that is to search a feasible set of geological properties showing the reliable future perfor- mance. Cancelliere et al. [8] discussed benefits, limitations and drawbacks of assisted history matching, based on multi objective optimization and heuristic strategies. Attention was focused on the possibility offered by these methodologies of Hindawi Publishing Corporation Journal of Applied Mathematics Volume 2014, Article ID 105636, 7 pages http://dx.doi.org/10.1155/2014/105636

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Page 1: Research Article Determine the Inflow Performance ...downloads.hindawi.com/journals/jam/2014/105636.pdf · Research Article Determine the Inflow Performance Relationship of Water

Research ArticleDetermine the Inflow Performance Relationship of WaterProducing Gas Well Using Multiobjective Optimization Method

Xiao-Hua Tan,1 Jian-Yi Liu,1 Jia-Hui Zhao,1 Xiao-Ping Li,1 Guang-Dong Zhang,1

Chuan Tang,2 and Li Li3

1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Xindu Road 8,Chengdu 610500, China

2 Shell China Exploration & Production Co. Ltd., 8F Yanlord Landmark Office Building, No. 1, Section 2, Renmin South Road,Chengdu 610500, China

3Oil & Gas Technology Research Institute, PetroChina Changqing Oilfield Company, Xi’an 710018, China

Correspondence should be addressed to Xiao-Hua Tan; [email protected]

Received 12 December 2013; Accepted 26 May 2014; Published 16 June 2014

Academic Editor: Nachamada Blamah

Copyright © 2014 Xiao-Hua Tan et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

During the development of water drive gas reservoirs, the phenomena of gas escaping from water and water separating out fromgas will change the seepage characteristics of formation fluid. Therefore, the traditional gas-water two-phase inflow performancerelationship (IPR) models are not suitable for calculating the water producing gas well inflow performance relationship in waterdrive gas reservoirs. Based on the basic theory of fluid mechanics in porous medium, using the principle of mass conservation,and considering the process of dissolution and volatilization of gas and water formation, this paper establishes a newmathematicalmodel of gas-water two-phase flow.Multiobjective optimizationmethod is used to automatically match the sample well productiondata in water drive gas reservoirs and then we can achieve the sample well’s productivity equation, relative permeability curve, waterinflux intensity, and single well controlled reserves. In addition, the influence of different production gas water ratios (GWR) andgas-soluble water coefficients on absolute open flow rate (𝑞AOF) is discussed. This method remedied the limitation of well testingon site and was considered to be a new way to analyze the production behaviors in water producing gas well.

1. Introduction

Well productivity is one of primary concerns in field devel-opment and provides the basis for field development strategy[1]. Xiaoping and Birong [2] put forward a method to deducethe binomial productivity equation which could calculatethe inflow performance relationship (IPR) curve of waterproducing gas well and presented the application of theIPR curve in determining gas and water production ratefrom water producing gas well. Zhu et al. [3] proposedthree new formation evaluation parameters for low perme-ability gas reservoir, On the basis of the rate controlledmercury injection, nuclear magnetic resonance and physicalsimulation technologies. Wang et al. [4] analyzed gas andwater phase relative permeability through cores with threedifferent permeability leaves by the establishment of physical

simulation experiment system and experimental process ofwater-gas mutual flooding.

Park et al. [5] proposed a fuzzy nonlinear programmingapproach to design production systems of gas fields. Thesynthetic optimization method could find a globally com-promise solution and offer a new alternative with significantimprovement over the existing conventional techniques.Cardoso [6] found that reduced-order model is well suitedfor reservoir simulation. Han et al. [7] presented a multi-objective evolutionary algorithm applied to history matchingof water flooding projects, that is to search a feasible setof geological properties showing the reliable future perfor-mance. Cancelliere et al. [8] discussed benefits, limitationsand drawbacks of assisted history matching, based on multiobjective optimization and heuristic strategies. Attention wasfocused on the possibility offered by these methodologies of

Hindawi Publishing CorporationJournal of Applied MathematicsVolume 2014, Article ID 105636, 7 pageshttp://dx.doi.org/10.1155/2014/105636

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2 Journal of Applied Mathematics

obtaining a number of calibrated reservoirmodels. Shelkov etal. [9] described a comparison of single and multi-objectivehistory matching of a medium-sized field in Western Siberiawith nearly 100 wells and over 10 years of history. And theycompared the performance of both single andmulti objectiveversions of particle swarm optimization. Tan et al. studiedthe transient flow and two-phase flow behaviors in porousmedia [10–12]. Some of their research results can be usedto solute the problem of inflow performance relationship ofwater producing gas well.

