A fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs

Abstract

The present invention discloses a fracturing-water plugging process method for the development of ultra-low permeability fractured oil reservoirs, comprising the following steps: S1, determining the direction of water penetration; S2, unidirectional water penetration and water plugging fracturing: S2-1, original fracture plugging; S2-2, potential layer fracturing; S3, bidirectional water penetration and water plugging fracturing: S3-1, original fracture plugging; S3-2, potential layer fracturing; S4, multi-directional water penetration and water plugging fracturing: S4-1, original fracture plugging; S4-2, potential layer fracturing. The method of the present invention is mainly aimed at the different directions of water penetration in the well of ultra-low permeability fractured oil reservoirs, and provides a variety of construction schemes, reasonably selects corresponding water plugging construction parameters according to the direction of water penetration, and optimizes the formula of fracturing fluid after water plugging, provides fracturing fluid that meets the ultra-low permeability fractured oil reservoir, and monitors the slope of the relationship curve between the length of the seam and the pressure and time in real time during the fracturing process, adjusts the optimal fracturing parameters, and plays a guiding role in the development of ultra-low permeability fractured oil reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic fracturing and production increase, and in particular to a fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs. Background Art

[0002] Low permeability oil fields refer to oil fields with low permeability, low abundance, and low single-well production capacity in the oil layer reservoir. Low permeability oil and gas fields are of great significance in my country's oil and gas development. The distribution of low permeability oil and gas resources in my country is characterized by high oil and gas content, multiple oil and gas reservoir types, wide distribution area, and "upper gas and lower oil, mainly marine gas, and both terrestrial oil and gas". Among the proven reserves, the proportion of low permeability oil reservoirs is very high, accounting for more than 2 / 3 of the national reserves, and the development potential is huge. However, low permeability oil fields are difficult to exploit, and the high water content in the later stage of development has always been a difficult problem to solve. Especially for ultra-low permeability oil reservoirs, the permeability is lower, the pore structure is worse, and the exploitation of ultra-low permeability oil reservoirs with developed fractures is more difficult.

[0003] Hydraulic fracturing is a measure to increase the production of oil and gas wells with broad application prospects. Hydraulic fracturing is the main form of oil and natural gas extraction. A large amount of water mixed with chemicals is injected into the rock formation for hydraulic fracturing to release oil and gas. In the process of oil field development, water production in the oil layer will have a serious impact on the development of the oil field and even reduce the final recovery rate of the oil field. After the oil well produces water, the water-producing layer is first determined, and then the water plugging method is used to plug it. The purpose of water plugging is to control the flow of water in the water-producing layer and change the flow direction of water in water-driven oil, improve the efficiency of water-driven oil, and try to make the water production of the oil field decrease or stabilize over a period of time, so as to maintain the increase or stable production of the oil field and improve the final recovery rate of the oil field.

[0004] There is no systematic fracturing-water plugging process for ultra-low permeability fractured reservoirs. The invention patent with announcement number CN111963132B discloses a method for controlling water and increasing oil production by water plugging and fracturing in the same layer of newly drilled infilled wells in the mid-term of low permeability water injection development. First, the extension law of artificial fractures in hydraulic fracturing in the infilled area is clarified, and the fracture scale that achieves the target production of a single well is designed under the conditions of the infilled well network. The main controlling factors affecting the morphology of artificial fractures in hydraulic fracturing under the conditions of water injection status and ground stress in the infilled area are determined, and water plugging materials are selected, pumping timing, pumping mode, main fracturing construction method steps, etc. are optimized, and a single upper sealing pipe string is lowered to complete the fracturing construction in one continuous operation, and the well is shut down according to the properties of the water plugging material, and the suction intensity is controlled. After stabilization, the pump is lowered for production. Although this patent is an effective way to increase the production of a single well and control water or flooding in high water-seeping risk areas, there is still no systematic development method for the downhole environment with different water-seeping directions for ultra-low permeability fractured reservoirs. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention provides a fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs.

[0006] The technical solution of the present invention is:

[0007] A fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs, comprising the following steps:

[0008] S1. Determine the direction of water breakthrough: Detect the direction of water breakthrough of the oil production well. If the water breakthrough layer is a single stratigraphic level, the water breakthrough direction of the oil production well is determined to be unidirectional. If the water breakthrough layer is two adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be bidirectional. If the water breakthrough layer is more than two stratigraphic levels or two non-adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be multidirectional.

