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Wanting to calibrate new center to record analysis, a straightforward low-linear regression relationships is run in Matlab eight

Wanting to calibrate new center to record analysis, a straightforward low-linear regression relationships is run in Matlab eight

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 latest evaluation anywhere between unmodified ray indexes and center-mentioned clay contents. Black circle Fuel producing really data items, black right up-leading triangle non-creating better investigation products

Thickness versus GR on center samples of the fresh Shurijeh Formation. Black circle Energy generating well studies items, and you may black right up-leading triangle low promoting really study circumstances

Hence, the values of linear gamma ray, potassium, and you may thorium indexes was in fact changed, playing with each of the empirically derived low-linear alter equations brought by the Larinov , Clavier , Steiber , Dewan , otherwise Bhuyan and Passey (the matchmaking are listed in Dining table step 1) to acquire a reduced incorrect estimation out-of Shurijeh clay blogs

Since the problems associated with the early in the day improvement made a somewhat highest differences toward results, you will need to derive an empirical relationship for the clay posts estimations contained in this development. 11.0 software. Found lower than ‘s the obtained non-linear calibration matchmaking toward Shurijeh Formation in the way of a rational function anywhere between sheer gamma beam list given that separate changeable in addition to laboratory-derived pounds percent clay in line with the X-beam diffraction study since the based adjustable:

Figure 8 shows the relationship regarding pounds per cent clay from the XRD sized each other wells and you may modified natural gamma ray directory having fun with additional equations along with very consolidated Larionov change, 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 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.

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