Saturation Modeling in a Multilayered Carbonate Reservoir Using Log-Derived Saturation-Height Function

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe conventional and widely used way of distributing saturation arrays in reservoir simulation models is through porosity-weighted water saturation values. In this way, each grid cell has an assigned porosity and initial water saturation. The porosity and water saturation are estimated with the help of well logs using established procedures. However, for producing reservoirs, log derived saturations may not represent initial saturations due to various reasons like depletion due to production and effect of water injection etc. One of the ways to estimate the initial water saturation is by the use of relationship between depth and bulk volume of water (BVW). Such relationship, known as Saturation-Height function is used to estimate saturation values away from the well locations and to calculate the hydrocarbons in place volumetrically. This approach has been used in a multi layered carbonate reservoir of an Indian offshore field. Layer-wise saturation height functions are developed by establishing relationships between height above the free water level and bulk volume of water derived from the wells drilled in the initial phase of field development. The scatter in the BVW plot has been reduced by further classifying the data for different porosity facies. These porosity intervals are treated as rock types for that layer. Since each layer has a particular range of porosity, different porosity based rock types are identified. Height above the free water level versus water saturation plots are then generated for different rock types using the relationship developed for each geological layer.These equations were used to assign initial water saturation in the reservoir simulation model.

Transition zones analysis using empirical capillary pressure model from well logs and 3D seismic data on ‘Stephs’ field, onshore, Niger Delta, Nigeria

“…Two non-miscible fluids sharing the same porous space tend to occupy different positions depending on their density contrast (Glover 2000;Pascoal 2015). Vavra et al (1992), Hartmann and Beaumont (1999), Larsen et al (2000), Sarwaruddin et al (2001), Kumar et al (2002), Wiltgen et al (2003), Johan and Svein (2005), Okoli and Ujanbi (2007), Jamiolahmady et al (2007), Zhao et al (2008), Renzo et al (2010) and Goda (Sam) et al (2011) have employed a different approach to analyse the oil transition zone and saturation height above free water level using semi-empirical relationship from Leverett (1941), Skelt and Harrison (1995), Christiansen (2001), Wu (2004), amongst others, with special core analysis (SCAL) under laboratory conditions. Hydrocarbon saturation in a reservoir can be overestimated when the effect of mobile water occurring in the transition zones within the reservoir is not accounted for while estimating reserves (Fig.…”

Saturation modeling in a carbonate reservoir using capillary pressure based saturation height function: a case study of the Svk reservoir in the Y Field

“…The conventional and globally accepted method of saturation modeling is based on the capillary pressure curve data, which is obtained from the special core analysis (Jamiolahmady et al 2007;Kumar et al 2002;Zhao et al 2008). The water saturation distribution above the FWL in an oil reservoir is controlled by the balance of capillary pressure and gravity forces, and when the capillary pressure is available, the water saturation at any given height will be known.…”

Modeling and Validation of Initial Water Saturation in the Transition Zone of Carbonate Oil Reservoirs

“…A significant amount of work to generate saturation height functions is available in the literature [1][2][3] . These functions calculates Sw based on one or more of the parameters like porosity, oil water contact, gas water contact, irreducible water saturation, height above contacts, etc.…”