Natural selection dessert and fracturing construction method for dual-medium oil reservoir

Abstract

The invention belongs to the technical field of petroleum and natural gas development, and provides a natural dessert selection and fracturing construction method for a dual-medium oil reservoir. According to the method, the perforation position and the bridge plug position are selected by preliminarily judging gas logging parameters, the minimum horizontal principal stress difference and the brittleness index, perforation and bridge plug placement are carried out, and natural dessert selection is completed; then, large-displacement slick water is combined with small-particle-size quartz sand for fracturing construction; according to the method, the technical thought that the dominant reservoir is fully transformed through in-section multi-cluster natural selection desserts is determined, full transformation of the dominant reservoir is guaranteed under the condition that the fracturing scale and cost are not increased, and meanwhile, large-displacement slick water is combined with a small-particle-size quartz sand propping agent to effectively support a fracture network; and the potential of the dual-medium oil reservoir is fully exerted.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas development, and relates to a dual-medium reservoir natural selection sweet spot and a fracturing construction method. Background Art

[0002] Volume fracturing technology is an important measure to increase the production of tight oil and gas reservoirs, but the effect of some fracturing is poor. In order to improve the development efficiency, it is necessary to strengthen the research and analysis of reservoir geological characteristics and fracturing properties, and establish the optimization criteria of volume fracturing "sweet spots" to achieve the optimal fracturing layer section.

[0003] Chinese invention patent CN109102180B discloses a comprehensive parameter evaluation method for double sweet spot evaluation of tight sandstone reservoirs. By establishing a multi-parameter three-dimensional geological model, introducing the analytic hierarchy process and fuzzy comprehensive evaluation, and carrying out transformation and integration that meet the needs of "double sweet spot" evaluation, the ambiguity and inconsistency of manual judgment and other problems are solved, and the reliability of "sweet spot" evaluation is improved; the disadvantage is that the steps of establishing the three-dimensional model are relatively complicated, and this method is aimed at the "sweet spot" evaluation of tight sandstone reservoirs and is not suitable for other reservoirs.

[0004] Chinese invention patent CN112282750B discloses a method for comprehensive identification of geological-engineering double sweet spots in shale gas reservoirs. The method determines the geological-engineering double sweet spot comprehensive evaluation factor based on the geological sweet spot evaluation factor of the shale gas reservoir, the engineering sweet spot evaluation factor of the shale gas reservoir and the evaluation factor of the degree of natural fracture development, and then comprehensively identifies the geological-engineering double sweet spots of the shale gas reservoir based on the geological-engineering double sweet spot comprehensive evaluation factor. The identification method is comprehensive and belongs to a method for calculating the absolute geological-engineering comprehensive sweet spot identification factor of the shale gas reservoir. The evaluation result is suitable for vertical and horizontal comparison between different blocks of shale gas promotion, but the disadvantage is that it is only for shale reservoirs.

[0005] Chinese invention patent CN103835691B discloses a volume fracturing method for temporary plugging of sweet spots by natural selection. According to the size and direction of the in-situ stress preset on the length of the horizontal section, the horizontal well orientation, length, reservoir Young's modulus, Poisson's ratio and logging interpretation results data, the reservoir stress profile distribution is obtained. After determining the horizontal well segmentation plan, the packer segment is lowered to naturally select the sweet spot in each target segment to open multiple fractures. After the fractures are opened, a high-strength water-soluble granular temporary plugging agent is added to complete the preset number of fractures in the target segment. This method is suitable for horizontal well fracturing and repeated fracturing transformation of various old wells. The disadvantage is that it is only for open hole packer ball sleeve temporary plugging fracturing, and cannot be applied to cemented wells.

[0006] Well logging data can guide oil and gas exploration and play an important role in the process of oil and gas exploration and development. It can not only timely discover and evaluate oil and gas layers, but also is the most direct and effective means to discover and evaluate oil and gas reservoirs. Well logging data contains relevant data such as the spatial coordinate position, direction, orientation of the left static equipment and the address attribute characteristics of the rock formations around the drilling, which contains a large amount of rich geological information.

