RU2211239C1 - Hydrocarbon-based emulsion drilling mud - Google Patents

Abstract

FIELD: oil and gas production. SUBSTANCE: objective of invention is physicochemical action on formation during primary exposure of productive oil pools. Drilling mud contains, wt %: liquid petroleum product 25-60, surface-active emulsifier 1.0-2.5, hydrophobized dispersed chalk 3-10, mineralized water phase (base component), and additionally co-emulsifier, in particular chemically modified silica with 40-70% degree of substitution of surface silanol groups by alkyl-aryl radicals, 0.6- 1.5. Above-indicated alkyl-aryl radicals are, in particular, methyl, ethyl, propyl, or phenyl. Chalk is hydrophobized by mechanically mixing it with 0.5-1.0% of chemically modified silica having 99.8-99.9% hydrophobicity and particle size 0.005 to 0.1 mcm. EFFECT: decreased water loss, prevented clogging of pore space of borehole environment during primary exposure of productive formation. 4 cl, 3 tbl, 14 ex

Description

 The invention relates to the oil and gas industry, and in particular to physicochemical methods of stimulating the formation during the initial opening of productive oil deposits.

When the productive formation is opened during drilling in the repression mode, the mud filtrate enters the formation. As a result of this, there is a decrease in permeability of the bottom-hole zone of the productive reservoir and, as a result, an unjustified decrease in the potential production rate of the well. Water or mud filtrate trapped in the reservoir forces oil from the near-wellbore zone deeper into the reservoir and causes a decrease in oil permeability of the reservoir. The reasons for this are
- swelling of clay particles contained in the rocks that make up the reservoir;
- the blocking effect of water due to capillary and surface phenomena;
- the formation of insoluble sediments in the pore space as a result of the interaction of the filtrate and formation fluids;
- clogging of pores with solid particles (clays) penetrating into the reservoir together with the filtrate.

 A large number of studies have been devoted to the problem of reducing the fluid loss of drilling fluids and preventing the clogging of the pore space of the near-wellbore zone. Various reagents have been proposed that reduce the amount of filtrate entering the formation and reduce its negative effect on the bottom hole of the wells (starch, polysaccharides, carboxymethyl cellulose, surfactants, hydrocarbon-based solutions, hydrophobic-emulsion solutions) / 1 /.

The closest analogue to the claimed solution is an emulsion drilling fluid, including an emulsifier - emulsol of the indicated grades, saturated aqueous solution of calcium chloride, hydrophobized dispersed chalk, liquid oil - diesel fuel in the following ratio of ingredients, wt.%:
Emulsifier - emulsol of the specified brands - 6 -12
Saturated aqueous solution of calcium chloride - 24 - 50
Gidrofobizirovanny dispersed chalk - 15 - 25
Liquid Oil - Diesel - Other / 2 /
The aim of this invention is the development of an invert emulsion drilling mud - IEBR, which has a reduced water loss and prevents colmatization of the pore space of the near-wellbore zone during the initial opening of the reservoir.

The technical result is achieved in that the hydrocarbon-based emulsion drilling fluid, including liquid petroleum product, surface-active emulsifier, hydrophobized dispersed chalk, mineralized aqueous phase, contains an aqueous phase of varying degrees of mineralization and, in addition, a co-emulsifier - chemically modified silica with 40-70% - the degree of substitution of surface silanol groups for alkyl-aryl radicals - Polysil-DF, in the following ratio of ingredients, wt.%:
Liquid petroleum product - 25-60
The specified emulsifier is 1.0-2.5
Indicated chalk - 3-10
Polysil-DF - 0.6-1.5
Indicated aqueous phase - Rest
Alkyl-aryl radicals that modify the surface of silica are CH ₃ , C ₂ H ₅ , C ₃ H ₇ , C ₆ H ₅ . The specified chalk is hydrophobized by mechanical mixing with chemically modified silica with 99.8-99.9% hydrophobicity and with a concentration of 0.5-1.0%. The size of the discrete particles of chemically modified silica is from 0.005 to 0.1 microns.

 The ratio of the volumes of the dispersed phase and the dispersion medium varies from 0.40 / 0.60 to 0.75 / 0.25.

Polysil-DF obtained according to / 3 / under conditions providing a 40-70% substitution of surface silanol groups of silica (aerosil, white soot, perlite filter, etc.) with alkyl-aryl radicals, in an invert emulsion drilling fluid, performs two features:
a) is a solid emulsifier with high stabilizing ability;
b) is a structural builder, providing the formation on the walls of the well of a thin dense crust that protects the reservoir from the negative effects of the drilling fluid.

 The filter cake is an oleogel from a gelled hydrophobic emulsion with a high content of active finely divided filler. During well development, the filter cake due to its oleophilic properties does not interfere with oil filtration and is washed out by a stream of hydrocarbon fluid from the pores of the near-well zone of the reservoir.

 The presence of a surface-active emulsifier in the emulsion leads to an additional decrease in the interfacial tension at the water-oil interface and thereby ensures the formation of a stable microemulsion.

 Examples of specific performance.

The EDB is prepared as follows:
Polysil-DF and an emulsifier are introduced into diesel fuel with stirring and, after dissolution (10-15 minutes), the mineralized aqueous phase is dispersed portionwise dispersed in the resulting hydrocarbon suspension with vigorous stirring (at least 5000 rpm). The optimal mixing time of the resulting invert emulsion is determined by the value of the parameter "electrical stability", which is usually about 30 minutes. Further, if necessary, carry out the weighting of the drilling fluid with chalk, barite or marble chips.

 Table 1 shows the properties of invert emulsions obtained with a dispersion: dispersion ratio of 1: 1 and a constant concentration of Polysil-DF and emulsifier. All emulsion solutions were obtained with stirring with a paddle mixer with a speed of 5000 rpm.