[0009] S2, one-way water-blocking fracturing:

[0010] S2-1. Sealing the original fractures: First, place the packer at the original fractures, inject light mud to displace the original fractures, and then inject polymer microspheres to seal the small pores at the inner ends of the original fractures. Then, inject the pre-gel plugging fluid, enhanced plugging fluid, and post-gel plugging fluid in sequence, and finally inject cement to seal the original fractures, and shut down the well for solidification.

[0011] S2-2, potential layer fracturing: find 1 to 2 potential layers within 20m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of perforations for each potential layer is 2 to 4, and the fracturing fluid displacement is 0.3 to 0.6m 3 / min, the crack length is 30-90m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.35*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.55*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 1*(real-time crack length / expected crack length), the pump is stopped;

[0012] S3, bidirectional water-blocking fracturing:

[0013] S3-1. Sealing the original fractures: Seal the two original fractures in sequence. First, place the packer at the original fracture, inject light mud to displace the original fracture, and then inject polymer microspheres to seal the small pores at the end of the original fracture. Then, inject gel sealing fluid and enhanced sealing fluid in sequence, and finally inject cement to seal the original fracture. Then shut down the well and wait for solidification, and then continue to seal the next original fracture.

[0014] S3-2, potential layer fracturing: find 1 to 2 potential layers within 20m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of perforations for each potential layer is 1 to 3, and the fracturing fluid displacement is 0.2 to 0.4m3 / min, the crack length is 20-60m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.45*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.85*(real-time crack length / expected crack length), the pump is stopped;

[0015] S4. Multi-directional water-blocking fracturing:

[0016] S4-1. Sealing of original fractures: Simultaneously seal the original fractures of multiple adjacent layers. First, place packers at multiple original fractures, inject light mud to displace them, open the original fractures, then inject polymer microspheres to seal the small pores at the ends of the original fractures, then inject pre-gel sealing fluid, enhanced sealing fluid and post-gel sealing fluid in sequence, and finally inject cement to seal the original fractures. Then shut down the well and wait for cement to solidify, and continue to seal the next original fracture or multiple original fractures in adjacent layers.

[0017] S4-2, potential layer fracturing: find 1 to 2 potential layers within 40m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of perforations for each potential layer is 2 to 4, and the fracturing fluid displacement is 0.2 to 0.4m 3 / min, the crack length is 10-40m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), the pump is stopped.

[0018] Furthermore, in S2-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4 to 0.6 m 3 / min injection displacement injection 8~12m 3 , the front gel plugging fluid is 0.5~0.8m 3 / min injection rate injection 10~20m 3 , strengthen the plugging fluid with 0.5~0.8m 3 / min injection rate injection 20~40m 3 , the gel plugging fluid is 0.5~0.8m 3 / min injection rate injection 5~10m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m3 , shut down the well and let it cool for 68 to 72 hours.

[0019] Description: By optimizing the water plugging system, the small channels at the ends of the original cracks can be plugged first, and then the cracks can be plugged by using two-stage gel plugging fluid in combination with enhanced plugging fluid, which can play a shielding role, reduce filtration loss and weaken the fingering of water, and can effectively plug deeper and higher cracks.

[0020] Furthermore, in S3-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.6-0.8m 3 / min injection rate injection 8~12m 3 , gel plugging fluid with 0.6~1m 3 / min injection rate injection 20~30m 3 , strengthen the plugging fluid with 0.6~1m 3 / min injection rate injection 20~40m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m 3 , shut down the well and let it cool for 68 to 72 hours.

[0021] Note: Compared with one-way water plugging, the original crack height is higher during two-way water plugging, and water breakthrough is more likely to occur. Therefore, it is necessary to increase the injection amount of gel plugging fluid, strengthen the shielding effect, and at the same time increase the injection speed of the enhanced plugging fluid to shorten the crack plugging time.

[0022] Furthermore, in S4-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4 to 0.6 m 3 / min injection rate injection 6~10m 3 , the front gel plugging fluid is 0.4~0.6m 3 / min injection rate injection 10~30m 3 , strengthen the plugging fluid with 0.4~0.6m 3 / min injection rate injection 20~60m 3 , the gel plugging fluid is 0.4~0.6m 3 / min injection rate injection 10~20m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m 3 , shut down the well and let it cool for 68 to 72 hours.

[0023] Note: Compared with unidirectional water blocking, multi-directional water blocking can block multiple adjacent layer cracks at the same time to improve construction efficiency. Therefore, the displacement is reduced and the injection volume is increased to ensure that each crack is blocked effectively.

[0024] Furthermore, the light mud is prepared by mixing barite powder with a density of 1.4 to 1.6 g / cm 3 of mud.

[0025] Note: Ensure that the original fractures in the well are opened through light mud displacement.

