Method for determining economic depth of heating cable for thin and heavy oil doped well and application of method

Abstract

The invention provides a method for determining the economic depth of a heating cable for a thin heavy oil doped well and application of the method, and relates to the field of heavy oil recovery. The method for determining the economical depth of the heating cable is a method for determining the depth of the cable through an actual thin oil blending dynamic isothermal point, and the thin oil blending dynamic isothermal point T1 and the corresponding well depth D1 are determined through actual production data when an oil well is only subjected to thin oil blending without heating the thin oil blending ratio C1; according to the previous cable heating viscosity reduction level of other heavy oil wells in the block, the blending ratio C2 of the to-be-constructed well after cable matching blending production is predicted, and when the C2 blending ratio is found through the blending ratio-viscosity-temperature curve, the oil well depth D2 corresponding to the thin oil isothermal point is the economic depth. And design is carried out from the angle of safety redundancy, oil well productivity release is considered, and the lower depth can be increased by 5-10% on the basis of D2. The method for determining the economical depth of the heating cable is applied to exploitation of thickened oil, the oil well productivity is improved, and the economic efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of heavy oil mining, and particularly relates to a method for determining the economic depth of a heating cable for a dilute heavy oil well and an application thereof. Background Art

[0002] In heavy oil production, after crude oil is extracted from the ground, its viscosity is low due to the high formation temperature, resulting in good fluidity. However, as the crude oil flows and cools on the surface, its viscosity gradually increases, affecting its transportation and processing. To maintain its fluidity, the crude oil is typically heated. For example, researchers in the field have proposed using electric heating combined with traditional dilution processes to exploit the strong thermal sensitivity of heavy oil viscosity to reduce its viscosity, allowing it to be smoothly lifted to the surface and enabling smooth production from heavy oil wells. However, this technology currently suffers from discrepancies between simulation and actual field production, and there are uncertainties regarding the cable's depth, its determination method, and the resulting economic benefits, limiting its practical application.

[0003] For example, Chinese invention patent CN112502678A discloses a method for optimizing construction parameters for a mineral-insulated cable heating process to reduce the viscosity of heavy oil. This patent optimizes process parameters based on a temperature field theoretical model, determines the appropriate cable depth and electric heating power, avoids excessive waste of development resources, and provides theoretical guidance for on-site construction. However, this patented method is merely a simulation method that requires the collection of a large number of parameters and suffers from significant discrepancies between simulation errors and actual production, making it unsuitable for actual production applications.

[0004] Chinese utility model patent CN207505163U discloses a mineral insulated cable heating device for heavy oil pipelines. Crude oil in the pipeline is heated by the mineral insulated heating cable to a temperature of 70-90°C, significantly reducing the viscosity of the crude oil. The cable length can be tailored to the length of the pipeline, meeting the need for long-distance, low-cost transportation of heavy oil with reduced viscosity. However, the patent does not address a method for determining the depth of the cable in the wellbore.

[0005] In "Application of Mineral Insulated Heating Cables in Tahe Super-Heavy Oil Production," Liang Zhiyan describes the application of a new mineral insulated heating cable. The proposed application method increased average well temperature by 35°C and reduced the average dilution-viscosity ratio by 46%. The authors conclude that mineral insulated heating cable technology, with its stable and reliable performance, effective temperature increase, and high dilution-oil savings, holds great potential for widespread application in Tahe super-heavy oil production. The five wells in which this technology was applied all had their run-down depths based on the viscosity-temperature inflection point, with an average run-down depth of 3,000 meters. However, the document standardizes the cable run-down depth to be below the viscosity-temperature inflection point, without any economic optimization. Therefore, applying the technology in this document does not necessarily lead to improved economic returns.

[0006] In his paper "Research on Heating Technology of Mineral-Insulated Cables for Ultra-Deep, Ultra-Heavy Oil in the Tahe Oilfield," Cheng Zhongfu details a new type of mineral-insulated cable with copper as the heating conductor. The cable, deployed at depths between 2200 and 2500 meters, was used in three wells in the Tahe Oilfield, resulting in an average increase in wellhead temperature of 37.8°C, outperforming conventional cables. This paper focuses on optimizing cable performance and does not examine its application at depths.

