where I record denotes the total natural gamma ray/potassium/thorium reading in the zone of interest, A minute shows the average natural gamma ray/potassium/thorium response of the clean (clay free) zone, A max indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
There are a few degree where the Th/You proportion was utilized to identify the new depositional environment [39, 40]
However, some variations of the above-mentioned parameters can induce large effects on the log responses, so that the linear equation, called gamma ray index (IA in Table 1 when A is the gamma ray log readings), gives an overestimate of the clay contents in the reservoirs. Thus, the linear gamma ray index should be modified using one of the empirically derived non-linear calibration equations such as those introduced by Larinov , Clavier , Steiber , Dewan , or Bhuyan and Passey (Table 1). These transforms are all in the non-linear form except for that of Bhuyan and Passey , which is developed based on the assumption that the estimation of weight percent clay can be modified by multiplying the gamma ray/potassium/thorium index by an empirical correction factor, i.e., C. This factor is basically determined from the weight percent clay content of average shale adjacent to the zone of interest , and commonly ranges from 50 to 70 [10, 13, 14]. Accordingly, the rock can be differentiated as clean, if the calculated clay content is less than 10%; shaly sand if it ranged from 10 to 33% and if it is more than 33%, it is considered to be shale .
The fresh new gamma ray activity on creation isn’t entirely related on the clay nutritional elements. Therefore, even though the natural gamma beam logs are often an informed indicators of your own clay articles, they need to be combined with warning [10, 11]. The newest mistakes on estimate of clay blogs away from wireline logs can be less, if they’re calibrated up against the mineralogy research obtained from cores. Multiple studies put a correlations between the laboratory-derived clay content material and the thinking determined throughout the altered absolute gamma beam diary and its spectral elements analysis while the other people didn’t support this fact. Such, Heslop argued your altered sheer gamma beam diary give good correlations into the X-ray diffraction data. Johnson and you may Linke , according to research by the cation change capability data when you look at the Mackensie delta area, determined that kod rabatowy mocospace brand new modified pure gamma ray method does supply the credible clay material. Instead of, Causey revealed the modified absolute gamma ray diary try by far the most precise clay indication inside the investigation, though it performed overestimate this new clay articles when compared to new research study. Jurado verified the changed natural gamma beam as well as spectral parts data are of help and energetic products in the identification/measurement of the clay nutrients, due to their high and you will reduced indication regarding shale and clean areas, correspondingly. Most other various studies have already been accomplished using the integration out of the fresh new research, while the diary-derived clay mineral values regarding subsurface formations [18, 29,29,32,33,34].
The new thorium so you’re able to uranium (Th/U) ratio may differ into the sedimentary processes and you may facts including toward depositional environment; for this reason, you can use it to acknowledge new environments and processes
The potassium and thorium concentrations are not only linked to the clay content, but also to the changes in the weathering regime of sediments in the source lands [35,36,37]. The Th/U ratios in the sedimentary rocks range from less than 0.02 to more than 21 . This ratio in the continental, oxidizing environment, weathered soils are above 7, while the most marine deposits, gray and green shales, and graywackes have ratios that are > 2 and < 7. However, in marine black shales and phosphates, it reaches below 2 . Schlumberger has developed several cross-plots to estimate the clay mineralogy in the subsurface formations in the absence of laboratory data. Many authors used them to recognize different clay minerals types [18, 20, 42, 43].