A beneficial is the gamma ray/potassium/thorium index, A

where I _{log denotes the total natural gamma ray/potassium/thorium reading gleeden odwiedzajД…cych 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 numerous degree where Th/You ratio was used to recognize the new depositional ecosystem [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 (I_A 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 new gamma beam pastime regarding creation isn’t only related into the clay nutrition. For this reason, even though the natural gamma beam logs are generally the best symptoms of your own clay articles, they need to be used in combination with caution [ten, 11]. The new mistakes on the estimate of clay content away from wireline logs is going to be smaller, if they’re calibrated from the mineralogy investigation taken from cores. Several training lead a beneficial correlations amongst the research-derived clay articles and viewpoints determined on the altered natural gamma ray log as well as spectral areas data while the anybody else didn’t support this reality. Particularly, Heslop argued that the changed sheer gamma beam diary render a good correlations to the X-ray diffraction data. Johnson and you can Linke , according to research by the cation exchange skill data from inside the Mackensie delta urban area, concluded that the new altered pure gamma beam approach really does supply the reputable clay articles. As opposed to, Causey realized that the changed natural gamma beam log try probably the most specific clay signal within his investigation, although it did overestimate the fresh new clay information when compared to the fresh new laboratory analysis. Jurado confirmed your changed sheer gamma ray and its spectral parts data are helpful and you will energetic devices throughout the identity/quantification of the clay vitamins, due to their large and you may reasonable indication regarding the shale and you will clean areas, respectively. Almost every other individuals research has been achieved making use of the combination regarding the research, plus the diary-derived clay nutrient philosophy regarding subsurface structures [18, 30,30,32,33,34].

The fresh thorium so you’re able to uranium (Th/U) proportion may vary to the sedimentary processes and you may circumstances plus towards depositional ecosystem; hence, it can be used to distinguish the latest surroundings 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].