Multiscale geological-geophysical characterization of the epigenic origin and deeply buried paleokarst system in Tahe Oilfield, Tarim Basin

Spectral Decomposition and a Waveform Cluster to Characterize Strongly Heterogeneous Paleokarst Reservoirs in the Tarim Basin, China

“…Hydrocarbon reservoirs have been identified in Triassic, Carboniferous, Devonian, and Ordovician strata. The Ordovician paleokarst reservoirs account for approximately 73% of total oil and gas production [23]. From the bottom to the top, the Ordovician strata are divided into the Penglaiba Formation, the Yingshan Formation and the Yijianfang group, the Querbake Formation, the Lianglitage Formation, and the Santamu Formation (shown in Figure 1c) [24].…”

Three-Dimensional Geophysical Characterization of Deeply Buried Paleokarst System in the Tahe Oilfield, Tarim Basin, China

“…In the long geological history, soluble rocks are subjected to leaching by liquid, especially rainwater, for a long period. The dissolution of soluble rocks results in formation of large karst caves that formed in the vicinity of unconformity, which is called a paleokarst system [10]. Paleokarst is the general term for ancient karst features that have been fossilized or preserved.…”

“…Among them, the Tahe Oilfield is dominated by Ordovician carbonate karst reservoirs at a depth of more than 5500 m [18]. It is China's largest Paleozoic marine oilfield, with a hydrocarbon reserve greater than 15 × 10 8 m 3 [10,18]. The main storage spaces for oil and gas in the reservoirs are caves and fractures.…”

“…The main storage spaces for oil and gas in the reservoirs are caves and fractures. After experiencing multiple geological processes, such as epigenetic dissolution, structural rupture, burial dissolution, collapse, and filling, the paleokarst reservoirs in the Tahe Oilfield have strong heterogeneity both vertically and horizontally [10,13,[18][19][20]. Production proves that the productivity of the reservoirs is mainly controlled by the degree of development of caves, and the structure of the caves represents the main structure of the paleokarst reservoir [18,20].…”

“…Using ground penetrating radar (GPR), core samples, and typical outcrops in the Lower Ordovician Ehrenberg Group near Marble Falls in central Texas, McMechan et al [21], and Loucks et al [22][23][24] established the three-dimensional (3D) structure of a collapsed paleocave system, which became a classic model for understanding paleocaves [18,20,[25][26][27]. Through detailed outcrop investigations and core sample observations, Tian et al described the paleocave structure, and then used multivariate logging data to identify characteristics of subsurface paleocaves that were drilled by wells [10,26]. Using a 3D seismic amplitude dataset, Zeng et al [27,28] and Basso et al [29] characterized the structure of paleocave reservoirs and pointed out the associated relationship between faults and paleocaves.…”