2. Gas-Water Two Phase IPR Equation

We assume the reservoir is homogeneous with uniformthickness, total compressibility of rock and fluid is low andconstant. The water phase flow is isothermal and Darcy flow,and the gas phase flow is isothermal and non-Darcy flow athigh velocity, ignoring the impact of gravity and capillaryforces. No chemical reaction exists between gas and waterphase. Fundamental filtration equations for the gas and waterphase are defined as [13]

𝑑𝑝

𝑑𝑟=

𝜇𝑔

𝑘𝑘𝑟𝑔

V𝑔 + 𝛽𝑔𝜌𝑔V2

𝑔,

𝑑𝑝

𝑑𝑟=

𝜇𝑤

𝑘𝑘𝑟𝑤

V𝑤,

(1)

where, 𝑝 is pressure, 𝑟 is radial distance, 𝜇𝑔, 𝜇𝑤 is gas andwater viscosity, respectively, 𝑘 is absolute permeability, 𝑘𝑟𝑔,𝑘𝑟𝑤 is gas and water phase relative permeability respectively,V𝑔, V𝑤 is gas and water phase flow velocity, 𝛽𝑔 is turbulencevelocity coefficient, 𝜌𝑔 is gas density.

Under the boundary condition of steady radial state flow,the integral of (1) can be written as follows [14]

𝑝𝑅

𝑝𝑤𝑓

𝑘𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

𝑑𝑝 = ∫

𝑟𝑒

𝑟𝑤

𝑞𝑔

2𝜋𝑟ℎ𝑑𝑟 +

𝑞2

𝑔

4𝜋2ℎ2∫

𝑟𝑒

𝑟𝑤

𝛽𝑔𝜌𝑔𝑘𝑘𝑟𝑔𝐵𝑔

𝜇𝑔𝑟2

𝑑𝑟,

𝑝𝑅

𝑝𝑤𝑓

𝑘𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

𝑑𝑝 = ∫

𝑟𝑒

𝑟𝑤

𝑞𝑤

2𝜋𝑟ℎ𝑑𝑟,

(2)

where 𝑝𝑅 is reservoir pressure, 𝑝𝑤𝑓 is bottom hole flowingpressure, 𝑟𝑒, 𝑟𝑤 is external boundary and wellbore radiusrespectively, 𝐵𝑔𝐵𝑤 is gas and water volume factor, respec-tively, 𝑞𝑔𝑞𝑤 is gas and water production rate, respectively, ℎis reservoir thickness.

Fevang andWhitson [15] defined the gas and water phasepseudo pressure in two phase filtration. The equations are asfollows

Δ𝑚(𝑝)𝑔= ∫

𝑝𝑅

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

𝑅𝑠𝑔𝑤 +𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

)𝑑𝑝,

Δ𝑚(𝑝)𝑤= ∫

𝑝𝑅

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

+𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

𝑅𝑠𝑤𝑔)𝑑𝑝,

(3)

where, 𝑅𝑠𝑔𝑤 is solution gas water ratio and 𝑅𝑠𝑤𝑔 is solutionwater gas ratio.