[0007] However, volcanic reservoirs have complex lithology and lithofacies, and strong heterogeneity, making it difficult to identify sweet spots in volcanic reservoirs with conventional logging. In the early stage, horizontal wells mainly adopted the fracturing mode of continuous tubing dragging staged fracturing + cluster spacing of about 40m, or bridge plug perforation staged fracturing + single stage 2 clusters + cluster spacing of 35-40m. The cluster spacing is relatively large, which reduces the possibility of contacting the dominant reservoir and easily leads to insufficient reservoir transformation. The transformation effect is highly correlated with the dominant lithofacies and natural fracture distribution. There is an urgent need for a fracturing sweet spot selection method suitable for volcanic dual-medium reservoirs. Summary of the invention

[0008] In order to solve the problem that the existing technical methods are not applicable to volcanic rock dual-medium oil reservoirs, the present invention provides a dual-medium oil reservoir natural selection sweet spot and fracturing construction method, determines the technical idea of ​​fully transforming the dominant reservoir through multiple clusters of natural selection sweet spots in the segment, and expands natural fractures and forms effective support through a pumping process using large-volume slick water combined with small-particle quartz sand construction, thereby giving full play to the potential of dual-medium oil reservoirs.

[0009] One of the technical solutions of the present invention is:

[0010] A method for naturally selecting a sweet spot in a dual-medium oil reservoir comprises the following steps:

[0011] (1) Collect well logging data and gas logging data, and calculate the minimum horizontal stress difference and brittleness index through the well logging data;

[0012] (2) Selecting perforation locations and perforations: Select locations where the total hydrocarbon content in the gas logging data is greater than 1000 ppm, the minimum horizontal principal stress difference is ≤5 MPa, and the brittleness index is greater than 40%, and perforate;

[0013] (3) Select the bridge plug location and place the bridge plug: Select the bridge plug location and place the bridge plug according to the principle that the distance between the bridge plug and the casing collar should be more than 2 m and the bridge plug should not be in the same casing as the perforation cluster;

[0014] (4) COMPLETE NATURAL SELECTION DESSERT.

[0015] Furthermore, after selecting the perforation positions in step (2), perforation is performed according to the length of each section being 90-110 m, 4-6 perforation clusters per section, and 6-8 holes per cluster.

[0016] Furthermore, the perforation adopts the first section of continuous tubing transmission perforation to establish a channel between the wellbore and the reservoir, and the remaining section of hydraulic pumping cable transmission perforation.

[0017] Furthermore, the outer diameter of the perforating gun is 86 mm or 89 mm, and it uses equal-aperture perforating bullets or deep-penetrating perforating bullets, with spiral hole arrangement and a phase angle of 60°.

[0018] Further, in step (1), the logging data is obtained after the well is drilled, including: density and acoustic wave time difference;

[0019] The gas logging data is the total hydrocarbon content, which is obtained through gas logging; the total hydrocarbons include: total hydrocarbons, methane, ethane, propane, n-butane, isobutane, n-pentane and isopentane;

[0020] The minimum horizontal principal stress is calculated from the density and acoustic wave time difference in the well logging data;

[0021] The brittleness index is calculated from Young's modulus and Poisson's ratio. The Young's modulus is calculated from density and acoustic wave time difference in well logging data. The Poisson's ratio is calculated from acoustic wave time difference in well logging data.

[0022] Furthermore, the slick water pumping process is: using slick water to carry 40-70 mesh quartz sand to press open the reservoir to form a fracture network support.

[0023] The present invention uses a large amount of slick water combined with small-diameter quartz sand for construction, expanding natural cracks and forming effective support. 3 / min large displacement, open and expand natural fractures, form complex fracture network; 40-70 mesh small-size quartz sand proppant is used to effectively support the fracture network, giving full play to the potential of dual-media reservoirs.

[0024] Furthermore, the amount of sand added in the pumped slickwater process is designed to open two cracks, with 45-50m3 of sand added to each crack. 3 , add 90-100m of sand per section 3 .

