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 max indicates the average natural gamma ray/potassium/thorium response of the pure clay zone .
There are a few degree where Th/U proportion was applied to identify the latest 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 brand new gamma beam passion regarding creation is not only relevant to the clay nutrients. For this reason, whilst natural gamma ray logs are usually an educated indicators of your clay content, they should be used in combination with alerting [ten, 11]. The fresh new errors regarding the estimation of clay content of wireline logs might be quicker, if they are calibrated up against the mineralogy data extracted from cores. Several training lead good correlations between your lab-derived clay content and also the philosophy calculated about modified absolute gamma beam diary and its own spectral components analysis while the other people don’t help this fact. Like, Heslop argued that the altered absolute gamma ray journal give good correlations for the X-beam diffraction research. Johnson and you can Linke , based on the cation change potential analysis in Mackensie delta town, determined that the brand new changed absolute gamma ray approach does provide the credible clay contents. Unlike, Causey learned your altered pure gamma beam log is the most appropriate clay signal within his data, though it performed overestimate the newest clay articles when compared with the latest laboratory studies. Jurado affirmed that changed natural gamma beam and its own spectral portion research are useful and you may energetic tools regarding the identity/measurement of the clay nutritional elements, because of their highest and you can lowest readings on the shale and brush zones, respectively. Most other certain studies have started carried out by using the combination regarding new lab, additionally the journal-derived clay mineral thinking on the subsurface structures [18, 30,31,32,33,34].
The latest thorium so you can uranium (Th/U) ratio may vary towards sedimentary procedure and you may factors along with on the depositional environment; for this reason, it can be used to distinguish the latest surroundings and processes
The potassium and http://datingranking.net/pl/caffmos-recenzja 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].