Effect of Permeability on Foam-model Parameters and the Limiting Capillary Pressure

Abstract

SUMMARYAccurate modelling of foam rheology on the field scale requires detailed understanding of the correlation between the fundamental properties of foam and the scalable parameters of the porous medium. It has been experimentally observed that foam experiences an abrupt coalescence when the capillary pressure in the porous medium approaches a certain value referred to as the "limiting capillary pressure", Pc*. Current foam models that treat foam texture implicitly mimic this fundamental behaviour with a so-called dry-out function, which contains adjustable parameters like fmdry and epdry (in the STARS foam simulator). Parameter fmdry (called Sw* in other models) represents the water saturation corresponding to the limiting capillary pressure Pc* and epdry determines the abruptness of foam coalescence as a function of water saturation. In this paper, using experimental data, we examine the permeability-dependence of these parameters. We find that the value of fmdry decreases with increasing permeability. We also find that, for the data examined in this paper, the transition from high-quality regime to low-quality regime is more abrupt in lower-permeability rocks. This implies that in high-permeability rocks foam might not collapse abruptly at a single water saturation; instead there is range of water saturation over which foam weakens. In addition, we address the question of whether Pc* is dependent on formation permeability. We estimate Pc* from data for foam mobility in vs. foam quality, and find, as did Khatib et al. (1988), who introduced the limiting capillary pressure concept, that Pc* can vary with permeability. It increases as permeability decreases, but not enough to reverse the trend of increasing foam apparent viscosity as permeability increases.

Tuning Foam Parameters for Mobility Control using CO2 Foam: Field Application to Maximize Oil Recovery from a High Temperature High Salinity Layered Carbonate Reservoir

“…In foam displacement experiments in porous medium, as gas saturation increases, capillary pressure also increases until it reaches a certain point called the limiting capillary pressure, beyond which the foam films start to break and become coarser in texture. 37 It has been observed that as foam quality increases and water saturation decreases correspondingly, there reaches a value of S w below which the coalescence of foam occurs and it starts drying up, thus becoming coarser in texture. 37 The capillary pressure corresponding to this water saturation value as mentioned earlier is known as limiting capillary pressure.…”

“…37 It has been observed that as foam quality increases and water saturation decreases correspondingly, there reaches a value of S w below which the coalescence of foam occurs and it starts drying up, thus becoming coarser in texture. 37 The capillary pressure corresponding to this water saturation value as mentioned earlier is known as limiting capillary pressure. It must be noted that if the foam collapse is abrupt then the transition region between high and low quality regime occurs at one particular value of water saturation which is represented as S w *.…”

“…If the foam collapse is not abrupt then the transition between high and low quality foam regimes depends on a range of water saturation values. 37 The presence of oil has significant effect on the formation and breakdown of foam. The interactions between oil phase and foam lamellae are extremely complex.…”

“…In foam displacement experiments in porous medium, as gas saturation increases, capillary pressure also increases until it reaches a certain point beyond which the foam films do not survive and become coarser in texture. 37 This concept is depicted in Figure 2.…”

Relationship between Blocking Performance and Foam Texture in Porous Media

“…It was found that finer-textured foam led to larger flow resistance [39][40][41]. Some foam flow models have been proposed to simulate foam flow and reveal the blocking mechanism [42][43][44][45][46]. There was one thing in common in all models that foam texture was considered to be a determining factor for foam flow behavior.…”