A method for improving the initial oil saturation of heterogeneous cast cores

Abstract

The present invention provides a method for increasing the initial oil saturation of heterogeneous cast cores, belonging to the technical field of oil and gas field development. The present invention provides a core complex to be saturated with a specific structure; then the core complex to be saturated is evacuated and saturated with water to obtain a water-saturated core; the water-saturated core is longitudinally saturated with oil to obtain a longitudinally oil-saturated core; and the longitudinally oil-saturated core is transversely saturated with oil to obtain an oil-saturated artificial heterogeneous core. The oil-saturated artificial heterogeneous core obtained by the method for increasing the initial oil saturation of heterogeneous cast cores provided by the present invention has a saturation of up to 87%, can increase the saturation of the low-permeability layer of the heterogeneous cast core, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of the core displacement experiment, and providing a guarantee for formulating a plan on site.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and particularly relates to a method for improving the initial oil saturation of heterogeneous cast cores. Background Art

[0002] Polymer flooding and formation water absorption profile adjustment are targeted at heterogeneous reservoirs. Therefore, heterogeneous cores must be used in indoor core flow experiments. However, it is almost impossible to obtain heterogeneous natural cores that meet the requirements of core flow experiments. Therefore, artificial cemented heterogeneous cores are generally used in laboratory research. For the convenience of production, strip-shaped longitudinal heterogeneous cores are generally made according to the simulated formation permeability profile.

[0003] For heterogeneous cores, due to the heterogeneity of the cores, the existing single-directional oil saturation during the oil saturation process often results in a very high saturation in the high-permeability layer and a very low saturation in the medium and low-permeability layers, making it difficult to simulate the actual formation situation. In this case, when conducting core displacement experiments, the water flooding and chemical flooding recovery rates are often too high, and the data obtained are difficult to reflect the actual situation, thus misleading the oil production technology implemented in the field.

[0004] Therefore, how to increase the saturation of the low-permeability layer of heterogeneous cast cores, obtain an oil-saturated artificial heterogeneous core closer to the initial oil saturation of natural cores, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of core displacement experiments, and providing a guarantee for formulating field plans has become an urgent technical problem in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the initial oil saturation of heterogeneous cast cores. The method for improving the initial oil saturation of heterogeneous cast cores provided by the present invention can increase the saturation of the low-permeability layer of heterogeneous cast cores, obtain an oil-saturated artificial heterogeneous core closer to the initial oil saturation of natural cores, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of core displacement experiments, and providing a guarantee for formulating field plans.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for improving the initial oil saturation of heterogeneous cast cores, comprising the following steps:

[0008] (1) Provide a core complex to be saturated;

[0009] The core complex to be saturated includes a longitudinal heterogeneous core, a plate, and a first epoxy resin layer;

[0010] The plate includes a transverse plate covering two transverse end faces of the longitudinal heterogeneous core and a longitudinal plate covering two opposite longitudinal end faces of the longitudinal heterogeneous core; the first epoxy resin layer is coated on the outer surfaces of the longitudinal heterogeneous core and the plate;

[0011] A groove is provided on the inner side of the plate; a through hole penetrating the plate and the first epoxy resin layer is provided on the groove;

[0012] (2) After evacuating the saturated core composite obtained in the step (1), saturate it with water to obtain a water-saturated core;

[0013] (3) Vertically saturate the water-saturated core obtained in the step (2) with oil to obtain a vertically oil-saturated core;

[0014] (4) Horizontally saturate the vertically oil-saturated core obtained in the step (3) with oil to obtain an oil-saturated artificial heterogeneous core.

[0015] Preferably, the number of through holes on each groove in the step (1) is two.

[0016] Preferably, a valve matching the hole size is installed on each through hole in the step (1).

[0017] Preferably, the thickness of the plate in the step (1) is 1 - 2.5 cm.

[0018] Preferably, a second epoxy resin layer is coated on the two longitudinal end faces of the longitudinal heterogeneous core not covered by the plate in the step (1).

[0019] Preferably, the second epoxy resin layer is cured from a high-viscosity epoxy resin, and the viscosity of the high-viscosity epoxy resin is 80 - 100 cP.

[0020] Preferably, the longitudinal heterogeneous core in the step (1) includes permeable layers with different permeabilities, and partitions are provided at both ends close to the longitudinal plate between adjacent permeable layers.

[0021] Preferably, the thickness of the partition is 0.05 - 0.15 cm, the width is 0.4 - 0.6 cm, and the length is 4 - 4.5 cm.

[0022] Preferably, after the vertical oil saturation in the step (3), it further includes injecting a filler into the groove of the transverse plate and then curing.

