Preparation method and application of composite gel plugging agent suitable for fractured reservoir

Abstract

The invention discloses a preparation method and application of a composite gel plugging agent suitable for a fractured reservoir, and belongs to the technical field of oilfield chemistry. The gel plugging agent is prepared from the following components: hydrolyzed polyacrylamide (PHPA) serving as a plugging main agent, organic zirconium serving as a cross-linking agent and water, a large number of polar groups such as acylamino and carboxyl exist on a branched chain of the hydrolyzed polyacrylamide, and the polar groups can be complexed with polynuclear hydroxyl bridge complex ions formed by hydrolysis, hydroxyl bridge action and the like of organic zirconium to form complexed and crosslinked polymer PHPA gel with a three-dimensional network structure. After gel reinforcing agents such as walnut shells, water-soluble short fibers and polymer AAC are compounded, the composite gel plugging agent can be suitable for fractured reservoirs with the formation fracture width of about 1.0-3.0 mm at the temperature of 60-80 DEG C, after the plugging gel is weighted, the plugging pressure can reach 4-5 MPa, the plugging performance is excellent, and the problems that a conventional plugging material for the fractured formation is low in strength, poor in plugging performance and the like can be effectively solved. The blocking capacity is insufficient; the retention capacity in a leakage layer is poor, and the like.

Description

Technical Field

[0001] The invention discloses a preparation method and application of a composite gel plugging agent applicable to fractured reservoirs, belonging to the field of oilfield chemistry. Background Technique

[0002] In China, the geological conditions of oil and gas reservoirs are complex and the drilling scale is huge. Basically, various strata that may be encountered in the world have been drilled, resulting in a variety of well leakage problems in drilling, thus accumulating rich experience in leakage prevention and plugging. With the continuous development of plugging technologies at home and abroad and the continuous improvement of plugging mechanisms, for the serious leakage problems in fractured formations, the plugging technologies that have been applied on a large scale currently mainly include bridging plugging technology, chemical gel plugging technology, etc.

[0003] With the frequent occurrence of serious leakage in fractured formations, the conventional bridging plugging technology also has many limitations: ① The fracture channels are complex and changeable, making it difficult to ensure a good matching degree between the particle size distribution of the bridging plugging material and the fracture size; ② During the bridging process of the bridging plugging material in the fracture channel, it will be compacted under the action of pressure difference, and under the influence of factors such as gravity settlement and fluid scouring, its residence in large fractures with larger fracture width and higher longitudinal extension is poor, and the plugging success rate is low. Therefore, for the serious leakage in fractured formations, chemical gel plugging technology is now more commonly used for on-site plugging.

[0004] The chemical gel plugging technology has the following advantages: (1) The density of the plugging gel is relatively low; (2) The setting time can be adjusted within a large range; (3) The solid content of the plugging gel is relatively low, and it is not restricted by the size and shape of the leakage channel; (4) It has good compatibility with inert materials and can be compounded with other materials to improve the plugging performance of the gel system; (5) After plugging, the drill cuttings have no adverse effect on the performance of the mud.

[0005] Therefore, the development and research of gel plugging agents are a research goal that still needs to be improved and developed in the current drilling fluid plugging process. It can not only solve the serious leakage problem, but also specifically solve the complex problems such as well leakage in the drilling and production process of most fractured reservoirs in China, and has a quite broad market prospect. Summary of the Invention

[0006] The invention is a preparation method and application of a composite gel plugging agent applicable to fractured reservoirs. The main technical problem to be solved is: for the well leakage problem during the drilling process of fractured reservoirs, the on-site used bridging plugging technology mainly uses mica flakes, calcium carbonate and oil well cement plugging technology. Among them, the plugging materials of the bridging plugging technology have low strength and poor pressure-bearing capacity; while the used oil well cement material has a high density and a low viscosity, and its retention ability in the leakage layer is poor, and the success rate of one-time plugging is low. Therefore, for the research on the plugging technology for the leakage of fractured formations, a preparation method of a composite gel plugging agent applicable to fractured reservoirs is provided.

[0007] To prepare a composite gel plugging agent, the first aspect of the present invention provides a preparation method, which includes:

[0008] (1) Measure deionized water with a graduated cylinder and add it to a drilling fluid cup. Weigh crosslinking agent B and add it to the drilling fluid cup, and stir to dissolve crosslinking agent B to obtain an aqueous solution of crosslinking agent B.

