A method for oil displacement in a high water cut stage of a sandstone reservoir with strong bottom water

Abstract

The application discloses a kind of strong bottom water sandstone reservoir high water cut development late oil displacement method, adopt double horizontal well injection mixed gas mode, double horizontal well includes horizontal injection well and horizontal oil production well, mixed gas includes carbon dioxide and nitrogen.For the main contradiction of low water drive efficiency, and water cone is secondary contradiction reservoir, adopt bottom horizontal well injection mixed gas, top horizontal well oil production;For the main problem of water cone, and low water drive efficiency is secondary contradiction reservoir, adopt top horizontal well injection mixed gas, bottom horizontal well oil production, after effectively controlling water cone, and then play oil displacement effect.The double horizontal well injection mixed gas method provided by the application not only gives full play to nitrogen pressure cone mechanism, suppresses bottom water channeling, improves sweep efficiency.Meanwhile, it also utilizes the good miscibility of CO2 to improve the oil washing efficiency during displacement, which can solve the problem of bottom water coning and low water drive efficiency faced by strong bottom water sandstone reservoirs in the later stage of exploitation.

Claims

1. A method for oil displacement in the later stages of development of high water-cut sandstone reservoirs with strong bottom water, characterized in that... A dual-horizontal-well mixed gas injection mode is adopted, wherein the dual-horizontal wells include a horizontal injection well and a horizontal production well, and the mixed gas is a mixture of carbon dioxide and nitrogen. For bottom-water reservoirs where low water drive efficiency is the primary issue and water cone penetration is a secondary issue, a bottom injection and top production model is adopted, involving bottom horizontal wells for mixed gas injection and top horizontal wells for oil production. This model includes the following steps: Step 1: If the mixed gas can be miscible with the formation crude oil, i.e., the minimum miscibility pressure is less than or equal to the formation saturation pressure, then the range of the mixed gas ratio under miscibility conditions is determined. The steps for determining the minimum miscibility pressure are as follows: extract formation crude oil samples through a downhole sampler, measure the formation crude oil physical properties, and determine the minimum miscibility pressure of the mixed gas by conducting a fine tube experiment based on the formation temperature and pressure. Step two: Inject mixed gas into the horizontal gas injection well of the reservoir, and produce oil through the horizontal production well.

2. The method for late-stage oil displacement in high water-cut sandstone reservoirs according to claim 1, characterized in that... The optimal ratio of the mixed gas in step one is determined by: determining the optimal ratio of carbon dioxide to nitrogen based on the actual oil displacement efficiency of the three-dimensional physical model experiment of the mixed gas injection.

3. The method for late-stage oil displacement in high water-cut sandstone reservoirs according to claim 1, characterized in that... In step two, the mixed gas is injected multiple times.

4. The method for late-stage oil displacement in high water-cut sandstone reservoirs according to claim 3, characterized in that... Multiple injections of the gas mixture include the following steps: a. Calculate the gas injection rate of the reservoir, and convert the daily water injection rate during water-driven oil recovery into the daily gas injection rate. b. Close the horizontal oil production well and inject mixed gas into the horizontal gas injection well. After the gas injection is completed, shut the well until the internal pressure of the horizontal gas injection well and the horizontal oil production well reaches stability. c. Open the horizontal oil well for oil production operations. After the preset oil production time is reached, stop oil production and close the oil well. d. Repeat steps b and c until the injection volume of the mixed gas reaches the preset requirement.

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