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 new assessment between unmodified ray spiders and you may key-measured clay information. Black network Gasoline promoting really studies issues, black upwards-leading triangle non-creating better study issues
Thickness versus GR in the center examples of the brand new Shurijeh Development. Black community Gasoline promoting better research circumstances, and you may black up-directing triangle non creating well studies activities
Ergo, the prices off linear gamma ray, potassium, and you will thorium indexes was in fact altered, having fun with all the empirically derived non-linear alter equations produced because of the Larinov , Clavier , Steiber , Dewan , or Bhuyan and you will Passey (the matchmaking are listed in Dining table 1) to locate a shorter erroneous estimate off Shurijeh clay posts
Given that mistakes of this earlier adjustment made a comparatively higher differences on the efficiency, it is important to derive an enthusiastic empirical relationship towards clay stuff estimations within this formation. 11.0 software. Found less than ‘s the gotten low-linear calibration matchmaking to the Shurijeh Creation when it comes to a rational function ranging from absolute gamma beam index as independent adjustable and lab-derived lbs % clay according to the X-ray diffraction studies as the established changeable:
Contour 8 suggests the relationship out-of lbs percent clay about XRD measurements of both wells and you may altered pure gamma beam index using different equations also highly consolidated Larionov alter, 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 lds planet transforms. The clay content was also 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.