A method and device for studying the influence of wax deposition on reservoirs in high-wax condensate gas reservoirs

Abstract

The present invention relates to a method for studying the influence of wax deposition on a reservoir in a high-wax condensate gas reservoir, comprising the following steps: (1) measuring the wax precipitation temperature of a sample condensate oil under a reservoir pressure; (4) injecting a first fluid into a first core sample, measuring a first permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a second permeability of the first core sample under an equidistantly reduced temperature condition; (5) injecting condensate oil into the first core sample, repeating step (4); (6) calculating the influence of the wax deposition on the reservoir according to the first permeability, the second permeability, the third permeability and the fourth permeability. The method for studying the influence of wax deposition on a reservoir in a high-wax condensate gas reservoir can effectively analyze the influence of reservoir temperature, reservoir pressure and reservoir physical properties on wax deposition of crude oil in the reservoir, and can accurately measure rock permeability under different conditions.

Description

Technical Field

[0001] The present invention relates to the field of wax deposition reservoir damage assessment for high wax condensate gas reservoirs, and in particular to a method and device for studying the influence of wax deposition on reservoirs in high wax condensate gas reservoirs. Background Art

[0002] In oil and gas production, the wax deposition problem is a research hotspot and difficulty in the petroleum industry at home and abroad. Studies have shown that the deposition of paraffin is irreversible, that is, once paraffin is precipitated from the solution, it is difficult to dissolve again in the same fluid, even if the original formation temperature is restored. Therefore, it is necessary to study how the porosity and permeability of the formation change after paraffin deposition, so as to provide a theoretical support for simulating the dynamics of oil and gas production after paraffin deposition.

[0003] Wax deposition during the production of waxy oils is usually related to the reservoir properties. Pressure and temperature are key parameters that influence the formation of organic scale in the pore volume of the reservoir. However, the processes and their occurrence in the reservoir are difficult to solve. In addition, at temperatures below the WAT, the wax is partially dissolved and suspended in the oil and partially adsorbed on the surfaces of the pore throats, causing changes in the reservoir porosity and permeability. Traditional methods (rheology, filtration and light scattering methods and nuclear magnetic resonance) cannot accurately characterize the damage caused by paraffin deposition to the reservoir. Summary of the invention

[0004] In view of the above problems, one object of the present invention is to provide a method for studying the influence of wax deposition on the reservoir of high wax condensate gas reservoirs, which can effectively analyze the influence of reservoir temperature, reservoir pressure and reservoir physical properties on the wax deposition of reservoir crude oil. The method is simple to operate, with standardized steps, and can accurately measure the rock permeability under different conditions. Another object of the present invention is to provide a device for studying the influence of wax deposition on the reservoir of high wax condensate gas reservoirs.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] One aspect of the present invention provides a method for studying the influence of wax deposition on the reservoir of a high wax condensate gas reservoir, comprising the steps of:

[0007] Measure the wax precipitation temperature of sample condensate oil under reservoir pressure;

[0008] Selecting a first core sample and a second core sample having similar porosity and core permeability;

[0009] By injecting a first fluid into a first core sample, measuring a first permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a second permeability of the first core sample under an equidistantly decreasing temperature condition;

[0010] By injecting condensate into the first core sample, measuring a third permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a fourth permeability of the first core sample under an equidistantly decreasing temperature condition;

[0011] The influence of the wax deposition on the reservoir is calculated according to the first permeability, the second permeability, the third permeability and the fourth permeability.

[0012] Furthermore, the method further comprises the steps of:

[0013] measuring the pore parameters of the first core sample before the test;

[0014] measuring pore parameters of the first core sample after the test;

[0015] Whether the calculation result is accurate is verified according to the pore parameters of the first core sample before the test and the pore parameters of the first core sample after the test.

