where I record denotes the total natural gamma ray/potassium/thorium reading in the zone of interest, A minute 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 several training where in actuality the Th/You proportion was applied to recognize the fresh 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 .
The brand new gamma ray interest regarding creation is not solely relevant on the clay nutrition. Hence, whilst sheer gamma beam logs are usually an educated symptoms of your own clay blogs, they need to be used with warning [10, 11]. The newest problems regarding the quote out-of clay content off wireline logs can be reduced, if they are calibrated against the mineralogy investigation extracted from cores. Numerous degree introduced a beneficial correlations amongst the laboratory-derived clay content material therefore the viewpoints computed in the altered sheer gamma beam diary as well as spectral elements research since the others didn’t help this reality. Like, Heslop debated that the altered absolute gamma ray log give a beneficial correlations towards the X-ray diffraction analysis. Johnson and you may Linke , based on the cation change skill analysis in the Mackensie delta town, figured brand new altered sheer gamma beam method does deliver the legitimate clay content. In lieu of, Causey learned your changed pure gamma ray journal are by far the most appropriate clay indication in his studies, though it did overestimate the new clay articles when comparing to the new research analysis. Jurado verified your modified pure gamma ray as well as spectral areas research are of help and you will energetic devices on the identity/quantification of clay nutrients, for their higher and you may reasonable readings from the shale and you will brush zones, correspondingly. Other individuals studies have become accomplished making use of the integration out of this new lab, and diary-derived clay nutrient beliefs on subsurface formations [18, 30,29,thirty two,33,34].
This new thorium to uranium (Th/U) proportion may differ into the sedimentary procedure and you may points including on the depositional ecosystem; thus, it can be utilized to identify the fresh new environment and https://datingranking.net/pl/connexion-recenzja/ 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].