[0009] (2) Weigh gel main agent A and add it to the aqueous solution of crosslinking agent B in step (1). Continue to stir for a period of time, then let it stand at the corresponding temperature. After waiting for a period of time, the reaction is complete to obtain a gel.

[0010] (3) Immerse the gel obtained in step (2) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain a composite gel plugging agent.

[0011] The second aspect of the present invention provides a composite gel plugging agent prepared by the method described in the first aspect above. Using PHPA as the gel main agent, its branches contain a large number of polar groups such as —CONH2 and —COO-. The polynuclear hydroxy-bridged complex ions formed by the hydrolysis and hydroxy-bridging action of the crosslinking agent organic zirconium are a kind of active ions. The —COO- on PHPA can provide lone pair electrons and can act as a ligand to complex with the polynuclear hydroxy-bridged complex ions to form a complex crosslinked polymer PHPA gel with a three-dimensional network structure. The crosslinking process is shown in Figure 1 .

[0013] The third aspect of the present invention provides a composite gel plugging system suitable for fractured reservoirs. This plugging system contains the composite gel plugging agent described in the second aspect above. And to improve the strength and high-temperature stability of the plugging gel, polymer AAC is introduced. Polymer AAC is a high-molecular polymer copolymerized from polymerization monomers such as 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM). Its copolymerization reaction process is as Figure 2 shown.

[0015] Through the above technical solutions, the present invention can achieve the following excellent effects:

[0016] (1) The composite gel plugging agent provided by the present invention has good gel-forming properties, and the gel-forming time for plugging can be controlled within a certain range.

[0017] (2) The composite gel plugging system described in the present invention can maintain good rheological properties during the weighting process. And as the density increases, it can effectively plug cracks with a width of 1-3 mm, and the plugging pressure can reach 5 MPa.

[0018] (3) The composite gel plugging system of the present invention, wherein the organic zirconium crosslinking agent can form polynuclear hydroxy-bridged ions with high crosslinking activity through hydrolysis and hydroxy-bridging complexation in an aqueous solution, and then perform binary complexation with the polar groups in PHPA and AAC. The inert material plays a bridging and filling role therein, and finally a plugging gel with a three-dimensional network structure is formed. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the crosslinking process between PHPA and organic zirconium in the composite gel plugging agent prepared in the second aspect of the invention; Figure 2 Schematic diagram of the copolymerization reaction process of polymer AAC introduced to improve the strength and high-temperature stability of the plugging gel in the plugging system of the third aspect of the invention; Figure 3 Graph of the test results of the plugging performance of the plugging gel examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] The ranges and values of the materials described in the present invention are not precisely between the exact ranges. All ranges and values described in the present invention include the values within these ranges or values. For these given numerical ranges, combinations can be made between the ranges and at the range endpoints to form a new numerical range, and these newly combined numerical values should also be regarded as the content disclosed by the present invention.

[0020] Note that the following provides a detailed description of the specific embodiments of the present invention. The specific embodiments described herein are only used to illustrate and explain the present invention and do not limit the present invention.

[0021] The first aspect of the present invention provides a preparation method, which includes:

[0022] (1) Measure deionized water with a measuring cylinder and add it to a drilling fluid cup. Weigh the crosslinking agent B and add it to the drilling fluid cup, and stir to dissolve the crosslinking agent B to obtain an aqueous solution of the crosslinking agent B;

[0023] (2) Weigh the gel main agent A and add it to the aqueous solution of the crosslinking agent B in step (1). Continue to stir for a period of time, then let it stand at the corresponding temperature. After waiting for a period of time, the reaction is complete to obtain a gel;

[0024] (3) Immerse the gel obtained in step (2) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain a composite gel plugging agent.

[0025] According to the present invention, in steps (1) to (2), the raw materials include the following components in parts by weight: the weight ratio of the gel main agent A: the crosslinking agent B: deionized water is (2 - 60):(10 - 140):(2000 - 3000);

[0026] Preferably, the weight components are preferably in a weight ratio of gel main agent A: crosslinking agent B: deionized water of (20 - 60):(20 - 80):2000

[0027] According to the present invention, for the gel main agent A in the composite gel plugging agent, it is characterized in that the gel main agent material is one of guar gum, xanthan gum (#1, #2), and hydrolyzed polyacrylamide PHPA (with a molecular weight of 2 million - 14 million, and a molecular weight of 15 million - 18 million);

[0028] Preferably, the gel main agent A is preferably hydrolyzed polyacrylamide PHPA (with a molecular weight of 15 million - 18 million).