[0016] Furthermore, the method further comprises the steps of:

[0017] Replacing the first core sample with a second core sample, changing the pressure value, injecting the first fluid into the second core sample, measuring the first permeability of the second core sample under the second pressure condition and the constant temperature condition, and measuring the second permeability of the second core sample under the condition of equidistantly decreasing temperature;

[0018] By injecting condensate into the second core sample, measuring a third permeability of the second core sample under a second pressure condition and a constant temperature condition, and measuring a fourth permeability of the second core sample under an equidistantly decreasing temperature condition;

[0019] The influence of the wax deposition on the reservoir of the second core sample under the second pressure condition is calculated according to the first permeability, the second permeability, the third permeability and the fourth permeability.

[0020] Furthermore, the first fluid is kerosene.

[0021] Furthermore, under different pressure conditions, the influence of wax deposition on reservoir permeability is calculated as shown in formula (1):

[0022]

[0023] Where L refers to the influence of wax deposition on reservoir permeability, %; K TN Refers to the third permeability of condensate oil at a constant temperature; K CNRefers to the fourth permeability of condensate at reservoir temperature; K TM Refers to the first permeability of kerosene at a constant temperature; K CM Refers to the second permeability of kerosene at reservoir temperature.

[0024] Furthermore, the constant temperature condition is to maintain the temperature at 10°C higher than the wax precipitation temperature for 4 hours to ensure the temperature stability of the equipment.

[0025] Furthermore, before injecting condensate oil into the first core sample, the method further includes: cleaning the experimental equipment with petroleum ether.

[0026] Another aspect of the present invention provides a research device for the influence of wax deposition on the reservoir of a high wax condensate gas reservoir, which is used to implement the research method for the influence of wax deposition on the reservoir of a high wax condensate gas reservoir, comprising:

[0027] A core holder, the core holder having a function of holding a core;

[0028] a confining pressure pump, used for applying confining pressure to the core;

[0029] a first fluid pump, wherein an output end of the first fluid pump is connected to the core through a pipeline and is used to inject a first fluid into the core;

[0030] a condensate oil pump, the output end of which is connected to the core through a pipeline, for injecting condensate oil into the core;

[0031] A temperature sensor and a first pressure sensor, wherein the temperature sensor and the first pressure sensor are used to detect the temperature and pressure value of the core respectively;

[0032] A flow meter and a back pressure valve, wherein the flow meter is disposed between the core holder and the back pressure valve and is used to detect the flow rate at the outlet of the core and calculate the permeability according to the flow rate;

[0033] A recovery device is connected to the outlet of the back pressure valve and is used to recover the first fluid or condensate oil.

[0034] Furthermore, the first fluid pump and the condensate oil pump each include two, and the outlet ends of the two first fluid pumps and the two condensate oil pumps are directly connected to the core through an injection pipeline. An oil three-way valve is also arranged on the injection pipeline, and the first end of the three-way valve is connected to the first fluid pump, the second end is connected to the condensate oil pump, and the third end is connected to the core.

[0035] Furthermore, it also includes a second pressure sensor, which is used to detect the outlet pressure of the kerosene pump and the condensate oil pump.

[0036] Due to the adoption of the above technical scheme, the present invention has the following advantages: the research method of the influence of wax deposition on the reservoir of high wax condensate gas reservoir provided by the present invention can effectively analyze the influence of reservoir temperature, reservoir pressure and reservoir physical properties on the wax deposition of reservoir crude oil. The method is simple to operate and has standardized steps, and can accurately measure the rock permeability under different conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] By reading the detailed description of the preferred embodiment below, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only used to illustrate the purpose of the preferred embodiment and are not considered to be limitations of the present invention. In the entire drawings, the same reference numerals are used to represent the same components.

[0038] In the attached picture:

[0039] Figure 1 This is a schematic diagram of the results of the research device for the effect of wax deposition on the reservoir in a high wax condensate gas reservoir;

[0040] The symbols in the accompanying drawings are as follows:

[0041] 1-core holder, 2-confining pressure pump, 3-kerosene pump, 4-condensate pump, 5-pressure sensor, 6-flow meter, 7-three-way valve, 8-test tube recovery device, 9-pressure sensor, 10-back pressure valve. DETAILED DESCRIPTION

[0042] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0043] The present invention relates to a method and device for studying the effect of wax deposition on the reservoir of high wax condensate gas reservoirs, mainly focusing on the fact that at a temperature below WAT, the wax partially dissolves and suspends in the oil, and partially adsorbs on the surface of the pore throat, causing changes in the reservoir porosity and permeability. Existing rheological methods cannot accurately characterize the damage of paraffin deposition to the reservoir.

