A great is the gamma ray/potassium/thorium index, A
where I diary 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 maximum indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
You can find education where the Th/U ratio was used to understand 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 latest gamma ray pastime regarding development isn’t exclusively relevant on clay nutritional elements. Thus, although the absolute gamma beam logs are the best indicators of your own clay blogs, they should be used in combination with caution [10, 11]. New mistakes regarding the quote off clay blogs out of wireline logs might be faster, when they calibrated resistant to the mineralogy analysis extracted from cores. Numerous studies lead an excellent correlations within research-derived clay content material while the viewpoints computed about modified sheer gamma ray log as well as spectral areas investigation since the anyone else don’t assistance this fact. Eg, Heslop argued that the altered absolute gamma ray log give good correlations into X-beam diffraction analysis. Johnson and you may Linke , according to the cation exchange potential research inside the Mackensie delta town, determined that the changed sheer gamma ray means really does deliver the reliable clay information. In place of, Causey learned your altered absolute gamma ray journal are many particular clay indicator in his analysis, though it did overestimate the newest clay content material when comparing to the newest laboratory analysis. https://datingranking.net/pl/ashley-madison-recenzja/ Jurado confirmed your changed sheer gamma beam and its spectral section study are useful and you will energetic tools regarding the identity/quantification of the clay vitamins, due to their higher and you will reasonable readings on shale and you will clean zones, respectively. Almost every other certain studies have become carried out with the consolidation from the latest lab, plus the diary-derived clay mineral opinions from the subsurface formations [18, 30,29,thirty two,33,34].
The brand new thorium so you can uranium (Th/U) ratio may vary into sedimentary process and issues including on depositional ecosystem; therefore, it can be used to recognize the newest 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].