Source rock assessment within a sequence stratigraphic framework of the Yogou Formation in the Termit Basin, Niger

Abstract

A preliminary sequence stratigraphic geochemical investigation was carried out to assess the areal distribution and hydrocarbon generation potential of marine mudstones of the Upper Cretaceous Yogou Formation in the Termit Basin, Niger. A total of three third‐order sequences (YSQ1, YSQ2, and YSQ3, from bottom to top) and nine systems tracts were identified in the Yogou Formation. Mudstones of each sequences are widely distributed throughout the study area with their maximum cumulative thickness of ~600–900 m in the Dinga and Moul depressions. The ΔlogR method was applied to establish a prediction model for predicting the total organic carbon (TOC) content of the Yogou Formation mudstones. The results of this source rock evaluation indicate that thick offshore mudstones with fair to good hydrocarbon generation potential and dominated Type II to Type III kerogen widely occur in YSQ1, YSQ2, and in the LST (lowstand systems tract) and TST (transgressive systems tract) of YSQ3, while the thin lower shoreface mudstone intervals in the HST (highstand systems tract) of YSQ3 are characterized by good to excellent hydrocarbon generation potential, dominated by Type II kerogen. The present‐day thermal maturation level of source beds from the YSQ3, YSQ2, and YSQ1 has overpassed the main zone of oil generation in the depocenter of Dinga Depression, whereas the YSQ3 and part of YSQ2 source beds were still within the oil window in the depocenter of Moul Depression. The organic matter richness and hydrocarbon generation potential of source beds varies within the Yogou Formation because of changes in organic matter source during evolution of Western Africa rift basins and global sea‐level fluctuations. This study provides a practical sequence stratigraphic geochemical framework which will give a better understanding for the geochemical characteristics of source rock and support improved assessment of petroleum resources.

Source rock types, distribution and their hydrocarbon generative potential within the Paleogene Sokor-1 and LV formations in Termit Basin, Niger

“…The input data used for numerical modelling of these three wells are shown in Table 3. The modelled thermal evolution profiles obtained by the numerical modelling are shown in Figure 11, and the calculated R o curves show a good match to the measured R o data from Lai et al (2019), suggesting that the reconstruction of burial and thermal histories of these three wells is reasonable. The burial and thermal histories of well DD-3, which is located in the western marginal area of the Dinga Depression (Figure 1(a)), suggest that source rocks within the Sokor-1 and LV formations are mainly in the early mature stage (Figure 11(a)).…”

“…The sequence stratigraphic framework of Termit Basin has been discussed in previous studies (Fu et al, 2012;Lai et al, 2018Lai et al, , 2019Tang et al, 2015;Wang et al, 2016). Two first-order sequences (FS1 and FS2) and four second-order sequences (TS1, TS2, TS3, and TS4) have been identified on the basis of four sets of regional unconformities in Termit Basin (Lai et al, 2019). The top and bottom boundaries of the Paleogene are consistent with those of the TS3 second-order sequence (Lai et al, 2019).…”

“…It is reasonable to deduce that Paleogene source rocks from the Yogou Slope, Fana Uplift, and northern Moul Depression mainly stay in the immature stage. Lai et al, (2019). LV Fm.…”

“…The geological and geochemical characteristics of the source kitchen of the Sokor-Yogou (!) petroleum system have been reported in detail in recent years (Harouna and Philp, 2012; Harouna et al., 2017; Lai et al., 2018, 2019; Liu et al., 2015; Tang et al., 2017; Xiao et al., 2019). However, the spatial distribution and hydrocarbon generative potential of probable source rocks of the Sokor–Sokor (!)…”

“…Geographic location and schematic structure of the Agadem Block in the Termit Basin (a), the representative geological profile (section A-Aʹ) showing the stratum and faults (b) and the generalized stratigraphic column of the Termit Basin (c). (Modified after Genik, 1993; Lai et al., 2018, 2019; Wan et al., 2014). Quat.…”