Research progress and key technologies for exploration of onshore tight sandstone gas by CNOOC
In 2012,CNOOC obtained mining rights and embarked on the exploration and development of tight sandstone gas in the eastern margin of the Ordos Basin.Having undergone the stages of local breakthroughs,rapid reserve growth,and steady reserve growth,CNOOC achieved proven geological reserves exceeding 2 800 × 108m3 and an annual gas production of over 27 × 108m3,making outstanding contributions to its establishment of onshore trillion cubic meter gas region.Through over a decade of theoretical exploration and technological innovation,a new understanding of the"selective-discontinuous"accumulation and enrichment patterns of tight sandstone gas in the basin margin has emerged.This has led to the establishment of three-level area selection technology,effective reservoir prediction technology,and geological sweet spot characterization technology,while also pointing out future directions for reserve growth and technological breakthroughs.The research indicates that:①Due to the heterogeneity of effective reservoirs and varying hydrocarbon generation intensities,natural gas in the gentle belt converges towards coal-measure source rocks from south to north,exhibiting a"selective-discontinuous"accumulation pattern vertically.In the areas with medium-to-high hydrocarbon generation intensity in the south,gas layers develop in multiple strata,while in the areas with low hydrocarbon generation intensity in the north,gas layers are scarce and concentrated within coal-measure source rocks.②The Zijinshan uplift belt and fault terrace zone experience intense tectonic activity with diverse fault patterns.Locally developed structural-lithologic gas reservoirs can be found in areas with medium-to-high hydrocarbon generation intensity,while only water layers develop in areas with low hydrocarbon generation intensity.③Based on the primary controlling factors of accumulation,a three-level area selection technology has been established focusing on"source-controlled potential,fault-sandstone-determined layers,and enriched optimal reservoirs."④For different lithologic combinations in favorable sedimentary microfacies,effective reservoir and gas layer prediction technologies have been developed.According to natural gas charging mechanisms,a multi-level geological sweet spot characterization technology that integrates precise prediction,drilling learning,and stepwise iteration has been established.The widespread application of these insights and technologies has supported the confirmation of reserves and the establishment of efficient well platforms.In the future,the focus in structurally deformed areas within medium-to-high hydrocarbon generation intensity will be on exploring structural-lithologic gas reservoirs,while structurally stable areas will prioritize the discovery of sweet spot lithologic gas reservoirs.Deepening understanding of high-quality reservoir formation and gas-water distribution patterns and developing key technologies such as fine characterization of faults and gas-bearing sand bodies represent the primary research directions for future advancements.
eastern margin of Ordos Basintight sandstone gasexploration historyaccumulation theoryexploration technologies
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