RU2194843C2 - Method of bottom water shutoff in porous-fractured reservoir - Google Patents

Abstract

FIELD: oil-gas producing industry; applicable in restriction of formation water inflow to well, and some other operations involved in well construction and operation. SUBSTANCE: method includes injection of composition based on hydrocarbon fluid with addition of surfactant. Said addition is injected together with the first portion of hydrocarbon fluid, and injected with the last portion of hydrocarbon fluid is rubber crumb. In this case, formation pressure gradient is periodically increased and well is allowed to stand for at least 72 h. Surfactant is added in excessive concentration to ensure composition surface tension on hydrocarbon-formation water interface not more 2•10³ N/m. EFFECT: higher efficiency of operations involved in bottom water shutoff to porous-fractured reservoir. 3 cl, 1 tbl

Description

 The invention relates to the oil and gas industry and can be used to limit the influx of formation water into the well and a number of other operations that occur during the construction and operation of oil and gas wells, especially in the conditions of a pore-fractured reservoir.

 There are ways to isolate the entry of bottom water into the well, based on the injection of plugging, sedimentary and other insulating mixtures into the aquifer. It is especially difficult to isolate the inflow of formation water in the case of a pore-fracture reservoir, since the opening of most of the cracks is from 0.005 to 0.05 mm, and the opening of tectonic cracks can reach 1 mm.

 A known method of isolating water in fractured formations according to the patent of the Russian Federation 2112875 dated 06/04/96, IPC 6 E 21 B 43/32, 33/13, according to which, after the insulating material, an additional suspension (rubber crumb in the liquid) is pumped with a particle size of 0, 1-3.5 mm.

 The disadvantage of this method is that the proposed size of the rubber crumb on the upper limit is 3.5 times larger than the maximum possible size of the cracks, and on the lower limit is 2 times larger than the minimum size of the crack, so most of the rubber crumb, the dimensions of which do not correspond to the size of the cracks, will not clog them and, therefore, fulfill their purpose.

 The closest technical solution, taken as a prototype, is a method of isolating bottom water in a gas well according to the patent of the Russian Federation 2136877 dated 05.21.97, IPC 6 E 21 B 43/32, 33/13, since in accordance with it the injection of liquid hydrocarbons is carried out in portions, and as liquid hydrocarbons use oil products with the addition of surface-active substances (surfactants).

 However, the prototype does not determine the optimal values of the concentration of surfactants and surface tension of liquid hydrocarbons and the order of input of surfactants. Meanwhile, the effectiveness of the work on isolating plantar water, especially in a pore-fracture formation, significantly depends on this.

 The present invention solves the specific problem of improving the quality of insulation of bottom water under the condition of a pore-crack collector by establishing the order of supply of the insulating composition and the sequential formation of two insulating screens.

 The essence of the method is as follows.

To increase the efficiency of plantar water isolation works, a composition based on hydrocarbon fluid with the addition of a surfactant and crumb rubber is pumped into a pore-crack reservoir. Surfactants are fed into the first portion of the hydrocarbon liquid, and crumb rubber with a size of not more than 1 mm in the last. In this case, surfactants are added in excess concentration, which ensures the surface tension of the composition at the hydrocarbon-formation water interface not more than 2 • 10 ³ N / m. This creates favorable conditions both for more complete hydrophobization of the pore-fracture space of the formation, and for additional emulsification of plantar water in a hydrocarbon fluid and increase the viscosity of the composition. To increase the intensity of emulsification of plantar water, after pumping the composition into the aquifer, a periodic change in the pressure gradient is carried out. Thus, a remote screen is formed from a highly viscous emulsion in the pore part of the collector and in small cracks. Rubber crumb, fixed in cracks of medium and maximum sizes, forms a second screen. After injection of the composition into the aquifer, for uniform distribution of ingredients in the pore-fracture reservoir due to capillary absorption, increasing the degree of hydrophobization of the collector surface during surfactant adsorption, the well is left alone for a period of at least 72 hours.

 This method of isolating plantar water in a pore-fracture reservoir will significantly improve the quality of work.

 EXAMPLE.

 The influence of the method of isolating bottom water in a pore-fracture reservoir was assessed at the AKM-core test bench, which allows simulating filtration conditions through a pore-crack specimen. Natural carbonate samples taken from the Bashkir pore-fissure deposits of the Astrakhan gas condensate field from a depth of 3900-4100 m were used as a model of a pore-fracture formation.

