where I log 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 many training where in actuality the Th/U proportion was applied to spot the fresh 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 beam interest on the formation is not only associated into clay nutrients. Thus, while the sheer gamma beam logs are usually the best indications of your clay content, they need to be used in combination with warning [ten, 11]. New problems regarding estimate out of clay stuff out of wireline logs is going to be faster, if they’re calibrated up against the mineralogy analysis extracted from cores. Multiple training lead a beneficial correlations involving the lab-derived clay contents plus the opinions calculated regarding altered sheer gamma ray journal and its spectral areas investigation because someone else didn’t service this particular fact. Instance, Heslop debated that changed absolute gamma ray record bring a good correlations with the X-ray diffraction data. Johnson and you will Linke , according to the cation exchange capabilities study inside Mackensie delta urban area, concluded that the latest altered sheer gamma beam means do provide the reliable clay content material. Rather than, Causey found out your changed sheer gamma beam journal was the quintessential direct clay signal inside the study, though it performed overestimate the brand new clay material when comparing to the latest laboratory investigation. Jurado confirmed that the altered sheer gamma ray and its spectral areas analysis are helpful and you may energetic tools regarding the character/quantification of clay vitamins, for their high and you will reasonable indication in the shale and you may brush zones, correspondingly. Other individuals studies have been carried out by using the combination from the new profil mobifriends research, therefore the record-derived clay nutrient values from the subsurface formations [18, 29,30,thirty-two,33,34].
Brand new thorium in order to uranium (Th/U) ratio varies towards sedimentary process and you may issues along with into the depositional environment; for this reason, it can be utilized to acknowledge the new environment and operations
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].