[0023] Preferably, the filler is an oily epoxy resin.

[0024] The present invention provides a method for improving the initial oil saturation of heterogeneous cast cores, comprising the following steps: (1) providing a core complex to be saturated; the core complex to be saturated includes a longitudinally heterogeneous core, a plate, and a first epoxy resin layer; the plate includes a transverse plate covering two transverse end faces of the longitudinally heterogeneous core and a longitudinal plate covering two opposite longitudinal end faces of the longitudinally heterogeneous core; the first epoxy resin layer covers the outer surfaces of the longitudinally heterogeneous core and the plate; a groove is provided on the inner side of the plate; a through hole penetrating the plate and the first epoxy resin layer is provided on the groove; (2) evacuating the core complex to be saturated obtained in step (1) and then saturating it with water to obtain a water-saturated core; (3) longitudinally saturating the water-saturated core obtained in step (2) with oil to obtain a longitudinally oil-saturated core; (4) transversely saturating the longitudinally oil-saturated core obtained in step (3) with oil to obtain an oil-saturated artificial heterogeneous core. By installing a plate with grooves and through holes on the transverse and longitudinal end faces of the longitudinally heterogeneous core, the present invention enables oil to enter the groove through the through hole and contact the core during the oil saturation process, which can expand the contact area between oil and the core during the oil saturation process and achieve sufficient oil saturation in a single direction; longitudinally saturating with oil and then transversely saturating with oil enables the core to be completely saturated longitudinally and transversely, improves the saturation of the low-permeability layer of the heterogeneous cast core, and obtains an oil-saturated artificial heterogeneous core closer to the initial oil saturation of the natural core, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of the core displacement experiment, and providing a guarantee for formulating a plan on site. The results of the examples show that the saturation of the oil-saturated artificial heterogeneous core obtained by the method for improving the initial oil saturation of heterogeneous cast cores provided by the present invention can reach 87%, which can improve the saturation of the low-permeability layer of the heterogeneous cast core, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of the core displacement experiment, and providing a guarantee for formulating a plan on site. Description of the Drawings

[0025] Figure 1 Schematic structural diagram of the longitudinally heterogeneous core and the plate in Example 1 of the present invention;

[0026] Figure 2 Exploded view of the structure of the longitudinally heterogeneous core and the plate in Example 1 of the present invention. Detailed Embodiments

[0027] The present invention provides a method for improving the initial oil saturation of heterogeneous cast cores, comprising the following steps:

[0028] (1) Providing a core complex to be saturated;

[0029] The core complex to be saturated includes a longitudinally heterogeneous core, a plate, and a first epoxy resin layer;

[0030] The plate includes a transverse plate covering two transverse end faces of the longitudinal heterogeneous core and a longitudinal plate covering two opposite longitudinal end faces of the longitudinal heterogeneous core; the first epoxy resin layer coats the outer surfaces of the longitudinal heterogeneous core and the plate;

[0031] A groove is provided on the inner side of the plate; a through hole penetrating the plate and the first epoxy resin layer is provided on the groove;

[0032] (2) After evacuating the to-be-saturated core complex obtained in the step (1), saturate it with water to obtain a water-saturated core;

[0033] (3) Vertically saturate the water-saturated core obtained in the step (2) with oil to obtain a vertically oil-saturated core;

[0034] (4) Horizontally saturate the vertically oil-saturated core obtained in the step (3) with oil to obtain an oil-saturated artificial heterogeneous core.

[0035] The present invention provides a to-be-saturated core complex.

[0036] In the present invention, the to-be-saturated core complex includes a longitudinal heterogeneous core, a plate, and a first epoxy resin layer; the plate includes a transverse plate covering two transverse end faces of the longitudinal heterogeneous core and a longitudinal plate covering two opposite longitudinal end faces of the longitudinal heterogeneous core; the first epoxy resin layer coats the outer surfaces of the longitudinal heterogeneous core and the plate; a groove is provided on the inner side of the plate; a through hole penetrating the plate and the first epoxy resin layer is provided on the groove.

[0037] In the present invention, the to-be-saturated core complex includes a longitudinal heterogeneous core.

[0038] In the present invention, the longitudinal heterogeneous core preferably includes permeable layers with different permeabilities.

[0039] In the present invention, the number of the permeable layers is preferably more than 2 layers, more preferably 2 - 4 layers. In an embodiment of the present invention, the longitudinal heterogeneous core includes a high-permeability layer and a low-permeability layer.

[0040] In the present invention, the permeability of the high-permeability layer is preferably 2000 - 3000 mD; the thickness of the high-permeability layer is preferably 2 - 4 cm, more preferably 3 cm; the permeability of the low-permeability layer is preferably 800 - 1500 mD; the thickness of the low-permeability layer is preferably 2 - 4 cm, more preferably 3 cm.

