[1] The Kashi anticline is a north vergent, asymmetric, doubly plunging detachment fold located in the SW Tian Shan foreland. We combine structural, magnetostratigraphic, and topographic data to define the fold's lateral propagation, surface uplift, and concomitant exhumation. Two new magnetostratigraphic sections indicate that the fold began growing at $1.4 Ma and by 1.07 Ma, deformation had propagated eastward $13 km at an average rate of $40 km/Myr. Subsequently, propagation rates increased at least twofold, until the fold reached >60 km in length by 0.8 ± 0.3 Ma. Since then, eastward fold propagation slowed to $15 km/Myr, and the eastern 15-25% of the fold remains buried in the rapidly aggrading foreland. The structure and topography of the emergent fold support interpretations of fold growth in three stages: initial symmetric lateral growth both east and west to a total length of $30 km followed by, first, rapid and, then, slower eastward lengthening to 72 ± 10 km total length. Shortening rates as high as 1.9 À0.2 +0.3 mm/yr characterize the western part of the fold but decrease toward the east. Significant dissection of the emergent fold does not occur until topographic relief is sufficient ($200 m) to permit stripping of protective conglomerates from across the fold's upper surface. As differential rock uplift continues following breaching of the conglomerate, $75% of the rock raised above local base level is subsequently eroded at rates as high as 2.4 km/Myr. Despite extensive erosion, the modern fold topography mimics spatial patterns of both long-term shortening and variations in rock uplift.

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The effectiveness of CO2 injection as a Huff-n-Puff process in tight oil reservoirs with complex fractures needs to be investigated due to the fast decline of primary production and low recovery factor. Although numerous experimental and numerical studies have proven the potential of CO2 Huff-n-Puff, relatively few numerical compositional models exist to comprehensively and efficiently simulate and evaluate CO2 Huff-n-Puff considering CO2 molecular diffusion, nanopore confinement, and complex fractures based on an actual tight-oil well. The objective of this study is to introduce a numerical compositional model with an embedded discrete fracture model (EDFM) method to simulate CO2 Huff-n-Puff in an actual Eagle Ford tight oil well. Through non-neighboring connections, the EDFM method can properly and efficiently handle any complex fracture geometries without the need of local grid refinement (LGR) nearby fractures. Based on the actual Eagle Ford well, we build a 3D reservoir model including one horizontal well and multiple hydraulic and natural fractures. Six fluid pseudocomponents were considered. We performed history matching with measured flow rates and bottomhole pressure using the EDFM and LGR methods. The comparison results show that a good history match was obtained and a great agreement between EDFM and LGR was achieved. However, the EDFM method performs faster than the LGR method. After history matching, we evaluated the CO2 Huff-n-Puff effectiveness considering CO2 molecular diffusion and nanopore confinement. The traditional phase equilibrium calculation was modified to calculate the critical fluid properties with nanopore confinement. The simulation results show that the CO2 Huff-n-Puff with smaller CO2 diffusion coefficients underperforms the primary production without CO2 injection; nevertheless, the CO2 Huff-n-Puff with larger CO2 diffusion coefficients performs better than the primary production. In addition, both CO2 molecular diffusion and nanopore confinement are favorable for the CO2 Huff-n-Puff effectiveness. The relative increase of cumulative oil production after 7300 days with CO2 diffusion coefficient of 0.01 cm2/s and nanopore size of 10 nm is about 12% for this actual Eagle Ford well. Furthermore, when considering complex natural fractures, the relative increase of cumulative oil production is about 8%. This study provides critical insights into a better understanding of the impacts of CO2 molecular diffusion, nanopore confinement, and complex natural fractures on well performance during CO2 Huff-n-Puff process in the Eagle Ford tight oil reservoirs.

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