[0044] Example 1

[0045] This embodiment 1 provides a method for studying the influence of high wax condensate gas reservoir deposition on reservoirs, and the method for studying the influence of high wax condensate gas reservoir wax deposition on reservoirs comprises the steps of:

[0046] (1) Measure the wax precipitation temperature of sample condensate oil under reservoir pressure;

[0047] The measurement of the wax precipitation temperature may specifically be carried out by using a conventional solid phase deposition device to measure the wax precipitation temperature (WAT) of the sample condensate oil under reservoir pressure.

[0048] (2) selecting a first core sample and a second core sample having similar porosity and core permeability;

[0049] (3) measuring pore parameters of the first core sample and the second core sample;

[0050] The core samples were subjected to CT scanning and nuclear magnetic resonance to obtain pore parameters before the experiment;

[0051] (4) injecting a first fluid into a first core sample, measuring a first permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a second permeability of the first core sample under an equidistantly decreasing temperature condition;

[0052] The constant temperature condition is specifically: constant temperature to 10°C higher than the wax precipitation temperature, constant temperature for 4 hours, to ensure the temperature of the equipment is stable;

[0053] The injected fluid sample is selected as kerosene, and after the temperature is stabilized, the permeability of the first core sample is measured at 10°C higher than the wax precipitation temperature;

[0054] The temperature was lowered by 1°C and the second permeability of the core samples at different temperatures was measured;

[0055] It should be noted here that the first fluid is not limited to kerosene, but can also be white oil, etc. The selection of the first fluid material can ensure the measurement of the experimental permeability, and has no effect on the core pore structure, does not change the core wettability, etc., and is easy to clean and does not affect the subsequent experimental results.

[0056] The temperature reduction of 1°C is not limited to 1°C, as long as the temperature reduction condition is met.

[0057] Use petroleum ether to clean the experimental equipment.

[0058] In the invention, kerosene is first used for measurement. This is because the core porosity and permeability are affected by temperature and pressure, and the permeability needs to be measured under different experimental conditions (different temperatures and pressures) during the experiment. In order to consider the effect of wax deposition on the core permeability alone, it is necessary to exclude the influence of other factors (temperature, pressure) on the core permeability.

[0059] First, kerosene injection was chosen to measure the effects of other factors (temperature, pressure) on core permeability, and the core can be cleaned with petroleum ether after kerosene injection. In addition, after condensate oil injection, the core porosity and permeability will change due to wax deposition, and the change is poorly reversible, which is easy to cause experimental errors.

[0060] (5) injecting condensate into the first core sample, measuring a third permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a fourth permeability of the first core sample under an equidistantly decreasing temperature condition;

[0061] The constant temperature condition is specifically: maintaining the temperature at 10°C higher than the wax precipitation temperature for 4 hours to ensure that the equipment temperature is stable, which is the same as in the above experimental step (4).

[0062] During the displacement process using condensate oil, when the temperature reaches the wax precipitation point of condensate oil, the wax deposition in the condensate oil will affect the core permeability. Since wax exists in two states after deposition, namely free state and adsorbed state. The free state is dissolved in the condensate oil and has little effect on the core permeability. The adsorbed state is filled in the core pores and has an important impact on the core porosity and permeability.

[0063] Traditional wax deposition test can only test the wax deposition amount, but cannot characterize the wax deposition state and its influence on the core porosity and permeability. The present invention studies the influence of wax deposition on the core permeability through permeability test experiment, which has certain engineering significance.

[0064] (6) Calculating the influence of the wax deposition on the reservoir based on the first permeability, the second permeability, the third permeability and the fourth permeability.

