where I journal 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 maximum indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
You will find several training where the Th/You ratio was applied to determine the newest 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 geek2geek. 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 gamma beam craft in the formation isn’t exclusively relevant towards clay nutritional elements. Ergo, although the absolute gamma beam logs are usually a knowledgeable signs of clay stuff, they should be combined with caution [10, 11]. The fresh mistakes throughout the quote regarding clay content regarding wireline logs will be shorter, when they calibrated against the mineralogy data taken from cores. Numerous training delivered good correlations involving the laboratory-derived clay contents as well as the thinking calculated from the altered pure gamma beam journal and its own spectral portion investigation while the anybody else don’t assistance this particular fact. Including, Heslop contended that the altered absolute gamma ray record give an excellent correlations to your X-ray diffraction data. Johnson and Linke , in line with the cation replace skill data into the Mackensie delta city, determined that the fresh new changed absolute gamma ray method do deliver the reliable clay articles. In the place of, Causey found out the altered absolute gamma beam journal is actually by far the most exact clay sign within his research, although it performed overestimate the latest clay content when compared with the newest lab studies. Jurado verified your changed absolute gamma beam and its own spectral elements analysis are of help and energetic tools on identification/quantification of one’s clay minerals, because of their higher and lower indication on shale and you may brush zones, correspondingly. Most other some research has become accomplished making use of the combination of the newest research, therefore the diary-derived clay mineral thinking throughout the subsurface formations [18, 30,30,32,33,34].
The fresh new thorium to uranium (Th/U) proportion may differ into the sedimentary process and you may issues plus toward depositional ecosystem; ergo, it can be used to distinguish the brand 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].