[0025] By comparing and analyzing the previous horizontal wells, it was found that the cluster spacing had little effect on the production of Carboniferous horizontal wells; the fiber optic monitoring outside the pipe showed that 3-6 clusters of fracturing in the section could be opened, but the main expansion was in 2 clusters, and temporary plugging had limited effect on adjusting the balance of each cluster in the Carboniferous reservoir section; thus, the technical idea of ​​fully transforming the dominant reservoir through the natural selection of sweet spots by multiple clusters in the section was determined, and the amount of sand added was designed according to opening 2 fractures, and 45-50m of sand was added to each fracture. 3 , single stage sand adding 90-100m 3, ensuring full transformation of the advantageous reservoir without increasing the scale and cost of fracturing.

[0026] The second technical solution of the present invention is:

[0027] A fracturing construction method based on a naturally selected sweet spot is provided, that is, fracturing construction is performed in a naturally selected sweet spot area, specifically comprising the following steps:

[0028] S1: Set safe construction pressure;

[0029] S2: Pre-fluid stage: using slippery water to initiate fracture;

[0030] S3: Determine whether the construction pressure reaches the safe construction pressure. If so, take pre-slug treatment to treat multiple cracks near the wellbore and grind the perforation holes to reduce the construction pressure; and proceed to the next step; if not, directly proceed to the next step;

[0031] S4: Sand carrying stage: using slippery water to carry sand;

[0032] S5: Determine the pressure fluctuation range during the sand adding process: ① Pressure fluctuation range ≤ 3MPa, continue to add sand, the highest sand concentration is 330-360kg / m 3 ;②3MPa≤Pressure fluctuation range<6MPa, sand concentration reduction value is 60-120kg / m 3 ③ Pressure fluctuation range ≥ 6MPa, stop sand, replace, wait for the pressure to stabilize and be lower than 60-120kg / m before stopping sand replacement 3 Continue adding sand;

[0033] S6: Construction completed.

[0034] Furthermore, in step S3, the specific operation of reducing the construction pressure is: using 3-5 slugs and a sand concentration of 30-120 kg / m 3 , total dosage 3-5m 3 1-1.5 wellbore volumes of fracturing fluid are injected between each segment plug to displace the segment plug into the fracture.

[0035] Furthermore, in step S4, the sand carrying stage is carried out at a rate of 30-90 kg / m 3 Sand concentration starts to be added, and the sand concentration increases by 30-40kg / m3 each time during the sand adding process 3 .

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The sweet spot identification method of the present invention is obtained through continuous summary and iterative progress in field practice, which can effectively solve the problem of difficult selection of sweet spots in volcanic rock dual-medium reservoirs; and by fully transforming the sweet spots in the fracture development zone, it provides a new idea for increasing oil recovery;

[0038] 2. The present invention improves the contact rate of natural fractures by multi-cluster perforation, realizes the natural selection of sweet spots in the fracturing section of horizontal wells in volcanic rock reservoirs, is easy to use and has wide applicability;

[0039] 3. Compared with the control wells, the multi-cluster naturally selected sweet spot wells in the segment of the present invention have high initial production and long-term stable production capabilities, which fully proves the effectiveness of this method; compared with the previous conventional segment length of about 70m, the segment length of 90-110m in this method can greatly reduce the number of fracturing stages; according to calculations, the horizontal segment length of 1200m greatly reduces the fracturing cost, which has a significant cost-reducing and efficiency-increasing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the overall flow chart of the natural selection of sweet spots and fracturing construction of the present invention;

[0041] Figure 2 It is a schematic diagram of the process of pumping slippery water according to the present invention. DETAILED DESCRIPTION

[0042] The following non-limiting examples can enable ordinary technicians in the field to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of protection claimed by the present invention. Those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of protection claimed by the present invention;

[0043] Combine the following Figure 1 The natural selection dessert and pumping construction process shown and Figure 2 The schematic diagram of the process of pumping slick water is used to further illustrate the present invention in the form of a specific embodiment.

