A self-generated carbon dioxide microbubble oil displacement agent, its preparation method and uses

Technical Field

This invention relates to the field of oilfield development technology, specifically to a self-generated carbon dioxide microbubble oil displacement agent, its preparation method, and its uses.

Background Technology

Currently, foam flooding can effectively expand the swept volume and significantly improve oil washing efficiency, and has gradually become an important method for enhancing oil recovery. Self-generating foam flooding technology is a recently developed novel foam flooding technology. It involves injecting a mixture of salt, foaming agent, and foam stabilizer into the formation, where gas, typically carbon dioxide or nitrogen, is spontaneously generated under formation temperature and pressure, thus forming a foam system to achieve enhanced oil recovery. Compared to conventional foam flooding technology, self-generating foam flooding does not require large gas injection equipment, occupies less space, and requires less investment, making it particularly suitable for offshore platforms with severely limited space.
    The mechanism of self-generated carbon dioxide foam flooding is that the gas generator ( sodium bicarbonate ) and the gas release agent ( hydrochloric acid ) release carbon dioxide through a chemical reaction, as shown in the following chemical reaction formula:

NaHCO3+HCl → NaCl+H2O+CO2 ↑

Existing technologies typically involve injecting gas-generating agent solutions and gas-releasing agent solutions into the formation using different slugs. The two solutions react in the formation to generate carbon dioxide, thus promoting oil recovery. For example, CN103711467A discloses a formulation for enhancing oil recovery using self-generated CO2 . Its components include: 5-15 parts ammonium bicarbonate, 1-5 parts bioactive agent , and the balance being water at a temperature not exceeding 35 °C. During use, it is directly injected into the formation, where CO2 is generated through formation heat decomposition . When the formation temperature is below 35 °C, the effect is a combined effect produced by matching the bioactive agent. This approach can be applied in oilfield flooding, fracturing, and well workover to enhance oil recovery and promote fracturing fluid flowback. Simultaneously with gas formation, foam is generated; the foam has high stability, effectively preventing gas channeling, and also provides foam-driven oil recovery and foam-driven well control.
    However, existing foam displacement methods still suffer from low oil displacement efficiency and poor oil displacement effect.

Summary of the Invention

In view of the problems existing in the prior art, the purpose of the present invention is to provide a self-generated carbon dioxide microbubble oil displacement agent, its preparation method and uses, so as to solve the problems of low oil displacement efficiency and poor oil displacement effect that still exist in foam oil displacement schemes.
    To achieve this objective, the present invention adopts the following technical solution:
    In a first aspect, the present invention provides a self-generated carbon dioxide microbubble oil displacement agent, the self-generated carbon dioxide microbubble oil displacement agent comprising:
    Microemulsions, aqueous solutions, and foam solutions
with a volume ratio of (0.1-1):(0.1-1):(0.1-1) ;    The microemulsion comprises a first gas-generating agent, a surfactant, an organic solvent, and water;
    The aqueous solution comprises a second gas agent and water;
    The foaming liquid includes a foaming agent, a foam stabilizer, and water.
    The self-generated carbon dioxide microbubble oil displacement agent provided by this invention achieves excellent oil displacement effect by utilizing the synergistic effect between the components within the oil displacement agent, thereby significantly improving the oil displacement rate. Simultaneously, during the oil displacement process, the sub-agents in the oil displacement agent are injected in the form of microemulsions. Due to the controllable dosage of the drug in the microemulsion, it can be ensured that trace amounts of carbon dioxide are generated when the formation comes into contact with another agent, forming microbubbles, thus significantly improving the oil displacement effect.

Attached Figure Description

Figure 1 is a flowchart of the application of the self-generated carbon dioxide microbubble oil displacement agent provided in an embodiment of the present invention.

Preparation method:

This embodiment provides a self-generated carbon dioxide microbubble oil displacement agent, comprising:
a microemulsion, an aqueous solution, and a foam liquid
in a volume ratio of 0.3:0.6:0.4 ; the microemulsion comprises a first gas agent, a surfactant, an organic solvent, and water in a mass ratio of
1:0.2:125:8 ; the aqueous solution comprises a second gas agent and water in a mass ratio of
1:30 ; the foam liquid comprises a foaming agent, a foam stabilizer, and water in a mass ratio of
1:0.5:150 ; the first gas agent is a carbonate ( sodium carbonate ) ; the surfactant is cetyltrimethylammonium bromide; the organic solvent is gasoline; the second gas agent is an acid ( hydrochloric acid, mass concentration of 2 % ) ; the foaming agent is sodium α – olefin sulfonate; and the foam stabilizer is carboxymethyl cellulose.

The preparation process is as follows:
A first gaseous agent, surfactant, organic solvent, and water are mixed under a first stirring to obtain a microemulsion;
a second gaseous agent and water are mixed under a second stirring to obtain an aqueous solution;
a foaming agent, foam stabilizer, and water are mixed under a third stirring to obtain a foam liquid;
wherein the stirring rate of the first stirring is 500 r/min ; the stirring time of the first stirring is 20 min ; the stirring rate of the second stirring is 300 r/min ; the stirring time of the second stirring is 20 min ; the stirring rate of the third stirring is 700 r/min ; and the stirring time of the third stirring is 40 min . The difference
between Comparative Example 1
and Example 1 is only that the first and second gaseous agents are mixed and reacted on the ground to generate carbon dioxide foam before being injected into the formation. The difference
between Comparative Example 2
and Example 1 is that only water flooding is performed.
The oil displacement results of the examples and comparative examples are detailed in Table 1 .

Table 1

Recovery rate / %
Example 1	58.2
Comparative Example 1	50.2
Comparative Example 2	39.4

The results of the above embodiments and comparative examples demonstrate that the self-generated carbon dioxide microbubble oil displacement agent provided by this invention achieves excellent oil displacement effect by utilizing the synergistic effect between the components within the oil displacement agent, thereby significantly improving the oil displacement rate. Simultaneously, during the oil displacement process, the sub-agents in the oil displacement agent are injected in the form of microemulsions. Due to the controllable dosage of the drug in the microemulsion, it can be ensured that trace amounts of carbon dioxide are generated to form microbubbles when the formation comes into contact with another agent, thus significantly improving the oil displacement effect.