Relative-Permeability Coupled Saturation-Height Models Based on Hydraulic (Flow) Units in a Gas Field

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSaturation-height functions based on unique flow units have been developed as part of an integrated petrophysical analysis of a gas field. Furthermore, coupling the saturation functions with appropriate relative permeability models has effectively quantified hydrocarbon saturation, classified producibility of intervals and defined critical water saturation. The results show that linking depositional and diagenetic rock fabric to flow units, and then linking the flow units to zones with similar core capillary pressure and relative permeability relationships, have enhanced the utility of the saturation models. The saturation-height functions provided accurate water saturation, and they can potentially overcome uncertainties associated with log interpretation, using Archie or shaly sand models.The saturation-height models were developed from core capillary pressure (Pc) data to calculate water saturation versus depth, which is independent of logs. The relative permeability models were obtained from special core analysis (SCAL). Consequently, the core-based saturation height functions can be useful in the calibration of log-based petrophysical models and, via relative permeability, can also be used to estimate water gas ratios and critical water saturation.Capillary pressure and relative permeability curves from special core analysis studies were distributed into corresponding flow units, based on the calculated flow zone indicators. Saturation-height functions were then developed for each unit and used to calculate water saturation in the study field. The most accurate flow unit-based saturation model that evolved is a function of only porosity and height above free water level, does not require permeability in its application, and performed better than the Leverett J-function in this field.Coupled with hydraulic unit (HU)-based relative permeability curves, the saturation models will provide more comprehensive petrophysical interpretation in gas bearing formations as well as highlight potential differences in reservoir producibility.

Evaluating Factors Controlling Damage and Productivity in Tight Gas Reservoirs

“…Liquid invasion into tight formations can increase water saturation around the wellbore from S wi to a higher value, and then as the near wellbore zone is cleaned up by gas production, water saturation is reduced gradually, but not further than S wc (Amabeoku et al, 2006). This process as illustrated in Fig.…”