Method for enhancing the recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point

Abstract

The present invention discloses a method for enhancing the recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point, and the method is aimed at the development of heavy oil reservoir by water injection under the condition that the performance parameters of crude oil emulsion meet the following three specific requirements: (A) The viscosity of the crude oil is less than 6,000 mPa.Math.s; (B) At the reservoir temperature, the phase inversion point of the crude oil emulsion is greater than or equal to 70%, and the emulsion viscosity corresponding to the phase inversion point is 2-6 times of the crude oil viscosity; (C) At the reservoir temperature, when the water cut is less than or equal to the phase inversion point, the flow rate ratio of crude oil emulsion to crude oil is 0.2 to 0.9.

Claims

1. A method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point to develop a heavy oil reservoir comprising: performing water injection into a heavy oil reservoir under a condition when performance parameters of a crude oil emulsion meet three specific requirements, wherein the three specific requirements comprise: (A) viscosity of the crude oil is less than 6,000 mPa.Math.s; (B) phase inversion point of the crude oil emulsion at reservoir temperature, is greater than or equal to 70%, and emulsion viscosity corresponding to the phase inversion point is two-to-six times of the crude oil viscosity; and (C) at the reservoir temperature, when water content is less than or equal to the phase inversion point, a flow rate ratio of crude oil emulsion to crude oil is 0.2 to 0.9.

2. The method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point according to claim 1, wherein the condition of performance parameters of crude oil emulsion meeting the three specific requirements is determined using the following steps: Step 1: taking a crude oil sample from the heavy oil reservoir, determining the crude oil viscosity, and determining whether the crude oil viscosity meets the requirement of less than 6,000 mPa.Math.s; if it does, proceed to Step 2; Step 2: measuring the phase inversion point of the crude oil emulsion at the reservoir temperature, and determining whether the phase inversion point is greater than or equal to 70% and whether the emulsion viscosity corresponding to the phase inversion point is two-to-six times of the crude oil viscosity; if it does, proceed to Step 3; Step 3: measuring the flow rate ratio of crude oil emulsion to crude oil when the water content is less than or equal to the phase inversion point at the reservoir temperature, and then determining whether the flow rate ratio of crude oil emulsion to crude oil is within a range of 0.2 to 0.9, which indicates that water injection is applicable to the development of the heavy oil reservoir.

3. The method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point according to claim 2, wherein at the reservoir temperature in Step 2, the phase inversion point of the crude oil emulsion is determined using the steps of: Step (1) preheating the crude oil and produced water of the heavy oil reservoir to the reservoir temperature respectively; Step (2) mixing the preheated crude oil and produced water in different volume ratios to form a system with different measures of water content, and stirring the system with an emulsifier for 60 minutes at the reservoir temperature and shear rate of 150 s.sup.−1 to form a crude oil emulsion; Step (3) measuring the viscosity of the crude oil emulsion at 7.34 s.sup.−1 and reservoir temperature with a rotary viscometer; forming a curve based on a relationship between the crude oil emulsion viscosity and the different measures of water content, wherein the water content of the system is plotted on an x-axis and the crude oil emulsion viscosity on a y-axis; and determining a water content percentage corresponding to a maximum viscosity of the crude oil emulsion as the phase inversion point.

4. The method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point according to claim 2, wherein at the reservoir temperature in Step 3, the method for determining the flow rate ratio of crude oil emulsion to crude oil is as follows: (1) Select natural or artificial cores that represent porosity and permeability of the reservoir, and vacuum the cores and saturate them with water; (2) Inject crude oil into the cores at a flow rate ν corresponding to a shear rate of 150 s.sup.−1 until a pressure is stable and record a stable pressure value P.sub.crude oil, then co-inject the crude oil and water produced in the cores with a specific oil-water flow rate ratio at the same flow rate ν into the cores to simulate formation of in-situ crude oil emulsion at a specific water content, continue to inject until the pressure is stable, and record a stable pressure value P.sub.emulsion; calculate a ratio of P.sub.crude oil to P.sub.emulsion, which is the flow rate ratio of crude oil emulsion to crude oil at the specific water content; (3) Repeat Step (1), then change the oil-water flow rate ratio, and repeat Step (2) to obtain the flow rate ratios of crude oil emulsion to crude oil at different measures of water content.

5. The method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point according to claim 4, wherein the flow rate ν is calculated as follows: $v=\frac{4n}{3n+1}\frac{\gamma \sqrt{150K\varphi }}{12},$ where, n is a flow behavior index, K is permeability, in D, ϕ is porosity, and γ is shear rate.

6. The method for enhancing a recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point according to claim 4, wherein the natural or artificial cores are 3.8 cm×8 cm in size.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a bar chart of the viscosity and its increase multiple of crude oil emulsion formed at different water cuts (55° C.).