[0029] According to the present invention, for the crosslinking agent B in the composite gel plugging agent, it is characterized in that the crosslinking agent material is one of organic zirconium, organic boron, organic titanium, phenolic resin, and formaldehyde;

[0030] Preferably, the crosslinking agent B is preferably organic zirconium.

[0031] According to the present invention, for the preparation method of the composite gel plugging agent, in step (1), the stirring speed for dissolving the crosslinking agent B is 6000 - 8000 r / min, and the stirring time is 5 - 10 min;

[0032] Preferably, the stirring speed is preferably 8000 r / min, and the stirring time is preferably 10 min.

[0033] According to the present invention, for the preparation method of the composite gel plugging agent, in step (2), when the gel main agent is added to the aqueous solution of the crosslinking agent B, the stirring speed is 8000 - 12000 r / min, and the stirring time is 10 - 30 min;

[0034] Preferably, the stirring speed is preferably 10000 r / min, and the stirring time is preferably 30 min.

[0035] According to the present invention, for the preparation method of the composite gel plugging agent, in step (2), the reaction is carried out at a reaction temperature, the temperature is 60 - 100 °C, and the reaction time is 8 - 24 h;

[0036] Preferably, the reaction temperature is preferably 60 - 80 °C, and the reaction time is preferably 10 - 12 h.

[0037] According to the present invention, in step (3), for the post - treatment alcohol washing process after the reaction, one of anhydrous ethanol and isopropyl alcohol is used, preferably anhydrous ethanol.

[0038] In the second aspect of the present invention, there is provided the composite gel plugging agent prepared as described in the first aspect, using PHPA as the main gel agent, and its branches contain a large number of polar groups such as —CONH 2 and —COO—. The polynuclear hydroxy-bridged complex ions formed by the hydrolysis and hydroxy-bridging action of organic zirconium are active ions. The —COO— on PHPA can provide lone pair electrons and can act as a ligand to complex with the polynuclear hydroxy-bridged complex ions to form a complex cross-linked polymer PHPA gel with a three-dimensional network structure, which has advantages such as high strength and controllable gelation time.

[0039] In the third aspect of the present invention, there is provided a composite gel plugging system for fractured reservoirs, and this system contains the composite gel plugging agent described in the aforementioned first and second aspects.

[0040] According to the present invention, the composite gel plugging system includes the following components: 1000 - 2000 parts by weight of deionized water, 30 - 60 parts by weight of hydrolyzed polyacrylamide (PHPA), 40 - 100 parts by weight of organic zirconium, 10 - 30 parts by weight of walnut shell, 10 - 40 parts by weight of water-soluble short fibers, and 0.5 - 2 parts by weight of gel strengthening agent (AAC);

[0041] Preferably, the composite gel plugging system includes the following components: 1000 parts by weight of deionized water, 35 - 40 parts by weight of hydrolyzed polyacrylamide (PHPA), 60 - 80 parts by weight of organic zirconium, 15 - 25 parts by weight of walnut shell, 20 - 30 parts by weight of water-soluble short fibers, and 1 - 1.5 parts by weight of gel strengthening agent (AAC).

[0042] The composite gel plugging system provided by the present invention has good rheological properties and sedimentation stability; the gelled slurry after weighting has good gelation properties and the gel strength is improved. At the same time, for the composite gel plugging system of the present invention, when not weighted, the plugging pressure of the plugging gel in steel cores with slit widths of 1 mm, 2 mm, and 3 mm can reach 2.5 MPa, and after weighting, the plugging pressure can continue to increase to 5 MPa, and the plugging performance is good.

[0043] According to the present invention, for the monomer preparation materials, unless otherwise specified, they are all chemically pure and can all adopt conventional commercially available brand products, and the present invention has no special limitation in this regard.

[0044] The present invention will be described in detail below through examples. In the preparation examples and examples of the present invention, unless otherwise specified, other materials used are all ordinary commercially available products.

