### Abstract

In multifractured horizontal wells producing from unconventional reservoirs, linear flow is commonly observed to be the dominant flow regime during early production. This linear flow regime may remain infinite-acting for a long stretch of time because of the ultralow permeability character of these formations. In this study, we first analytically corroborate that constant gas/oil ratio (GOR) should be expected in unconventional multiphase reservoirs (gas condensates and volatile oils below saturation conditions) exhibiting linear flow under constant-bottomhole-pressure (BHP) production constraint during infinite-acting periods (i.e., before pressure transient reaching the reservoir boundary). We propose a semianalytical solution to the multiphase governing partial-differential equations (PDEs) by applying the similarity method-also referred to as the Boltzmann transformation-to transform the system of PDEs to ordinary-differential-equation (ODE) form. The transformed system of ODEs and boundary conditions are solved by means of Runge-Kutta integration. By solving the equations for pressure and saturation, the GOR trend and value can be fully predicted before availability of production data. The results show that a constant GOR effect could be maintained as long as the flow regime remains infinite-acting and its value varies with BHP specifications for a given reservoir and fluid system.

Original language | English (US) |
---|---|

Pages (from-to) | 289-299 |

Number of pages | 11 |

Journal | SPE Journal |

Volume | 22 |

Issue number | 1 |

DOIs | |

State | Published - Feb 1 2017 |

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### All Science Journal Classification (ASJC) codes

- Energy Engineering and Power Technology
- Geotechnical Engineering and Engineering Geology

### Cite this

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*SPE Journal*, vol. 22, no. 1, pp. 289-299. https://doi.org/10.2118/175079-PA

**Analytical study of constant gas/oil-ratio behavior as an infinite-acting effect in unconventional multiphase reservoir systems.** / Zhang, Miao; Ayala H., Luis.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Analytical study of constant gas/oil-ratio behavior as an infinite-acting effect in unconventional multiphase reservoir systems

AU - Zhang, Miao

AU - Ayala H., Luis

PY - 2017/2/1

Y1 - 2017/2/1

N2 - In multifractured horizontal wells producing from unconventional reservoirs, linear flow is commonly observed to be the dominant flow regime during early production. This linear flow regime may remain infinite-acting for a long stretch of time because of the ultralow permeability character of these formations. In this study, we first analytically corroborate that constant gas/oil ratio (GOR) should be expected in unconventional multiphase reservoirs (gas condensates and volatile oils below saturation conditions) exhibiting linear flow under constant-bottomhole-pressure (BHP) production constraint during infinite-acting periods (i.e., before pressure transient reaching the reservoir boundary). We propose a semianalytical solution to the multiphase governing partial-differential equations (PDEs) by applying the similarity method-also referred to as the Boltzmann transformation-to transform the system of PDEs to ordinary-differential-equation (ODE) form. The transformed system of ODEs and boundary conditions are solved by means of Runge-Kutta integration. By solving the equations for pressure and saturation, the GOR trend and value can be fully predicted before availability of production data. The results show that a constant GOR effect could be maintained as long as the flow regime remains infinite-acting and its value varies with BHP specifications for a given reservoir and fluid system.

AB - In multifractured horizontal wells producing from unconventional reservoirs, linear flow is commonly observed to be the dominant flow regime during early production. This linear flow regime may remain infinite-acting for a long stretch of time because of the ultralow permeability character of these formations. In this study, we first analytically corroborate that constant gas/oil ratio (GOR) should be expected in unconventional multiphase reservoirs (gas condensates and volatile oils below saturation conditions) exhibiting linear flow under constant-bottomhole-pressure (BHP) production constraint during infinite-acting periods (i.e., before pressure transient reaching the reservoir boundary). We propose a semianalytical solution to the multiphase governing partial-differential equations (PDEs) by applying the similarity method-also referred to as the Boltzmann transformation-to transform the system of PDEs to ordinary-differential-equation (ODE) form. The transformed system of ODEs and boundary conditions are solved by means of Runge-Kutta integration. By solving the equations for pressure and saturation, the GOR trend and value can be fully predicted before availability of production data. The results show that a constant GOR effect could be maintained as long as the flow regime remains infinite-acting and its value varies with BHP specifications for a given reservoir and fluid system.

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U2 - 10.2118/175079-PA

DO - 10.2118/175079-PA

M3 - Article

VL - 22

SP - 289

EP - 299

JO - SPE Journal

JF - SPE Journal

SN - 1086-055X

IS - 1

ER -