Humans first turned clay minerals into pottery and ceramics about 25,000 years ago. Industries ranging from the production of food, medical pills, paper, and water containment facilities make use of their high specific surface area, ion exchange capacity, and their sealing properties as adsorbent, discoloration agents, catalyst, and liners. 

In oil and gas production, clay minerals are particularly important for many reasons:  as impermeable barriers or “seals”, a critical component in petroleum systems forming a barrier to fluid migration; as the main ingredient in drilling mud which helps with the lubrication and cooling of the drill bit, and removal of cuttings; and as indicators of depositional environment and diagenetic history. 

In mining, the presence of clays in an ore can be challenging for several reasons: they can lead to the reduction in efficiency of comminution because of their soft nature, leading to smearing of grinding media; or than can adversely affect flotation given their fine grain size and tendency to produce unwanted slimes; and in leaching processes, they are a nuisance because of their variable reactivity to reagents. 

Despite their economic importance, clay minerals prove difficult to study. Their sheet structure results in features that can only be resolvable at the sub-micron scale (<0.002 mm). They are also subtly variable in chemical composition (Fe, Mg, K, Al etc) and can be confused with each other and other silicates.

As a result, clay typing requires special analytical techniques. At FEI, we have made significant progress in Q1 of 2011 in clay typing by developing a new mineral identification protocol based on the new Spectral Analysis Engine. The Species Identification Protocol (SIP) discriminates a large variety of clay minerals and groups them into the most important groups:

Smectites (including beidellite, montmorillonite, also known as bentonite, nontronite, and saponite);  Kaolinite group; Illite group; Chlorite group; and Glauconite. 

The QEMSCAN® mineral identification protocol involves two steps; 1) elemental identification in the material under the electron beam using elemental reference standards; followed by 2) mineral identification using a statistical elemental range rule set, known as Species Identification Protocol (SIP). 

Calibration of QEMSCAN® has been performed on 15 Source and Special Clays from the Clay Mineral Society, including smectite, illite, chlorite clay mineral group samples, and one glauconite-bearing rock from a type locality. 

This study demonstrates that clay mineral identification and quantification based on the QEMSCAN® EDS spectral analysis method is a reliable alternative to conventional methods. 

Furthermore, our automated SEM-EDS solution approach provides additional textural information, and the resulting mineral maps can be used to differentiate, in the case of reservoir rocks,  pore linings, from granular mineral alteration products, from intergranular cements, and sedimentary laminations.