[0065] The influence of wax deposition on reservoir permeability is calculated as shown in formula (1):

[0066]

[0067] Where L refers to the influence of wax deposition on reservoir permeability, %; K TN Refers to the third permeability of condensate oil at a constant temperature; K CN Refers to the fourth permeability of condensate at reservoir temperature; K TM Refers to the first permeability of kerosene at a constant temperature; K CM Refers to the second permeability of kerosene at reservoir temperature.

[0068] The method further includes step (7): measuring the pore parameters of the first core after the test to verify whether the calculation result of step (6) is accurate. Specifically, the core sample after the experiment is subjected to CT scanning and nuclear magnetic resonance to obtain the porosity and permeability parameters after the experiment to verify the accuracy of the calculation result of step (6).

[0069] The wax precipitation test permeability experiment of the present invention is carried out under high temperature and high pressure, and the measurement temperature needs to be changed to test the effect of wax precipitation on the core permeability at different temperatures. Therefore, the pore parameter test in step (10) needs to be carried out after the core permeability test.

[0070] In the method of the present invention, the purpose of step (10) is to verify the accuracy of the experimental results. The changes in core porosity and permeability before and after the experiment are studied by CT scanning and nuclear magnetic resonance technology to verify that the core permeability change is affected by wax deposition during the entire experimental process.

[0071] The method also includes step (8): replacing the first core sample with a second core sample, changing the pressure value, repeating steps (4) and (5), measuring the first permeability, second permeability, third permeability and fourth permeability of the second core sample under the second pressure condition, and calculating the influence of the wax deposition on the reservoir of the second core sample under the second pressure condition based on the first permeability, second permeability, third permeability and fourth permeability under the second pressure condition.

[0072] In step (8), the calculation formula for calculating the influence of the wax deposition on the reservoir of the second core sample under the second pressure condition is the above formula (1), and then the influence of the wax deposition on the reservoir permeability under different pressure conditions is calculated.

[0073] The experiment is repeated using different core samples. This is because after the same core is tested for permeability at a certain pressure, it is difficult for the core to return to its pre-experimental state due to the influence of wax deposition on the core porosity and permeability. Therefore, the core sample can only be replaced at different pressures to test the core porosity and permeability under different pressures.

[0074] The method further comprises step (8), measuring the pore parameters of the second core sample after the test, and verifying the accuracy of the calculation result of step (8) based on the pore parameters of the second core sample before the test and the pore parameters after the test.

[0075] Implemented 2

[0076] Embodiment 2 of the present invention provides a research device for the influence of high wax condensate gas reservoir deposition on reservoirs, which is used for the research method for the influence of wax deposition on reservoirs in high wax condensate gas reservoirs described in embodiment 1, and comprises a core holder 1, a confining pressure pump 2, a first fluid pump 3, a condensate oil pump 4, a three-way valve 7 and a first pressure sensor 9, a flow meter 6 and a back pressure valve 10 and a recovery device 8. The core holder 1 has a core for clamping. The confining pressure pump 2 is used to apply confining pressure to the core. The output end of the first fluid pump 3 is connected to the core through a pipeline, and is used to inject a first fluid into the core. The output end of the condensate oil pump 4 is connected to the core through a pipeline, and is used to inject condensate into the core. The temperature sensor and the first pressure sensor 9 are used to detect the temperature and pressure value of the core, respectively. The flow meter is arranged between the core holder 1 and the back pressure valve 10, and is used to detect the flow rate of the outlet of the core, and calculate the permeability according to the flow rate. The recovery device 8 is connected to the outlet of the back pressure valve 10 and is used to recover the first fluid or condensate oil.

[0077] The first fluid pump 3 and the condensate oil pump 4 each include two, and the outlet ends of the two first fluid pumps 3 and the two condensate oil pumps 4 are directly connected to the core through an injection pipeline. An oil three-way valve 7 is also arranged on the injection pipeline, and the first end of the three-way valve 7 is connected to the first fluid pump 3, the second end is connected to the condensate oil pump 4, and the third end is connected to the core.

