Hydrostatic secondary hydrocarbon migration

S—It cirtiilif M—tixel brm No pralorrod l ourbon iMgralion drtchom 

Coinposite linear svininetrieal basin Preferred hydrocarbon migration towards centre of common flanks migration preference A over B over C 

Proforrod hydrocarbon Migration towards narrow concave Sidt B of the basM mgrahon prefarenca B over A 

Prtlorred hydrocarbon Migration towards concave long flank a migralion prafaronce A over B ovar C. 

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Hydrostatic secondary hydrocarbon migration systems, in which the dominant forces influencing hydrocarbon migration are the buoyancy forces and the capillary pressure gradients (Section 4.3.3). 

Secondary hydrocarbon migration under hydrostatic conditions... 

Under hydrostatic conditions the basin-wide secondary hydrocarbon migration patterns and consequently also the final distribution of the oil and gas accumulations in a sedimentary basin are closely linked to the stable basin geometry present during hydrocarbon expulsion from the source rocks. 

A quantitative analysis of present-day secondary hydrocarbon migration for basin evaluation can be restricted to the prospective parts of a sedimentaiy basin as selected on the basis of the previously described qualitative study (Chapter 7). The quantitative assessment of present-day hydrocarbon migration systems is described separately for hydrostatic and hydrodynamic conditions of the prospective parts of the basin (Sections 8.1, 8.2 and 8.3). Section 8.4 briefly describes the available approaches for a quantitative analysis of the evolution of secondary hydrocarbon migration systems. 

Figure 4.4 Secondary separate phase hydrocarbon migration under hydrostatic conditions (after Hobson and Tiratsoo, 1975. Reprinted by permission of Scientific Press Ltd.).

The process of migration may lead to focussed movement of hydrocarbons into economic accumulations. The secondary migration of hydrocarbons may occur under hydrostatic or hydrodynamic conditions. Under hydrostatic conditions, the hydrocarbons migrate through the water-saturated carrier-reservoir rocks as separate phase hydrocarbons. Under hydrodynamic conditions, the hydrocarbons may be transported in continuous separate phase, in suspension or in aqueous solution. Under both hydrostatic and hydrodynamic conditions, the hydrocarbons ultimately appear as separate phase hydrocarbons before they can accumulate in a trap (Tissot and Welte, 1984). 

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