[0024] Hereinafter, the present invention will be specifically described through exemplary embodiments. It should be understood, however, that elements, structures and features of one embodiment may be beneficially combined in other embodiments without further recitation.
[0025] Early strongly cemented sandstones are common in reservoirs, and the physical property evolution of this type of sandstone is usually only affected by early cementation and compaction before cementation.
[0026] In order to determine the physical properties of the sandstone reservoirs before the cementation of the above types of rocks, see figure 1 , an embodiment of the present invention provides a method for determining the physical properties of sandstone reservoirs before cementation occurs, and the specific steps are:
[0027] S1. For a certain sandstone reservoir, take a plurality of early strongly cemented rock samples, and drill, cut and grind each rock sample for pretreatment to obtain a rock sample with a diameter of 2.5cm and a length of 4cm, and remove the rock. Residual crude oil in the sample; dry the rock sample at 60℃ for 2 days to remove the residual water in the rock sample, and then test the porosity of the rock sample φ 0 and permeability K 0.
[0028] S2. Under normal temperature conditions, put the rock sample into a beaker, and add 0.3% acetic acid solution to the beaker until the rock sample is immersed. After standing for 1 hour, replace the acetic acid solution and repeat the above process until the rock sample has no bubbles. emerge.
[0029] S3. Wash the rock samples with deionized water several times, and dry the rock samples at a temperature of 60 °C for 2 days to remove the residual water in the rock samples, and then use the gas measurement method to test the porosity of the rock samples φ 1 and permeability K 1 , the measured porosity φ 1 and permeability K 1 That is, the physical properties of the reservoir before cementation occurs.
[0030] In this embodiment, in order to facilitate statistics of the area occupied by calcite cement, alizarin and potassium ferricyanide solutions are used to dye rock slices. When counting the area occupied by calcite cement, the calcite cement is dyed red.
[0031] In the above method of this embodiment, the physical properties of the early strongly cemented sandstone are measured, that is, the porosity φ is measured. 0 and permeability K 0 On the basis of , use dilute acetic acid to dissolve the sandstone samples, restore the sandstone state before strong cementation, and conduct gas measurement on the rock samples to determine the real physical properties of the historical period, effectively avoiding the human factors in the process of statistics and calculation. The impact is more consistent with the actual geological situation, and the results are more accurate.
[0032] In order to determine the physical properties of the sandstone reservoir before the cementation of the above types of rocks, continue to refer to Figure 1, another embodiment of the present invention provides a method for determining the physical properties of the sandstone reservoir before the cementation occurs, and the specific steps are as follows:
[0033] S1. For a certain sandstone reservoir, take a plurality of early strongly cemented rock samples, and drill, cut and grind each rock sample for pretreatment to obtain a rock sample with a diameter of 2.5cm and a length of 4cm, and remove the rock. Residual crude oil in the sample; drying the rock sample at 60°C for 2 days to remove the residual water in the rock sample, and then testing the porosity φ of the rock sample by gas measurement 0 and permeability K 0.
[0034] S2. Under normal temperature conditions, put the rock sample into a beaker, and add 0.3% acetic acid solution to the beaker until the rock sample is immersed. After standing for 1 hour, replace the acetic acid solution and repeat the above process until the rock sample has no bubbles. emerge.
[0035] S3. Wash the rock samples with deionized water several times, and dry the rock samples at a temperature of 60 °C for 2 days to remove the residual water in the rock samples, and then use the gas measurement method to test the porosity of the rock samples φ 1 and permeability K1 , the measured porosity φ 1 and permeability K 1 That is, the physical properties of the reservoir before cementation occurs.
[0036] S4. For each rock sample, select undissolved rock samples to grind rock slices with a thickness of 30 μm, dye the rock slices, and then select 10 representative rock slices for each rock slice by using a microscope and an image analysis system matched with the microscope Field of view, count the area S occupied by dyed calcite cement in rock slices 1 , calculate the total area S of the 10 viewsheds 2 , using the formula S=S 1 /S 2 ×100% Calculate the two-dimensional area ratio of rocks filled with calcite cement;
[0037] S5. Porosity φ obtained from multiple rock samples 0 , permeability K 0 , porosity φ 1 , permeability K 1 , area S 1 and the total area S 2 , the fitted porosity difference φ 1 -φ 0 and S, the permeability difference K 1 -K 0 Quantitative functional relationship with the two-dimensional area ratio S of the rock;
[0038] S6. On the basis of the delineation of the area ratio of the cement, and according to the quantitative function relationship, quantitatively restore the ancient property before the early strong cementation.