[0007] Therefore, in order to determine the economic depth of the heating cable, while improving the cable applicability and oil well productivity, and improving economic efficiency, the present invention provides an economically feasible method for determining the depth of the mineral insulated cable when laying a heavy oil well group, which has very important economic and technical significance in the study of the heavy oil production process. Summary of the Invention

[0008] In response to the problems existing in the prior art, the present invention provides a method for determining the economic depth of a heating cable for a thinned heavy oil well and its application. The method for determining the economic depth of a heating cable is a method for determining the cable depth by using the actual dynamic isothermal point of thinned oil. Specifically, the method comprises determining the dynamic isothermal point T1 of thinned oil when the oil well is only thinned without heating, the corresponding well depth D1, and the viscosity τ1 of the mixed liquid at this time by using actual production data; predicting the thinning ratio C2 of the cable to be constructed after thinning production based on the previous cable heating viscosity reduction levels of other heavy oil wells in the block; determining the economic depth of the oil well when the mixed oil viscosity reaches τ1 at the C2 thinning ratio through the thinning ratio-viscosity-temperature curve; and increasing the depth by 5-10% based on D2. The method for determining the economic depth of a heating cable is applied to the mining of heavy oil to improve the production capacity of oil wells, reduce the depth of the heating cable, and improve economic efficiency.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] In one aspect, the present invention provides a method for determining the economic depth of a heating cable for a thinned heavy oil well, wherein the method is based on the actual dynamic isothermal point of the thinned heavy oil, and comprises the following steps:

[0011] (1) Record the data of the oil well during normal production with diluted oil, determine the diluted oil ratio C1, the diluted oil wellhead temperature and the wellbore temperature change during stable production, monitor the depth D1 of the dynamic isothermal point of the diluted oil, and record the temperature T1 of the oil well at the depth D1;

[0012] (2) According to the dilution ratio of the oil well, the viscosity τ1 corresponding to the original normal production dilution ratio C1, depth D1, and temperature T1 of the well is determined by the dilution ratio-viscosity-temperature curve;

[0013] (3) Based on the previous cable heating viscosity reduction levels of other heavy oil wells in this block, the dilution ratio C2 of the cable in the well to be constructed after dilution production is predicted;

[0014] (4) Determine the corresponding temperature T2 when the dilution ratio is C2 and the viscosity of the mixed liquid is τ1 through the dilution ratio-viscosity-temperature curve of the oil well to be constructed;

[0015] (5) Based on the production temperature measurement data, determine the lower depth D2 corresponding to the temperature T2 when producing at the dilution ratio C1;

[0016] (6) Determine the depth D3 corresponding to the viscosity-temperature inflection point of the original heavy oil in the oil well based on the completion data;

[0017] (7) Finally confirm the effective depth range and economic depth of the cable.

[0018] Preferably, the dynamic isothermal point is the isothermal point after the cable is lowered into a deeper position and the dilution ratio is reduced.

[0019] Preferably, in step (2), the viscosity τ1 is the viscosity τ1 of the system after the thin oil and the formation production fluid are mixed.

[0020] Preferably, in step (3), the cable is a mineral insulated cable.

[0021] Preferably, in step (3), the predicted dilution ratio C2 of the cable in the well to be constructed after dilution production is based on the average-limit use effect of the cable in the block to which the oil well to be constructed belongs as the viscosity reduction target, that is, the degree of reduction in the dilution ratio after the cable is lowered is determined by the average-limit level of the cables used in other oil wells in the oil well block.

[0022] Preferably, in step (5), the production temperature measurement data is actually obtained through production logging.

[0023] Preferably, in step (6), the completion data is actually obtained through completion testing.

[0024] Preferably, in step (6), the viscosity-temperature inflection point is obtained by measuring viscosity-temperature data.

[0025] Preferably, in step (7), the effective depth range is between D1 and D3, and the economic depth is D2.

[0026] Further preferably, from the perspective of safety redundancy, the lower depth is increased by 5-10% on the basis of D2.

[0027] More preferably, the lower depth is increased by 5% based on D2.

[0028] In the present invention, the method for determining the economic depth of the heating cable takes into account the possibility of releasing the production capacity of the oil well on the basis of normal production.

[0029] On the other hand, the present invention provides an application of the above-mentioned method for determining the economic depth of the heating cable in heavy oil production.

[0030] Preferably, the method for determining the economical depth of the heating cable in the application is a method for determining the cable depth through the actual dilution dynamic isothermal point; the effective depth range of the heating cable is between D1-D3, and the economical depth is D2.

[0031] Further preferably, in the application, from the perspective of safety redundancy, the depth is increased by 5-10% based on D2.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The method for determining the economic depth of the heating cable of the present invention is a method for determining the cable depth through the actual dynamic isothermal point of the diluted oil, which not only improves the oil well productivity, but also reduces the depth of the heating cable, thereby improving economic efficiency; the possible release of oil well productivity is taken into account on the basis of normal production.

