The production of BG shale oil Block of Jinhu Sag of Subei Basin declines rapidly after fracturing

showing poor development efficiency. Enhancing the estimated ultimate reserves（EUR） of individual wells during later depletion stages is crucial for profitable development. While CO

2

huff-n-puff is a common stimulation technique

its high costs and variable effectiveness have limited its widespread adoption. Based on the geological characteristics of BG block

we carried out research on the mechanism of shale oil stimulation by water huff-n-puff by using core NMR

SEM

well test analysis and other methods

and clarified that water huff-n-puff can greatly develop the oil in 1~100 nm pores in imbibition process and improve the porosity and p

ermeability conditions. Given the Subei Basin shale oil's notable hydrophilicity

rich oil content

and extensive fracture network

water huff-n-puff technology was proposed and field-tested. Up to now

the cumulative oil increase of the two test wells is more than 7 600 tons

which shows good application prospects and economic benefits. And it has guiding significance for the low-cost and efficient production stimulation in the shale oil development in Subei Basin.