By combing (2) and (3), the gas and water phase pseudopressure can be expressed

Δ𝑚(𝑝)𝑔= 𝑞𝑔 (

1

𝑅𝑝𝑔𝑤

𝑟𝑒

𝑟𝑤

𝑅𝑠𝑔𝑤

2𝜋𝑟ℎ𝑘𝑑𝑟 + ∫

𝑟𝑒

𝑟𝑤

1

2𝜋𝑟ℎ𝑘𝑑𝑟)

+

𝑞2

𝑔

4𝜋2ℎ2∫

𝑟𝑒

𝑟𝑤

𝛽𝑔𝜌𝑔𝑘𝑘𝑟𝑔𝐵𝑔

𝜇𝑔𝑟2

𝑑𝑟,

Δ𝑚(𝑝)𝑤= 𝑞𝑤 (∫

𝑟𝑒

𝑟𝑤

1

2𝜋𝑟ℎ𝑘𝑑𝑟 + 𝑅𝑝𝑔𝑤 ∫

𝑟𝑒

𝑟𝑤

𝑅𝑠𝑔𝑤

2𝜋𝑟ℎ𝑘𝑑𝑟)

+

𝑞2

𝑤𝑅2

𝑝𝑔𝑤

4𝜋2ℎ2∫

𝑟𝑒

𝑟𝑤

𝛽𝑔𝜌𝑔𝑘𝑘𝑟𝑔𝐵𝑔

𝜇𝑔𝑟2

𝑑𝑟,

(4)

where 𝑅𝑝𝑔𝑤 is production gas water ratio.In order to simplify the expressions of gas andwater phase

pseudo pressure, we define four parameters

𝐴 = ∫

𝑟𝑒

𝑟𝑤

1

2𝜋𝑟ℎ𝑘𝑑𝑟,

𝐵 =1

4𝜋2ℎ2∫

𝑟𝑒

𝑟𝑤

𝛽𝑔𝜌𝑔𝑘𝑟𝑔𝐵𝑔

𝜇𝑔𝑟2

𝑑𝑟,

𝐶𝑔 = ∫

𝑟𝑒

𝑟𝑤

𝑅𝑠𝑔𝑤

2𝜋𝑟ℎ𝑘𝑑𝑟,

𝐶𝑤 = ∫

𝑟𝑒

𝑟𝑤

𝑅𝑠𝑤𝑔

2𝜋𝑟ℎ𝑘𝑑𝑟.

(5)

By combing (4), we obtain the gas-water two phase IPRequation (6).

𝑞𝑔 = ( − (𝐴 + (1

𝑅𝑝𝑔𝑤

)𝐶𝑔)

+√(𝐴 + (1

𝑅𝑝𝑔𝑤

)𝐶𝑔)

2

+ 4𝐵 ⋅ Δ𝑚(𝑝)𝑔)(2𝐵)

−1,

𝑞𝑤 = ( − (𝐴 + 𝑅𝑝𝑔𝑤𝐶𝑤)

+√(𝐴 + 𝑅𝑝𝑔𝑤𝐶𝑤)2

+ 4𝐵𝑅2𝑝𝑔𝑤

⋅ Δ𝑚(𝑝)𝑤)

× (2𝐵𝑅2

𝑝𝑔𝑤)−1

,

Δ𝑚(𝑝)𝑔= ∫

𝑝𝑟

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

𝑅𝑠𝑔𝑤 +𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

)𝑑𝑝,

Δ𝑚(𝑝)𝑤= ∫

𝑝𝑟

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

+𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

𝑅𝑠𝑤𝑔)𝑑𝑝.

(6)

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Journal of Applied Mathematics 3

This equation is determined by the four parameters𝐴, 𝐵, 𝐶𝑔, 𝐶𝑤, where 𝐴 is laminar coefficient, 𝐵 is turbulencecoefficient, 𝐶𝑔 is gas soluble coefficient, representing dis-solved gas within gas well control range, 𝐶𝑤 is water solublecoefficient, representing dissolved formation water in gaswithin the well control range.