где q - расход жидкости, см³/c;
l - длина керна, см;
μ - динамическая вязкость, спуаз;
ΔP - перепад давления, кг/см²;
F - площадь поперечного сечения керна, см².For the experiments, cylindrical samples with a diameter of 29-30 mm and a length of 40-45 mm were used. An artificial longitudinal crack was created in the sample with a given permeability, the sample was placed in a core holder and saturated with water. During the experiment, the pressure drop across the sample was 2.4 MPa, the temperature +20 ^o C. Then, water was pumped through the sample in the direction of reservoir-well until steady-state filtration. The initial permeability of the sample (K ₀ ) was determined by the Darcy formula

where q is the fluid flow rate, cm ³ / s;
l - core length, cm;
μ - dynamic viscosity, spoise;
ΔP - pressure drop, kg / cm ² ;
F - core cross-sectional area, cm ² .

 Then, a composition based on a hydrocarbon liquid with additives was pumped through a sample in the well-formation direction. Diesel fuel, hydrocarbon-soluble surfactants (for example, emulsion) were used as a hydrocarbon liquid, and butyl rubber based on butyl rubber with a size of 0.05-1.0 mm was used as a filler.

In the next step, in the direction of the "formation-well" again pumped water to a steady filtration and determined the permeability to water (K ₁ ).

 The permeability recovery coefficient (β) was used to evaluate the effectiveness of a particular method of isolating plantar water in a pore-fracture reservoir.

где К₀ - проницаемость образца по воде в направлении "пласт-скважина";
K₁ - проницаемость образца по воде после воздействия углеводородной жидкости с добавками в направлении "пласт-скважина".The permeability recovery coefficient was determined by the formula

where K ₀ - the permeability of the sample in water in the direction of "reservoir-well";
K ₁ - the permeability of the sample in water after exposure to hydrocarbon liquids with additives in the direction of the reservoir-well.

 The results of experimental studies are shown in the table.

The studies showed (see table) that in the case of a collector having a high permeability crack (2300-2600 • 10 ^-15 m), the coefficient β is 25-80% higher than for a low permeability collector (pore collector). Moreover, in the case of low surfactant concentrations (surface tension above 2 • 10 ³ N / m), the coefficient β depending on the concentration ranges from 24.6-52.0% in the case of a pore reservoir and from 37.7 to 65, 4 in the case of a fractured reservoir (experiments 2, 3). At the same time, an excess concentration of surfactants (experiments 4 and 5) made it possible to reduce the coefficient β for the pore reservoir by almost a factor of 5 and 3.4 times for the fractured reservoir.

 Even more significant advantages (up to 24%) were obtained in the case of periodic changes in the pressure gradient on the sample over several cycles. Moreover, with an increase in the number of cycles, the efficiency of water isolation in the sample (experiments 6–11) increases (up to 47%).

 A significant increase in the efficiency of water insulation occurs with a 2-portion injection of the composition. First, diesel fuel with emulsified was pumped, then diesel fuel with rubber crumb (experiments 12-14). In this case, the permeability recovery coefficient decreases to 4.9-7.6% for pore reservoirs and to 8.7-12.1% for fractured reservoirs.

 Thus, the proposed method for isolating plantar water in a pore-crack collector can significantly increase the efficiency of waterproofing due to the formation of two screens in series: a remote emulsion from a highly viscous emulsion in the pore part of the collector and a peripheral one due to finely dispersed crumb rubber fixed in cracks having larger sizes.

Claims (3)

 1. A method of isolating plantar water in a pore-fracture reservoir, comprising injecting a composition based on a hydrocarbon liquid with the addition of a surfactant into the aquifer, characterized in that the above additive is pumped with the first portion of the hydrocarbon liquid, and rubber is injected with the last portion of the hydrocarbon liquid crumb, while after injecting the composition, a periodic change in the pressure gradient is carried out, after which the well is left alone for a period of at least 72 hours 2. The method according to p. 1, characterized in that the surfactant is added in excess concentration, providing a surface tension of the composition at the hydrocarbon-formation water interface not more than 2 • 10 ³ N / m.  3. The method according to p. 1, characterized in that use rubber crumb size not exceeding 1 mm

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