A review of pressure transient analysis in reservoirs with natural fractures, vugs and/or caves
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REVIEW
A review of pressure transient analysis in reservoirs with natural fractures, vugs and/or caves Isah Mohammed1 · Teslim O. Olayiwola1 · Murtadha Alkathim1 · Abeeb A. Awotunde1 · Saad F. Alafnan1 Received: 24 September 2019 © The Author(s) 2020
Abstract A review of the pressure transient analysis of flow in reservoirs having natural fractures, vugs and/or caves is presented to provide an insight into how much knowledge has been acquired about this phenomenon and to highlight the gaps still open for further research. A comparison-based approach is adopted which involved the review of works by several authors and identifying the limiting assumptions, model restrictions and applicability. Pressure transient analysis provides information to aid the identification of important features of reservoirs. It also provides an explanation to complex reservoir pressuredependent variations which have led to improved understanding and optimization of the reservoir dynamics. Pressure transient analysis techniques, however, have limitations as not all its models find application in naturally fractured and vuggy reservoirs as the flow dynamics differ considerably. Pollard’s model presented in 1953 provided the foundation for existing pressure transient analysis in these types of reservoirs, and since then, several authors have modified this basic model and come up with more accurate models to characterize the dynamic pressure behavior in reservoirs with natural fractures, vugs and/or caves, with most having inherent limitations. This paper summarizes what has been done, what knowledge is considered established and the gaps left to be researched on. Keywords Natural fractures · Vugs · Caves · Pressure transient analysis List of symbols B Fracture depth C Gas concentration (m3/mol) c Compressibility cl Liquid of compressibility CDf Dimensionless fracture conductivity cm Matrix compressibility coefficient cp Shale compressibility (MPa−1) Edited by Yan-Hua Sun * Abeeb A. Awotunde [email protected] Isah Mohammed [email protected] Teslim O. Olayiwola [email protected] Murtadha Alkathim [email protected] Saad F. Alafnan [email protected] 1
College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum and Minerals, Dhahran, Kingdom of Saudi Arabia
Df Fractal wall roughness dimension (dimensionless) DK Knudsen diffusion coefficient (m2/s) gc Conversion factor h Reservoir thickness JK Knudsen diffusion flux [mol/(m2 s)] Jv Viscous flow flux [mol/(m2 s)] K2 Fracture permeability K∞ Viscous flow permeability (m2) Kapp Apparent permeability KK Knudsen diffusion apparent permeability Kv Apparent viscous flow permeability L Transport distance M Gas molar mass (kg/mol) P Pressure (Pa) P0 Initial pressure PD Dimensionless pressure Pf Fracture pressure PL Langmuir pressure (MPa) Pm Matrix pressure q Flow rate per unit length qwell Well flow rate R Universal gas constant [J/(mol K)] R Pore radius (m) r Reservoir radius
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