[0041] In an embodiment of the present invention, partitions are provided at both ends of the adjacent infiltration layers close to the longitudinal plate. In an embodiment of the present invention, partitions are provided at both ends of the high-infiltration layer and the low-infiltration layer close to the longitudinal plate. The present invention provides partitions at both ends of the high-infiltration layer and the low-infiltration layer close to the longitudinal plate, which can prevent the formation oil in the groove from directly flowing into the high-infiltration layer at the junction of the high-infiltration layer and the low-infiltration layer during the subsequent saturated oil process, and can improve the oil saturation rate and oil saturation degree of the low-infiltration layer.

[0042] In the present invention, the preparation method of the longitudinal heterogeneous core preferably includes the following steps:

[0043] (a) Mix quartz sands of different specifications with a cementing agent and a salt solution respectively to obtain mixtures of different specifications;

[0044] (b) Subject the mixtures of different specifications obtained in step (a) to high-pressure molding in a mold in sequence, and then cure them to obtain a longitudinal heterogeneous core.

[0045] The present invention preferably mixes quartz sands of different specifications with a cementing agent and a salt solution respectively to obtain mixtures of different specifications.

[0046] The present invention has no special limitation on the specifications of the quartz sand, and it can be selected according to the permeability of the core layer according to the common general knowledge in the art. In the present invention, the mesh number of the quartz sand is preferably 60-400 meshes. In the present invention, the quartz sand is a mixture of the above-mentioned quartz sands with different mesh numbers. In the present invention, the specific mesh number and proportion of the quartz sand can be selected according to the permeability of the core layer.

[0047] In an embodiment of the present invention, the quartz sand in the low-infiltration layer is a mixture of 60-mesh and 400-mesh quartz sands; the mass ratio of the 60-mesh quartz sand to the 400-mesh quartz sand in the mixture of the 60-mesh and 400-mesh quartz sands is 5:3; the quartz sand in the high-infiltration layer is a mixture of 60-mesh and 200-mesh quartz sands; the mass ratio of the 60-mesh quartz sand to the 200-mesh quartz sand in the mixture of the 60-mesh and 200-mesh quartz sands is 1:1.

[0048] In the present invention, the cementing agent preferably includes epoxy resin and an epoxy curing agent; the epoxy resin is preferably high-purity linear epoxy resin, and more preferably 669E epoxy resin. The present invention limits the types of the cementing agent within the above range to ensure the preparation of the core.

[0049] In the present invention, the mass ratio of the quartz sand to the cementing agent is preferably (8-9):(1-2), and more preferably 8.5:1.5. The present invention limits the mass ratio of the quartz sand to the cementing agent within the above range to ensure that the artificial core has properties similar to those of the natural core.

[0050] In the present invention, the solute in the salt solution is preferably sodium chloride and calcium chloride. The present invention does not have any special limitation on the mixing ratio of sodium chloride and calcium chloride. The liquid mixture of the present invention can make the raw materials mix evenly.

[0051] In the present invention, the ratio of the total mass of the quartz sand and the cement to the mass of the salt solution is preferably (10 - 15):1, more preferably (12 - 13):1. By limiting the ratio of the total mass of the quartz sand and the cement to the mass of the salt solution within the above range, the raw materials and the liquid mixture can be fully mixed together, making the raw materials obtained after stirring more homogeneous, without caking, and ensuring the quality of the artificial core.

[0052] In the present invention, the mixing of the quartz sand, the cement and the salt solution is preferably carried out in a rotary stirrer; there is no special limitation on the mixing time of the present invention, as long as the quartz sand, the cement and the liquid mixture can be mixed evenly.

[0053] After the mixing is completed, the present invention preferably screens the mixed product respectively to obtain mixed materials of different specifications. In the present invention, the screening is preferably through a 20-mesh sieve.

[0054] After obtaining the mixed materials of different specifications, the present invention preferably subjects the mixed materials of different specifications to high-pressure molding in a mold in sequence, and then cures them to obtain a longitudinally heterogeneous core.

[0055] The present invention preferably subjects one layer of the mixed material to high-pressure molding to obtain a layer of infiltration layer blank, and then lays the mixed material of the adjacent layer on the obtained infiltration layer blank for high-pressure molding until the high-pressure molding of all the infiltration layer blanks is completed. In the present invention, the pressure of the high-pressure molding of each layer of the mixed material is preferably independently 250 - 350 kN, more preferably 300 kN; the time of the high-pressure molding is preferably independently 25 - 35 min, more preferably 30 min. By limiting the pressure and time of the high-pressure molding within the above range, cores with corresponding permeabilities can be obtained.

