where I diary denotes the total natural gamma ray/potassium/thorium reading in the zone of interest, A min 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 in fact the Th/You ratio was applied to spot brand 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 (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 passion regarding formation is not solely related to your clay vitamins. Hence, whilst absolute gamma ray logs are usually an educated indicators of one’s clay posts eastmeeteast recenzja, they should be used with warning [ten, 11]. The fresh errors regarding the quote of clay posts off wireline logs is faster, when they calibrated contrary to the mineralogy research obtained from cores. Several education brought a beneficial correlations amongst the laboratory-derived clay material in addition to viewpoints computed regarding altered sheer gamma ray record and its spectral section research because other people failed to help this fact. Such as for instance, Heslop debated that altered sheer gamma ray diary provide a great correlations towards X-beam diffraction investigation. Johnson and you will Linke , based on the cation replace ability study inside the Mackensie delta town, figured the fresh modified absolute gamma ray approach really does deliver the reputable clay information. As opposed to, Causey realized that the modified sheer gamma beam journal is by far the most direct clay indicator within his investigation, though it performed overestimate this new clay information in comparison to the fresh lab research. Jurado affirmed that the altered pure gamma ray and its own spectral parts research are useful and you can productive devices on the identity/measurement of one’s clay nutrition, for their highest and reasonable readings on the shale and you can clean zones, correspondingly. Most other individuals studies have been carried out using the integration from this new research, in addition to record-derived clay nutrient beliefs on the subsurface formations [18, 31,29,32,33,34].
The newest thorium so you can uranium (Th/U) proportion varies for the sedimentary processes and you will points as well as toward depositional ecosystem; hence, it can be used to distinguish the brand new 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].