ESTIMATION OF SOURCE ROCK POTENTIAL OF THE SEMBAR FORMATION BY INTEGRATION OF WELL LOGS AND WELL CUTTINGS DATA IN THE SOUTHERN INDUS BASIN, PAKISTAN

Abstract

The Sembar Formation encountered in Khajari-01 and Miran-01 wells are located in the Sanghar-south district Sindh, and Gupchani Block of Nawabshah District, Sindh, Pakistan. The crucial indicator for evaluation of source rock potential is total organic carbon (TOC) content. TOC is generally measured by traditional methods like evaluation of side wall cores, well cuttings or cores in geochemical lab. Data obtained from these experimental techniques are not continuous and timeconsuming process. A solution to this problem is high resolution and continuous information from well logs. Different methods were used to estimate TOC through well logs. Out of these methods, four methods have been chosen to estimate TOC, i.e Schmoker and Hester, Fertl and Chilingar, Passey, and Multivariate fitting method. These estimated values have been correlated with well cuttings TOC values to optimize a method for TOC estimation through well logs. Fourteen well cuttings samples of Sembar Formation from well Khajari-01 and seven samples from Miran- 01 well have been evaluated for geochemical parameters, because every well logs TOC estimation method is restricted to some specific environments. These parameters were used for evaluation of the formation to determine the quality, quantity and maturity of organic matter. Van krevelen diagram of HI verses OI and Langford diagram of S2 verses TOC indicate that Sembar Formation of Khajari-01 well contain kerogen type-III which is gas prone, while that of Miran-01 contain Kerogen type-IV, which is nonproductive. TOC indicate the organic richness in Khajari-01 well as poor to very good and in Miran-01 fair to good, while S2 indicate poor potential yield in both wells. Maturity indicators i.e Tmax and Production Index show an immature to early mature zone for Khajari-01 well and over mature zone for Miran-01 in the Sembar Formation. Natural gamma-ray spectroscopy method has poor correlation coefficient values with cuttings tested TOC with R2 values of 0.1446 for well Khajari-01 and 0.2359 for well Miran-01. Schmoker and Hester method also gives poor R2 values of 0.2878 and 0.5828. Multivariate fitting method has also poor correlation coefficient values of 0.3556 and 0.0333. Passey method was best fitting method with high R2 values of 0.8018 for well Khajari-01 and 0.8306 for well Miran-01.