3. Gas-Water Two Phase ComprehensiveModel and the Solution

3.1. Gas andWater Relative Permeability. Gas andwater phaserelative permeability 𝑘𝑟𝑔, 𝑘𝑟𝑤 are needed in order to calculatethe gas-water two phase IPR equation. 𝑘𝑟𝑔, 𝑘𝑟𝑤 is a function ofwater saturation 𝑆𝑤, the empirical equations are representedas follows [15]

𝑘𝑟𝑔 = (1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷)) ,

𝑘𝑟𝑤 = (𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

,

(7)

where, 𝑆𝑤 is water saturation in reservoir, 𝑆𝑤𝑖 is initial watersaturation,𝐷 is relative permeability index.

From (7), we obtain

𝑘𝑟𝑔

𝑘𝑟𝑤

=

(1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷))

(𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

. (8)

Using the ratio of gas and water production, a methodaimed to obtain the ration of gas and water phase relativepermeability is proposed by Jokhio and Tiab [16].

𝑘𝑟𝑔

𝑘𝑟𝑤

= (𝐵𝑔𝜇𝑔

𝐵𝑤𝜇𝑤

)(𝑅𝑝𝑔𝑤 − 𝑅𝑠𝑔𝑤)

(1 − 𝑅𝑝𝑔𝑤𝑅𝑠𝑤𝑔). (9)

The parameters 𝜇𝑔, 𝜇𝑤, 𝐵𝑔, 𝐵𝑤, 𝑅𝑠𝑤𝑔, 𝑅𝑠𝑔𝑤 in (9) are func-tions of pressure𝑝.Therefore, the ratio of gas andwater phaserelative permeability 𝑘𝑟𝑔/𝑘𝑟𝑤 can be obtained by means of 𝑝and 𝑅𝑝𝑔𝑤. Then 𝑆𝑤 can be calculated. At last, 𝑘𝑟𝑔, 𝑘𝑟𝑤 can beobtained.

By Combining (8) and (9), we obtain:

(1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷))

(𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

= (𝐵𝑔𝜇𝑔

𝐵𝑤𝜇𝑤

)(𝑅𝑝𝑔𝑤 − 𝑅𝑠𝑔𝑤)

(1 − 𝑅𝑝𝑔𝑤𝑅𝑠𝑤𝑔).

(10)

Begin

Input known parameters (initialreservoir pressure, initial water

saturation, tubing head pressure, casinghead pressure, etc.)

Input the initial valueof unknown parameters

i = 1

Calculate water saturationby reservoir pressure

Calculate gas and water phasesaturation relative permeability

Calculate gas and waterproduction rate

n = i?

No

Ye s

Minimumerror?

No

Yes

Output results

Adjustparameters

End

Calculate error Ei

E+ = Ei

i++

Figure 1

From (7) and (10), the equations for calculating 𝑘𝑟𝑔, 𝑘𝑟𝑤are defined as follows

𝑘𝑟𝑔 = (1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷)) ,

𝑘𝑟𝑤 = (𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

,

(1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷))

(𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

= (𝐵𝑔𝜇𝑔

𝐵𝑤𝜇𝑤

)(𝑅𝑝𝑔𝑤 − 𝑅𝑠𝑔𝑤)

(1 − 𝑅𝑝𝑔𝑤𝑅𝑠𝑤𝑔).

(11)

Based on the material balance equation in the water drivegas reservoir, the relationships between average formation

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4 Journal of Applied Mathematics

pressure and geologic reserve, cumulative gas production andwater invasion intensity can be obtained in (12) [17]

𝑝

𝑧=

𝑝𝑖

𝑧𝑖

(1 − (𝐺𝑝/𝐺)

1 − (𝐺𝑝/𝐺)𝑅) , (12)

where, 𝑝, 𝑝𝑖 is current and initial reservoir pressure, respec-tively, 𝑧, 𝑧𝑖 is gas deviation factor under current and initialreservoir pressure, respectively, 𝐺𝑝, 𝐺 is cumulative gasproduction and dynamic reserves, respectively, 𝑅 is waterinvasion coefficient.

