Biodegradation in numerical basin modelling: a case study from the Gifhorn Trough, N-Germany

Abstract

A mass balance concept based on petroleum compositional description using 14 individual compound groups has been developed to reproduce the process of inreservoir petroleum biodegradation. Individual compound groups have been attributed different ''biodegradabilities'' and biodegradation rates to account for observed differences in their susceptibility to biodegradation. Petroleum compositional information is derived from basin modelling, in addition to temperature histories, filling rates and volumetric information. This new method has been subsequently applied to model the biodegradation processes in a petroleum system in the North German Basin. The case study area is situated in the Gifhorn Trough, where Jurassic reservoirs contain oils of variable API gravity (24°-33°), although present depth and temperature are similar.Numerical modelling revealed, however, that the filling histories of the individual reservoir structures differ considerably. Taking into account filling and temperature history of the reservoir structures, the newly developed biodegradation algorithm Biodexx predicted compositional data and API gravities similar to those observed in the study area, whereas earlier biodegradation approaches such as the biodegradation index (BDI) by Yu et al. (2002) did not reproduce the different biodegradation levels in the two investigated fields.

Predicted bulk composition of petroleum generated by Lower Cretaceous Wealden black shales, Lower Saxony Basin, Germany

“…All oil fields occur in the source rock maturity zone 0.5-0.9 % R 0 (Kockel et al 1994). Biodegradation plays a major role in defining oil quality (Blumenstein et al 2008). The oils generally have a low solution gas-oil ratio; density and viscosity vary (Fabian 1963;Lübben 1969).…”

12. Assessing biosphere-geosphere interactions over geologic time scales: insights from Basin Modeling

“…Head et al [8] propose mineral hydrolysis, organic matter maturation (aromatization) or even from the porewater itself, as both thermodynamic and microbiological data indicate [23,34], as sources of hydrogen. A similar approach to Haeseler et al [30] but including the dynamic reconstruction of basin evolution, petroleum generation, migration and accumulation was already presented a few years earlier by Blumenstein et al [35]. Also, in this case petroleum biodegradation is simulated assuming a limited number of compound groups, each with a definition of the proportion degradable and relative degradation rates.…”

“…Also, in this case petroleum biodegradation is simulated assuming a limited number of compound groups, each with a definition of the proportion degradable and relative degradation rates. The main difference of the Blumenstein et al [35] approach is that in addition to the compound group degradation properties, a temperature-dependent overall biodegradation rate control was defined. Figure 12.4 shows the assumed decrease in biodegradation rate with increasing geologic temperature as implemented in the model.…”

Integrated charge and seal assessment in the Monagas fold and thrust belt of Venezuela

“…Restoring of present-day geometries to obtain paleogeometries adds further uncertainty. Additional uncertainty is related to thermal boundary conditions such as paleoheat flow (Beha et al, 2008), and to geochemical properties such as source rock characteristics and petroleum generation kinetics, and calculation of biodegradation and petroleum density (Blumenstein et al, 2008). In addition to the pore pressure and thermal sensitivity analysis just described, we varied initial TOC within a range of 2% to 10%.…”