1. A deep high specific gravity acidable synthetic oil-based drilling fluid is characterized by comprising synthetic base oil, calcium chloride, bentonite, an emulsifier, calcium oxide, a filtrate reducer and a weighting agent; the weighting agent is subjected to organic modification pretreatment.

2. The drilling fluid according to claim 1, wherein the drilling fluid consists of the following components and the contents thereof: 75-95% v/v of synthetic base oil, 1-2g/ml of bentonite, 5-9g/ml of emulsifier, 2-4g/ml of calcium oxide, 2-5g/ml of filtrate reducer and CaCl₂5% -25% v/v of aqueous solution, and weighting agent; the addition amount W of the weighting agent satisfies the following formula:

w ═ V pulp × ρ 3 × (ρ 2- ρ 1)/(ρ 3- ρ 2)

In the formula, rho 3 is the density of the weighting agent, rho 2 is the density of the drilling fluid to be weighted, and rho 1 is the density of the original drilling fluid.

3. The drilling fluid according to claim 1, wherein the weighting agent organic modification pretreatment method comprises the following steps: adding weighting agent into the pretreatment solution containing organic solvent, stirring strongly until the suspension is light at the top and heavy at the bottom, and taking out the heavy suspension at the bottom.

4. The drilling fluid of claim 3, wherein the weighting agent is added to the pretreatment fluid at a weight ratio of 30% to 50%.

5. The drilling fluid according to claim 3, wherein the pretreatment fluid is prepared by mixing an organic solvent, an emulsifier and a calcium chloride aqueous solution, wherein the organic solvent accounts for 70-85% of the volume of the pretreatment fluid.

6. The drilling fluid of claim 5, wherein the organic solvent is a synthetic base oil.

7. The drilling fluid of claim 5, wherein the aqueous calcium chloride solution is 15-30% by volume of the pretreatment fluid.

8. The drilling fluid of claim 5, wherein the emulsifier concentration in the pretreatment fluid is 3-4 g/ml.

9. Drilling fluid according to claim 1 or 2, wherein the weighting agent is an acidifiable weighting agent, preferably the weighting agent is barium carbonate ore powder.

10. The drilling fluid according to claim 1 or 2, wherein the bentonite is an organic bentonite; preferably, the emulsifier consists of a main emulsifier and a co-emulsifier in a mass ratio of 3-4:2-5, wherein the main emulsifier is span 80 (C) which is a nonionic surfactant₂₄H₄₄O₆) The coemulsifier is polysorbate-80 (C)₂₄H₄₄O₆) (ii) a Preferably, CaCl used₂The calcium chloride concentration in the aqueous solution was 20% w/w.

Background

With the continuous decrease of conventional oil and gas resources, oil exploration and development gradually develop to deeper strata, and therefore, the well depth of an oil well is deeper and deeper. In the drilling of deep wells and ultra-deep wells, due to the fact that the temperature and pressure of the deep wells and the ultra-deep wells are high, the rheological property of high-density drilling fluid and the filtration wall building property are difficult to control in the drilling process, the stratum structure is complex, drilling is easy to meet high-pressure oil-gas layers, mud rock and brine layers, and complex conditions such as block falling, hole shrinkage and the like are easy to occur, so that accidents such as well collapse, drilling sticking and the like are caused.

The synthetic oil-based drilling fluid developed in recent years can better solve the defects of water-based drilling fluid, but also has the problems of high-temperature demulsification, poor rheological property, barite precipitation, solid-phase invasion of oil-contaminated layer, environmental pollution, difficult degradation and the like. Especially, the specific gravity of the drilling fluid in deep layers of western oil fields in China is basically over 1.8, even over 1.9 to 2.2. In order to obtain high specific gravity, a weighting material such as barite is usually added into the drilling fluid, and due to poor compatibility with the oil-based drilling fluid, various components in the weighted drilling fluid can be thickened, settled, invalid and the like, so that the performance of the drilling fluid is changed sharply, the drilling operation cannot be carried out normally in severe cases, and the barite is an insoluble material and can permanently and seriously pollute an oil layer once the barite invades the oil layer.

With the continuous exploration and development of western deep complex oil and gas reservoirs, the development of deep high-specific-gravity acidizable synthetic oil-based drilling fluid is necessary.

