In 2021,a great breakthrough has been made in discovery of crude oil in the risk exploration well,i.e.,Well Gulashou-1,in deep water area of Santos Basin in South America;a daily production of thousands of tons of high-yield oil flows was obtained in the drill stem tes-ting,thus determining a super large oil reservoir in the Alam block in Brazil and confirming its potential for large-scale commercial develop-ment.To better understand this major breakthrough,the tectonic-sedimentary environment,accumulation conditions and reservoir character-istics of Well Gulashao-1 were analyzed in detail based on the analysis of regional geological background,in combination with the exploration history.The results show as follows.(1)Alam block is located in the Alam-Uirapuru uplift belt of Santos Basin,facing with Lula oilfield in the Lula-Sugar uplift belt across a lake,and the both has a similar tectonic-sedimentary background.The large paleo-uplift in the center of the basin provides favorable conditions for carbonate sedimentation(2)Alam block is adjacent to the main hydrocarbon generating sag with abundant oil sources.(3)The inherited paleo-uplift controls the contiguous distribution of lacustrine carbonate reservoirs.(4)Salt rocks,post-salt calcilutites and mudstones have formed multiple effective seals on the oil reservoir.(5)The pre-salt anticlinal trap is developed on a large scale,demonstrating a favorable migration direction of oil and gas.(6)The pool in Well Gulashao-1 is an overpressure reservoir,which produces medium crude oil with low CO2 and H2S contents.The successful drilling of Well Gulashao-1 is a major breakthrough of oil explora-tion expanding from the pre-salt core area to the periphery in Santos Basin of Brazil.It is a major success achieved by PetroChina Company Limited(PetroChina)in adhering to overseas risk exploration and also a successful practice of overseas cooperation for deepwater oil and gas exploration in PetroChina.It is of guiding significance to the pre-salt oil and gas exploration in Santos Basin of Brazil and the development strategy of deepwater oil and gas business in PetroChina.
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