Table 4 summarizes the pertinent well data used for calculation of the gamma ray, potassium, and the thorium indexes. Their comparison with the actual measured clay content from the XRD analysis (Fig. 5) showed that the unmodified gamma ray, potassium, thorium indexes calculated from the linear Eq. (1) provided wide overestimation of the Shurijeh clay content, which leads eventually to the misestimating of the original hydrocarbon in place and reserves. According to the Shurijeh age (Early Cretaceous), Larinov calibration for highly consolidated formations was used and based on the data in Fig. 6, ? sh in Dewan equation which is corresponding to the highest gamma ray reading considered to be 2.75 g/cc units. The C factor in the Bhuyan–Passey modification was considered to be 60 for the Shurijeh Formation after measuring the clay contents of reference adjacent shale in many surface samples. The estimated clay content from modified gamma ray, potassium, and thorium indexes are given in Table 5.
The fresh testing anywhere between unmodified beam spiders and core-mentioned clay content. Black system Fuel producing well studies factors, black colored upwards-leading triangle low-creating really studies activities
Occurrence against GR regarding center types of brand new Shurijeh Development. Black circle Gas generating well investigation affairs, and you can black colored right up-pointing triangle non promoting well investigation facts
Therefore, the prices of linear gamma ray, potassium, and you will thorium indexes was changed, having fun with all the empirically derived non-linear alter equations lead because of the Larinov , Clavier , Steiber , Dewan , otherwise Bhuyan and you will Passey (all of the matchmaking is actually listed in Dining table step one) discover a shorter erroneous estimation from Shurijeh clay stuff
Just like the mistakes of the early in the day adjustment produced a comparatively higher difference into the show, it is vital to obtain an empirical dating towards clay posts estimations within formation. eleven.0 app. Found lower than is the obtained non-linear calibration relationships on Shurijeh Development in the way of a rational means anywhere between natural gamma ray index given that independent varying plus the research-derived pounds percent clay according to research by the X-ray diffraction study as based variable:
Shape 8 reveals the connection out of lbs per cent clay about XRD size of each other wells and you may changed sheer gamma beam directory using more equations as well as very consolidated Larionov change, Clavier et al
The natural gamma ray index was chosen for running the regression analysis due to the stronger correlation coefficient in compare to the potassium or thorium indexes, with the core clay contents in both wells. The unique feature of new equation is to calculate the clay content of less than 100% with a given IGR of 1.0, while all other previous modifications give clay content of 100% for such IGR value. The assumption used in developing the non-linear relationships was based on the fact that the entire radioactivity is not due to the clay minerals only. The goodness of agreement and the reliability of the regression equation were then both verified by a correlation coefficient of 0.992 upon application on some other core samples from another wells drilled in the Shurijeh Formation. It is clear from the data in Fig. 7 that the core data, verify both the very low and the medium range of clay contents, estimated from the non-linear empirical relationship. The average percent relative error was also minimized to 11.4%. Due to the statistical bias of comparing data samples with very different sizes and variances (76 samples versus 11 samples), the error cannot be reduced further. , Steiber, Dewan, Bhuyan–Passey and the empirical transforms. The clay content was also jackd estimated from the potassium and thorium indexes using the empirical non-linear calibration (Table 5) and a comparison of average percent relative errors for different equations has been shown in Fig. 9.