Capillary pressure and relative permeability correlations for transition zones of carbonate reservoirs

Abstract

A sizable oil reserves are held in a thick oil/ water capillary transition zones in the carbonate reservoirs, but it is an ongoing challenge to accurately describe the relationship between capillary pressure, relative permeability and oil/water saturation due to the complex wettability variation, pore geometry and heterogeneity throughout the reservoir column. It has been shown that a proper interpretation of relative permeability and capillary pressure including hysteresis has a substantial influence on the prediction and optimization of field production, especially for a heterogeneous carbonate reservoir with a thick transition zone. The conventional models, such as Corey method and Leverett J-function, cannot precisely present the behaviors of capillary pressure and relative permeability of transition zones in carbonate reservoirs. In the present work, a study has been conducted to provide an improved understanding of capillary pressure and relative permeability of the transition zones in carbonate reservoirs by implementing and optimizing recently developed models considering mixed-wet property and geological heterogeneity. For single core plug and each reservoir rock typing classified on the basis of petrophysical properties, the applicability to generate bounding drainage and imbibition curves of the models was tested with fitting parameters by comparing with experimental data. Also, a comprehensive assessment was provided about the feasibility and efficiency of the models along with an evaluation of the hysteresis between bounding drainage and imbibition curves. The results showed excellent matches in the case of Masalmeh model (SPE Reserv Eval Eng 10(02):191-204, 2007) with a correlation coefficient value of 0.95, in which mixed-wet and pore size distribution are taken into account. Therefore, it can be stated that the work conducted in this study could be used as a guide for further investigation and understanding of transition zones in carbonate reservoirs.

Representative Elementary Volumes, Hysteresis, and Heterogeneity in Multiphase Flow From the Pore to Continuum Scale

“…The increase of the water relative permeability during imbibition is captured in the model using a decrease in the power-law exponent, resulting in a good prediction of the experimental data. The slight raising in water relative permeability during imbibition has been seen in other experimental data (see Akbarabadi & Piri, 2012;Reynolds, 2016;Shi et al, 2017) and could be an impact of the heterogeneity in the system. Hysteresis appears more prominent in Core 2, which could be a consequence of the enhanced snap-off trapping in the low porosity region, which causes the water to displace the non-wetting phase in cooperative pore-filling events upstream.…”

“…For wetting relative permeability, there is less dependence on the trapping of the non-wetting phase during imbibition in water-wet media (Oak, 1980), although there have been examples of a slight raising of the wetting relative permeability during imbibition as is seen in the experiments here (see also C. Reynolds (2016); Shi et al (2017); Akbarabadi and Piri (2012)). This is caused primarily by the wetting fluid occupying larger pores during imbibition than in drainage (Blunt, 2017).…”

Proof-of-concept for a probe to measure pore water pressure in oil-water saturated porous rock

“…Between the two zones, there is an oil-water transition zone where oil and water, often called connate water, are simultaneously present but with different pressure regimes. The thickness of a transition zone may vary from a few centimetres in high-permeability reservoirs to almost 100m in low-permeability reservoirs such as carbonate reservoirs, due to its extreme heterogeneity (Shi, Belhaj and Bera, 2018). Considering the oil-water system at a z depth, the capillary pressure Pc is defined as the difference between the oil pressure, Poil, and the water pressure, Pwater:…”

Pore pressure variation at constant confining stress on water–oil and silica nanofluid–oil relative permeability

“…Relative permeability curves are essential in reservoir engineering as they are used in numerical modeling, dynamic analysis, and reservoir performance predictions (Abdelazim 2016;Akhlaghinia et al 2014;Li et al 2015;Parvazdavani et al 2017;Shi et al 2018;Tian et al 2015;Zhang et al 2014). However, relative permeability depends on internal and external applied stresses.…”