3.2. Gas-Water Two Phase Comprehensive Model. By Com-bining (6), (10) and (12), the gas-water two phase comprehen-sive model can be expressed

𝑞𝑔 = ( − (𝐴 +1

𝑅𝑝𝑔𝑤

𝐶𝑔)

+√(𝐴 +1

𝑅𝑝𝑔𝑤

𝐶𝑔)

2

+ 4𝐵 ⋅ Δ𝑚(𝑝)𝑔)(2𝐵)

−1,

𝑞𝑤 = ( − (𝐴 + 𝑅𝑝𝑔𝑤𝐶𝑤)

+√(𝐴 + 𝑅𝑝𝑔𝑤𝐶𝑤)2

+ 4𝐵𝑅2𝑝𝑔𝑤

⋅ Δ𝑚(𝑝)𝑤)

× (2𝐵𝑅2

𝑝𝑔𝑤)−1

,

Δ𝑚(𝑝)𝑔= ∫

𝑝𝑟

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

𝑅𝑠𝑔𝑤 +𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

)𝑑𝑝,

Δ𝑚(𝑝)𝑤= ∫

𝑝𝑟

𝑝𝑤𝑓

(𝑘𝑟𝑤

𝐵𝑤𝜇𝑤

+𝑘𝑟𝑔

𝐵𝑔𝜇𝑔

𝑅𝑠𝑤𝑔)𝑑𝑝,

𝑘𝑟𝑔 = (1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷)) ,

𝑘𝑟𝑤 = (𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

,

(1 − (𝑆𝑤 − 𝑆𝑤𝑖))2(1 − (𝑆𝑤 − 𝑆𝑤𝑖)

(5−𝐷)/(3−𝐷))

(𝑆𝑤 − 𝑆𝑤𝑖)(11−3𝐷)/(3−𝐷)

= (𝐵𝑔𝜇𝑔

𝐵𝑤𝜇𝑤

)(𝑅𝑝𝑔𝑤 − 𝑅𝑠𝑔𝑤)

(1 − 𝑅𝑝𝑔𝑤𝑅𝑠𝑤𝑔),

𝑃

𝑍=

𝑃𝑖

𝑍𝑖

(1 − (𝐺𝑝/𝐺)

1 − (𝐺𝑝/𝐺)𝑅) .

(13)

3.3. The Solution of Gas-Water Two Phase ComprehensiveModel. As (13) shows above, Laminar coefficient 𝐴, turbu-lence coefficient 𝐵, gas soluble coefficient 𝐶𝑔, water soluble

Table 1: The basic parameters of an actual well.

Welldepth(m)

Therelativedensityof gas

Therelativedensityof water

Formationpressure(MPa)

Formationtemperature

(∘C)

Initialwater

saturation

2994 0.78 1.02 30.08 78 0.35

Table 2: The target parameter in an actual well.

𝐴 𝐵 𝐶𝑔

𝐶𝑤

𝐷 𝑅 𝐺 (108 m3)1.41 × 10−5 5.23 × 10−10 0.12 4.21 × 10−6 −1.97 5.37 3.59

coefficient 𝐶𝑤, relative permeability index 𝐷, water invasioncoefficient 𝑅 and single well controlled reserves𝐺 are neededto solve. An automatic fitting multi-objective optimizationmethod is given in this paper to solve the problem inthe complicated percolation model mentioned above. Theessence of this method is seeking the best fitting betweentheoretical value and measured value.The solution is definedas follows

𝐸 =

𝑛

𝑖=1

(𝑞𝑔 (𝐴, 𝐵, 𝐶𝑔, 𝐶𝑤, 𝐷, 𝑅, 𝐺) − 𝑞𝑔)2

+

𝑛

𝑖=1

(𝑞𝑤 (𝐴, 𝐵, 𝐶𝑔, 𝐶𝑤, 𝐷, 𝑅, 𝐺) − 𝑞𝑤)2

,

(14)

where, 𝑞𝑔(𝐴, 𝐵, 𝐶𝑔, 𝐶𝑤, 𝐷, 𝑅, 𝐺) and 𝑞𝑤(𝐴, 𝐵, 𝐶𝑔, 𝐶𝑤, 𝐷,

𝑅, 𝐺) is theoretical gas and water production rate, respec-tively, 𝑞𝑔 and 𝑞𝑤 are actual gas and water production rate,respectively, 𝐸 is expressed as the target function to be fitted.The proper parameters can be obtained to minimum thetarget function by means of the automatic fitting method.The flow chart for plotting type curves is shown in Figure 1.

