**2.1 Petroleum formation and migration**

The focus of researchers in the 1940s and 1950s, during worldwide oil and gas exploration, was to investigate the origins of petroleum. Reactions between clays and subsurface fluids were studied extensively. At that time, the major concern was assessment of quality of organic source rocks and the mechanisms involved in generation of oil and gas. In this regard, researchers such as Weaver [2, 3] and Sarkissian [4] recognised that analyses of clay rocks (shales) could be used to track the generation and migration of petroleum in source rocks. Weaver [2] noted that expandable clays are capable of withholding their pore water to greater depths. He therefore inferred that waters in expandable clays at greater depths were responsible for transporting hydrocarbons to reservoir rocks. This inference was premised on

#### **Figure 1.**

*Schematics of typical clay fluid interaction research topics and outcomes relevant to hydraulic fracturing of shale formations.*

### *Review of Geochemical and Geo-Mechanical Impact of Clay-Fluid Interactions Relevant… DOI: http://dx.doi.org/10.5772/intechopen.98881*

and supported by earlier studies where over 20,000 samples from major petroleum producing basins in the US showed strong statistical correlation between expandable clay minerals and hydrocarbon production. Similar to Weaver [2], Sarkissian [4] also studied petroleum deposits in the USSR and reported that clay minerals in argillaceous rocks were significant in the formation and deposition of petroleum resources. Premising on earlier works alluded to above, other researchers also used clay rock analyses to determine the hydrocarbon emplacement and migration times and for petroleum system analysis [1, 5–9]. Some of these works are summarised below.

Hamilton [5] used K-Ar dating to assess the formation of illite relative to the timing of generation and migration of hydrocarbons. Considerable correlation was found to exist between these two events. He reported that, in most cases, the timing of the expulsion of hydrocarbons was the same time authigenic illite formation ceased. He concluded that the link between clay-fluid interaction and petroleum generation and migration was therefore established, thus presence of authigenic illite could be used as an indicator of petroleum formation and migration.

Kelly [7] used mineralisation history present in fractures to reconstruct the migration history of hydrocarbons to their current reservoir and found that most petroleum migration paths showed preponderance of illite and clay mineral precipitates. He concluded that illite and other clay mineral precipitates can be used as an indication of petroleum migration pathway.

Jiang [6] examined clay minerals from the oil and gas perspective and drew a lot of parallels between various types of clays, their structural and geochemical transformations as a function of formation and transport of hydrocarbons. Jiang's work is different from earlier works in the sense that he investigates comprehensively the transformations that take place from deposition of rock to when petroleum is formed and expunged.