Disclosure of Invention

The invention aims to provide a deep high-specific gravity acidizable synthetic oil-based drilling fluid which has good rheological property under the high-temperature and high-pressure conditions of western deep drilling, meets the requirements of deep wells and ultra-deep wells on the density of the drilling fluid, and can be used for carrying out acid washing and plugging removal on a solid phase invading into an oil layer after well completion.

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

the invention provides a deep high-specific gravity acidable synthetic oil-based drilling fluid, which comprises synthetic base oil, calcium chloride, bentonite, an emulsifier, calcium oxide, a filtrate reducer and a weighting agent; the weighting agent is subjected to organic modification pretreatment.

Preferably, the drilling fluid consists of the following components and contents thereof: 75-95% v/v of synthetic base oil, 1-2g/ml of bentonite, 5-9g/ml of emulsifier, 2-4g/ml of calcium oxide, 2-5g/ml of filtrate reducer and CaCl₂10% -20% v/v of aqueous solution and weighting agent; the addition amount W of the weighting agent satisfies the following formula:

w ═ V pulp × ρ 3 × (ρ 2- ρ 1)/(ρ 3- ρ 2)

Where ρ 3 is (weighting agent density), ρ 2 (density of drilling fluid to be weighted), ρ 1 (original drilling fluid density).

Preferably, the emulsifier is span 80 (C), a non-ionic surfactant₂₄H₄₄O₆) And polysorbate-80 (C)₂₄H₄₄O₆)。

Preferably, the fluid loss additive is any one or a mixture of oil-soluble resin, modified asphalt and organic lignite.

Preferably, the organic modification pretreatment method of the weighting agent comprises the following steps: adding weighting agent into the pretreatment solution containing organic solvent, stirring strongly until the suspension is light at the top and heavy at the bottom, and taking out the heavy suspension at the bottom.

Preferably, the weighting agent is added into the pretreatment liquid according to the weight ratio of 30-50%.

Preferably, the pretreatment solution is formed by mixing an organic solvent, an emulsifier and a calcium chloride aqueous solution, wherein the organic solvent accounts for 70-85% of the volume ratio of the pretreatment solution.

Preferably, the organic solvent is a synthetic base oil (oil from Shell gas).

Preferably, the calcium chloride aqueous solution accounts for 15-30% of the volume ratio of the pretreatment solution.

Preferably, the concentration of the emulsifier in the pretreatment solution is 3-4 g/ml.

Preferably, the weighting agent is an acidifiable weighting agent, and preferably, the weighting agent is barium carbonate ore powder. The barium carbonate mineral powder is preferably Shaanxi barium carbonate mineral powder with the density of 4.13g/cm³Acid solubility 83.11%. After organic pretreatment, the synthetic oil-based drilling fluid weighting agent can increase the specific gravity of the drilling fluid to 2.2 at most.

Preferably, the bentonite is an organobentonite; the preparation method of the organic bentonite comprises the following steps: the bentonite produced by 184 groups of Xinjiang Xiazijie is treated by a mixed solution of water, sodium carbonate, acrylamide and bromohexadecyl trimethyl ammonium by adopting a conventional organic soil wet preparation method to form hydrophobic organic bentonite; the indexes of the drilling fluid meet the technical requirements of drilling fluid organic soil Q/GWDC 0073-2017.

Preferably, the emulsifier consists of a main emulsifier and a co-emulsifier in a mass ratio of 3-4:2-5, wherein the main emulsifier is span 80 (C) which is a nonionic surfactant₂₄H₄₄O₆) The coemulsifier is polysorbate-80 (C)₂₄H₄₄O₆) (ii) a Preferably, CaCl used₂The calcium chloride concentration in the aqueous solution was 20% w/w.

The invention has the beneficial effects that:

the organic pretreated acidizable weighting agent has good compatibility with the drilling fluid, various components in the weighted drilling fluid cannot be thickened, settled, invalid and the like, and the drilling fluid has stable performance; the method selects the Shaanxi barium carbonate ore to carry out organic pretreatment as the weighting agent, can meet the requirement of drilling fluid with the specific gravity below 2.2, has high acid solubility, can carry out subsequent acidification and blockage removal operation after invading an oil layer, further liberates the oil layer and improves the productivity of an oil well.

