Geochemistry of borehole cutting shale and natural gas accumulation in the deepwater area of the Zhujiang River Mouth-Qiongdongnan Basin in the northern South China Sea

The Qiongdongnan Basin and Zhujiang River（Pearl River） Mouth Basin, important petroliferous basins in the northern South China Sea, contain abundant oil and gas resource. In this study, on basis of discussing impact of oil-base mud on TOC content and Rock-Eval parameters of cutting shale samples, the authors did comprehensive analysis of source rock quality, thermal evolution and control effect of source rock in gas accumulation of the Qiongdongnan and the Zhujiang River Mouth Basins. The contrast analysis of TOC contents and Rock-Eval parameters before and after extraction for cutting shale samples indicates that except for a weaker impact on Rock-Eval parameter S2, oil-base mud has certain impact on Rock-Eval S1, Tmax and TOC contents. When concerning oil-base mud influence on source rock geochemistry parameters, the shales in the Yacheng/Enping,Lingshui/Zhuhai and Sanya/Zhuhai Formations have mainly Type Ⅱ and Ⅲ organic matter with better gas potential and oil potential. The thermal evolution analysis suggests that the depth interval of the oil window is between 3 000 m and 5 000 m. Source rocks in the deepwater area have generated abundant gas mainly due to the late stage of the oil window and the high-supper mature stage. Gas reservoir formation condition analysis made clear that the source rock is the primary factor and fault is a necessary condition for gas accumulation. Spatial coupling of source, fault and reservoir is essential for gas accumulation and the inside of hydrocarbon-generating sag is future potential gas exploration area.

Impact of Timber Logging on Neighbouring Stands in a Forest of the South Western Cameroon

During conventional logging operations, there is always some damage to nearby stands. This study therefore assessed the damage caused after logging operations to surrounding stands in a Forest Management Unit (FMU) in south western Cameroon after logging operations. The damages assessed were snapped branches/trunks and uprooted trees. A total of 304 trees with a diameter ≥ 30 cm were cut and a total of 770 neighbouring harvestable and future trees were affected. It was observed that 375 of the neighbouring stand had their trunks snapped, 312 had their branches snapped, and 15 were uprooted. It was noted that 80% of the trees affected were those with diameters between 30 - 50 cm, which were called future trees for the next harvest, while the least damage was on protected/seed trees. Lophira alata caused the highest stand damage due to its abundance and large size, while Distemonanthus benthamianus caused the least domino damage. Damage to future trees negatively affects future concession holders as these trees are supposed to mature before the next harvest, hence the yield will be greatly reduced. Sustainable timber exploitation will greatly reduce residual damage as care will be taken to ensure falling timber causes less damage to the surrounding stand.