Method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well
A method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well by an optimized reservoir pressure, washing the horizontal well by sand flushing, injecting water into the reservoir to increase the stratum pressure around the horizontal well, and stopping the water injection when the pressure retention level is 100% at end stage of the water injection period. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well enables the crude oil in the pores of the matrix in the tight reservoir rock developed by the natural fracture to be further recovered. Comprehensive utilization of stratum energy boost, and imbibition replacement between the injected water and the reservoir crude oil improves the single-well production to enhance the oil recovery of a tight oil reservoir.
1. A method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well, the method comprising:
1) when a reservoir pressure is reduced to 10 MPa, washing the horizontal well by sand flushing, then injecting water into a reservoir with a specified daily water injection amount to increase a stratum pressure around the horizontal well, and stopping the water injection when a pressure retention level is 100% at end stage of a water injection period, with a cumulative water injection amount at this time equal to a cumulative liquid recovery amount of the horizontal well in a former production stage;
2) after a completion of water injection, shutting down the horizontal well and starting a huff-puff process of the horizontal well in the reservoir so as to initiate a well-closing stage in which reservoir crude oil enters a high-permeability channels relying on an imbibition replacement effect;
3) opening the well and starting oil extraction, and shutting down the well when the stratum pressure in a control area of the horizontal well drops to a rated pressure, to perform a second cycle of water injection, well-closing and oil extraction process.
2. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein
the reservoir is a single-layer reservoir with a thickness of 2-100 m, and reservoir matrix has an average permeability of less than 0.3 mD, an average porosity of 9% and an average fracture density of 0.29/m.
3. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 2 , wherein
the well of the reservoir is a horizontal well with a horizontal section of 850 m and a well spacing of 600 m, and the well is a well subjected to sectional volume fracturing modification and having an average fracture construction displacement of >6 m 3 /min, and an average fractured section interval of 80-100 m, when the well is completed and casing cemented.
4. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein
a pressure at the end of the oil extraction in step 3) is 10 MPa and the pressure retention level is 59%.
5. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein in step 1),
in a water injection stage, the daily water injection amount is a single-section daily water injection amount of 10-20 m 3 , and a single-well daily water injection amount is a sum of each single-section daily water injection amount.
6. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein in step 1),
the cumulative injection amount is a elastically changed volume of pores in a stratum, and the cumulative water injection amount as calculated at a time when the pressure retention level rises from a low level before the huff-puff to 100% is a cumulative water injection amount for a single huff-puff cycle.
7. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein in step 2),
in the huff-puff process of the horizontal well in the reservoir, the well-closing stage is 30 days.
8. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein in step 3),
a water content is high after the completion of water injection, relative to normal conditions at an initial stage of the well opening and oil extraction, and an initial-stage production is conducted by controlling a daily liquid volume of not exceeding 15 m 3 .
9. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well according to claim 1 , wherein
the cycle of water injection, well-closing and oil extraction process is repeated for 1-5 times.