[0026] Furthermore, the particle size of the polymer microspheres is less than 100 nm, and the polymer microspheres are applied by mixing the polymer microspheres with light mud to form a mixed mud with a mass concentration of 1 to 2%.

[0027] Description: Use polymer microspheres to seal matrix pores and small channels.

[0028] Furthermore, the pre-gel plugging liquid and the post-gel plugging liquid in S2-1 and S4-1, and the gel plugging liquid in S3-1 are all PEG-PLA hydrogel.

[0029] Description: It plays the role of strengthening blocking and shielding.

[0030] Furthermore, the components and mass proportions of the enhanced plugging fluid are: 0.4-0.6% of 2-acrylamide-2-methylpropanesulfonic acid polymer, 1.5-2% of hydroxyethyl starch, 0.2-0.4% of N,N-methylenebisacrylamide, 0.05-0.1% of heat stabilizer, 0.05-0.1% of sodium dodecyl sulfate, and the balance is water.

[0031] Note: The optimized enhanced plugging fluid can effectively reduce filtration loss and weaken the water fingering phenomenon, with low damage to the reservoir.

[0032] Furthermore, the fracturing fluid is a low-damage drag-reducing slickwater fracturing fluid, and its components and mass proportions are: 0.03% to 0.1% polyacrylamide, 0.05% to 0.1% polyanionic cellulose, 0.04% to 0.06% sodium dodecylbenzene sulfonate, 0.05% to 0.1% polyethylene terephthalate, 5% to 8% ceramsite with a particle size of 0.5 to 0.8, and the remainder is water.

[0033] Description: The optimized fracturing fluid has low friction and low viscosity properties, which is more suitable for producing complex fracture networks in ultra-low permeability reservoirs. It has strong sand carrying capacity and is more suitable for fractured reservoirs.

[0034] Furthermore, the real-time crack length is obtained through OSI-D equipment and optical cable fibers, and the expected crack length is fitted through Frac-pt software.

[0035] The beneficial effects of the present invention are:

[0036] (1) The present invention provides a fracturing-water plugging process for the development of ultra-low permeability fractured oil reservoirs, mainly targeting the different water breakthrough directions in the wells of ultra-low permeability fractured oil reservoirs, and provides a variety of construction schemes. The corresponding water plugging construction parameters are reasonably selected according to the water breakthrough direction, and the formula of the fracturing fluid is optimized after water plugging to provide a fracturing fluid suitable for ultra-low permeability fractured oil reservoirs. The slope of the relationship curve between the fracture length, pressure and time is monitored in real time during the fracturing process to adjust the optimal fracturing parameters, which plays a guiding role in the development of ultra-low permeability fractured oil reservoirs.

[0037] (2) The fracturing-water plugging process method for developing ultra-low permeability fractured oil reservoirs of the present invention can preferentially plug the small channels at the inner ends of the original fractures by optimizing the water plugging system, and then plug the fractures by using two-stage gel plugging fluid in combination with enhanced plugging fluid, which can play a shielding role, reduce filtration loss and weaken the fingering phenomenon of incoming water, effectively plug deeper and higher fractures, and reasonably optimize and adjust the water plugging system according to the direction of water breakthrough to achieve the best water plugging effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the relationship curve between the bottom hole pressure and time during construction in Experimental Example 1 of the present invention. DETAILED DESCRIPTION

[0039] Example 1

[0040] A fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs, comprising the following steps:

[0041] S1. Determine the direction of water breakthrough: Detect the direction of water breakthrough of the oil production well. If the water breakthrough layer is a single stratigraphic level, the water breakthrough direction of the oil production well is determined to be unidirectional. If the water breakthrough layer is two adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be bidirectional. If the water breakthrough layer is more than two stratigraphic levels or two non-adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be multidirectional.

[0042] S2, one-way water-blocking fracturing:

[0043] S2-1. Sealing the original fractures: First, place the packer at the original fractures, inject light mud to displace the original fractures, and then inject polymer microspheres to seal the small pores at the inner ends of the original fractures. Then, inject the pre-gel plugging fluid, enhanced plugging fluid, and post-gel plugging fluid in sequence, and finally inject cement to seal the original fractures, and shut down the well for solidification.

