Magnetic fluid enhanced electromagnetic heating device and method for preventing and treating secondary hydrate around well

Abstract

The invention provides a magnetofluid enhanced electromagnetic heating device and method for preventing and treating secondary hydrate around a well. At present, in the process of exploiting natural gas hydrates through a depressurization method, secondary hydrates or ice can be formed due to the fact that the temperature around a well is too low, a gas migration channel in sediment is blocked, and the gas production rate is affected. According to the device or method, a coil is arranged outside a shaft sleeve, and the coil generates a specific-frequency electromagnetic field radiated to stratum sediments. Under the action of the electromagnetic field, magnetite nano-particles naturally contained in the stratum sediment generate oscillating motion, and the aim of heating the stratum around the well is achieved due to heat generated by friction. In addition, in the hydraulic fracturing or slotting stage of the reservoir, the magnetofluid containing the ferromagnetic nanoparticles can be injected along with fracturing fluid, so that the magnetothermal effect of sediments is increased, and the heating effect is further enhanced. In this way, secondary hydrate or ice can be prevented from being formed around the well, pore channels in the sediment are kept unblocked, and therefore the exploitation efficiency of the natural gas hydrate is improved.

Description

technical field [0001] The invention belongs to the field of natural gas hydrate exploitation. Background technique [0002] Natural gas hydrates, commonly known as "combustible ice", are mainly found in the seafloor and permafrost zones of continental margins, with huge resources. Due to the lack of mature development technology, natural gas hydrate has not yet been commercialized on a large scale. Only Canada, the United States, Japan, and China have carried out depressurization, heat injection, injection suppression, CO 2 Exploration of some trial mining methods such as replacement method. Among them, the depressurization method reduces the reservoir pressure by pumping the fluid in the wellbore, resulting in the decomposition of natural gas hydrate into water and methane gas and production. Due to its low cost and high efficiency, the depressurization method is a promising method for hydrate recovery. In 2017 and 2020, my country carried out two rounds of test product...

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Problems solved by technology

[0006] Although this technical method is aimed at directly exploiting natural gas hydrate, and covers the remote heating of reservoir deposits outside the wellbore, it has obvious shortcomings or deficiencies. There are three main points: 1. The microwave generator of the above patent is placed inside the wellbore , because the stainless steel casing wall that constitutes the wellbore has a shielding effect on microwaves, so the microwave power reaching the reservoir is small, and the heating effect is not obvious

2. Injected liquid CO 2 In the reservoir will phase change to high pressure gaseous CO 2 , absorbing a large amount of latent heat of sediments and lowering the reservoir temperature; the resulting local low-temperature and high-pressure environment is actually not conducive to the decomposition of natural gas hydrate

3. Inject a large amount of liquid CO 2 After, due to CO 2 The replacement rate of methane hydrate is not high, and the flowback of CO from the reservoir 2 It will be mixed with the methane gas produced by hydrate decomposition to be produced together; in this case, gas separation must be carried out to obtain the expected natural gas for hydrate production, which will increase the production cost and is another unfavorable factor

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