[0056] In the present invention, the mold used in the preparation process of the longitudinally heterogeneous core preferably consists of side plates, end plates, a bottom plate and a pressing block; the mold preferably consists of a bottom plate, two opposite side plates, two opposite end plates and a pressing block placed opposite to the bottom plate to form a rectangular mold; the bottom plate, the side plates, the end plates and the pressing block are all made of steel structures.

[0057] In the present invention, the specific operation of subjecting each layer of the mixture to high-pressure forming is preferably as follows: evenly spread the mixture on the bottom plate in the mold or on the upper layer of the infiltration layer blank, then scrape the upper surface of the mixture smooth with a sand scraping plate, then place the pressing block into the mold to compact the mixture, adjust the position of the mold to keep it on the center line of the pressure plate of the press, then slowly increase the pressure to the forming pressure, relieve the pressure after stabilizing the pressure, and obtain the infiltration layer blank.

[0058] In the present invention, when a partition is provided between adjacent infiltration layers, it is preferably that after obtaining the first infiltration layer blank, partitions are placed at both ends of the first layer close to the longitudinal plate, and then the preparation of the second infiltration layer blank is carried out.

[0059] The present invention preferably cures after all the infiltration layer blanks are prepared. In the present invention, the temperature of the curing is preferably 80 - 100 °C, more preferably 80 - 90 °C; the time of the curing is preferably 6 - 8 h, more preferably 7 h. Limiting the temperature and time of the curing within the above ranges in the present invention can ensure complete curing.

[0060] In the present invention, the saturated core complex includes a plate; the plate includes a transverse plate covering two transverse end faces of the longitudinal heterogeneous core and a longitudinal plate covering two opposite longitudinal end faces of the longitudinal heterogeneous core.

[0061] As Figure 1 shown, in the embodiment of the present invention, transverse plates are covered on two transverse end faces (end face 1 and end face 2) of the longitudinal heterogeneous core, and longitudinal plates are covered on two opposite longitudinal end faces (end face 3 and end face 4). In the embodiment of the present invention, the sizes of the transverse plate and the longitudinal plate are the same as the sizes of the end faces they cover.

[0062] In the present invention, the thickness of the plate is preferably 1 - 2.5 cm; more preferably, the thickness of the transverse plate is 1.6 cm, and the thickness of the longitudinal plate is 1 cm.

[0063] In the present invention, the material of the plate is preferably bakelite.

[0064] In the embodiment of the present invention, the plate is covered on the surface of the longitudinal heterogeneous core by bonding. The present invention preferably uses epoxy resin for bonding. The present invention has no special limitation on the epoxy resin used for bonding, as long as it can ensure that the epoxy resin does not penetrate into the core and can firmly fix the plate on the core.

[0065] When the thickness of the said plate is less than 1.5 cm, the present invention preferably sets end caps on the outer surface of the plate. The present invention has no special limitation on the thickness of the said end caps, as long as the total thickness range of the plate and the end caps can be within 1.5 - 2.5 cm. Limiting the thickness of the plate or the total thickness of the plate and the end caps within the above range in the present invention can ensure the stability of installing valves on the through holes subsequently.

[0066] As Figure 2 shown, in an embodiment of the present invention, a groove is provided on the inner side of the said plate. By covering the two transverse end faces and the two opposite longitudinal end faces of the longitudinally heterogeneous core with a plate with grooves, the present invention can ensure that the underlying oil can be in full contact with the core during the subsequent oil saturation process.

[0067] In an embodiment of the present invention, the shape of the said groove is a cuboid; the length of the groove on the inner side of the transverse plate is 28 cm, the width is 2.8 cm, and the depth is 0.4 cm; the length of the groove on the inner side of the longitudinal plate is 5.5 cm, the width is 2.8 cm, and the depth is 0.4 cm.

[0068] The present invention has no special requirement for the way of opening the said groove, as long as it can ensure that the area of the groove is as large as possible.

[0069] In an embodiment of the present invention, a second epoxy resin layer is coated on the two longitudinal end faces of the longitudinally heterogeneous core that are not covered with a plate. By setting the second epoxy resin layer, the present invention can prevent the epoxy resin during the pouring process from entering the artificial heterogeneous core.

[0070] In the present invention, the said second epoxy resin layer is preferably cured from a high-viscosity epoxy resin; the viscosity of the high-viscosity epoxy resin is preferably 80 - 100 cP, more preferably 90 cP. Limiting the viscosity of the high-viscosity epoxy resin within the above range in the present invention can prevent the high-viscosity epoxy resin from entering the longitudinally heterogeneous core during brushing.