[0045] Preparation Example 1

[0046] (1-1) Measure 2000 parts of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 76 parts of crosslinking agent B and add it to the drilling fluid cup. Stir thoroughly at a speed of 8000 r / min for 10 min to obtain an aqueous solution of crosslinking agent B;

[0047] (1-2) Weigh 40 parts of gel main agent A and add it to the aqueous solution of crosslinking agent B in step (1-1). Stir thoroughly at a speed of 10000 r / min for 30 min to obtain an initial reaction solution;

[0048] (1-3) Place the drilling fluid cup in a constant temperature water bath under airtight conditions and heat it by water bath. Gel formation occurs at 80 °C. Observe the change in the solution state every 0.5 h,

[0049] After determining the gel formation, record the reaction time;

[0050] (1-4) Immerse the gel obtained in step (1-3) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain the composite gel plugging agent D1.

[0051] Preparation Example 2

[0052] (2-1) Measure 2000 parts of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 60 parts of crosslinking agent B and add it to the drilling fluid cup. Stir thoroughly at a speed of 8000 r / min for 10 min to obtain an aqueous solution of crosslinking agent B;

[0053] (2-2) Weigh 40 parts of gel main agent A and add it to the aqueous solution of crosslinking agent B in step (2-1). Stir thoroughly at a speed of 10000 r / min for 30 min to obtain an initial reaction solution;

[0054] (2-3) Place the drilling fluid cup in a constant temperature water bath under airtight conditions and heat it by water bath. Gel formation occurs at 80 °C. Observe the change in the solution state every 0.5 h,

[0055] After determining the gel formation, record the reaction time;

[0056] (2-4) Immerse the gel obtained in step (2-3) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain the composite gel plugging agent D2.

[0057] Preparation Example 3

[0058] (3-1) Measure 2000 parts of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 68 parts of crosslinking agent B and add it to the drilling fluid cup. Stir thoroughly at a speed of 8000 r / min for 10 min to obtain an aqueous solution of crosslinking agent B;

[0059] (3-2) Weigh 40 parts of gel base A and add it to the aqueous solution of crosslinking agent B in step (3-1). Stir thoroughly at a speed of 10,000 r / min for 30 min to obtain the initial reaction solution;

[0060] (3-3) Place the drilling fluid cup in a closed condition in a constant temperature water bath and heat it by water bath. Gel formation occurs at 80 °C. Observe the change in the solution state every 0.5 h,

[0061] After determining the gel formation, record the reaction time;

[0062] (3-4) Immerse the gel obtained in step (3-3) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain the composite gel plugging agent D3.

[0063] Preparation Example 4

[0064] (4-1) Measure 2000 parts of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 80 parts of crosslinking agent B and add it to the drilling fluid cup. Stir thoroughly at a speed of 8,000 r / min for 10 min to obtain the aqueous solution of crosslinking agent B;

[0065] (4-2) Weigh 40 parts of gel base A and add it to the aqueous solution of crosslinking agent B in step (4-1). Stir thoroughly at a speed of 10,000 r / min for 30 min to obtain the initial reaction solution;

[0066] (4-3) Place the drilling fluid cup in a closed condition in a constant temperature water bath and heat it by water bath. Gel formation occurs at 80 °C. Observe the change in the solution state every 0.5 h,

[0067] After determining the gel formation, record the reaction time;

[0068] (4-4) Immerse the gel obtained in step (4-3) completely in absolute ethanol, take it out after washing, dry it at low temperature and crush it to obtain the composite gel plugging agent D4.

[0069] Example 1

[0070] Measure 2000 parts by weight of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shell, 30 parts by weight of water-soluble short fiber and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of the composite gel plugging agent D1 and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup to obtain the composite gel plugging slurry S1.

[0071] The components and contents of S1 are shown in Table 1.

[0072] Example 2

[0073] Measure 2000 parts by weight of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shells, 30 parts by weight of water-soluble short fibers, and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of composite gel plugging agent D2, and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup, obtaining composite gel plugging slurry S2.

[0074] The components and contents of S2 are shown in Table 1.

[0075] Example 3

[0076] Measure 2000 parts by weight of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shells, 30 parts by weight of water-soluble short fibers, and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of composite gel plugging agent D3, and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup, obtaining composite gel plugging slurry S3.

[0077] The components and contents of S2 are shown in Table 1.