[0044] Among them, light mud is 1.5m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.5m3 / min injection rate injection 10m 3 , the front gel plugging fluid is 0.6m 3 / min injection displacement injection 18m 3 , strengthen the plugging fluid with 0.6m 3 / min injection rate injection 30m 3 , the gel plugging fluid is 0.6m 3 / min injection displacement injection 8m 3 , cement is 0.6m 3 / min injection displacement injection 17m 3 , shut down the well and let it cool for 70 hours;

[0045] S2-2, potential layer fracturing: find a potential layer within 20m near the original fracture, and perform hydraulic fracturing on the potential layer. The number of fracturing perforations for each potential layer is 3, and the fracturing fluid displacement is 0.5m 3 / min, the crack length is 50m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.35*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.55*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 1*(real-time crack length / expected crack length), the pump is stopped;

[0046] S3, bidirectional water-blocking fracturing:

[0047] S3-1. Sealing the original fractures: Seal the two original fractures in sequence. First, place the packer at the original fracture, inject light mud to displace the original fracture, and then inject polymer microspheres to seal the small pores at the end of the original fracture. Then, inject gel sealing fluid and enhanced sealing fluid in sequence, and finally inject cement to seal the original fracture. Then shut down the well and wait for solidification, and then continue to seal the next original fracture.

[0048] Among them, light mud is 1.5m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.7m 3 / min injection rate injection 10m 3 , gel plugging fluid with 0.8m 3 / min injection displacement injection 25m 3 , strengthen the plugging fluid with 0.8m 3 / min injection rate injection 30m 3 , cement is 0.6m 3 / min injection displacement injection 17m 3 , shut down the well and let it cool for 70 hours;

[0049] S3-2, potential layer fracturing: find two potential layers within 20m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of fracturing perforations for each potential layer is 2, and the fracturing fluid displacement is 0.3m 3 / min, the crack length is 40m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.45*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.85*(real-time crack length / expected crack length), the pump is stopped;

[0050] S4. Multi-directional water-blocking fracturing:

[0051] S4-1. Sealing of original fractures: Simultaneously seal the original fractures of multiple adjacent layers. First, place packers at multiple original fractures, inject light mud to displace them, open the original fractures, then inject polymer microspheres to seal the small pores at the ends of the original fractures, then inject pre-gel sealing fluid, enhanced sealing fluid and post-gel sealing fluid in sequence, and finally inject cement to seal the original fractures. Then shut down the well and wait for cement to solidify, and continue to seal the next original fracture or multiple original fractures in adjacent layers.

[0052] Among them, light mud is 1.5m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.5m 3 / min injection displacement injection 8m 3 , the front gel plugging fluid is 0.5m 3 / min injection rate injection 20m 3 , strengthen the plugging fluid with 0.5m 3 / min injection rate injection 40m 3 , the gel plugging fluid is 0.5m 3 / min injection rate injection 15m 3 , cement is 0.6m 3 / min injection displacement injection 17m 3 , shut down the well and let it cool for 70 hours;

[0053] S4-2, potential layer fracturing: find a potential layer within 40m near the original fracture, and perform hydraulic fracturing on the potential layer. The number of fracturing perforations for each potential layer is 3, and the fracturing fluid displacement is 0.3m 3 / min, the crack length is 30m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), the pump is stopped;

[0054] S2~S4 medium light mud is made of barite powder with a density of 1.5g / cm 3 The polymer microspheres are mixed with light mud to form a mixed mud with a mass concentration of 1.5%.

[0055] The pre-gel plugging solution and post-gel plugging solution in S2-1 and S4-1, and the gel plugging solution in S3-1 are all PEG-PLA hydrogels;

[0056] The components and mass proportions of the enhanced plugging fluid in S2-S4 are: 0.5% 2-acrylamide-2-methylpropanesulfonic acid polymer, 1.6% hydroxyethyl starch, 0.3% N,N-methylenebisacrylamide, 0.08% heat stabilizer, 0.08% sodium dodecyl sulfate, and the balance is water;

[0057] The fracturing fluid in S2-S4 is a low-damage drag-reducing slickwater fracturing fluid, and its composition and mass ratio are: 0.05% polyacrylamide, 0.06% polyanionic cellulose, 0.05% sodium dodecylbenzene sulfonate, 0.07% polyethylene terephthalate, 6% ceramsite with a particle size of 0.7, and the balance is water;

[0058] The real-time crack lengths in S2 to S4 are obtained through OSI-D equipment and optical cable fibers, and the expected crack lengths are fitted by Frac-pt software.

[0059] Example 2

[0060] The difference between this embodiment and embodiment 1 is that:

[0061] In S2-1, light mud is 1m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4m 3 / min injection displacement injection 8m 3 , the front gel plugging fluid is 0.5m 3 / min injection rate injection 10m 3 , strengthen the plugging fluid with 0.5m 3 / min injection rate injection 20m 3, the gel plugging fluid is 0.5m 3 / min injection rate injection 5m 3 , cement with 0.5m 3 / min injection rate injection 15m 3 , shut down the well and let it cool for 68h;

[0062] In S2-2, a potential layer was found within 20m near the original fracture, and hydraulic fracturing was performed on the potential layer. The number of perforations for each potential layer was 2, and the fracturing fluid displacement was 0.3m 3 / min, the crack length is 30m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.35*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.55*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 1*(real-time crack length / expected crack length), the pump is stopped.