[0071] In the present invention, the said high-viscosity epoxy resin is preferably mixed by epoxy resin type A and epoxy resin type B; the model of the type A epoxy resin is preferably 708A; the model of the type B epoxy resin is preferably 708B; the mass ratio of the type A epoxy resin to the type B epoxy resin is preferably 10:(6 - 8), more preferably 10:7.

[0072] The present invention preferably applies the said high-viscosity epoxy resin to the surface of the longitudinally heterogeneous core by scraping and then cures it to obtain the second epoxy resin layer. The present invention has no special limitation on the scraping operation, as long as it can ensure that there are no white particles on the surface of the artificial heterogeneous core.

[0073] In the present invention, the core complex to be saturated includes a first epoxy resin layer, and the first epoxy resin layer coats the outer surfaces of the longitudinally heterogeneous core and the plate.

[0074] In the present invention, the thickness of the first epoxy resin layer is preferably 7 - 8 cm, and more preferably 7.2 cm.

[0075] In the present invention, the first epoxy resin layer is preferably formed by curing epoxy resin; the viscosity of the epoxy resin is preferably 40 - 60 cP, and more preferably 50 cP. Limiting the viscosity of the epoxy resin within the above range in the present invention can ensure the smooth progress of the pouring process.

[0076] In the present invention, the epoxy resin is preferably a mixture of type A epoxy resin and type B epoxy resin; the model of the type A epoxy resin is preferably 919A; the model of the type B epoxy resin is preferably 919B; the mass ratio of the type A epoxy resin to the type B epoxy resin is preferably 10:3.

[0077] In the present invention, through holes penetrating the plate and the first epoxy resin layer are provided on the groove. In the present invention, by opening through holes at the groove position, oil can enter the core through the groove.

[0078] In an embodiment of the present invention, the number of through holes on each groove is two. In an embodiment of the present invention, the diameter of the through hole is 1 cm.

[0079] In an embodiment of the present invention, when an end cap is provided on the outer surface of the plate, the through holes on the groove penetrate the plate, the end cap and the first epoxy resin layer. As Figure 1 shown, in an embodiment of the present invention, an end cap is provided on the outside of the longitudinal plate; holes corresponding to the holes of the longitudinal plate are provided on the end cap.

[0080] In an embodiment of the present invention, a valve matching the size of the hole is installed on each through hole. In the present invention, the interior of the core complex to be saturated is connected to the external pipeline through the valve, and the opening and closing of the through hole are realized by controlling the opening and closing of the valve.

[0081] After obtaining the core complex to be saturated, in the present invention, the core complex to be saturated is evacuated and then saturated with water to obtain a water-saturated core.

[0082] In the present invention, the core complex to be saturated is preferably subjected to a leak test before evacuation; the operation of the leak test is preferably: ventilate one through hole of the core complex to be saturated, close the other through holes, and then immerse it in water to observe whether there are bubbles in the water. If no bubbles are generated in the water, it means there is no leak, meeting the test requirements for subsequent oil saturation.

[0083] When bubbles are observed in the water, the present invention preferably re-seals the position where bubbles are generated on the to-be-saturated core complex and continues the leak test until no bubbles are generated in the water.

[0084] In the present invention, the pressure of the vacuum pumping is preferably -0.08 to -0.1 MPa; the time of the vacuum pumping is preferably 4 h. In the present invention, the vacuum pumping is preferably to connect a through-hole in the to-be-saturated core complex to the vacuum pumping device and seal all the other through-holes for vacuum pumping.

[0085] In the present invention, the time of water saturation is preferably 4 h. In the present invention, the operation of water saturation is preferably: connecting at least one through-hole on each of the two longitudinal plates and all the through-holes on the upper transverse plate in the to-be-saturated core complex after vacuum pumping to an intermediate container containing formation water, and sealing the other through-holes. The purpose of water saturation in the present invention is to prepare for subsequent oil saturation, and the oil saturation degree is determined by observing whether water still comes out in the produced fluid.

[0086] In the embodiment of the present invention, the operation of water saturation is specifically: connecting at least one through-hole on each of the longitudinal plates on the 3 end face and the longitudinal plates on the 4 end face and all the through-holes on the transverse plate on the 1 end face in the to-be-saturated core complex after vacuum pumping to an intermediate container containing formation water.

[0087] After obtaining the water-saturated core, the present invention longitudinally saturates the water-saturated core with oil to obtain a longitudinally oil-saturated core.

[0088] In the present invention, the operation of longitudinal oil saturation is preferably: connecting two through-holes on one of the transverse plates of the water-saturated core to an intermediate container containing formation oil, sealing the through-holes on the longitudinal plates, and driving the water in the core out through the two through-holes on the other transverse plate by a pump.

