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 cuddli 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.
This new assessment ranging from unmodified ray indexes and center-counted clay contents. Black community Gas creating better investigation activities, black up-leading triangle low-generating better research situations
Density against GR from the center samples of brand new Shurijeh Creation. Black community Fuel generating better study factors, and black colored right up-pointing triangle low generating really study things
Ergo, the values regarding linear gamma ray, potassium, and you will thorium indexes was altered, playing with each one of the empirically derived non-linear changes equations produced by Larinov , Clavier , Steiber , Dewan , or Bhuyan and you will Passey (most of the relationships is actually placed in Dining table 1) to acquire a quicker incorrect estimate from Shurijeh clay stuff
Just like the problems associated with the earlier in the day variations generated a comparatively large difference to your efficiency, it is vital to derive a keen empirical relationship for the clay posts estimations within formation. 11.0 software. Shown below is the gotten low-linear calibration dating on the Shurijeh Formation in the way of a mental mode ranging from natural gamma beam list as the independent changeable in addition to lab-derived weight % clay in line with the X-beam diffraction study since situated changeable:
Figure 8 shows the relationship out-of weight % clay regarding XRD size of one another wells and you may modified absolute gamma beam list using some other equations as well as very consolidated Larionov changes, 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 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.