Abstract
Abstract Paleogeomorphology is the surface morphology formed by the deposition of strata in the basin in historical period, which is greatly affected by the regional tectonic movement; however, the effect of basin paleogeomorphology on reservoir has been underexplored. This study documents the basin paleogeomorphic terrain features and their implications for the depositional processes and oil migration and accumulation in the Jiyuan area of the Ordos Basin. Stratigraphic classification is achieved through well logging data analysis. A seismic fine interpretation of the Triassic–Jurassic paleogeomorphology is conducted. Typical drilling core observations were utilized in a well section analysis of the strata at the top of the Yanchang formation sedimentary facies characteristics. Studies have shown that the Chang 1 subsection on top of the Triassic Yanchang formation in the Jiyuan area was eroded by an ancient Jurassic river, and the residual strata are primarily distributed in the Dingbian and Jiyuan plateaus. The Chang 1 reservoir in the Jiyuan area is dominated by a delta distributary channel sand body. The reservoir is concentrated in a high reservoir sand body structure position, and is controlled by a combination of structural and rock characteristics. This study suggests that the Indosinian movement in the late Triassic caused the entire basin to uplift and denudate, and the strata at the top of the Yanchang formation suffered from weathering and river erosion. The residual strata in the upper part of the Yanchang formation are controlled by the late Triassic–early Jurassic paleogeomorphology.
Highlights
The Ordos Basin is the second largest basin in China, fluvial-lacustrine terrigenous clastic rock deposits were developed in the Mesozoic Triassic Yanchang formation and Jurassic Yan’an formation, and it is the main oilgenerating layer and reservoir in Ordos Basin [1,2,3,4,5]
By analyzing the waveforms and morphological features of the section, representative seismic exploration lines were selected, and the bottom of the Chang 7 subsection was leveled using the balanced section method to restore the Jurassic paleogeomorphology according to the geological characteristics of the TJ9 and TJ marker layers
The Ordos Basin was uplifted by the Indosinian movement in the late Triassic, and the strata at the top of the Yanchang formation in the study area experienced different degrees of river erosion, which formed the paleogeomorphic features of the pre-Jurassic at the top of the Yanchang formation
Summary
The Ordos Basin is the second largest basin in China, fluvial-lacustrine terrigenous clastic rock deposits were developed in the Mesozoic Triassic Yanchang formation and Jurassic Yan’an formation, and it is the main oilgenerating layer and reservoir in Ordos Basin [1,2,3,4,5]. There are few studies on the upper strata of the Yanchang formation, and the formation rule of the reservoir is still unclear, which affects the exploration and development process of the reservoir in the Ordos Basin. Based on the drilling and seismic data in the Jiyuan area of Ordos Basin, the Triassic–Jurassic paleogeomorphologic features were described in detail, and the enrichment rules of the top reservoirs of the Yanchang formation were studied. Chang 1 subsection is located at the top of the Triassic Yanchang formation in the Jiyuan area of Ordos Basin. This study will help to understand the distribution of oil reservoirs, and further evaluate the role of Jurassic palaeogeomorphologic morphology in the reservoir accumulation process at upper strata of the Yanchang
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