Direct method for manufacturing large model fractured core and maintaining original oil-water saturation

Abstract

A direct method for manufacturing a large model fractured core and maintaining original oil-water saturation, including the following steps: (1) determining the volume V, porosity , permeability K, oil saturation S.sub.o, water saturation S.sub.w and the like of a fractured core to be manufactured; (2) preparing simulated oil, and determining the used oil mass m.sub.o=V.sub.o.sub.o; (3) under the circumstance of no consideration of oil saturation, acquiring the mass of the used water, cement and quartz sand; (4) while establishing oil saturation, acquiring the mass m.sub.w of water for manufacturing the core as m.sub.w=aV.sub.o.sub.w; (5) mixing oil, water and an emulsifier evenly to prepare an oil-in-water emulsion; (6) adding cement and quartz sand into the emulsion and stirring evenly to obtain cement slurry; (7) when a cement sample is in a semi-solidified state, cutting the cement sample with a steel wire; and (8) solidifying the cement sample to the end.

Claims

1. A direct method for manufacturing a large model fractured core and maintaining an original oil-water saturation, comprising the following steps: (1) determining a volume V, a porosity , a permeability K, an oil saturation S.sub.o and a water saturation S.sub.w of a fractured core to be manufactured, and determining an oil volume V.sub.o of the fractured core as V.sub.o=VS.sub.o, and an water volume V.sub.w of the fractured core as V.sub.w=VS.sub.w; (2) preparing a simulated oil according to an oil-water viscosity ratio of a formation under experimental conditions, and determining an oil density as .sub.o and a water density as .sub.w, determining an oil mass m.sub.o for manufacturing the fractured core as m.sub.o=V.sub.o.sub.o; (3) under a circumstance of no consideration of the oil saturation; acquiring, through experiments, a water-cement ratio m and a cement-quartz sand ratio n based on the porosity and the permeability K; and thus acquiring masses of used water, cement and quartz sand are a, b and c respectively, the circumstance of no consideration of the oil saturation is that the water saturation is 100%; (4) while establishing the oil saturation, continuing to fill the V.sub.W with water, and replacing a fluid in V.sub.o with an oil, the fluid is water, wherein the water volume is reduced by V.sub.o, and a consumption of water for manufacturing the fractured core is reduced by V.sub.o.sub.w; and thus acquiring a mass m.sub.w of water for manufacturing the fractured core as m.sub.w=aV.sub.o.sub.w; (5) mixing the oil, water and an emulsifier evenly to prepare an oil-in-water emulsion, wherein the emulsifier accounts for 0.16% to 0.21% of a mass sum of the oil and the water; (6) adding the cement and the quartz sand into the emulsifier in the step (5) to form a mixed material and stirring the mixed material evenly to obtain a cement slurry; (7) applying the simulated oil to an inner surface of a core mold to form a thin oil film on the inner surface of the core mold; casting the cement slurry in the core mold to obtain a cement sample; enabling the cement sample to be in a sealed state to wait for a solidification; when the cement sample is in a semi-solidified state, taking the core mold down, and cutting the cement sample with a steel wire according to a fracture direction required by experiments, desired fractures are formed in places that are cut by the steel wire; and (8) keeping the cement sample isolated from outside world, and acquiring the large model fractured core, the original oil-water saturation is maintained after the solidification of the cement sample is completed.

2. The direct method for manufacturing the large model fractured core and maintaining the original oil-water saturation according to claim 1, wherein in the step (3), the water-cement ratio is a mass ratio of the water to the cement, the water-cement ratio is ranging from 0.3 to 0.5; and the cement-quartz sand ratio is a mass ratio of the cement to the quartz sand, the cement-quartz sand ratio is ranging from 1:1 to 1:3.

3. The direct method for manufacturing the large model fractured core and maintaining the original oil-water saturation according to claim 1, wherein the emulsifier in the step (5) is a mixture prepared from a sorbitan monooleate and a polyoxyethylene sorbitan monooleate according to a mass ratio of 1:10.

4. The direct method for manufacturing the large model fractured core and maintaining the original oil-water saturation according to claim 1, wherein, in the step (6), the cement is Portland cement, and the quartz sand has a particle size of 80-120 mesh.

Description

DETAILED DESCRIPTION

Embodiment of the Invention

(1) The present invention will be further described below according to an example.

Example 1

(2) A direct method for manufacturing a large model fractured core and maintaining original oil-water saturation comprises the following steps:

(3) (1) determining the size, volume V.sub.o porosity , permeability K, oil saturation S.sub.o and water saturation S.sub.w of a core to the manufactured as 30 cm30 cm30 cm, 27,000 cm.sup.3, 15%, 0.18 mD, 12.7% and 87.3% respectively, thereby acquiring the oil volume V.sub.o and the water volume V.sub.w of the core as 514.35 cm.sup.3 and 3535.65 cm.sup.3 respectively;

(4) (2) determining the oil-water viscosity ratio of the formation as 10, preparing simulated oil according to the oil-water viscosity ratio of the formation under experimental conditions, and determining the oil density .sub.o as 0.863 g/cm.sup.3 and the water density .sub.w as 1 g/cm.sup.3, thereby determining the mass m.sub.o of oil for manufacturing the core as m.sub.o=V.sub.o.sub.o, i.e., 443.88 g;

(5) (3) under the circumstance of no consideration of oil saturation; acquiring, through experiments, a water-cement ratio m and a cement-quartz sand ratio n, which are 0.4 and 1:3 respectively, based on the porosity and the permeability K; and thus acquiring the mass of the used water, cement and quartz sand, i.e. a, b and c which are 6615 g, 16537.5 g and 49612.5 g respectively, under the circumstance of no consideration of oil saturation, i.e., the water saturation is 100%;

(6) (4) under the circumstance of no consideration of oil saturation, filling pores of the core with water, such that V.sub.o and V.sub.w are both filled with water, and the water consumption at this time is a; while establishing oil saturation, continuing to fill V.sub.w with water, and replacing fluid, i.e., water in V.sub.o with oil, wherein the water volume is reduced by V.sub.o compared to that of a case before the oil saturation is established, and the consumption of water for manufacturing the core should be reduced by V.sub.o.sub.w, i.e., 514.35 g; and thus acquiring the mass m.sub.w of water for manufacturing the core as m.sub.w=aV.sub.o.sub.w, i.e., 6100.65 g;

(7) (5) mixing oil, water and an emulsifier evenly to prepare a oil-in-water emulsion, wherein the emulsifier is a mixture prepared from sorbitan monooleate (Span-80) and polyoxyethylene sorbitan monooleate (Tween-80) in a mass ratio of 1:10, and accounts for 0.2%, i.e., 13.09 g, of the mass sum of oil and water;

(8) (6) adding cement and quartz sand into the emulsifier in the step (5) and stirring evenly to obtain cement slurry, wherein the cement is Portland cement, and the quartz sand has a particle size of 80 mesh;

(9) (7) applying simulated oil to the inner surface of a core mold, such that a thin oil film is formed on the inner surface of the mold; casting the cement slurry in the core mold to obtain a cement sample; when the cement sample is in a semi-solidified state, taking the core mold down, and cutting the cement sample in the middle of the cement sample with a steel wire in a horizontal direction, wherein desired fractures are formed in places that are cut by the steel wire; and

(10) (8) keeping the cement sample isolated from the outside world, and waiting for the completion of the solidification of the cement sample.

(11) The large model fractured core manufactured by using the present invention has certain porosity and permeability, and can maintain the original oil-water saturation, and simulate the actual fractured carbonate rock reservoir better.