[0078] The first fluid is kerosene, and the first fluid pump is a kerosene pump 3 .

[0079] The research device for the influence of high wax condensate gas reservoir deposition on reservoir formations further comprises a second pressure sensor 5 , which is used to detect the outlet pressures of the kerosene pump 3 and the condensate oil pump 4 .

[0080] The entire experimental device is placed in a constant temperature heating box to ensure constant temperature during the experiment. Two kerosene pumps and condensate oil pumps are used during the experiment to ensure the sample quantity during the experiment, taking into account the continuity and high temperature and high pressure characteristics of the experimental process. Two oil pumps are set up during the experiment to ensure the continuity of the experiment and avoid interruption of the experimental process due to insufficient supply of displacement fluid, which leads to large deviations in the experimental results.

[0081] The three-way valve 7 can effectively ensure the experimental process. The flow meter 6 is placed between the core holder 1 and the back pressure valve 10 to ensure that the flow meter operates at a constant pressure and reduce experimental errors. The temperature sensor and pressure sensors 5 and 9 ensure the accuracy of the experiment.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for studying the influence of wax deposition on the reservoir in a high wax condensate gas reservoir, characterized in that: Includes steps: Measure the wax precipitation temperature of sample condensate oil under reservoir pressure; Selecting a first core sample and a second core sample having similar porosity and core permeability; By injecting a first fluid into a first core sample, measuring a first permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a second permeability of the first core sample under an equidistantly decreasing temperature condition; By injecting condensate into the first core sample, measuring a third permeability of the first core sample under a first pressure condition and a constant temperature condition, and measuring a fourth permeability of the first core sample under an equidistantly decreasing temperature condition; Calculating the influence of the wax deposition on the reservoir according to the first permeability, the second permeability, the third permeability and the fourth permeability; The first fluid is kerosene; Under different pressure conditions, the influence of wax deposition on reservoir permeability is calculated as shown in formula (1): (1) Where L refers to the influence of wax deposition on reservoir permeability, %; K TN Refers to the third permeability of condensate oil at a constant temperature; K CN Refers to the fourth permeability of condensate at reservoir temperature; K TM Refers to the first permeability of kerosene at a constant temperature; K CM Refers to the second permeability of kerosene at reservoir temperature.

2. The method for studying the influence of wax deposition on the reservoir in a high wax condensate gas reservoir according to claim 1, characterized in that: Also includes the steps: measuring the pore parameters of the first core sample before the test; measuring pore parameters of the first core sample after the test; Whether the calculation result is accurate is verified according to the pore parameters of the first core sample before the test and the pore parameters of the first core sample after the test.

3. The method for studying the influence of wax deposition on the reservoir in a high wax condensate gas reservoir according to claim 1 or 2, characterized in that: Also includes the steps: Replacing the first core sample with a second core sample, changing the pressure value, injecting the first fluid into the second core sample, measuring the first permeability of the second core sample under the second pressure condition and the constant temperature condition, and measuring the second permeability of the second core sample under the condition of equidistantly decreasing temperature; By injecting condensate into the second core sample, measuring a third permeability of the second core sample under a second pressure condition and a constant temperature condition, and measuring a fourth permeability of the second core sample under an equidistantly decreasing temperature condition; The influence of the wax deposition on the reservoir of the second core sample under the second pressure condition is calculated according to the first permeability, the second permeability, the third permeability and the fourth permeability.

4. The method for studying the influence of wax deposition on the reservoir in a high wax condensate gas reservoir according to claim 1, characterized in that: The constant temperature condition is to maintain the temperature at 10°C higher than the wax precipitation temperature for 4 hours to ensure the temperature stability of the equipment.

5. The method for studying the influence of wax deposition on the reservoir in a high wax condensate gas reservoir according to claim 1, characterized in that: Before injecting condensate into the first core sample, the method further includes the step of cleaning the experimental equipment with petroleum ether.

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