阅读说明：本技术 一种油田用不返排可转化为驱油剂的压裂液及其制备方法 (Fracturing fluid capable of being converted into oil displacement agent without flowback for oil field and preparation method thereof ) 是由 张荣军 屈乐 任大忠 陈刚 张洁 于 2019-11-14 设计创作，主要内容包括：本发明涉及一种油田用不返排可转化为驱油剂的压裂液及其制备方法。所述压裂液由下述方法制备得到：将聚丙烯酰胺类产品溶解于水中；向该胶液中加入上述胶液钾盐；再加入有机铬盐或/和有机铝盐,或酚醛树脂；将泵入压裂混砂罐,加入压裂砂；再加入破胶剂。所述方法不产生压裂返排液,避免了废水的处理,同时压裂液适度破胶后转化为驱油剂,能够提高驱油效果,实现了不返排压裂-驱油一体化作业,降低了压裂和驱油的费用。(The invention relates to a fracturing fluid which can be converted into an oil displacement agent without flowback for an oil field and a preparation method thereof. The fracturing fluid is prepared by the following method: dissolving a polyacrylamide product in water; adding the sylvite into the glue solution; adding organic chromium salt or/and organic aluminum salt or phenolic resin; pumping into a fracturing sand mixing tank, and adding fracturing sand; and adding a gel breaker. The method does not produce fracturing flowback fluid, avoids the treatment of wastewater, simultaneously converts the fracturing fluid into an oil displacement agent after moderate gel breaking, can improve the oil displacement effect, realizes the integral operation of non-flowback fracturing and oil displacement, and reduces the fracturing and oil displacement costs.)

1. A preparation method capable of converting oil displacement agent without flowback for oil fields is characterized by comprising the following steps:

1) dissolving the polyacrylamide product in water with purity higher than that for oil field fracturing in a liquid preparation tank, and uniformly stirring to prepare 0.3-0.8% of glue solution;

2) adding 1-3% potassium salt into the glue solution under stirring;

3) adding organic chromium salt or/and organic aluminum salt which accounts for 3-10% of polyacrylamide products or phenolic resin which accounts for 1-2 times of polyacrylamide products into the glue solution under stirring;

4) pumping the system into a fracturing sand mixing tank, and adding fracturing sand with the volume of 10-30% of the glue solution into the fracturing sand mixing tank;

5) adding a gel breaker with 0.05-0.1% of gel liquid into the mixed system.

2. The preparation method capable of being converted into the oil displacement agent without flowback for the oil field according to claim 1, characterized by comprising the following steps:

preferably, in step 1), the polyacrylamide product is polyacrylamide with molecular weight of 500-1500 ten thousand and purity above, partially hydrolyzed polyacrylamide ammonium salt, partially hydrolyzed polyacrylamide sodium salt, partially hydrolyzed polyacrylamide potassium salt, polyacrylamide hydrophobic association polymer containing long-chain alkyl monomer and sulfonic monomer, and composition thereof;

preferably, in the step 2), the potassium salt is industrial grade and above potassium chloride, potassium sulfate, potassium nitrate, potassium phosphate, potassium bromide and a composition thereof;

preferably, in step 3), the salt is industrial grade and above purity chromium acetate, chromium lactate, chromium tartrate, chromium citrate, chromium nitrilotriacetate, chromium iminodiacetate, chromium ethylenediaminetetraacetate, aluminum acetate, aluminum lactate, aluminum tartrate, aluminum citrate, aluminum nitrilotriacetate, aluminum iminodiacetate, aluminum ethylenediaminetetraacetate, and a combination thereof, and the phenolic resin is industrial grade and above purity oilfield common polyacrylamide crosslinking agent;

preferably, in the step 4), the fracturing sand is industrial grade quartz sand or ceramic sand with a purity diameter of 0.3-1mm above the industrial grade quartz sand or ceramic sand and a composition thereof;

preferably, in the step 5), the gel breaker is ammonium persulfate, sodium persulfate, potassium persulfate and a combination thereof with the purity of industrial grade and above.

3. The non-flowback fracturing fluid for the oil field is characterized by being prepared by the following method:

1) dissolving the polyacrylamide product in water with purity higher than that for oil field fracturing in a liquid preparation tank, and uniformly stirring to prepare 0.3-0.8% of glue solution;

2) adding 1-3% potassium salt into the glue solution under stirring;

3) adding organic chromium salt or/and organic aluminum salt which accounts for 3-10% of polyacrylamide products or phenolic resin which accounts for 1-2 times of polyacrylamide products into the glue solution under stirring;

4) pumping the system into a fracturing sand mixing tank, and adding fracturing sand with the volume of 10-30% of the glue solution into the fracturing sand mixing tank;

5) adding a gel breaker with 0.05-0.1% of gel liquid into the mixed system.