[0034] 2. The method for determining the economic installation depth of a heating cable according to the present invention provides an economically feasible method for determining the installation depth of a mineral insulated cable when installing it in a heavy oil well group. In actual heavy oil production applications, the cable installation depth is reduced by 33.3% compared to the historical average, and the cable power utilization rate is increased from 66% to over 80%. The dilution ratio is reduced by 43.5%, and the oil well production capacity is increased by 25.7%. The heating effect is consistent with the historical average. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a viscosity-temperature curve diagram of different dilution ratios of a certain well in Tahe Oilfield S according to the present invention. DETAILED DESCRIPTION

[0036] The following non-limiting examples can make those of ordinary skill in the art understand the present invention more comprehensively, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of protection of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and they should also fall within the scope of protection of the present invention. When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified in the present invention, the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those of ordinary skill in the art to which the present invention belongs.

[0037] The present invention will be further described below by way of specific embodiments.

[0038] Example 1

[0039] This embodiment provides a method for determining the economic depth of a heating cable for a thin-oil-doped heavy oil well. The method is based on the actual dynamic isothermal point of the thin-oil-doped heavy oil well to determine the cable depth, including the following steps:

[0040] (1) Record the data of the oil well during normal production with diluted oil, determine the diluted oil ratio C1, the diluted oil wellhead temperature and the wellbore temperature change during stable production, monitor the depth D1 of the dynamic isothermal point of the diluted oil, and record the temperature T1 of the oil well at the depth D1;

[0041] (2) According to the dilution ratio of the oil well, the viscosity τ1 of the system after the dilution ratio and formation fluid are mixed at the original normal production dilution ratio C1, depth D1, and temperature T1 of the well is determined by the dilution ratio-viscosity-temperature curve;

[0042] (3) Based on the previous cable heating viscosity reduction levels of other heavy oil wells in this block, the dilution ratio C2 of the cable in the well to be constructed after dilution production is predicted;

[0043] (4) Determine the corresponding temperature T2 when the dilution ratio is C2 and the viscosity of the mixed liquid is τ1 through the dilution ratio-viscosity-temperature curve of the oil well to be constructed;

[0044] (5) Obtaining production temperature measurement data through production logging, and determining the depth D2 corresponding to the temperature T2 when producing at a dilution ratio C1 based on the production temperature measurement data;

[0045] (6) obtaining completion data through completion testing, and determining the depth D3 corresponding to the viscosity-temperature inflection point of the original heavy oil in the oil well (obtained through viscosity-temperature data measurement) based on the completion data of the oil well;

[0046] (7) Finally confirm the effective cable depth range D1-D3 and the economic depth D2; considering the safety redundancy, the depth is increased by 5-10% based on D2.

[0047] A 5% increase in depth is preferred.

[0048] Example 2

[0049] The method for determining the economic run-down depth of a heating cable for a thinned heavy oil well, described in Example 1, was applied to heavy oil production at Well S in the Tahe Oilfield. The economic run-down depth of the heating cable was determined, improving economic efficiency and cable power utilization. Well S is a development well in Block 10 of the Tahe Oilfield, drilled to a depth of 6,200 meters. Testing of heavy oil samples taken after completion revealed that the viscosity-temperature inflection point corresponded to a depth of 2,745 meters. The original run-down depth of the cable was 3,000 meters.

[0050] Before the mineral insulated cable was laid, the company used dilute blending to produce 35 tons of liquid, 35 tons of oil, and 65 tons of dilute blending per day. The temperature monitoring system indicated a wellhead produced fluid temperature of 48°C, with the dilute oil dynamic isotherm at 58°C, corresponding to a well depth of 879 meters.

[0051] The viscosity-temperature curves of different dilution ratios of a certain well S show that the viscosity of the produced fluid with a dilution ratio of 1.86 is 1531mPa.s at 58°C while ensuring normal external transportation from the wellhead. For details, see Figure 1 .

[0052] Statistics on other mineral insulated cables used in the S block of the Tahe Oilfield show that cable heating reduces the dilution ratio by an average of 33%, with a maximum of 46%. Based on this, it is predicted that the dilution ratio in other construction wells can be reduced to a maximum of 1.00 after cable heating. A query of the family curves of different dilution ratios for this well (S well) shows that the corresponding temperature is approximately 70°C when the dilution ratio is 1.00 and the mixed liquid viscosity is 1531mPa.s (see for details). Figure 1 ).

[0053] The temperature monitoring system showed that the temperature of the oil well before the mineral insulated cable was lowered was 70℃, corresponding to a depth of 1901m in the D2 well.

[0054] Taking into account the overall increase in wellbore temperature after the mineral insulated cable is installed and the oil well productivity will increase after the dilution ratio is reduced, the cable depth is lowered by 5% to 2000m from the perspective of stable production of the oil well and safety redundancy.

[0055] The mineral insulated cable was lowered to 2000m, and the well was started for production according to the original dilution ratio. The electric heating device was started and the dilution ratio was gradually reduced to stabilize the various parameters of the mineral cable until the power utilization rate reached 80%. The dilution ratio was further adjusted until the viscosity of the mixed liquid at the wellhead was 3000mPa.s.

