Article

Radiogenic Heat Production in the Cretaceous Sediments of Yola Arm of Nigeria Benue Trough: Implications for Thermal History and Hydrocarbon Generation

Journal of Applied Sciences 01/2005; 5:696-701. DOI: 10.3923/jas.2005.696.701

ABSTRACT Yola Arm is an east-west extension of the upper Benue Trough of Nigeria
with Cretaceous sediments of Albian to Senonian ages. Thirteen samples
which are mainly sandstone, shale, mudstone, clay, siltstone, limestone
and coal were collected from six different geological units namely: Bima
Sandstone (BS), Yolde Formation (YF), Dukul Formation (DF), Sukuliye
Formation (SF), Numanhan Formation (NF) and Lamja Sandstone (LS). This
is to determine their radioactive heat production and implications for
thermal history and hydrocarbon generation. The result shows that
concentration and rate of heat production of 40K,
232Th and238U in the samples varies widely with
lithologies and stratigraphic intervals. Three groups of total Heat
Production (HP) were identified and designated as low (LHP), moderate
(MHP) and high (HHP). The LHP includes sandstones of BS, limestone of DF
and coal of LS with total heat production of <750 pW kg-1.
Clay of BS, siltstone of YF, limestone of SF and NF and sandstone of LS
belong to MHP with total heat production of between 750 and 1500 pW
kg-1. Shale of YF, SF and NF with total heat production of
>1500 pW kg-1 belong to HHP. The HHP group corresponds to
shale units at different ages in the study area and are the possible
source rock for hydrocarbon generation. The total heat production
studies have suggested that the Cretaceous sediments experienced complex
temperature history with at least two sudden thermal pulses. They could
have been related to Cretaceous synsedimentary volcanism or to the
emplacement of the basaltic pluton.

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    ABSTRACT: The estimation of thermal conductivity is of great importance for all studies on thermal evolution of sedimentary basins. Due to the paucity of core samples, the approach proposed here is the reconstruction of mineralogical model for the studied rock units by interpreting the well, logs data. Then, the determination of the response equations of the minerals present in each mineralogical model for extracting the frequency of existing minerals and total porosity of some Upper Cretaceous rock units, such as the Bahariya Formation and Abu Roash "D,E,F and G" Members at the north western part of Abu El-Gharadig Basin, W estern Desert, Egypt. To estimate the thermal conductivity, from a mixing formula, the geometric average of the individual conductivities weighted by the volumetric proportion of each component; the radiogenic heat production and heat flow can be defined. The mineralogic model of Bahariya Formation indicated that, clay minerals as illite, kaolinite, smectite and quartz are the main minerals present in the studied wells, in combination with some calcite and dolomite. W hereas in A/R"G" M ember, it reflects that, clay minerals as illite, kaolinite and smectite are the main minerals in association with some quartz, calcite and dolomite, sometimes with glauconite. Calcite and quartz are the main minerals present in A/R"F" Member with some clay minerals as illite and kaolinite associated with dolomite and k-feldspars. The same mineral constituents are present in A/R"E" Member, but with higher content of clay minerals. At A/R"D" Member, the quartz and calcite are the main minerals with some clays as illite, kaolinite and smectite, in combination with some dolomite and k-feldspars. The calculated porosity is varied between low and high values, and filled with variable quantities of water and hydrocarbons. The average thermal conductivities (ThC) of the different lithologic intervals of Bahariya Formation; which is considered as a reservoir rock; are ranges between 1.57W /m/K in shaley and 2.78W /m/K in sandstone intervals. W hereas, these of A/R"G" Member are varies from1.37W /m/K in shaley to 3.32W /m/K in limestone intervales, A/R"F" (sandy limestone) Member ranges from 2.48W /m/K to 2.7 W /m/K. In A/R "E" Member (ThC), varies between 1.54W /m/K and 3.18W /m/K. Eventually, the A/R "D" Member has higher (ThC) ranges from 1.74W /m/K to 2.91W /m/K. The radiogenic heat production (Rhp) of Bahariya Formation varies between low values of 3.96µw/m and reached maximum 3 values attain from 7.48 to 9.09µw/m . In A/R "D" M ember, it ranged between 8.074 and 9.152µw/m , 3 3 eventually the (Rhp) of A/ R"F", which mainly composed of limestone, is low (3.284µw/m and 3 4.01µw/m), whereas in A/R "E" Member, the lower part shows lower values, then increase again in some 3 wells across the study area. The apparent heat flow (HF) of Bahariya Formation is ranged between 67.6 (shale) and 95.2mW /m and reached 102.4mW /m in limestone intervals; whereas in sandstone, the (HF) 2 2 reached 134.7mW /m .
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