[0063] Example 3

[0064] The difference between this embodiment and embodiment 1 is that:

[0065] In S2-1, light mud is 2m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.6m 3 / min injection displacement injection 12m 3 , the front gel plugging fluid is 0.8m 3 / min injection rate injection 20m 3 , strengthen the plugging fluid with 0.8m 3 / min injection rate injection 40m 3 , the gel plugging fluid is 0.8m 3 / min injection rate injection 10m 3 , cement is 0.8m 3 / min injection rate injection 20m 3 , shut down the well and let it cool for 72 hours;

[0066] In S2-2, two potential layers were found within 20 m of the original fracture. The potential layers were hydraulically fractured. Each potential layer was perforated 4 times and the fracturing fluid displacement was 0.6 m 3 / min, the crack length is 90m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.35*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.55*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 1*(real-time crack length / expected crack length), the pump is stopped.

[0067] Note: In Examples 1 to 3, the required parameters are reasonably adjusted according to the well type scale. For example, if the wellbore size is large, the injection volume at each stage is appropriately increased. If the well depth at the fracture location is deep, the injection displacement is appropriately reduced, and vice versa. At the same time, the fracture length during fracturing is also positively correlated with the fracturing fluid displacement, and the required fracture length is reasonably selected according to needs.

[0068] Example 4

[0069] The difference between this embodiment and embodiment 1 is that:

[0070] In S3-1, light mud is 1m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.6m 3 / min injection displacement injection 8m 3 , gel plugging fluid with 0.6m 3 / min injection rate injection 20m 3 , strengthen the plugging fluid with 0.6m 3 / min injection rate injection 20m 3 , cement with 0.5m 3 / min injection rate injection 15m 3 , shut down the well and let it cool for 68h;

[0071] In S3-2, a potential layer was found within 20m near the original fracture, and hydraulic fracturing was performed on the potential layer. The number of fracturing perforations in each potential layer was 1, and the fracturing fluid displacement was 0.2m 3 / min, the crack length is 20m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.45*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.85*(real-time crack length / expected crack length), the pump is stopped.

[0072] Example 5

[0073] The difference between this embodiment and embodiment 1 is that:

[0074] In S3-1, light mud is 2m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.8m 3 / min injection displacement injection 12m 3 , gel plugging fluid with 1m 3 / min injection rate injection 30m 3 , strengthen the plugging fluid to 1m 3 / min injection rate injection 40m 3 , cement is 0.8m 3 / min injection rate injection 20m 3 , shut down the well and let it cool for 72 hours;

[0075] In S3-2, two potential layers were found within 20 m of the original fracture. The potential layers were hydraulically fractured. The number of perforations for each potential layer was 3 and the fracturing fluid displacement was 0.4 m 3 / min, the crack length is 60m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.45*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.85*(real-time crack length / expected crack length), the pump is stopped.

[0076] Note: In Example 1, Example 4 and Example 5, the required parameters are reasonably adjusted according to the scale of the well type. For example, if the wellbore size is large, the injection volume at each stage is appropriately increased. If the well depth at the location of the fracture is deep, the injection displacement is appropriately reduced, and vice versa. At the same time, the fracture length during fracturing is also positively correlated with the fracturing fluid displacement, and the required fracture length is reasonably selected according to needs.

[0077] Example 6

[0078] The difference between this embodiment and embodiment 1 is that:

[0079] In S4-1, light mud is 1m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4m 3 / min injection displacement injection 6m 3 , the front gel plugging fluid is 0.4m 3 / min injection rate injection 10m 3 , strengthen the plugging fluid with 0.4m 3 / min injection rate injection 20m 3 , the gel plugging fluid is 0.4m 3 / min injection rate injection 10m3 , cement with 0.5m 3 / min injection rate injection 15m 3 , shut down the well and let it cool for 68h;

[0080] In S4-2, a potential layer was found within 40m near the original fracture, and hydraulic fracturing was performed on the potential layer. The number of perforations for each potential layer was 2, and the fracturing fluid displacement was 0.2m 3 / min, the crack length is 10m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), the pump is stopped.