[0078] Example 4

[0079] Measure 2000 parts by weight of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shells, 30 parts by weight of water-soluble short fibers, and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of composite gel plugging agent D4, and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup, obtaining composite gel plugging slurry S4.

[0080] The components and contents of S4 are shown in Table 1.

[0081] Example 5

[0082] Measure 2000 parts by weight of deionized water with a measuring cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shells, 30 parts by weight of water-soluble short fibers, and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of composite gel plugging agent D1, and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup. Finally, weigh 160 parts by weight of barite and stir at a stirring speed of 1200 r / min for 30 min until there is no precipitate at the bottom of the cup, obtaining composite gel plugging slurry S5.

[0083] The components and contents of S5 are shown in Table 1.

[0084] Example 6

[0085] Measure 2000 parts by weight of deionized water with a graduated cylinder and add it to the drilling fluid cup. Weigh 20 parts by weight of walnut shells, 30 parts by weight of water-soluble short fibers, and 1.5 parts by weight of gel enhancer AAC and add them to the drilling fluid cup. Stir at a stirring speed of 1200 r / min for 30 min, then add 100 parts by weight of composite gel plugging agent D1, and continue to stir at a stirring speed of 1200 r / min for 30 min until there is no precipitation at the bottom of the cup. Finally, weigh 1890 parts by weight of barite and stir at a stirring speed of 1200 r / min for 30 min until there is no precipitation at the bottom of the cup to obtain composite gel plugging slurry S6.

[0086] The components and contents of S6 are shown in Table 1.

[0087] Comparative Example 1

[0088] According to the method of Example 1, the difference is that the hydrolyzed polyacrylamide PHPA in gel main agent A is replaced with guar gum as the gel main agent by following the steps of Preparation Example 1, and the other implementation conditions are the same as those in Example 1 to obtain composite gel plugging slurry DS1.

[0089] The components and contents of DS1 are shown in Table 2.

[0090] Comparative Example 2

[0091] According to the method of Example 1, the difference is that the hydrolyzed polyacrylamide PHPA in gel main agent A is replaced with xanthan gum #1 as the gel main agent by following the steps of Preparation Example 1, and the other implementation conditions are the same as those in Example 1 to obtain composite gel plugging slurry DS2.

[0092] The components and contents of DS2 are shown in Table 2.

[0093] Comparative Example 3

[0094] According to the method of Example 1, the difference is that the hydrolyzed polyacrylamide PHPA in gel main agent A is replaced with xanthan gum #2 as the gel main agent by following the steps of Preparation Example 1, and the other implementation conditions are the same as those in Example 1 to obtain composite gel plugging slurry DS3.

[0095] The components and contents of DS3 are shown in Table 2.

[0096] Comparative Example 4

[0097] According to the method of Example 1, the difference is that the hydrolyzed polyacrylamide PHPA in the gel main agent A is replaced with hydrolyzed polyacrylamide PHPA (molecular weight 2,000,000 - 14,000,000) as the gel main agent by adopting the steps of Preparation Example 1, and the remaining implementation conditions are the same as those of Example 1, obtaining the composite gel plugging slurry DS4.

[0098] The components and contents of DS4 are shown in Table 2.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103]

[0104] Test Example

[0105] The gel plugging agents D1 - D4 prepared in Preparation Examples 1 - 4 were subjected to gel strength tests. Here, the simple gel strength determination method - visual inspection code method was selected to evaluate whether they have plugging strength. The rheological properties of the gel plugging slurries prepared in Examples 1 - 6 and Comparative Examples 1 - 4 were tested according to GB / T 16783.1 - 2014 "Petroleum and natural gas industries - Drilling fluids - Field testing - Part 1: Water - based drilling fluids", and the plugging performance tests were carried out. The self - developed nitrogen cylinder pressurizing device and plugging instrument were used for the plugging performance tests. In the following test examples,

[0106] The visual inspection gel strength code standard is shown in Table 3.

