In recent years, horizontal well fracturing water injection huff and puff technology has become the main development technology of tight oil.In the initial stage of water injection huff and puff, higher production was achieved,however,with the increase of huff and puff times,the production decreased rapidly and the oil⁃water replacement efficiency was low.Based on the compact oil data of Jimusaer Oilfield in Xinjiang,through laboratory core water injection huff and puff experiment and single well water injection huff and puff numerical simulation research,the effects of injection volume,time of water injection huff and puff,injection speed, huff and puff times,soaking time and production speed on water injection huff and puff recovery are analyzed.The single well geological model is established,and the influencing factors of water injection huff and puff are fitted by multi⁃nonlinear function.The empirical formulas of five parameters and three parameters of water injection huff and puff are deduced for the first time. The prediction error is within 8%, which provides important reference for the development of water injection huff and puff in the study area and similar tight reservoirs.

The permeability and absorption experiments of low permeability sandstone core under the actual formation temperature and pressure were carried out,which were used to analyze the waterflooding huff⁃puff 's oil recovery law of imbibition and compared with imbibition experiments of normal temperature⁃pressure.The experiments show that the imbibition efficiency of normal temperature⁃pressure is 18%~24%,with an average of 21%.The permeability rate of core in the first six hours is the fastest,which is 0.8~1.7 %/h.The imbibition efficiency of actual reservior's temperature and pressure conditions is 24%~31%,with an average of 27%;Imbibition rate is the fastest in the first round,which is 2.6~3.6 %/h.Compared with imbibition of normal temperature⁃pressure,the imbibition of actual reservior 's temperature and pressure conditions can promote the imbibition efficiency by 5% to 7%,and the imbibition rate is also significantly higher than the imbibition of normal temperature⁃pressure.The analysis believes that imbibition of actual reservior 's temperature and pressure conditions can increase the imbibition's power and reduce the imbibition's resistance,which is more conducive to oil⁃water displacement.Furthermore,the theoretical calculation model of the imbibition depth is established, and the cores' imbibition depth is about 0.25~0.63 cm.It is considered that the depth of the early rapid imbibition stage is in the centimeter range,and the imbibition depth increases with the imbibition efficiency.According to the comprehensive research,increasing the reservior's pressure and large⁃area fracturing can effectively improve the imbibition efficiency.

Due to the strong stress sensitivity and threshold pressure gradient of the tight oil reservoir in Jimsar, Xinjiang, the current nonlinear seepage model cannot reflect the seepage characteristics of the tight reservoirs. Therefore, based on the physical simulation experiment of indoor core flooding, a new nonlinear seepage model of compact reservoir considering threshold pressure gradient and stress sensitivity is established, and the pressure gradient utilization map is drawn according to the model. The results show that the threshold pressure gradient of the tight reservoir has logarithmic relationship with permeability. The error between the seepage characteristic curve of the new model and the actual seepage characteristic curve of the reservoir is less than 5.00%, which can truly reflect the actual seepage characteristics of the reservoir. The higher the permeability, the higher the pressure gradient utilization rate (N), the less the pressure loss. With the pressure gradient increases, N increases logarithmically. Therefore, in order to improve the effective utilization of the tight reservoir pressure gradient, it is necessary to increase the production pressure difference, and take acidizing and fracturing measures to improve the reservoir permeability.