[0089] After the longitudinal oil saturation is completed, the present invention preferably injects a filler into the groove of the transverse plate and cures it to obtain a longitudinally oil-saturated core.

[0090] In the present invention, the filler is preferably an oily epoxy resin; the model of the oily epoxy resin is preferably an oily epoxy resin magnetic self-polymerizing slurry.

[0091] In the present invention, the operation of injecting the filler is preferably as follows: inject oily epoxy resin into a through-hole on one of the transverse plates, displace the formation oil in the groove from another through-hole on this transverse plate, and after standing for 24 h, wait for the epoxy resin to completely solidify; then inject oily epoxy resin into a through-hole on the other transverse plate, displace the formation oil in the groove from another through-hole on this transverse plate, and after standing for 24 h, wait for the epoxy resin to completely solidify. The purpose of injecting the filler in the present invention is to block the two transverse end faces (end face 1 and end face 2) to prevent the formation oil from flowing out from the two transverse end faces (end face 1 and end face 2) when the transverse is saturated with oil.

[0092] After obtaining the longitudinally oil-saturated core, the present invention subjects the longitudinally oil-saturated core to transverse oil saturation to obtain an oil-saturated artificial heterogeneous core.

[0093] In the present invention, the operation of transverse oil saturation is preferably as follows: connect two through-holes on one longitudinal plate of the longitudinally oil-saturated core to an intermediate container containing formation oil, and displace the water in the core through a pump to flow out from the two through-holes on the other longitudinal plate.

[0094] By installing plates with grooves and through-holes on the transverse end faces and longitudinal end faces of the longitudinally heterogeneous core in the present invention, during the oil saturation process, oil enters the groove through the through-hole to contact the core, which can expand the contact area between the oil and the core during the oil saturation process and perform sufficient oil saturation in one direction; sequentially performing longitudinal oil saturation and transverse oil saturation enables the core to be completely saturated longitudinally and transversely, improves the saturation of the low-permeability layer of the heterogeneous cast core, and obtains an oil-saturated artificial heterogeneous core closer to the initial oil saturation of the natural core, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of the core displacement experiment, and providing a guarantee for formulating a plan on site.

[0095] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0096] Example 1

[0097] The present invention provides a method for improving the initial oil saturation of a heterogeneous cast core, which consists of the following steps:

[0098] (1) Provide a core complex to be saturated; the core complex to be saturated consists of a longitudinally heterogeneous core, a plate, an end cap, a first epoxy resin layer, and a second epoxy resin layer;

[0099] The preparation method of the core complex to be saturated is as follows: A layer of high-viscosity epoxy resin is evenly applied to the 5th end face and the 6th end face of the longitudinally heterogeneous core with a length of 30 cm, a width of 2.25 cm, and a height of 6 cm. Subsequently, two transverse plates are bonded to the two transverse end faces and (the 1st end face and the 2nd end face) of the longitudinally heterogeneous core using type 708 epoxy resin, and two longitudinal plates are bonded to the two longitudinal end faces (the 3rd end face and the 4th end face) using type 708 epoxy resin. The material of the plates is bakelite, and grooves are provided on the inner side of the bakelite plates. The thickness of the two transverse plates is 1.6 cm, and the thickness of the two longitudinal plates is 1 cm. The size of the grooves in the two transverse plates is length × width × height = 28 cm × 2.8 cm × 0.4 cm, and the size of the grooves in the two longitudinal plates is length × width × height = 5.5 cm × 2.8 cm × 0.4 cm. Two end caps are respectively adhered to the outer surfaces of the two longitudinal plates, and epoxy resin is applied to the inner side of the end caps and adhered to the two longitudinal plates. The size of the two end caps is length × width × height = 2 cm × 2 cm × 0.6 cm, obtaining the core complex; An epoxy resin layer with a thickness of 7.2 cm is poured on the surface of the core complex. After the epoxy resin layer is cured, through holes with a diameter of 1 cm that penetrate the plates, (end caps), and the first epoxy resin layer are opened at each groove position, and valves matching the hole size are installed on each through hole, obtaining the core complex to be saturated; The viscosity of the epoxy resin used in the poured epoxy resin is 50 cP, and the epoxy resin used in the poured epoxy resin is obtained by mixing type A epoxy resin of model 919 and type B epoxy resin of model 919 in a mass ratio of 10:3;