The organized 184-group bentonite can reach the required viscosity and rheological property at the concentration of 1-2% as an auxiliary agent of the synthetic oil-based drilling fluid, and more solid phase ranges are reserved for subsequent weighting agents.

The drilling fluid disclosed by the invention has good rheological property under the high-temperature and high-pressure condition of deep well drilling in west, meets the requirements of deep wells and ultra-deep wells on the density of the drilling fluid, and can be used for carrying out acid washing and deblocking on solid phases invading oil layers after well completion.

Drawings

FIG. 1 is a schematic view of a pretreatment apparatus for organic pretreatment of weighting agents;

1. a pretreatment tank; 2. a high-speed stirrer; 3. a bottom gate; 4. a pump; 5. supernatant light clear liquid; 6. the lower layer is heavy turbid liquid.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.

In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

The instruments, reagents, materials and the like used in the following examples are conventional instruments, reagents, materials and the like in the prior art and are commercially available in a normal manner unless otherwise specified. Unless otherwise specified, the experimental methods, detection methods, and the like described in the following examples are conventional experimental methods, detection methods, and the like in the prior art.

Example 1 deep high specific gravity acidizable synthetic oil-based drilling fluid

The drilling fluid comprises 95% v/v of synthetic base oil, 1g/ml of bentonite, 3g/ml of main emulsifier, 2g/ml of auxiliary emulsifier, 2g/ml of calcium oxide, 2g/ml of fluid loss additive and 20% w/w of CaCl₂5% v/v of aqueous solution, barium carbonate mineral powder; the adding amount W of the barium carbonate mineral powder meets the following formula:

w ═ V pulp × ρ 3 × (ρ 2- ρ 1)/(ρ 3- ρ 2)

Where ρ 3 is (weighting agent density), ρ 2 (density of drilling fluid to be weighted), ρ 1 (original drilling fluid density).

The organic modification pretreatment method of the weighting agent comprises the following steps: adding 30 weight percent of the barium carbonate mineral powder produced in Shaanxi into pretreatment liquid containing an organic solvent, strongly stirring the mixture until the mixture is in a suspension state with a light upper layer and a heavy lower layer, and taking out heavy turbid liquid on the lower layer.

The pretreatment solution is formed by mixing 70% v/v of synthetic base oil, 3g/ml of emulsifier and 30% v/v of calcium chloride aqueous solution.

The density of the barium carbonate mineral powder produced in Shaanxi is 4.13g/cm³Acid solubility 83.11%.

The bentonite is organic bentonite; the preparation method of the organic bentonite comprises the following steps: the bentonite produced by 184 groups of Xinjiang Xiazijie is treated by a mixed solution of water, sodium carbonate, acrylamide and bromohexadecyl trimethyl ammonium by adopting a conventional organic soil wet preparation method to form hydrophobic organic bentonite; the indexes of the drilling fluid meet the technical requirements of drilling fluid organic soil Q/GWDC 0073-2017.

Example 2 deep high specific gravity acidizable synthetic oil-based drilling fluid

The drilling fluid comprises 75% v/v of synthetic base oil, 2g/ml of bentonite, 4g/ml of main emulsifier, 5g/ml of auxiliary emulsifier, 4g/ml of calcium oxide, 5g/ml of fluid loss additive and 20% w/w of CaCl₂25% v/v aqueous solution of barium carbonate ore powder; addition W of barium carbonate mineral powderThe following formula is satisfied:

w ═ V pulp × ρ 3 × (ρ 2- ρ 1)/(ρ 3- ρ 2)

Where ρ 3 is (weighting agent density), ρ 2 (density of drilling fluid to be weighted), ρ 1 (original drilling fluid density). .

The organic modification pretreatment method of the weighting agent comprises the following steps: adding the powder of the barium carbonate mineral produced in Shaanxi into a pretreatment solution containing an organic solvent according to the weight ratio of 50%, strongly stirring the mixture until the mixture is in a suspension state with a light upper layer and a heavy lower layer, and taking a heavy turbid solution at the lower layer.

The pretreatment solution is formed by mixing 85% v/v of synthetic base oil, 4g/ml of emulsifier and 15% v/v of calcium chloride aqueous solution.