(2) FIG. 2 is a dynamic curve of reservoir development in Block J of Xinjiang Oilfield.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) In the following detailed description of the preferred embodiments of the present invention, reference is made to the accompanying drawings. It is to be understood that the preferred embodiments described herein are only used to illustrate and interpret the present invention and are not intended to limit the present invention.

(4) The heavy oil reservoir in Block J of Xinjiang Oilfield was studied as an example to explain the specific application of the method for enhancing the recovery factor of heavy oil by in-situ oil-water emulsion with high phase inversion point disclosed in the present invention.

(5) Step 1: Measure the viscosity of the dehydrated heavy oil produced in Block J of Xinjiang Oilfield as 990 m.Math.Pas at a reservoir temperature of 55° C., meeting the requirement of less than 6,000 m.Math.Pas.

(6) Step 2: Determine the viscosity and phase inversion point of the crude oil emulsion:

(7) Preheat the dehydrated heavy oil and produced water to 55° C. respectively, and then mix the heavy oil and water at different volume ratios to control the water cuts as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%, respectively, with water cut=water volume/(total volume of crude oil and water), and use an emulsifier to stir the mixture under the condition of 55° C. and 150 s.sup.−1 for 60 minutes to prepare crude oil emulsion; measure the apparent viscosity of the crude oil emulsion prepared at different water cuts under the condition of 55° C. and 7.34 s.sup.−1 with a rotary viscometer, and develop a data analysis chart as shown in FIG. 1. The results show that the phase inversion point of the crude oil emulsion was 70%, and the emulsion viscosity corresponding to the phase inversion point was 5.17 times of the crude oil viscosity, meeting the requirement that the phase inversion point of the crude oil emulsion is greater than or equal to 70% and the emulsion viscosity corresponding to the phase inversion point is 2-6 times of the crude oil viscosity.

(8) Step 3: Determine the flow rate ratio of crude oil emulsion to crude oil:

(9) Select natural cores (φ3.8 cm×8 cm in size) from Block J of Xinjiang Oilfield, and vacuum the cores and saturate them with water; inject the dehydrated crude oil (with phase inversion point of 70%) into the core at a flow rate ν corresponding to a shear rate of 150 s.sup.−1 until the pressure is stable and record the stable pressure value P.sub.crude oil; then inject the crude oil and produced water with different flow ratios (oil-water flow ratio: 4:1, 3:2, and 2:3) into the core at the same flow rate ν until the pressure is stable, and record the stable pressure value P.sub.emulsion; calculate the ratio of P.sub.crude oil to P.sub.emulsion to obtain the flow rate ratio of crude oil emulsion to crude oil at different water cuts. The experimental results are shown in Table 1, indicating that when the water cut was from 20% to 60%, the flow rate ratio of crude oil emulsion to crude oil was between 0.57 and 0.72, meeting the requirement that the flow rate ratio of crude oil emulsion to crude oil is 0.2 to 0.9.

(10) TABLE-US-00001 TABLE 1 Flow Rate Ratios of Crude Oil Emulsion to Crude Oil at Different Water Cuts Core Porosity Fluid-based Oil-water Water cut Flow rate No. (%) permeability (md) flow ratio (%) ratio 50-2  15.6 32.8 4:1 20 0.57 50-8  17.4 24.3 3:2 40 0.72 50-10 15.5 28.7 2:3 60 0.59

(11) Through the above Steps 1 to 3, it is judged that water injection is applicable to the development of the oil reservoir in Block J of Xinjiang Oilfield.

(12) The effect of field application of in-situ emulsification with high phase inversion point to heavy oil production is as follows: the viscosity of the crude oil in Block J of Xinjiang Oilfield was 900 to 2,000 m.Math.Pas, the permeability was 100 mD, and the temperature was 55° C. According to the mechanism of conventional water flooding, it can be predicted that the recovery factor of this reservoir will be only 15% when the water cut reaches 98% by water flooding in this reservoir. However, due to the in-situ emulsification with high phase inversion point formed in the water injection for crude oil production (the phase inversion point of the crude oil emulsification is 70%), the water cut is only 40% (FIG. 2) and the recovery percent is higher than 18% after the water flooding has been applied to reservoir development for nearly 10 years. Thus, it can be seen that the method disclosed by the present invention is highly reliable.

(13) The above are not intended to limit the present invention in any form. Although the present invention has been disclosed as above with embodiments, it is not intended to limit the present invention. Those skilled in the art, within the scope of the technical solution of the present invention, can use the disclosed technical content to make a few changes or modify the equivalent embodiment with equivalent changes. Within the scope of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still regarded as a part of the technical solution of the present invention.