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 maximum indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
You will find several education where Th/U proportion was applied to recognize the fresh 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 gamma beam interest on the formation is not exclusively associated to your clay minerals. Ergo, even though the pure gamma ray logs are often an educated signs of one’s clay blogs, they need to be used in combination with caution [ten, 11]. The errors throughout the estimation out-of clay blogs out of wireline logs shall be faster, when they calibrated resistant to the mineralogy analysis taken from cores. Numerous studies delivered a good correlations between the lab-derived clay content material additionally the thinking computed regarding altered sheer gamma ray log and its spectral elements study as other people don’t assistance this reality. Including, Heslop argued your changed natural gamma beam journal promote a great correlations into the X-beam diffraction data. Johnson and you can Linke , in accordance https://datingranking.net/pl/blackplanet-recenzja/ with the cation exchange strength studies during the Mackensie delta area, figured the newest altered natural gamma beam approach really does supply the credible clay information. Rather than, Causey discovered that the altered sheer gamma beam record is actually more perfect clay signal in his research, though it performed overestimate the fresh new clay information when compared with brand new lab study. Jurado affirmed that altered pure gamma ray and its particular spectral elements data are helpful and productive devices regarding the identity/quantification of your clay nutritional elements, because of their large and you may reduced readings regarding shale and you will brush zones, correspondingly. Other certain studies have already been carried out utilising the consolidation from this new lab, in addition to diary-derived clay mineral beliefs from the subsurface formations [18, 30,31,thirty two,33,34].
This new thorium to uranium (Th/U) proportion varies on sedimentary process and you will situations and additionally into depositional ecosystem; ergo, it can be utilized to identify 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].