where I record 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 faceflow zaloguj siД™, A maximum indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
There are numerous education the spot where the Th/U proportion was applied to identify the brand new 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. 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 .
New gamma ray activity in the creation is not exclusively associated to the clay minerals. For this reason, even though the absolute gamma ray logs are generally a knowledgeable indications of your clay stuff, they need to be used with caution [ten, 11]. The errors regarding quote out-of clay blogs regarding wireline logs would be faster, if they are calibrated resistant to the mineralogy data obtained from cores. Several studies brought a good correlations between the research-derived clay information and also the thinking computed throughout the altered natural gamma beam record and its spectral portion data since the anyone else failed to assistance this reality. Including, Heslop debated your modified natural gamma ray record provide an effective correlations towards the X-ray diffraction analysis. Johnson and Linke , according to research by the cation change capability investigation in the Mackensie delta city, figured the newest modified absolute gamma beam strategy do deliver the reputable clay content material. In place of, Causey revealed that the modified sheer gamma ray journal is by far the most accurate clay indicator in the study, although it did overestimate the clay information in comparison with new laboratory studies. Jurado confirmed that the changed natural gamma ray and its spectral portion study are useful and you will effective equipment from the identity/quantification of the clay nutritional elements, due to their high and you may low readings throughout the shale and clean areas, correspondingly. Other certain studies have come achieved utilising the integration off this new research, and diary-derived clay mineral viewpoints on subsurface formations [18, 31,29,thirty-two,33,34].
The new thorium so you’re able to uranium (Th/U) ratio varies on sedimentary procedure and you may things including towards the depositional ecosystem; thus, you can use it to distinguish new environments 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].