[0100] (2) Tighten the valves on the core complex to be saturated obtained in step (1), place the core complex to be saturated in water to ensure that no part leaks. Connect a pipeline to the valve on the lower end cap of one of the longitudinal plates (the 3rd end face), close the remaining valves, turn on the compressor at the other end of the pipeline, control the pressure between 0.04 and 0.2 MPa, and observe whether there are bubbles on the surface of the core to be saturated. If no bubbles appear, it means the core is leak-free during pouring. Then, open each valve in sequence and observe whether there are bubbles at each valve to check whether the inside of the core is permeable. Then, connect the valve on the longitudinal plate (the 3rd end face) of the core to be saturated to a vacuum device, close all the remaining valves, turn on the switch of the vacuum device, maintain the vacuum pressure at -0.08 MPa for four hours, and then perform water saturation after vacuuming to obtain a water-saturated core; The operation of water saturation is as follows: Connect the valves on the upper end cap of the longitudinal plate (the 3rd end face) to the two valves on the transverse plate (the 1st end face) in a four-way joint, connect the two valves on the other opposite longitudinal plate (the 4th end face) in a three-way joint, then connect this three-way joint and a four-way joint to another three-way joint, close all the remaining valves, connect the other end of this three-way joint to an intermediate container containing formation water, and saturate for 4 hours;

[0101] (3) Vertically saturate the water-saturated core obtained in step (2) with oil to obtain a vertically oil-saturated core; the operation of vertically saturating with oil is as follows: close the valves on the two vertical plates (end faces 3 and 4), open all 4 valves on the two horizontal plates (end faces 1 and 2), connect the intermediate container containing formation oil to the two valves on one horizontal plate (end face 1) of the core, and sample the two valves on the other horizontal plate (end face 4) respectively. Displace the formation water in the core by a pump, and set the flow rate of the pump to 0.3 mL / min until no more water flows out of the two valves on the other horizontal plate (end face 4); after the vertical oil saturation is completed, inject a filler into the groove of the horizontal plate and then cure it; the operation of injecting the filler is as follows: unscrew the valve on one horizontal plate (end face 1), inject oily epoxy resin from one valve on the groove, displace the formation oil in the groove from the other valve, after standing for 24 h, wait until the epoxy resin completely solidifies, turn the core over, unscrew the valve on the other horizontal end face (end face 2), inject oily epoxy resin from one valve on the groove, displace the formation oil in the groove from the other valve, after standing for 24 h, wait until the epoxy resin completely solidifies;

[0102] (4) Horizontally saturate the vertically oil-saturated core obtained in step (3) with oil to obtain an oil-saturated artificial heterogeneous core; the operation of horizontally saturating with oil is as follows: connect the intermediate container containing formation oil to the two valves on one vertical plate (end face 3) of the core, inject formation oil, set the flow rate of the pump to 0.3 mL / min, and extract the liquid from the valve on the other vertical plate (end face 4) of the core until there is no drop of water in the extracted liquid.

[0103] The preparation method of the vertical heterogeneous core is as follows:

[0104] (a) Take 600 g of 400-mesh quartz sand and 1000 g of 60-mesh quartz sand, stir the two kinds of quartz sand evenly, 120 g of epoxy resin powder and 20 g of epoxy curing agent powder. Then pour the evenly stirred quartz sand and cementing agent into a rotary stirrer and mix well for 30 min, and then mix them with a mixed solution of sodium chloride and calcium chloride for the second time. The process of the second mixing is to put the liquid mixture into a spray bottle, spray the liquid while mixing the raw materials until the raw materials are mixed homogeneously without small blocky sand bodies, and pass through a 20-mesh sieve to obtain a low-permeability layer mixture; take 900 g of 200-mesh quartz sand and 900 g of 60-mesh quartz sand and operate according to the above steps to obtain a high-permeability layer mixture;

[0105] (b) Evenly spread the low-permeability layer mixture on the bottom plate inside the mold, and use a sand scraping board to scrape the upper surface of the raw material until the raw material is evenly distributed and the upper surface is smooth. Then, slowly place the pressing block flat into the mold to compact the raw material. Adjust the position of the mold to keep it on the center line of the pressure machine's bearing plate. Then, slowly increase the pressure. When the pressure reaches 300 kN, keep the pressure stable for 30 minutes and then release the pressure. Take out the pressing block to obtain the first layer of the core (low-permeability layer); Place two 1-mm-thick bakelite boards at the positions parallel to the side plates at the left and right ends on the low-permeability layer. The size of the bakelite board is length × width × height = 4.5 cm × 0.5 cm × 0.1 cm. Then, evenly spread the high-permeability layer mixture on the low-permeability layer. Then, repeat the high-pressure pressing of the low-permeability layer to obtain the second layer of the core (high-permeability layer); Cure at a constant temperature of 85 °C for 7 hours to obtain a longitudinally heterogeneous core; The length of the mold is 30 cm and the width is 4.5 cm; The artificial heterogeneous core is cut by a wire cutting machine into two heterogeneous cores with a length of 30 cm, a width of 2.25 cm, and a height of 6 cm for subsequent casting use; The permeability of the low-permeability layer of the core is 1000 mD and the thickness is 3 cm; The permeability of the high-permeability layer of the core is 2500 mD and the thickness is 3 cm.