4. Case Analysis

4.1. Calculating of the Target Parameter. During the pro-cess of acquiring the parameters like laminar coefficient 𝐴,turbulence coefficient 𝐵, gas soluble coefficient 𝐶𝑔, watersoluble coefficient 𝐶𝑤, relative permeability index 𝐷, waterinvasion intensity 𝑅 and single well controlled reserve 𝐺, thetheoretical gas and water production can be obtained basedon (13). By fitting the practical gas and water productionon the basis of the automatically fitting method in (14), theresult shown in Figure 2 can be acquired. It is clearly thatthe theoretical results verified with the practical ones whichindicates the reliability of the results. The basic parameters ofan actual well are shown in Table 1.

The parameters like laminar coefficient 𝐴, turbulencecoefficient 𝐵, gas soluble coefficient 𝐶𝑔, water soluble coef-ficient 𝐶𝑤, relative permeability index 𝐷, water invasionintensity 𝑅 and single well controlled reserve 𝐺 are shown inTable 2.

The value of water soluble coefficient in this table is verysmall which suggests that the content of the formation waterdissolving into the natural gas is little. And the energy of the

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Journal of Applied Mathematics 5

05

101520

0 1000 2000 3000 4000Time (day)

Actual water rateFitting water rate

Gas

rate

(104

m3/d

)

(a)

0 1000 2000 3000 400005

101520

Time (day)

Actual water rateFitting water rate

Wat

er ra

te (1

04

m3/d

)

(b)

Figure 2

0.4 0.5 0.6 0.7 0.8 0.90.00

0.05

0.10

0.15

0.20

0.25

Rela

tive p

erm

eabi

lity

krgkrw

Sw

Figure 3

Table 3: The absolute open flow rates in different production gaswater ratios.

GWR (104 m3/m3) 𝑞AOF (104 m3/d)

1 32.760.5 31.710.2 28.790.1 24.61

formation water in the well controlled range is weak whenthe water invasion intensity is greater than 4. The gas andwater phase relative permeability curve in different watersaturations is obtained. The results are shown in Figure 3.

4.2. The IPR Curves of Water Producing Gas Well. TheIPR curves in different production gas water ratios (GWR)are expressed in Figure 4. It is noted that the IPR curvesexpressed with a left offset when production gas water ratiodecreases. Because when the GWR decreases, the watersaturation in formation increases, and the flow resistanceincreases too. It becomes harder to flow in formation whenthe GWR decreases. The absolute open flow rates (𝑞AOF) of

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35

Gas rate (104 m3/d)

pwf

(MPa

)

GWR (104 m3/m3) = 1

GWR (104 m3/m3) = 0.5

GWR (104 m3/m3) = 0.2

GWR (104 m3/m3) = 0.1

Figure 4

water producing gas well in different production gas waterratios can be shown in Table 3. From the curves, when theproduction gas water ratios is 1, 0.5, 0.2 and 0.1, respectively,the absolute open flow rates reduced 32.76, 31.71, 28.79, and24.61 × 104m3/d accordingly. The absolute open flow rates isreducing by 3.21%, 12.12% and 24.88% when compared to theone whose production gas water ratio is 0.1. It is shown thatwater invasionwill greatly reduce the gas production capacityof water producing gas well.

The IPR curves in different gas soluble coefficient areshown in Figure 5. It can be concluded that the IPR curvesexpressed with a left offset when the gas soluble coefficientincreases. Gas soluble coefficient represents the solubility ofgas in water, which lead to a bigger flow resistance. Theabsolute open flow rates (𝑞AOF) of water producing gas well indifferent gas soluble coefficient can be shown inTable 4. Fromthe curves, it is clearly that when gas soluble coefficient is 0.1,0.5, 1 and 2, respectively, absolute open flow rates is 32.94,29.57, 25.91 and 20.22 × 104m3/d, respectively. The absoluteopen flow rates are reduced by 10.23%, 21.34% and 38.62%when compared to the onewhose gas soluble coefficient is 0.1.It is shown that themore gas dissolved in the formationwater,the more liquid phase will exist in the formation fluid. It willincrease the gas flowing resistance and result in the greaterproductivity impairment.