4. The non-flowback fracturing fluid for oil fields according to claim 3, which is characterized in that:

preferably, in step 1), the polyacrylamide product is polyacrylamide with molecular weight of 500-1500 ten thousand and purity above, partially hydrolyzed polyacrylamide ammonium salt, partially hydrolyzed polyacrylamide sodium salt, partially hydrolyzed polyacrylamide potassium salt, polyacrylamide hydrophobic association polymer containing long-chain alkyl monomer and sulfonic monomer, and composition thereof;

preferably, in the step 2), the potassium salt is industrial grade and above potassium chloride, potassium sulfate, potassium nitrate, potassium phosphate, potassium bromide and a composition thereof;

preferably, in step 3), the salt is industrial grade and above purity chromium acetate, chromium lactate, chromium tartrate, chromium citrate, chromium nitrilotriacetate, chromium iminodiacetate, chromium ethylenediaminetetraacetate, aluminum acetate, aluminum lactate, aluminum tartrate, aluminum citrate, aluminum nitrilotriacetate, aluminum iminodiacetate, aluminum ethylenediaminetetraacetate, and a combination thereof, and the phenolic resin is industrial grade and above purity oilfield common polyacrylamide crosslinking agent;

preferably, in the step 4), the fracturing sand is industrial grade quartz sand or ceramic sand with a purity diameter of 0.3-1mm above the industrial grade quartz sand or ceramic sand and a composition thereof;

preferably, in the step 5), the gel breaker is ammonium persulfate with the purity of industrial grade and above,

Sodium persulfate, potassium persulfate, and combinations thereof.

5. The use method of the non-flowback fracturing fluid for the oil field according to claim 3 or 4, which is characterized by comprising the following steps: pumping the non-flowback fracturing fluid for the oil field into a stratum and then taking an aqueous solution containing 0.05-0.5% of a catalyst as a displacement fluid, closing a well for 12-64 hours, moderately breaking the oxidation glue solution of the catalytic gel breaker to form an oil displacement agent, connecting a daily water injection pipe of the well for water injection when the pressure of the well mouth is reduced to the daily water injection pressure range of the well, wherein the catalyst is industrial-grade and above-purity ferric citrate, cobalt citrate, ferrous tartrate, copper tartrate, nickel tartrate, copper iminodiacetate, ferrous glutamate, copper glutamate, nickel glutamate and a composition thereof.

6. Use of the non-flowback fracturing fluid for oil fields according to claim 3 or 4 in petrochemical industry.

Technical Field

The invention relates to the technical field of efficient production of oil fields, in particular to a fracturing fluid which can be converted into an oil displacement agent without flowback for an oil field and a using method thereof.

Background

Fracturing is a common means of oilfield production by injecting fluids into the formation through a high pressure pump at the surface. The fracturing fluid is an important component of the fracturing method technology, the main functions are to make cracks and convey proppant along the opened cracks, and therefore the viscosity of the fluid is important. Successful fracturing operations require that the fluid, in addition to having a high viscosity in the fracture, also be able to break the gel quickly; the flow can be quickly reversed after operation; the liquid loss can be well controlled; the friction resistance during pumping is low; while still being economically feasible.

In the later stage of the fracturing operation, the fracturing fluid breaks gel in the stratum in modes of oxidation or biodegradation and the like, the viscosity is reduced, and about 30-80% of the injected fluid in the earlier stage is discharged back from the stratum after the well mouth is opened. On one hand, a large amount of waste liquid of oilfield operation is generated and needs to be treated, and on the other hand, energy carried by a large amount of fluid injected in the early stage is released, so that more than 90% of energy is lost. However, as crude oil is produced, the formation energy is gradually depleted, and the formation energy must be supplemented by a large amount of water injection, which is in significant supply and demand relationship with the complete release of energy in the later stage of fracturing.

The basic method for solving the problems is to carry out relatively thorough gel breaking on the existing fracturing fluid, ensure that the existing fracturing fluid has no blocking effect on a reservoir after gel breaking, and directly follow up water injection to form an operation measure without flowback. At present, a high-molecular material of a fracturing fluid system is used as a thickening agent and is crosslinked by a crosslinking agent to be used as a sand carrying fluid in the fracturing fluid, the sand carrying is completed and then is broken by a gel breaker (generally an oxidant), the viscosity is reduced and then the broken polymer is discharged back, but the existing gel breaking method cannot completely degrade the high polymer, so that the high polymer needs to be discharged back, and in addition, insoluble substances (residues) are generated after the gel breaking of some high-molecular materials and also needs to be discharged back. Therefore, a polymer with good solubility and a strong gel breaker are required to be adopted for providing a non-return fracturing liquid system, and insoluble substances are not generated after oxidation gel breaking, so that the non-return fracturing liquid system is ensured to be free from return and oil displacement is carried out along with water injection.

Disclosure of Invention

In order to overcome the defects of the existing fracturing fluid, the invention aims to provide a non-flowback fracturing fluid system for an oil field water injection well and a use method thereof.

