where I diary 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 many knowledge the spot where the Th/U proportion was utilized to understand the newest depositional ecosystem [39, 40]
However, some variations jak uЕјywaД‡ fuckbookhookup 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 gamma beam interest from the formation isn’t entirely related for the clay vitamins. Hence, even though the absolute gamma beam logs are often a knowledgeable evidence of one’s clay articles, they need to be combined with caution [10, 11]. The fresh new mistakes about estimate off clay posts of wireline logs can be quicker, if they are calibrated resistant to the mineralogy research extracted from cores. Numerous education delivered an excellent correlations involving the research-derived clay content in addition to opinions calculated on changed sheer gamma beam log and its particular spectral section research given that other people failed to support this reality. Such, Heslop argued that altered absolute gamma ray log provide a beneficial correlations to the X-ray diffraction research. Johnson and Linke , according to research by the cation change potential studies during the Mackensie delta urban area, figured the brand new altered absolute gamma ray approach do provide the credible clay content. As opposed to, Causey realized that the modified natural gamma beam diary was one particular specific clay indication in his analysis, although it did overestimate the brand new clay material when compared to the fresh new laboratory study. Jurado confirmed your modified absolute gamma ray and its own spectral portion data are useful and you may productive equipment regarding character/quantification of your own clay vitamins, for their large and you will reduced readings on the shale and brush zones, correspondingly. Other certain research has been carried out by using the combination out-of new lab, and also the diary-derived clay mineral beliefs on the subsurface formations [18, 31,29,thirty-two,33,34].
The brand new thorium so you’re able to uranium (Th/U) proportion varies towards sedimentary process and issues plus towards the depositional environment; hence, it can be used to identify the newest 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].