[0044] Example

[0045] Take a horizontal well in a Carboniferous reservoir in Xinjiang Oilfield as an example: Figure 1 The process shown is to carry out natural selection of sweet spots and pumping construction, the specific steps are:

[0046] (1) Collect the conventional logging data and gas logging data of the well, and calculate the minimum horizontal stress difference and brittleness index through the logging data;

[0047] (2) Select the perforation location:

[0048] Select the location where the total hydrocarbon content in the gas logging data is greater than 1000ppm, the minimum horizontal principal stress difference is less than or equal to 5MPa, and the brittleness index is greater than 40%;

[0049] According to the collected data, the minimum horizontal principal stress of 17.1-22.8MPa, the brittleness index of 40.6%-95.1%, and the gas test of 1070-53710ppm can meet the requirements, and the results are shown in Table 1. Perforation is carried out; the perforation position results are shown in Table 2. As shown in Table 2, 2 clusters are perforated in the first section, 5 clusters are perforated in the fourth and sixth sections respectively, and 4 clusters are perforated in the remaining sections;

[0050] Table 1 Reservoir parameter data table

[0051]

[0052] (3) Select the bridge plug location:

[0053] According to the principle that the bridge plug and casing collar should be kept at least 2m away and not be in the same casing as the perforation cluster, the bridge plug placement position is selected, see Table 2;

[0054] In this embodiment, the distance between each level of bridge plug and coupling is 3.09-5.4m;

[0055] The results of segmentation and clustering of the horizontal well are shown in Table 2. The length of the transformation is 1294.0 m (1346.0-2639.79 m), which is divided into 12 segments and 48 clusters. The segment spacing is 69.0-136.0 m, with an average of 107.8 m; the cluster spacing is 20.0-46.0 m, with an average of 26.8 m. There are 4 clusters in the main single segment and 5 clusters at most.

[0056] Table 2. Clustering of horizontal wells in natural selection sweet spot mode

[0057]

[0058] (4) Fracturing construction:

[0059] Combined with Figure 2 The pumping method shown in the figure is used for the slick water pumping construction. The specific pumping steps of this embodiment are as follows:

[0060] ① According to the casing's internal pressure resistance and the pressure bearing capacity of the wellhead device, a construction pressure limit is set, under which the casing's internal pressure resistance safety factor is greater than 1.25; at the same time, a safe construction pressure is set, which is about 10MPa less than the construction pressure limit.

[0061] ② In the pre-fluid stage, slick water liquid is used to initiate cracking, with a dosage of 80m 3 ;

[0062] ③At this time, the construction pressure reaches the safe construction pressure, and the displacement is less than 8m 3 / min, adopt pre-segment plug treatment to deal with multiple fractures near the wellbore and grind the perforation holes to reduce the construction pressure. The number of segment plugs is 4, and the sand concentration is 50kg / m 3 , total consumption 4m 3 , inject one wellbore volume of fracturing fluid between each segment plug to displace the segment plug into the fracture;

[0063] ④ In the sand-carrying stage, slippery water is used to carry sand at a rate of 50 kg / m 3 Sand concentration starts to be added, and the sand concentration increases by 30kg / m at each stage 3 ;

[0064] ⑤ During the sand adding process, the pressure fluctuation does not exceed 3MPa. Continue to add sand, and the maximum sand concentration is 330kg / m 3 ;

[0065] ⑥Complete the construction.

[0066] This method was applied to 28 wells in the deep Carboniferous reservoirs in Area 1 and the Carboniferous reservoirs in the Che 43 well area in one year, and 26 wells reached the designed production capacity; the average daily oil production of the multi-cluster natural selection sweet spot wells in the segment was 7.9t in 60 days, 13.8t in 180 days, and 17.1t in one year. The average daily oil production of the comparison wells in the same block was 5.0t in 60 days, 9.1t in 180 days, and 11.8t in one year; according to statistics, the average daily oil production of the multi-cluster natural selection sweet spot wells in the segment increased by about 45% in one year compared with the comparison wells in the same block; therefore, the natural selection sweet spot mode has the ability to maintain long-term stable production, which fully proves the effectiveness of this method. At the same time, compared with the previous conventional segment length of about 70m, the segment length of 90-110m in this method can greatly reduce the number of fracturing stages, and the fracturing cost is reduced by 30%, which has a significant cost-reducing and efficiency-increasing effect.