On the premise of ensuring normal completion of fracturing of a water injection well, the fracturing liquid system utilizes a proper amount of gel breaker and an optimized catalyst to reduce the viscosity of the fracturing liquid system to a polymer oil displacement viscosity range suitable for an oil reservoir, improves the fluidity, does not generate insoluble substances, and then follows up with water injection. On one hand, the generation and post-treatment of a large amount of flowback liquid are avoided, on the other hand, the energy carried by the fluid in the fracturing process is almost 100 percent utilized and is supplemented into the stratum, and the improvement of the stratum energy is beneficial to the improvement of the recovery ratio of crude oil.

In order to achieve the purpose, the invention adopts the technical scheme that:

a fracturing fluid which can be converted into an oil displacement agent without flowback for an oil field and a using method thereof comprise the following steps:

firstly, dissolving a polyacrylamide product in water with purity higher than that for oil field fracturing in a liquid preparation tank, uniformly stirring to prepare 0.3-0.8% of glue solution, wherein the polyacrylamide product is polyacrylamide with molecular weight of 500-1500 ten thousand and purity higher than that, partially hydrolyzed polyacrylamide ammonium salt, partially hydrolyzed polyacrylamide sodium salt, partially hydrolyzed polyacrylamide potassium salt, polyacrylamide type hydrophobic association polymer containing long-chain alkyl monomers and sulfonic monomers and a composition thereof;

secondly, adding 1-3% of potassium salt into the glue solution under stirring, wherein the potassium salt is industrial potassium chloride, potassium sulfate, potassium nitrate, potassium phosphate, potassium bromide and a composition thereof with the purity higher than that of the industrial potassium chloride;

thirdly, adding organic chromium salt or/and organic aluminum salt with the content of 3-10% of polyacrylamide products or phenolic resin with the content of 1-2 times that of polyacrylamide products into the glue solution under stirring, wherein the salt is industrial chromium acetate, chromium lactate, chromium tartrate, chromium citrate, chromium nitrilotriacetate, chromium iminodiacetate, chromium ethylenediaminetetraacetate, aluminum acetate, aluminum lactate, aluminum tartrate, aluminum citrate, aluminum nitrilotriacetate, aluminum iminodiacetate, aluminum ethylenediaminetetraacetate and a composition thereof with the purity of more than the industrial chromium acetate, chromium lactate, chromium tartrate, chromium iminodiacetate, aluminum iminodiacetate and a composition thereof, and the phenolic resin is an industrial polyacrylamide cross-linking agent with the purity of more than the industrial polyacrylamide products commonly used in oil fields;

pumping the system into a fracturing sand mixing tank, and adding fracturing sand with the volume of 10-30% of the glue solution into the fracturing sand mixing tank, wherein the fracturing sand is industrial grade and above quartz sand or ceramic sand with the purity and the diameter of 0.3-1mm and a composition of the quartz sand or the ceramic sand;

fifthly, adding a gel breaker with 0.05-0.1% of gel liquid into the mixed system, wherein the gel breaker is ammonium persulfate, sodium persulfate, potassium persulfate and a composition thereof with industrial grade and above purity;

and sixthly, pumping the mixture obtained in the fifth step into a stratum by adopting a conventional fracturing method, taking an aqueous solution containing 0.05-0.5% of catalyst as a displacement fluid, closing the well for 12-64 hours, properly breaking the oxidized gel solution of the catalytic gel breaker to form an oil displacement agent, connecting the oil displacement agent into a daily water injection pipe of the well for water injection when the pressure of the well head of the oil displacement agent is reduced to the daily water injection pressure range of the well, wherein the catalyst is industrial-grade ferric citrate, cobalt citrate, ferrous tartrate, copper tartrate, nickel tartrate, copper iminodiacetate, ferrous iminodiacetic acid, ferrous glutamate, copper glutamate, nickel glutamate and a composition thereof.

The invention has the beneficial effects that: the fracturing fluid is not discharged back to a constructed water injection well, oilfield operation wastes are not generated, the treatment of waste water is avoided, and the cost is reduced; in the fracturing process, energy carried by injected fluid into the stratum is almost not lost, and the injected fluid completely enters the stratum, so that the energy of the stratum is supplemented to the maximum extent; the molecular chain of the polymer is broken by catalyzing the oxidation of persulfate in the reservoir by using a catalyst, the viscosity of the colloid is reduced until gel breaking, the viscosity is reduced to 1-10mPa ∙ s, the gel is suitable for the range of polymer flooding of the stratum, the gel liquid is pushed to flow forwards after follow-up water injection, the effect of polymer flooding is achieved, insoluble substances are not generated in the gel breaking process, and new damage to the stratum is avoided. An oil displacement experiment is carried out by adopting a SY/T6424-2014 composite oil displacement system performance test method, and the experiment result shows that the recovery ratio can be improved by over 12 percent on the basis of water displacement.

Examples

The invention is further illustrated by the following examples. It should be understood that the method described in the examples is only for illustrating the present invention and not for limiting the present invention, and that simple modifications of the preparation method of the present invention based on the concept of the present invention are within the scope of the claimed invention.