Characteristic of igneous rock and its impact on sedimentation in Donghe oilfield, Tarim Basin, West China

Igneous rocks are widely developed within Permain strata in Tarim basin. However, due to the limitation of drilling data in the early stage as well as the lack of high resolution 3-D seismic data, there are some weaknesses... [ view full abstract ]

Igneous rocks are widely developed within Permain strata in Tarim basin. However, due to the limitation of drilling data in the early stage as well as the lack of high resolution 3-D seismic data, there are some weaknesses about understanding the characteristic of igneous rock and its impact on sedimentation.
Based on previous studies , the lithofacies of igneous rocks in Donghe oilfield, Tabei uiplift were divided with log data. The igneous lithology identification chart was established with lithology-sensitive log curves. The model of volcanic apron fan was restored with core data (grain size data and thin section) and the wave impedance of seismic inversion data.
Results suggest that the natural gamma ray log, resistivity log and caliper log are the most sensitive log tools to the variation of igneous rocks lithofacies. Compared with the homogeneous lava and pyroclastic rock, the radioactivity intensity and the resistivity of igneous rocks decrease in magnitude, while caliper is increased. The linear eruption in the seismic profile is arc-like strong reflection, being characterizing of a bilateral symmetry with 2-3 phase, while pipe eruption is taper chaotic blank reflection. Laterally, volcano vent can was responded by strong root-mean-square amplitude.
Also, the magmation within Permain strata included major linear eruption and minor pipe eruption in Tabei Uplift. The igneous rocks were divided into eastern basic volcanic rock zone, northern basic intrusive igneous rock zone, southern volcanogenic sedimentary-facies zone and the normal sedimentation zone in the west, whose thickness of shows a general increasing trend from north to south. The buninoid topographic prominence of volcano provides depositional source for the volcanic apron fan system formed around the volcano. The root segment of volcanic apron fan was generally located in the volcano zone, resulting in the grain size of volcanic debris gradually decreasing from volcano to basin. The sediments near the volcano are mainly tuffaceous sandstone and tuffaceous glutinite, while the end of the sedimentary system was usually comprised of tuffaceous silt-fine sandstone and tuffaceous mudstone. Superimposition volcanic apron fan is formed with repeated cycles.
The above study suggests that igneous rocks can identified by the crossplot of well logging and its distribution can be identified with wave-impedance and seismic attributes. Accumulation bodies of volcanic vent can provide volcaniclsatic for basin sediment zones and are beneficial to form volcanic apron fan around volcanic vent.