[0067] 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 dual medium reservoir natural selection sweet spot method, characterized in that: The following steps are involved: (1) Collect well logging data and gas logging data, and calculate the minimum horizontal stress difference and brittleness index through the well logging data; (2) Selecting perforation locations and perforations: Select locations where the total hydrocarbon content in the gas logging data is greater than 1000 ppm, the minimum horizontal principal stress difference is ≤5 MPa, and the brittleness index is greater than 40%, and perforate; (3) Select the bridge plug location and place the bridge plug: Select the bridge plug location and place the bridge plug according to the principle that the distance between the bridge plug and the casing collar should be more than 2 m and the bridge plug should not be in the same casing as the perforation cluster; (4) COMPLETE NATURAL SELECTION DESSERT.

2. The method according to claim 1, characterized in that In step (2), after selecting the perforation positions, perforation is performed according to the length of each section of 90-110 m, 4-6 clusters of perforations per section, and 6-8 holes per cluster.

3. The method according to claim 2, characterized in that The perforation adopts the first section of continuous tubing transmission perforation to establish a channel between the wellbore and the reservoir, and the remaining section of hydraulic pumping cable transmission perforation.

4. The method according to claim 2, characterized in that: The perforating gun has an outer diameter of 86 mm or 89 mm, uses equal-aperture perforating bullets or deep-penetrating perforating bullets, has spiral hole arrangement, and a phase angle of 60°.

5. The method according to claim 1, characterized in that The logging data include: density and acoustic wave time difference; The gas measurement data is the total hydrocarbon content; the total hydrocarbons include: methane, ethane, propane, n-butane, isobutane, n-pentane and isopentane; The minimum horizontal principal stress is calculated from the density and acoustic wave time difference in the well logging data; The brittleness index is calculated from Young's modulus and Poisson's ratio. The Young's modulus is calculated from density and acoustic wave time difference in well logging data. The Poisson's ratio is calculated from acoustic wave time difference in well logging data.

6. The method according to claim 1, characterized in that The second stage of slickwater pumping technology is: use slickwater to carry 40-70 mesh quartz sand to press open the reservoir and form a fracture network support.

7. The method according to claim 6, characterized in that The pumping slick water process is as follows: the amount of sand added is designed according to opening two cracks, and 45-50m3 of sand is added to each crack. 3 , add 90-100m of sand per section 3 .

8. A fracturing construction method based on natural selection sweet spots, characterized in that: The fracturing operation is carried out in the naturally selected sweet spot area, which specifically includes the following steps: S1: Set safe construction pressure; S2: Pre-fluid stage: using slippery water to initiate fracture; S3: Determine whether the construction pressure reaches the safe construction pressure. If so, take pre-slug treatment to treat multiple cracks near the wellbore and grind the perforation holes to reduce the construction pressure; and proceed to the next step; if not, directly proceed to the next step; S4: Sand carrying stage: using slippery water to carry sand; S5: Determine the pressure fluctuation range during the sand adding process: ① Pressure fluctuation range ≤ 3MPa, continue to add sand, the highest sand concentration is 330-360kg / m 3 ;②3MPa≤Pressure fluctuation range<6MPa, sand concentration reduction value is 60-120kg / m 3 ③ Pressure fluctuation range ≥ 6MPa, stop sand, replace, wait for the pressure to stabilize and be lower than 60-120kg / m before stopping sand replacement 3 Continue adding sand; S6: Construction completed.

9. The method according to claim 8, characterized in that In step S3, the specific operation of reducing the construction pressure is: using 3-5 slugs and a sand concentration of 30-120 kg / m 3 , total dosage 3-5m 3 1-1.5 wellbore volumes of fracturing fluid are injected between each segment plug to displace the segment plug into the fracture.

10. The method according to claim 8, characterized in that In step S4, the sand carrying stage is carried out at a rate of 30-90 kg / m 3 Sand concentration starts to be added, and the sand concentration increases by 30-40kg / m3 each time during the sand adding process 3 .

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