[0056] Through the method for determining the economic depth of the heating cable described in the present invention, the oil well currently produces 44t / d, the dilution rate is 46t / d, the wellhead temperature is 76°C, the production is stable, and it is still in effective operation.

[0057] Using the method for determining the economical depth of a heating cable, the cable run depth in this well was reduced by 33.3% compared to the historical average, and the cable power utilization rate increased from 66% to over 80%. The dilution ratio decreased by 43.5%, and the oil well productivity increased by 25.7%, with the heating effect consistent with the historical average.

[0058] Cable depth reduction rate % = (original cable depth - current cable depth) / original cable depth × 100% = (3000-2000) / 3000 × 100% = 33.3%.

[0059] Lean ratio reduction rate (%) = (original lean ratio - current lean ratio) / original lean ratio = (65÷35-46÷44) / (65÷35) = 43.5%; Lean ratio = daily lean ratio / daily oil production.

[0060] Comparative Example 1

[0061] The traditional method of determining the depth of the heating cable can only determine the effective depth range of the heating cable, but cannot accurately determine the economic depth, resulting in a reduced proportion of the effective heating section of the cable, which is not economically applicable. In addition, the reduction in the dilution ratio is limited, and oil production has not increased significantly, failing to achieve the purpose of saving dilute oil and releasing formation production capacity.

[0062] According to experience, in a heavy oil-blocked well, a mineral insulated cable was lowered to a depth of 3000m, where the viscosity-temperature inflection point of heavy oil in a well in the tenth district of Tahe is located. The parameters before and after the cable was used are shown in Table 1:

[0063] Table 1

[0064]

[0065]

[0066] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for determining the economic depth of a heating cable for a thin-coated heavy oil well, characterized in that: The method of determining the cable depth by the actual dynamic isothermal point of diluted oil includes the following steps: (1) Record the data of the oil well during normal production with diluted oil, determine the diluted oil ratio C1, the diluted oil wellhead temperature and the wellbore temperature change during stable production, monitor the depth D1 of the dynamic isothermal point of the diluted oil, and record the temperature T1 of the oil well at the depth D1; (2) According to the dilution ratio of the oil well, the viscosity τ1 corresponding to the original normal production dilution ratio C1, depth D1, and temperature T1 of the well is determined by the dilution ratio-viscosity-temperature curve; (3) Based on the previous cable heating viscosity reduction levels of other heavy oil wells in this block, the dilution ratio C2 of the cable in the well to be constructed after dilution production is predicted; (4) Determine the corresponding temperature T2 when the dilution ratio is C2 and the viscosity of the mixed liquid is τ1 through the dilution ratio-viscosity-temperature curve of the oil well to be constructed; (5) Based on the production temperature measurement data, determine the lower depth D2 corresponding to the temperature T2 when producing at the dilution ratio C1; (6) Determine the depth D3 corresponding to the viscosity-temperature inflection point of the original heavy oil in the oil well based on the completion data; (7) Finally confirm the effective depth range and economic depth of the cable.

2. The method for determining the economic depth of a heating cable according to claim 1, characterized in that: The dynamic isothermal point is the isothermal point after the cable is lowered into a deeper position and the dilution ratio is reduced.

3. The method for determining the economic depth of a heating cable according to claim 1, characterized in that: In step (3), the predicted dilution ratio C2 of the cable in the well to be constructed after dilution production is based on the average-limit use effect of the cable in the block to which the well to be constructed belongs as the viscosity reduction target, that is, the degree of reduction in the dilution ratio after the cable is laid deep is determined by the average-limit level of the cables used in other oil wells in the oil well block.

4. The method for determining the economic depth of a heating cable according to claim 1, characterized in that: The production temperature measurement data described in step (5) is actually obtained through production logging; the completion data described in step (6) is actually obtained through completion testing.

5. The method for determining the economic depth of a heating cable according to claim 1, characterized in that: In step (6), the viscosity-temperature inflection point is obtained by measuring viscosity-temperature data.

6. The method for determining the economic depth of a heating cable according to claim 1, characterized in that: In step (7), the effective depth range is between D1 and D3, and the economic depth is D2.

7. The method for determining the economic depth of a heating cable according to claim 6, characterized in that: From the perspective of safety redundancy, the depth is increased by 5-10% based on D2.

8. Application of the method for determining the economic depth of a heating cable according to any one of claims 1 to 7 in heavy oil production.

9. The use according to claim 8, characterized in that The method for determining the economical lower depth of the heating cable in the application is a method for determining the lower depth of the cable through the actual dilution dynamic isothermal point.

10. The use according to claim 9, characterized in that The economical depth of the heating cable is D2, and the effective depth range of the heating cable is between D1 and D3. From the perspective of safety redundancy, the depth is increased by 5-10% on the basis of D2.

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