Method for cleaning compact core-soluble slat

Abstract

The invention discloses a method for cleaning compact core-soluble salt, which comprises the following steps: (1) putting the dried core into a high-pressure container, and vacuumizing at 60 DEG C; (2) filling the high-pressure container with absolute methanol under a vacuum condition; (3) injecting absolute methanol into the high-pressure container to reach the set saturation pressure, wherein the methanol saturation pressure is the formation pressure of the reservoir of the core; (4) by taking two days as a cycle, releasing pressure and applying pressure to the high-pressure container once every 6 hours; and (5) collecting the methanol solution in the high-pressure container, and dropwise adding a silver nitrate solution; observing whether milk white precipitate is generated to judge whether salt is dissolved in the methanol solution; discharging the remaining methanol solution in the high-pressure container; taking out the core and drying; and repeating the steps (1) to (4) until the milk white precipitate is not generated when the methanol solution taken out of the high-pressure container meets the silver nitrate solution. The method disclosed by the invention guarantees the accuracy of a follow-up core experiment result, and lays a foundation to the accurate evaluation of a compact reservoir.

Description

technical field [0001] The invention relates to a method for cleaning soluble salts in tight rock cores in the field of oil and natural gas tight reservoir core analysis, and belongs to an experimental method for core analysis in the oil and gas exploration and development process. Background technique [0002] Against the backdrop of declining production of conventional oil and gas resources and increasing demand for oil and gas, tight reservoirs (mainly including tight sandstone oil and gas reservoirs, tight carbonate rock oil and gas reservoirs and shale oil and gas reservoirs) are playing an increasingly important role in the growth of oil and gas reserves and energy supply. increasingly important role. Understanding the geological characteristics of oil and gas reservoirs and studying rock physical properties must be based on accurate core analysis. However, tight reservoirs generally have formation water with high salinity, small pore throats, high capillary pressure, ...

AI Technical Summary

Problems solved by technology

[0005] First, the cleaning effect is poor

Since tight cores generally have the characteristics of low porosity and low permeability, the capillary pressure is generally high, and there is adsorbed gas in the nanopore throat, for several methods mentioned in the standard, methanol (or other solvents that can dissolve salt ) is difficult to enter most of the pores in the core. Even if the methods listed in the standard are used for gas drive solvent extraction, pressurized solvent flushing or centrifuge flushing, it is difficult for methanol under a certain pressure to enter the tiny pores previously occupied by air. Pore ​​throats, which make it impossible for the soluble salts in a large number of micropores in the tight core to be completely washed out

[0006] Second, the experimental efficiency is low

As mentioned in the standard, the method of flushing with a pressurized solvent can be used to drive through the core with methanol to dissolve and bring out the soluble salt in the core. Since the flow rate of methanol through the core is very low, the pressure is difficult to pass through the core. To obtain stable pressure The flow rate needs a lot of time, and it is impossible to ensure that a large number of micropores in the tight core are washed by methanol solution, and the number of cores cleaned each time is also very limited

[0007] Third, high equipment requirements

Compared with other methods, the liquefied gas extraction and gas flooding solvent extraction listed in the standard can indeed clean the soluble salts in the core better, but the equipment required for this type of method is complicated, the cost of the experiment is high, and through The above analysis also shows that it is impossible to completely wash away the soluble salt in the core

[0008] If there are soluble salts in the pore throats of tight cores, it will have a great impact on all core experiments, affect the actual reservoir evaluation, and restrict the exploration and development of tight oil and gas resources. The current salt washing method can no longer adapt In order to meet the development needs of tight oil and gas reservoirs, it is of great significance to form a method for efficiently cleaning soluble salts in tight rock cores for the whole process protection of tight reservoirs and their economic development

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