[0081] Example 7

[0082] The difference between this embodiment and embodiment 1 is that:

[0083] In S4-1, light mud is 2m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.6m 3 / min injection rate injection 10m 3 , the front gel plugging fluid is 0.6m 3 / min injection rate injection 30m 3 , strengthen the plugging fluid with 0.6m 3 / min injection rate injection 60m 3 , the gel plugging fluid is 0.6m 3 / min injection rate injection 20m 3 , cement is 0.8m 3 / min injection rate injection 20m 3 , shut down the well and let it cool for 72 hours;

[0084] In S4-2, two potential layers were found within 40 m of the original fracture. The potential layers were hydraulically fractured. Each potential layer was perforated 4 times and the fracturing fluid displacement was 0.4 m 3 / min, the crack length is 40m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), the pump is stopped.

[0085] Note: In Example 1, Example 6 and Example 7, in addition to reasonably adjusting the required parameters according to the well type scale, it is also necessary to consider the number and spacing of the original cracks. The larger the spacing, the more appropriate it is to increase the injection volume at each stage, and vice versa. At the same time, the crack length during fracturing is also positively correlated with the fracturing fluid displacement, and the required crack length is reasonably selected according to needs.

[0086] Example 8

[0087] The difference between this embodiment and embodiment 1 is that:

[0088] S2~S4 medium light mud is made of barite powder with a density of 1.4g / cm 3 The polymer microspheres have a particle size of less than 100 nm and are applied by mixing the polymer microspheres with light mud to prepare a mixed mud having a mass concentration of 1%.

[0089] Example 9

[0090] The difference between this embodiment and embodiment 1 is that:

[0091] The light mud in S2~S4 is made of barite powder with a density of 1.6g / cm 3 The polymer microspheres have a particle size of less than 100 nm and are applied by mixing the polymer microspheres with light mud to prepare a mixed mud with a mass concentration of 2%.

[0092] Note: In Example 1, Example 8 and Example 9, the density of the light mud is reasonably adjusted according to the well depth where the fracture is located. If the well depth is deeper, the density of the light mud and the concentration of the polymer microspheres are appropriately increased, and vice versa.

[0093] Example 10

[0094] The difference between this embodiment and embodiment 1 is that:

[0095] The components and mass proportions of the enhanced plugging fluid in S2~S4 are: 0.4% 2-acrylamide-2-methylpropane sulfonic acid polymer, 1.5% hydroxyethyl starch, 0.2% N,N-methylenebisacrylamide, 0.05% heat stabilizer, 0.05% sodium dodecyl sulfate, and the balance is water.

[0096] Embodiment 11

[0097] The difference between this embodiment and embodiment 1 is that:

[0098] The components and mass proportions of the enhanced plugging fluid in S2~S4 are: 0.6% 2-acrylamide-2-methylpropane sulfonic acid polymer, 2% hydroxyethyl starch, 0.4% N,N-methylenebisacrylamide, 0.1% heat stabilizer, 0.1% sodium dodecyl sulfate, and the balance is water.

[0099] Note: In Example 1, Example 10 and Example 11, the selected parameters are all reasonably selected within the preferred parameter range given in the present invention.

[0100] Example 12

[0101] The difference between this embodiment and embodiment 1 is that:

[0102] The fracturing fluid in S2~S4 is a low-damage drag-reducing slickwater fracturing fluid, and its components and mass proportions are: 0.03% polyacrylamide, 0.05% polyanionic cellulose, 0.04% sodium dodecylbenzene sulfonate, 0.05% polyethylene terephthalate, 5% ceramsite with a particle size of 0.5, and the remainder is water.

[0103] Embodiment 13

[0104] The difference between this embodiment and embodiment 1 is that:

[0105] The fracturing fluid in S2~S4 is a low-damage drag-reducing slickwater fracturing fluid, and its components and mass proportions are: 0.1% polyacrylamide, 0.1% polyanionic cellulose, 0.06% sodium dodecylbenzene sulfonate, 0.1% polyethylene terephthalate, 8% ceramsite with a particle size of 0.8, and the remainder is water.

[0106] Note: In Example 1, Example 12 and Example 13, the selected parameters are all reasonably selected within the preferred parameter range given in the present invention.

[0107] Experimental Example 1

[0108] First, we start from indoor test, verify the feasibility and actual effect of the method of the present invention, adopt large-scale true triaxial fracturing simulation test system, simulate the extension of hydraulic fracture in wellbore.Mix concrete by cement and quartz sand according to equal volume, cast into cubic specimen, scale in equal proportion, wellbore is placed in the center of unsolidified concrete.According to step S4-2 in embodiment 1, operate, start fracturing and carry out optical fiber monitoring, and draw the relationship curve of bottom hole pressure and time during construction in real time, when the slope of curve is greater than 0.15* (real-time crack length / expected crack length), reduce the displacement of fracturing fluid to 80% of original displacement, when the slope of curve is greater than 0.25* (real-time crack length / expected crack length), reduce the displacement of fracturing fluid to 60% of original displacement, when the slope of curve is greater than 0.65* (real-time crack length / expected crack length), stop pump.

