Water Saturation Calculation Using Archie’s Equation for Shally Sand Formation : Case Study from Talang Akar Non Marine Formation, North West Java

Abstract

Water saturation is one of the physical parameters of reservoir rocks that is important in determining the volumetric reserves of oil and gas fields. Several factors, including rock and fluid properties, also affect the diversity of water saturation values in reservoir rocks. One of the oldest methods, still used today, for determining Water Saturation values is the Archie method, which is based on the relationship between porosity, resistivity, and saturation. However, because reservoir rocks are heterogeneous, there are three (3) parameters that reflect rock characteristics: a (tortuosity factor), m (cementation exponent), and n (saturation exponent). The purpose of this study is to determine the Archie parameters a, m, and n in wells with shally sand lithology of the Lower Talang Akar Formation, and verify whether the water saturation value with the Archie equation is valid when applied to the well. The data used was obtained from the "Jeruk-2" well, in the form of well logs and core data (Routine Core Analysis and Special Core Analysis). As a result, it is found that the a and m values ​​from the Jeruk-2 well were 1.47 and 1.81. The parameter n cannot be calculated because rock resistivity values ​​at 100% brine saturation (Ro) are unavailable, so n = 2 is used following the literature. The calculation results using the Archie formula indicate that the water saturation in the Zone of Interest "Jeruk-2" ranges from 0.22 to 1.00. The results of this calculation are verified with the water saturation value from SCAL data, giving a correlation coefficient of 0.79. This shows that for shally sand lithology of the Talang Akar Non Marine Formation around the Jeruk-2 well, the Archie equation can be used to calculate water saturation using the Archie parameters a = 1.47, m = 1.81, and n = 2. However, it is still recommended to calculate the Archie parameters for each well and formation to get more accurate results.