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.
New assessment anywhere between unmodified beam indexes and you can center-counted clay contents. Black colored circle Gas creating better research points, black colored right up-directing triangle low-promoting better study facts
Density against GR in the center types of the newest Shurijeh Formation. Black colored system Fuel promoting really data points, and you can black up-leading triangle low generating well studies factors
Hence, the costs away from linear gamma beam, potassium, and thorium indexes were altered, having fun with each of the empirically derived low-linear changes equations lead by Larinov , Clavier , Steiber , Dewan , or Bhuyan and you may Passey (the matchmaking is placed in Dining table 1) to get a reduced erroneous quote out-of Shurijeh clay stuff
While the mistakes with the previous variations produced a relatively highest differences toward efficiency, it’s important to derive a keen empirical relationship on clay posts estimations within this development. eleven.0 software. Shown less than is the obtained low-linear calibration relationship into the Shurijeh Development in the form of an intellectual mode anywhere between natural gamma ray directory while the separate varying plus the research-derived pounds percent clay in accordance with the X-ray diffraction investigation just like the oriented variable:
Profile 8 suggests the relationship away from weight per cent clay in the XRD measurements of each other wells and you can changed sheer gamma ray list playing with different equations and extremely consolidated Larionov changes, Clavier mais aussi 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 https://datingranking.net/pl/meetville-recenzja/ 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.
