In this study,we developed a high-resolution stratigraphic framework for the Yanchang Formation in the Huachi Block of the Qingyang Oilfield,located in the Ordos Basin,northwest China.Using well log and seismic data,w...In this study,we developed a high-resolution stratigraphic framework for the Yanchang Formation in the Huachi Block of the Qingyang Oilfield,located in the Ordos Basin,northwest China.Using well log and seismic data,we traced and correlated sweet-spot sand bodies in tight oil reservoirs.Three long-term base-level cycles were identified in the Yanchang Formation,and five medium-term base-level cycles were delineated from the Chang 72 sub-Member to the Chang 4+5 Members,corresponding to five distinct oil groups.The primary production layer,Oil Group 3,was further divided into short-term and very short-term base-level cycles to facilitate the prediction of hydrocarbon target zones.Sweet-spot sand bodies were traced and correlated within very short-term cycles.The sweet-spot sand bodies are mainly sublacustrine channel deposits in the delta front,which were mainly developed in the five single layers(3-1-2,3-1-3,3-1-4,3-2-2,3-2-3 and 3-2-5)of the small layers 3-1 and 3-2 during the regression periods of base-level cycles.The sweet spot sand bodies within the small layer 3-2 are derived from three sets of sources in the northeast,northwest,and south of the basin.The Class I sweet spot is distributed within the single layer 3-2-5,with an average thickness of about 6 m,covering about 25%of the study area.The Class II sweet spot is developed in all five single layers,with the thickest and largest sweet-spot sand body in the Single layer 3-2-3,covering about 90%of the study area.This study highlights the critical importance of establishing a high-resolution sequence stratigraphic framework for the refined delineation of sweet-spot sand bodies within a deltaic-lacustrine depositional system.Additionally,sublacustrine fan deposits formed during the regressive semi-cycle were identified as key sweet spots in the study area.展开更多
基金supported by the National Key Research and DevelopmentProgram of China(Grant No.2023YFF0804300 and 2023YFF0804303).
文摘In this study,we developed a high-resolution stratigraphic framework for the Yanchang Formation in the Huachi Block of the Qingyang Oilfield,located in the Ordos Basin,northwest China.Using well log and seismic data,we traced and correlated sweet-spot sand bodies in tight oil reservoirs.Three long-term base-level cycles were identified in the Yanchang Formation,and five medium-term base-level cycles were delineated from the Chang 72 sub-Member to the Chang 4+5 Members,corresponding to five distinct oil groups.The primary production layer,Oil Group 3,was further divided into short-term and very short-term base-level cycles to facilitate the prediction of hydrocarbon target zones.Sweet-spot sand bodies were traced and correlated within very short-term cycles.The sweet-spot sand bodies are mainly sublacustrine channel deposits in the delta front,which were mainly developed in the five single layers(3-1-2,3-1-3,3-1-4,3-2-2,3-2-3 and 3-2-5)of the small layers 3-1 and 3-2 during the regression periods of base-level cycles.The sweet spot sand bodies within the small layer 3-2 are derived from three sets of sources in the northeast,northwest,and south of the basin.The Class I sweet spot is distributed within the single layer 3-2-5,with an average thickness of about 6 m,covering about 25%of the study area.The Class II sweet spot is developed in all five single layers,with the thickest and largest sweet-spot sand body in the Single layer 3-2-3,covering about 90%of the study area.This study highlights the critical importance of establishing a high-resolution sequence stratigraphic framework for the refined delineation of sweet-spot sand bodies within a deltaic-lacustrine depositional system.Additionally,sublacustrine fan deposits formed during the regressive semi-cycle were identified as key sweet spots in the study area.