[0107] Table 3

[0108]

[0109]

[0110] The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), and yield point (YP, Pa) were measured using a six - speed rotational viscometer according to the method specified in GB / T 29170 - 2012;

[0111] The manufacturer of the six - speed rotational viscometer is Sidi Laibo Company, and the model is ZNN - D6S;

[0112] The simulated core is a steel core with a length of 5 cm and a diameter of 2.5 cm, showing an S - shape as a whole, which can simulate the complex trend of formation fractures to a certain extent. Steel cores with different slit widths are used to simulate fractures with different widths, and the plugging pressure of the plugging material in the steel cores with different slit widths is measured to characterize the plugging performance of the plugging gel system;

[0113] Combined with the fact that the original formation fracture width generally ranges from 1 to 1.5 mm, steel cores with fracture widths of 1 mm, 2 mm, and 3 mm were selected in the test example to conduct simulation experiments on fracture plugging performance evaluation.

[0114] 1. Gel strength test

[0115] Take 100 parts by weight of the prepared composite gel plugging agents D1 - D4 respectively in a stirring cup, add 2000 parts by weight of deionized water to it, stir at a speed of 10000 r / min, and heat in a constant temperature water bath at 60 °C and 80 °C. Observe the change of the solution state every 0.5 h to determine the gel time. The test results are shown in Table 4.

[0116] Table 4 Gel strength test results

[0117]

[0118]

[0119] The gelation times of the plugging agents D1 - D4 prepared in the preparation examples are all between 10 - 12 h. At 60 °C and 80 °C, the maximum gel strength can reach grade E low - fluidity gel. It can be seen that the gel plugging agent of the present invention has good gelation performance, and the gelation performance is less affected by temperature and the gelation time range is more moderate. Therefore, the gel plugging agent of the present invention has plugging gel strength.

[0120] 2. Gel viscosity test

[0121] Referring to GB / T16783.1 - 2014 "Petroleum and natural gas industries - Drilling fluids - Field testing - Part 1: Water - based drilling fluids", the composite gel plugging slurries prepared in Examples 1 - 6 and Comparative Examples 1 - 4 were evaluated. The test results are shown in Table 5.

[0122] Table 5 Gel viscosity test results

[0123]

[0124]

[0125] From the test results in Table 5, it can be seen that the gel plugging system prepared in the examples has good dissolution and dispersion properties. There is no agglomeration phenomenon in the gel system, and the apparent viscosity also has stability. It has good rheological properties at 60 °C and 80 °C, and the overall change trend is small. It can also maintain good shear rheological properties during the weighting process of Examples S5 and S6.

[0126] 3. Plugging performance test

[0127] The plugging performance test is carried out using a nitrogen cylinder pressurization device and a leak stoppage detector. Since the present invention is directed to the study of plugging for fractured formations, this device is used in conjunction with a steel core. The steel core is 5 cm long and 2.5 cm in diameter, and is in an S shape as a whole. It can simulate the complex trend of formation fractures to a certain extent, and steel cores with different slit widths are used to simulate fractures with different widths. The plugging pressure of the plugging material in the steel cores with different slit widths is measured to characterize the plugging performance of the plugging gel system.

[0128] The test method is to immerse the steel core in the gel plugging system slurry prepared in Examples 1-6, make it fully contact with the gel slurry, and place it in a roller heating furnace to form a gel; then rotate the connecting bolt, remove the three-way body of the leak stoppage detector, screw the steel core with the gel plugging agent into the outlet of the ball valve, then screw the connecting bolt in and tighten it, close the gas valve, and unscrew the sealing nut below the leak stoppage detector; open the ball valve, place a graduated collecting bucket at the outlet, pour 400 mL of drilling fluid into the sleeve of the leak stoppage detector; screw in the screw cap of the reverse drainage device, fix the pin to connect the three-way assembly, and rotate the pressure increasing valve clockwise to increase the pressure at a speed of 0.01 MPa each time. After each pressure increase, maintain it for 10 minutes until the pressure is increased to 0.07 MPa, and then increase the pressure at a speed of 0.07 MPa each time. Also ensure that it is maintained for 10 minutes after each pressure increase. Observe whether there is liquid discharge in the collecting bucket during the pressure increase process. When a large amount of liquid is discharged, stop pressurizing, and record the previous pressure as the maximum plugging pressure of the gel; gradually increase the slit width of the steel core, repeat the above experiment, and record the experimental results.

[0129] The composite gel plugging agent of the present invention is applicable to formation fractures with a slit width of 1-1.5 mm. In the experimental test, steel cores with slit widths of 1 mm, 2 mm, and 3 mm are selected for the plugging performance evaluation experiment. The experimental results of the plugging performance test are shown in Figure 3 .

