Underground gel-forming blocking agent suitable for medium-high temperature high-salt low-permeability reservoirs and preparation method therefor

Abstract

The invention provides an underground gel-forming blocking agent suitable for medium-high temperature high-salt low-permeability reservoirs and a preparation method therefor. By taking the total weight of the blocking agent as reference, the blocking agent comprises the following raw materials: 1% to 4% of water-soluble phenol-formaldehyde resin, 0.5% to 2% of stabilizer, 0 to 10% of flexibilizer and the balance of water. The preparation method of the blocking agent comprises the following steps: selecting the raw materials in proportion, and uniformly mixing so as to obtain the underground gel-forming blocking agent suitable for the medium-high temperature high-salt low-permeability reservoirs. The blocking agent provided by the invention is a homogeneous-phase, transparent and low-viscosity water solution before gel forming; the blocking agent can be selectively injected in a deep stratum water flow preferential migration passage, the shearing, adsorption and chromatographic separation of a stratum for the blocking agent can be ignored, and deep placement does not influence the concentration ratio of the blocking agent; and the polycondensation is delayed at the high temperature in the deep stratum, so that the formed gel has the advantages of high blocking rate, high blocking strength, water flow impact resistance, high temperature resistance and high hydrolysis resistance.

Description

technical field [0001] The invention relates to an underground gel-forming plugging agent, in particular to an underground gel-forming plugging agent suitable for medium-high temperature, high-salt and low-permeability oil reservoirs and a preparation method thereof, belonging to the technical field of petroleum exploitation. Background technique [0002] With the development of high-temperature, high-salt and low-permeability oilfields in my country and some oil wells have successively entered high water-cut periods, high temperatures above 90°C and salinity above 100,000ppm, water control and oil stabilization in low-permeability oilfields rich in fractures and improvement of water flooding has become increasingly urgent. The low-efficiency circulation of injected water in the large pores of the formation significantly shortens the operating cycle of high-temperature oil fields. The existing mature and applied plugging control technology is not suitable for this type of re...

AI Technical Summary

Problems solved by technology

The main problem is that the reaction speed is too fast, the low temperature will form gel instantly, and the construction risk and difficulty are great. Before use, the layer to be treated must be detected and isolated. The treatment radius is usually limited to within 30cm in the radial direction around the bottom of the well. In case of misplugging Unblockable, almost impossible to use alone

[0004] In order to solve the problem of instant gelation, the method of direct injection of phenol, hydroquinone, resorcinol, acid, formaldehyde or hexamethylenetetramine was used in the 1950s to avoid the step of synthesizing water-soluble phenolic resin on the ground. Self-polymerization, the product is not resistant to water, and the requirements of environmental protection and safety are rarely used now.

In the 1970s, black wattle extract and rubber extract with phenolic structure were used instead of part of phenol. The extract itself has a large molecule and can participate in the reaction. The concentration of phenolic structure is low, and the poor reactivity leads to high gelation temperature and low plugging strength. and formulation cost

From 2005 to 2009, Chang 2 Block of Changqing Ansai Oilfield used phenolic polyacrylamide plugging agent to conduct oil well water plugging tests for more than 10 well times. The average single well oil increase increased by 30%, and the average comprehensive water cut decreased by 20%. However, the amide bond is hydrolyzed at low temperature in water and shrinks when encountering salt, so the validity period of the construction in low-permeability reservoirs is less than 3 months

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