DOC-20250114-WA0017

Effects of Porosity and Permeability on Invasion Depth During Drilling Mud-filtrate Invading into a Reservoir Dynamically

Author and Contact

  • Jianhua Zhang

  • Science College, Xi’an Shiyou University, Xi’an, 710065, China

  • Email: jhzhang@xsyu.edu.cn

Keywords

  • Invasion

  • Depth

  • Time

  • Porosity

  • Permeability

Abstract

  • Mud-filtrate invasion into a reservoir is a dynamic process initiated during oil exploration when a formation is opened.

  • The invasion depth correlates with time; as time progresses, the invasion profiles of formation resistivity change.

  • Fluid flow equations help to calculate invasion profiles and depths, revealing that invasion depth increases with greater permeability and lower porosity.

Introduction

  • During petroleum exploration, mud facilitates drilling; mud filtrate invades into porous formations to create an invaded zone, distinct from the original formation.

  • This invaded zone significantly affects resistivity logging, crucial for evaluating reservoirs.

  • Conventional invasion models often fail to account for the time-dependent nature of invasion processes.

  • The dynamic invasion model incorporated fluid flow theory to better understand real-time invasion behaviors and its impacts on well logging.

Dynamic Invasion Equations

  • Mud filtrate displaces native fluids in porous formations radially; the invasion is influenced by several parameters:

    • Formation permeability (k)

    • Formation porosity (ϕ)

    • Original saturation

    • Fluid viscosities and densities

  • Two key fluid flow equations help determine pressure and saturation over time:

    • Equation (1)

    • Equation (2)

  • Salinity distribution changes as mud filtrate mixes with native water, described by:

    • Equation (3)

  • Formation resistivity, influenced by salinity, is calculated through:

    • Equation (4)

    • and Equation (5)

Time-dependent Invasion Depth

  • A synthetic formation model analyzed dynamic invasion behaviors with specific parameters (k, ϕ, saturation, salinity).

  • The invasion process, characterized by the construction of the mud cake and changing saturation profiles, demonstrates a rapid initial invasion rate that slows over time.

The Effects of Porosity and Permeability

  • Invasion is heavily influenced by formation parameters of porosity and permeability.

  • Porosity (ϕ): Volume occupied by pore spaces; higher porosity means a larger volume for fluids.

  • Permeability (k): Measures fluid flow capability; higher permeability leads to greater invasion depths.

  • Observations on invasion depth related to porosity at varied permeabilities emphasize the inverse relationship between porosity and invasion rate, especially evident over time.

Conclusions

  • Invasion processes are shaped by formation and fluid characteristics, with porosity and permeability being critical factors.

  • High permeability results in deeper invasion depths due to better fluid flow, while high porosity reduces invasion rates as more mud filtrate is necessary to replace native fluids.

References

  1. A. Y. Windarto et al. - Modeling of mud filtrate invasion and damage zone formation

  2. S. Davydycheva - Sensitivity to radial invasion profile

  3. M. S. Bittar et al. - Invasion profiling methods

  4. D. P. Tobola & S. A. Holditch - Reservoir permeability estimations

  5. C. Y. Yao & S. A. Holditch - Time-lapse log data

  6. J. H. Zhang et al. - Formation resistivity estimation

  7. Z. H. Liu et al. - Dynamic Dual-Laterolog Responses

  8. A. Akinsete & O.Oluwatoyin - Effects of mud filtrate invasion

  9. A. N. Berntsen et al. - Brine diffusion investigations

  10. K. Ling et al. - Estimating invasion radius for drilling fluid filtrate.