[0131] According to the results of the plugging ability performance test of the plugging gel, when the plugging gel system of the present invention contains 118 parts by weight of the composite gel plugging agent, the plugging pressures in the steel cores with slit widths of 1 mm, 2 mm, and 3 mm are 2.55 MPa, 1.70 MPa, and 1.50 MPa respectively. As the content of the composite plugging gel increases, the plugging pressure increases significantly. And after the gel plugging system is weighted with barite, the plugging pressures in the steel cores with slit widths of 1 mm, 2 mm, and 3 mm can reach 5 MPa, which proves that the composite gel plugging agent and the composite gel plugging system of the present invention have excellent overall plugging performance and relatively high strength.

Claims

1. A preparation method and application of a composite gel plugging agent suitable for fractured reservoirs, comprising the following steps: (1) Using a measuring cylinder to measure deionized water, add it to a drilling fluid cup, weigh the crosslinking agent B, add it to the drilling fluid cup, stir to dissolve the crosslinking agent B, and obtain a crosslinking agent B aqueous solution; (2) Weighing the gel main agent A and adding it to the aqueous solution of the crosslinking agent B in step (1), stirring for a period of time, and then standing at a corresponding temperature for a period of time until the reaction is complete and a gel is obtained; (3) The gel obtained in step (2) is completely immersed in alcohol, taken out after washing, dried at low temperature, and crushed to obtain a composite gel plugging agent.

2. The method according to claim 1, wherein: In steps (1) to (2), the raw materials include the following components in weight: the weight ratio of gel main agent A: cross-linking agent B: deionized water is (2-60): (10-140): (2000-3000); Preferably, the weight ratio of the components is preferably (40-60): (60-80): 2000.

3. The gel main agent A in the composite gel plugging agent according to claim 2, characterized in that: The main material of the gel is one of guar gum, xanthan gum (#1, #2) and hydrolyzed polyacrylamide PHPA (molecular weight of 200w-1400w, molecular weight of 1500w-1800w); Preferably, the gel main agent A is preferably hydrolyzed polyacrylamide PHPA (molecular weight is 1500w-1800w).

4. The crosslinking agent B in the composite gel plugging agent according to claim 2, characterized in that: The cross-linking agent material is one of organic zirconium, organic boron, organic titanium, phenolic resin and formaldehyde; Preferably, the crosslinking agent B is organic zirconium.

5. According to the present invention, in step (3), the post-reaction alcohol washing process uses one of anhydrous ethanol and isopropanol, preferably anhydrous ethanol.

6. The method for preparing the composite gel plugging agent according to claim 1, wherein: In step (1), the crosslinking agent B is dissolved and stirred at a speed of 6000-8000 r / min, and the stirring time is 5-10 min; Preferably, the stirring speed is preferably 8000 r / min, and the stirring time is preferably 10 min.

7. The method for preparing the composite gel plugging agent according to claim 1, wherein: In step (2), the stirring speed of adding the gel main agent into the aqueous solution of the crosslinking agent B is 8000-12000 r / min, and the stirring time is 10-30 min; Preferably, the stirring speed is preferably 10000 r / min, and the stirring time is preferably 30 min.

8. The method for preparing the composite gel plugging agent according to claim 1, wherein: In step (2), the reaction is carried out at a response temperature of 60-100° C. and a reaction time of 8-24 h; Preferably, the reaction temperature is 60-80°C, and the reaction time is 10-12h.

9. The application of the composite gel plugging agent described in claims 1-8 is a composite gel plugging system suitable for fractured reservoirs.

10. A composite gel plugging system for fractured reservoirs according to claim 10, wherein: The composite gel plugging system comprises the following components: 1000-2000 parts by weight of deionized water, 30-60 parts by weight of hydrolyzed polyacrylamide (PHPA), 40-100 parts by weight of organic zirconium, 10-30 parts by weight of walnut shell, 10-40 parts by weight of water-soluble short fibers, and 0.5-2 parts by weight of gel enhancer (AAC); Preferably, the composite gel plugging system comprises the following components: 1000 parts by weight of deionized water, 35-40 parts by weight of hydrolyzed polyacrylamide (PHPA), 60-80 parts by weight of organic zirconium, 15-25 parts by weight of walnut shell, 20-30 parts by weight of water-soluble short fibers, and 1-1.5 parts by weight of gel enhancer (AAC).

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