[0106] Use a constant flow pump to test the saturation of the oil-saturated artificial heterogeneous core in Example 1. The saturation of the artificial heterogeneous core in Example 1 is 87%, and the total duration of oil saturation is 5 hours.

[0107] Example 2

[0108] The difference between Example 2 and Example 1 is only that no bakelite boards are placed at the positions parallel to the side plates at the left and right ends on the low-permeability layer during the preparation process of the longitudinally heterogeneous core, and the others are the same as in Example 1.

[0109] Use a constant flow pump to test the saturation of the oil-saturated artificial heterogeneous core in Example 2. The saturation of the artificial heterogeneous core in Example 2 is 83%, and the total duration of oil saturation is 6 hours.

[0110] Comparative Example 1

[0111] Comparative Example 1 is an oil-saturated artificial heterogeneous core obtained by the core holder displacement method.

[0112] The saturation of the oil-saturated artificial heterogeneous core obtained by the oil saturation method used in Comparative Example 1 is 75%.

[0113] The saturation of the oil-saturated artificial heterogeneous core obtained by the method for increasing the initial oil saturation of the heterogeneous cast core provided by the present invention can reach 87%. In Example 1, the saturation is increased by 16% compared with Comparative Example 1, and in Example 2, the saturation is increased by 10.7% compared with Comparative Example 1. A partition plate is added during the preparation of the heterogeneous core in Example 1 compared with Example 2, which can make the heterogeneous core saturated completely faster and has a higher saturation. Therefore, the method for increasing the initial oil saturation of the heterogeneous cast core provided by the present invention can increase the saturation of the low-permeability layer of the heterogeneous cast core, thereby improving the accuracy of subsequent water flooding and chemical flooding, ensuring the accuracy of the core displacement experiment, and thus providing a guarantee for formulating a plan on site.

[0114] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for increasing the initial oil saturation of a heterogeneous cast core, comprising the following steps: (1) providing a core complex to be saturated; The core composite to be saturated includes a longitudinally heterogeneous core, a plate and a first epoxy resin layer; The plate comprises a transverse plate covering two transverse end surfaces of the longitudinal heterogeneous core and a longitudinal plate covering two opposite longitudinal end surfaces of the longitudinal heterogeneous core; the first epoxy resin layer is coated on the outer surface of the longitudinal heterogeneous core and the plate; A groove is provided on the inner side of the plate; a through hole is provided on the groove, penetrating the plate and the first epoxy resin layer; (2) evacuating the core complex to be saturated obtained in step (1) and saturating it with water to obtain a water-saturated core; (3) saturating the water-saturated core obtained in step (2) with oil vertically to obtain a vertical oil-saturated core; (4) saturating the longitudinally oil-saturated core obtained in step (3) with oil in a transverse manner to obtain an oil-saturated artificial heterogeneous core; The first epoxy resin layer is formed by curing epoxy resin; the viscosity of the epoxy resin is 40 to 60 cP; In the step (1), a second epoxy resin layer is coated on two longitudinal end surfaces of the longitudinal heterogeneous core uncovered plate; The second epoxy resin layer is formed by curing a high-viscosity epoxy resin, and the viscosity of the high-viscosity epoxy resin is 80-100 cP.

2. The method according to claim 1, characterized in that In the step (1), the number of through holes on each groove is two.

3. The method according to claim 1 or 2, characterized in that: In the step (1), each through hole is installed with a valve matching the hole size.

4. The method according to claim 1, characterized in that In the step (1), the thickness of the plate is 1 to 2.5 cm.

5. The method according to claim 1, characterized in that The longitudinal heterogeneous core in step (1) comprises permeable layers with different permeabilities, and partitions are provided between adjacent permeable layers near both ends of the longitudinal plate.

6. The method according to claim 5, characterized in that The separator has a thickness of 0.05 to 0.15 cm, a width of 0.4 to 0.6 cm, and a length of 4 to 4.5 cm.

7. The method according to claim 1, characterized in that After the longitudinal saturation of oil in step (3) is completed, it also includes injecting a filler into the groove of the transverse plate and then solidifying it.

8. The method according to claim 7, characterized in that The filler is oily epoxy resin.

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