The density of the barium carbonate mineral powder produced in Shaanxi is 4.13g/cm³Acid solubility 83.11%.

The bentonite is organic bentonite; the preparation method of the organic bentonite comprises the following steps: the bentonite produced by 184 groups of Xinjiang Xiazijie is treated by a mixed solution of water, sodium carbonate, acrylamide and bromohexadecyl trimethyl ammonium by adopting a conventional organic soil wet preparation method to form hydrophobic organic bentonite; the indexes of the drilling fluid meet the technical requirements of drilling fluid organic soil Q/GWDC 0073-2017.

Example 3 deep high specific gravity acidizable synthetic oil-based drilling fluid

The drilling fluid comprises 80% v/v of synthetic base oil, 1.5g/ml of bentonite, 3.4g/ml of main emulsifier, 3g/ml of auxiliary emulsifier, 2.5g/ml of calcium oxide, 3g/ml of filtrate reducer and 20% w/w of CaCl₂20% v/v of aqueous solution, barium carbonate mineral powder; the adding amount W of the barium carbonate mineral powder meets the following formula:

w ═ V pulp × ρ 3 × (ρ 2- ρ 1)/(ρ 3- ρ 2)

Where ρ 3 is (weighting agent density), ρ 2 (density of drilling fluid to be weighted), ρ 1 (original drilling fluid density).

The organic modification pretreatment method of the weighting agent comprises the following steps: adding the barium carbonate mineral powder produced in Shaanxi into a pretreatment liquid containing an organic solvent according to the weight ratio of 40%, strongly stirring until the suspension is light at the top and heavy at the bottom, and taking out the heavy turbid liquid at the bottom.

The pretreatment solution is formed by mixing 80% v/v of synthetic base oil, 3.5g/ml of emulsifier and 20% v/v of calcium chloride aqueous solution.

The density of the barium carbonate mineral powder produced in Shaanxi is 4.13g/cm³Acid solubility 83.11%.

The pretreatment method specifically comprises the following steps:

a pretreatment tank shown in figure 1 is adopted and installed on a drilling fluid circulation tank before construction, a large amount of solid phase auxiliary agents needing to be added into the drilling fluid are added into organic pretreatment liquid according to the proportion of 40% 12 hours in advance, the mixture is strongly stirred by a high-speed stirrer 2 to form a solid-liquid mixed state, the surface property of solid phase particles is changed into oleophylic, the solid phase weighting agent after organic pretreatment is in a suspension liquid state with a light upper part and a heavy lower part, therefore, a gate 3 and a pump 4 are arranged at the bottom of the pretreatment tank 1, the light clear liquid 5 at the upper layer is discharged by the pump 4, the gate 3 at the bottom is opened, and the heavy turbid liquid 6 at the lower layer is added into the drilling fluid.

The bentonite is organic bentonite; the preparation method of the organic bentonite comprises the following steps: the bentonite produced by 184 groups of Xinjiang Xiazijie is treated by a mixed solution of water, sodium carbonate, acrylamide and bromohexadecyl trimethyl ammonium by adopting a conventional organic soil wet preparation method to form hydrophobic organic bentonite; the indexes of the drilling fluid meet the technical requirements of drilling fluid organic soil Q/GWDC 0073-2017.

The results of laboratory tests on the organobentonite and pretreated weighting agent used in the present invention are shown in table 1 below.

TABLE 1 permanent 3-Flat 1 well site drilling fluid indoor test

The deep high-specific gravity acidizable synthetic oil-based drilling fluid prepared in the Yong 3-Ping 1 well according to the formula in the embodiment 3 is normally used, no complex condition occurs in the whole drilling process, and the drilling cost of the well is effectively reduced.

The formulation of example 3 above was selected for use in placing deep high gravity acidizable synthetic oil-based drilling fluids in permanent 3-plan 1 wells and tested according to the drilling fluid conventional method (GB/T16783.2-2012) to obtain the properties as shown in table 2 below.

Table 2: permanent 3-flat 1 well field drilling fluid performance test

As can be seen from the data in Table 2, the ultra-deep high-specific gravity acidizable synthetic oil-based drilling fluid of the embodiment of the invention has the advantages of smooth weighting process, good rheological property and higher electrical stability.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.