[0109] The relationship curve between bottom hole pressure and time during construction is as follows: Figure 1 As shown, it can be seen that the pressure rises after the fracturing fluid is injected, the crack opens at 30 minutes, the pressure drops, and the fracturing fluid begins to enter the crack; at 65 minutes, the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the pressure drops slightly when the fracturing fluid displacement is reduced, and then rises steadily;

[0110] At around 133 minutes, the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), and the fracturing fluid displacement is reduced. At this time, the fracturing fluid begins to enter the developed longitudinal cracks. Until around 140 minutes, the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), sand blockage occurs, and the pump is stopped.

[0111] Through analysis, it is found that during hydraulic fractures, the fractures tend to turn and extend in the direction of the development of cleats and natural fractures. The pressure drop corresponds to the main fracture being pressed open. At the same time, the injection displacement is adjusted according to the pressure curve according to the method in Example 1, so that multiple fractures are developed vertically, and the fracturing effect is good.

[0112] Example 2

[0113] We conducted tests on actual development wells on site. The test area was the ultra-low permeability fractured oilfield development area in the Ordos Basin. Three production wells that met the requirements were subjected to water plugging and fracturing to increase production according to the method in Example 1. The production capacities of the three wells are shown in Table 1.

[0114] Table 1 Productivity of the three wells before production increase

[0115] hashtag <![CDATA[Nissan liquid m 3 > Production days Moisture content% Cumulative oil production Wu 8# 20.1 812 60.5 4335 Wu 23# 13.6 421 53.7 2618 Wu 40# 18.7 345 48.5 2098

[0116] Among them, Wu 8# well has a long development time, high water content, and complex water breakthrough direction. It adopts S4 water plugging and fracturing measures. Wu 23# and Wu 40# wells both have unidirectional water breakthrough. They adopt S2 water plugging and fracturing measures. The production capacity of the three wells after production increase is shown in Table 2.

[0117] Table 2 Productivity of the three wells after production increase

[0118] hashtag <![CDATA[Nissan liquid m 3 > Moisture content% Initial weekly oil production Wu 8# 43.2 51.9 131 Wu 23# 36.5 46.5 152 Wu 40# 40.8 42.3 163

[0119] From the comparison of the data in Table 1 and Table 2, it can be seen that after using the water plugging fracturing production increase measures in Example 1 of the present invention, the daily liquid production has been greatly improved, indicating that the fracturing and water plugging effect is good, the water content is reduced, the oil production is increased, the initial weekly oil production is high, and the water plugging fracturing has achieved good results.

Claims

1. A fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs, characterized in that: The following steps are involved: S1. Determine the direction of water breakthrough: Detect the direction of water breakthrough of the oil production well. If the water breakthrough layer is a single stratigraphic level, the water breakthrough direction of the oil production well is determined to be unidirectional. If the water breakthrough layer is two adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be bidirectional. If the water breakthrough layer is more than two stratigraphic levels or two non-adjacent stratigraphic levels, the water breakthrough direction of the oil production well is determined to be multidirectional. S2, one-way water-blocking fracturing: S2-1. Sealing the original fractures: First, place the packer at the original fractures, inject light mud to displace the original fractures, and then inject polymer microspheres to seal the small pores at the inner ends of the original fractures. Then, inject the pre-gel plugging fluid, enhanced plugging fluid, and post-gel plugging fluid in sequence, and finally inject cement to seal the original fractures, and shut down the well for solidification. S2-2, potential layer fracturing: find 1 to 2 potential layers within 20m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of perforations for each potential layer is 2 to 4, and the fracturing fluid displacement is 0.3 to 0.6m 3 / min, the crack length is 30-90m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.35*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.55*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 1*(real-time crack length / expected crack length), the pump is stopped; S3, bidirectional water-blocking fracturing: S3-1. Sealing the original fractures: Seal the two original fractures in sequence. First, place the packer at the original fracture, inject light mud to displace the original fracture, and then inject polymer microspheres to seal the small pores at the end of the original fracture. Then, inject gel sealing fluid and enhanced sealing fluid in sequence, and finally inject cement to seal the original fracture. Then shut down the well and wait for solidification, and then continue to seal the next original fracture. S3-2, potential layer fracturing: find 1 to 2 potential layers within 20m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of fracturing perforations for each potential layer is 1 to 3, and the fracturing fluid displacement is 0.2 to 0.4m 3 / min, the crack length is 20-60m, and the relationship curve between bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.45*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.85*(real-time crack length / expected crack length), the pump is stopped; S4. Multi-directional water-blocking fracturing: S4-1. Sealing of original fractures: Simultaneously seal the original fractures of multiple adjacent layers. First, place packers at multiple original fractures, inject light mud to displace them, open the original fractures, then inject polymer microspheres to seal the small pores at the ends of the original fractures, then inject pre-gel sealing fluid, enhanced sealing fluid and post-gel sealing fluid in sequence, and finally inject cement to seal the original fractures. Then shut down the well and wait for cement to solidify, and continue to seal the next original fracture or multiple original fractures in adjacent layers. S4-2, potential layer fracturing: find 1 to 2 potential layers within 40m near the original fracture, and perform hydraulic fracturing on the potential layers. The number of perforations for each potential layer is 2 to 4, and the fracturing fluid displacement is 0.2 to 0.4m 3 / min, the crack length is 10-40m, and the relationship curve between the bottom hole pressure and time during construction is drawn in real time. When the slope of the curve is greater than 0.15*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 80% of the original displacement; when the slope of the curve is greater than 0.25*(real-time crack length / expected crack length), the fracturing fluid displacement is reduced to 60% of the original displacement; when the slope of the curve is greater than 0.65*(real-time crack length / expected crack length), the pump is stopped.

2. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: In S2-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4 to 0.6 m 3 / min injection displacement injection 8~12m 3 , the front gel plugging fluid is 0.5~0.8m 3 / min injection rate injection 10~20m 3 , strengthen the plugging fluid with 0.5~0.8m 3 / min injection rate injection 20~40m 3 , the gel plugging fluid is 0.5~0.8m 3 / min injection rate injection 5~10m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m 3 , shut down the well and let it cool for 68 to 72 hours.

3. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: In S3-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.6-0.8m 3 / min injection rate injection 8~12m 3 , gel plugging fluid with 0.6~1m 3 / min injection rate injection 20~30m 3 , strengthen the plugging fluid with 0.6~1m 3 / min injection rate injection 20~40m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m 3 , shut down the well and let it cool for 68 to 72 hours.

4. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: In S4-1, the light mud is 1 to 2 m 3 / min injection rate until the mud in the well is completely replaced by light mud, and the polymer microspheres are injected at a rate of 0.4 to 0.6 m 3 / min injection rate injection 6~10m 3 , the front gel plugging fluid is 0.4~0.6m 3 / min injection rate injection 10~30m 3 , strengthen the plugging fluid with 0.4~0.6m 3 / min injection rate injection 20~60m 3 , the gel plugging fluid is 0.4~0.6m 3 / min injection rate injection 10~20m 3 , cement is 0.5~0.8m 3 / min injection rate injection 15 ~ 20m 3 , shut down the well and let it cool for 68 to 72 hours.

5. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The light mud is prepared by mixing barite powder with a density of 1.4 to 1.6 g / cm 3 of mud.

6. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The particle size of the polymer microspheres is less than 100 nm, and the polymer microspheres are mixed with light mud to form a mixed mud with a mass concentration of 1 to 2% and applied.

7. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The front gel plugging liquid and the rear gel plugging liquid in S2-1 and S4-1, and the gel plugging liquid in S3-1 are all PEG-PLA hydrogels.

8. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The components and mass proportions of the enhanced plugging fluid are: 0.4-0.6% of 2-acrylamide-2-methylpropanesulfonic acid polymer, 1.5-2% of hydroxyethyl starch, 0.2-0.4% of N,N-methylenebisacrylamide, 0.05-0.1% of heat stabilizer, 0.05-0.1% of sodium dodecyl sulfate, and the balance is water.

9. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The fracturing fluid is a low-damage drag-reducing slickwater fracturing fluid, and its components and mass proportions are: 0.03% to 0.1% polyacrylamide, 0.05% to 0.1% polyanionic cellulose, 0.04% to 0.06% sodium dodecylbenzene sulfonate, 0.05% to 0.1% polyethylene terephthalate, 5% to 8% ceramsite with a particle size of 0.5 to 0.8, and the remainder is water.

10. The fracturing-water plugging process for developing ultra-low permeability fractured oil reservoirs according to claim 1, characterized in that: The real-time crack length is obtained through OSI-D equipment and optical cable fibers, and the expected crack length is fitted by Frac-pt software.

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