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6 Journal of Applied Mathematics

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35

Gas rate (104 m3/d)

pwf

(MPa

)

Cg = 0.1

Cg = 0.5Cg = 2Cg = 5

Figure 5

Table 4: The absolute open flow rate in different gas-solublecoefficients.

𝐶𝑔

𝑞AOF (104 m3/d)

0.1 32.940.5 29.572 25.915 20.22

5. Conclusions

Based on the basic theory of fluid mechanics in porousmedium, taking the solution and volatilization of gas andwater into consideration, a gas-water two phase IPR equationwas established. Combining with gas-water two phase IPRequation, relative permeability equation andmaterial balanceequation in the water drive gas reservoir, we deduced the gas-water two phase comprehensive model, which is influencedby laminar coefficient, turbulence coefficient, gas solublecoefficient, water soluble coefficient, relative permeabilityindex, water invasion intensity and single well controlledreserve. The influences of different production gas waterratios and gas soluble coefficients on the absolute open flowrate were discussed. The method proposed in this paperprovided a new theoretical method for single well analysisof productivity and inflow performance, and got rid of thelimitation that the well productivity can be only determinedaccording to field well test.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgment

The authors are grateful for financial support from theNational Science Fund for Distinguished Young Scholars ofChina (Grant No. 51125019).

References

[1] M. Kelkar, Natural Gas Engineering, PennWell Books, 2008.[2] L. Xiaoping and Z. Birong, “A new IPR curve of gas-water well

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[3] G. Zhu, X. Liu, S. Miao, and S. Gao, “New formation evaluationparameters of low permeability water bearing gas reservoirs andits application,” in Proceedings of the International Oil and GasConference and Exhibition in China, pp. 2683–2690, Society ofPetroleum Engineers, Beijing, China, June 2010.

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[5] H. J. Park, J. S. Lim, J. Roh, J. M. Kang, and B. H. Min, “Pro-duction system optimization of gas fields using hybrid fuzzy-genetic approach,” in Proceedings of the SPE Europec/EAGEAnnual Conference and Exhibition, pp. 813–820, Society ofPetroleum Engineers, Vienna, Austria, June 2006.

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[8] M. Cancelliere, F. Verga, and D. Viberti, “Benefits and limita-tions of assisted historymatching,” in Proceedings of theOffshoreEurope Oil and Gas Conference and Exhibition, pp. 935–943,Aberdeen, UK, September 2011.

[9] V. Shelkov, M. Christie, D. Eydinov, D. Arnold, V. Demyanov,and J. Talbot, “Use of multi-objective algorithms in historymatching of a real field,” in Proceedings of the SPE ReservoirSimulation Symposium, pp. 57–67, The Woodlands, Tex, USA,February 2013.

[10] X. H. Tan, X. P. Li, J. Y. Liu, C. Tang, and J. M. Li, “Pressuretransient analysis of dual fractal reservoir,” Journal of AppliedMathematics, vol. 2013, Article ID 137518, 9 pages, 2013.

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[12] X. H. Tan, J. Y. Liu, J. H. Zhao, X. P. Li, G. D. Zhang, andC. Tang, “A pressure transient model for power-law fluids inporous media embedded with a tree-shaped fractal network,”Mathematical Problems in Engineering, vol. 2014, Article ID405640, 8 pages, 2014.

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Journal of Applied Mathematics 7

[16] S. A. Jokhio and D. Tiab, “Establishing Inflow PerformanceRelationship (IPR) for gas condensate wells,” in Proceedingsof the SPE Gas Technology Symposium, pp. 33–52, Society ofPetroleum Engineers, Alberta, Canada, May 2002.

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