 As can be seen from the table, the presence in the emulsion of only Polysil-DF or emulsion (examples 1-3) does not provide the formation of emulsions with high aggregate stability and low values of the filtration rate.

 When both Polysil-DF and emulsal are contained in the emulsion (example 4), indicators such as sedimentation stability, electrical stability, and filter recovery are sharply improved. The replacement of fresh water with a saturated solution of calcium chloride does not lead to a sharp change in the characteristics of the IEBR (see examples 4 and 5), but the mineralization of the aqueous phase reduces the risk of unwanted hydration of clay rocks due to the osmotic transfer of water from the solution.

 Replacing diesel fuel with oil with a viscosity of 4.9 MPa s leads to a noticeable increase in the viscosity of the system and to a sharp decrease in the filtration rate (cf. examples 5 and 6). When comparing the properties of the IEBR obtained according to the invention and the prototype (examples 5 and 7), it is seen that the filtration rate of the claimed composition is significantly reduced.

 An analysis of the presented results shows that the proposed composition of the IEBR, while maintaining sedimentation stability and the required viscosity and structural parameters, is superior to those known for such an important indicator as filter recovery.

 The technological properties of the IEBR are significantly affected by the phase ratio, the concentration of emulsifiers and the preparation conditions (Table 2). So, the emulsion prepared with stirring with a paddle mixer (example 8) after additional dispersion in a mixer (11000 rpm) has a filtration rate an order of magnitude lower than the original. Such characteristics as static shear stress, filtering, do not change for 2-20 days (examples 8 and 9).

 The increase in the content of the dispersion phase in the emulsion (examples 8-12) leads to a decrease in the rheological parameters of the system, but the filtration rate varies slightly. With a decrease in the concentration of Polysil below 0.6 and the emulsifier below 1 wt.% (Example 13), the hydrocarbon phase is released, which indicates the unsatisfactory stability of the IEBR.

 Example 14

 An increase in the rheological characteristics and weighting of the IEBR is achieved both by increasing the fraction of the mineralized dispersed phase and by introducing into the solution such solid dispersed fillers as chalk, barite, marble chips, etc.

For this purpose, an emulsion solution of the following composition was prepared, wt.%:
Diesel - 30
Polysil-DF - 1,0
Emultal - 2.2
Dispersed chalk - 5.0
The aqueous phase (10% solution of CaCl ₂ ) - 61.8
To impart water-repellent properties, the chalk was pre-mixed with chemically modified silica with hydrophobicity of 99.8% (trademark Polysil P1) and with a concentration of 0.5 wt.%.

 Table 3 shows the characteristics of the IEBR stabilized by Polysil-DF and containing hydrophobic chalk as a weighting agent and structure former.

As can be seen from table 3, the introduction of a hydrophobic dispersed chalk into the emulsion leads to the formation of a protective crust with a thickness of less than 0.5 mm, which prevents the penetration of the cement slurry during subsequent cementing of the near-trunk zone of the reservoir. Such a crust can be easily removed by acid treatment. The system weighted with chalk has a heat resistance of more than 150 ^o C and high clay capacity (50%). In addition, the addition of hydrophobic chalk to the emulsion increases its rheological characteristics and expands the use of such systems as drilling fluids during the initial opening of reservoirs.

Given in the table. 1-3 data allow to establish optimal IEBR formulations for various conditions of the initial opening of the reservoir, depending on the geological and physical properties of the reservoir and the physico-chemical characteristics of the fluids saturating it. In terms of the combination of rheological properties, electrical stability, and filtration rate, the most effective compositions are the following component ranges:
- the dispersion ratio: the dispersion phase from 0.40 / 0.60 to 0.75 / 0.25, respectively;
- the concentration of chemically modified silica with a 40-70% degree of substitution of surface silanol groups by alkyl-aryl radicals from 0.6 to 1.5 wt.%;
- concentration of emulsifier (ionic or nonionic surfactant) -1.0-2.5 wt.%;
- the content of hydrophobic chalk in the IEB 3-10 wt.%
Sources of information
1. Kasyanov N. M., Shtyrlin V. F., "Issues of improving the quality of opening of productive formations", Drilling series, VNIIOENG, M., 1969, p. 3-88.

 2. USSR author's certificate 958463, С 09 К 7/06, 09/15/1982.

3. Makarov A. S. et al. "Study of the structural and mechanical properties of inverse emulsions based on aerosil", Colloid Journal, 1975, v. 37, ¹ 5, p. 889-893.

Claims (3)

1. A hydrocarbon-based emulsion drilling fluid, including liquid petroleum product, a surface-active emulsifier, a hydrophobized dispersed chalk, a mineralized aqueous phase, characterized in that it contains an aqueous phase of varying degrees of mineralization and additionally an emulsifier - chemically modified silica with 40-70% - the degree of substitution of surface silanol groups by alkyl-aryl radicals - Polysil-DF in the following ratio of ingredients, wt. %:
Liquid petroleum product - 25-60
The specified emulsifier is 1.0-2.5
Indicated chalk - 3-10
Polysil-DF - 0.6-1.5
Indicated aqueous phase - Rest
2. The solution according to claim 1, characterized in that the alkyl-aryl radicals are CH ₃ , C ₂ H ₅ , C ₃ H ₇ , C ₆ H ₅ .  3. The solution according to claim 1, characterized in that said chalk is hydrophobized by mechanical mixing with chemically modified silica with 99.8-99.9% hydrophobicity and with a concentration of 0.5-1.0%.  4. The solution according to p. 1 or 3, characterized in that the size of the discrete particles of chemically modified silica is 0.005-0.1 microns.

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