[0039] In this embodiment, in order to facilitate statistics of the area occupied by calcite cement, alizarin and potassium ferricyanide solutions are used to dye rock slices. When counting the area occupied by calcite cement, the calcite cement is dyed red.
[0040] In the above method of this embodiment, the physical properties of the early strongly cemented sandstone are measured, that is, the porosity φ is measured. 0 and permeability K 0 On the basis of , use dilute acetic acid to dissolve the sandstone samples, restore the sandstone state before strong cementation, and conduct gas measurement on the rock samples to determine the real physical properties of the historical period, effectively avoiding the human factors in the process of statistics and calculation. The impact is more consistent with the actual geological situation, and the results are more accurate. In the present invention, the two-dimensional area ratio S of carbonate cements is calculated by dyed rock slices, and the porosity difference φ before and after acid dissolution is fitted. 1 -φ 0 , the permeability difference K 1 -K 0 According to the functional relationship, the ancient properties before the early strong cementation can be quantitatively recovered for rock samples with similar characteristics, which can provide reference for other regions, and thus provide a reference for the recovery of physical properties evolution of sandstone reservoirs in geological history.
[0041] The above-mentioned method of the present invention is described below by taking the determination process of the physical properties of the sandstone reservoir before the occurrence of rock cementation of the XX reservoir in a certain area of Dagang Oilfield as an example.
[0042] S1. For the XX reservoir rock in a certain area of Dagang Oilfield, select 4 early strongly cemented rock samples, and obtain rock samples with a diameter of 2.5cm and a length of 4cm by drilling, cutting and grinding. Wash the oil to remove the residual crude oil in the rock samples; dry the rock samples at a temperature of 60 °C for 2 days to remove the residual water in the rock samples, and then use the gas measurement method to test the porosity of the rock samples φ 0 and permeability K 0 , and its specific physical properties are shown in Table 1.
[0043] Table 1
[0044] Numbering rock sample 1 rock sample 2 rock sample 3 rock sample 4 φ 0 /%
[0045] S2. Under normal temperature conditions, put the rock sample into a 50ml beaker, and add 0.3% acetic acid solution to the beaker until the rock sample is immersed. After standing for 1 hour, replace the acetic acid solution and repeat the above process until the rock sample has no Bubble emerges, and the photo of the rock sample after the dissolution of the rock sample is shown in figure 2.
[0046] S3. Wash the rock samples with deionized water several times, and dry the rock samples at a temperature of 60 °C for 2 days to remove the residual water in the rock samples, and then use the gas measurement method to test the porosity of the rock samples φ 1 and permeability K 1 , the measured porosity φ 1 and permeability K 1 It is the physical properties of the reservoir before cementation occurs, and the physical properties of the rock samples after dissolution are shown in Table 2.
[0047] Table 2
[0048] Numbering rock sample 1 rock sample 2 rock sample 3 rock sample 4 φ 1 /%
[0049] S4. For each rock sample, select undissolved rock samples to grind rock slices with a thickness of 30 μm, dye the rock slices, and then select 10 representative rock slices for each rock slice by using a microscope and an image analysis system matched with the microscope Field of view, count the area S occupied by dyed calcite cement in rock slices 1 , calculate the total area S of the 10 viewsheds 2 , using the formula S=S 1 /S 2 ×100% Calculate the two-dimensional area ratio of the rock filled with calcite cement, see the photo of the undissolved part of the rock thin section image 3.
[0050] S5. The porosity φ obtained from each rock sample 0 , permeability K 0 , porosity φ 1 , permeability K 1 , area S 1 and the total area S 2 , the fitted porosity difference φ 1 -φ 0 and S, the permeability difference K 1 -K 0 Quantitative functional relationship with the rock two-dimensional area ratio S, the functional relationship diagram is shown in Figure 4.
[0051] S6. On the basis of the delineation of the area ratio of the cement, and according to the quantitative function relationship, quantitatively restore the ancient property before the early strong cementation.
[0052] In order to illustrate the advantages of the above method of the present invention more clearly, for the same rock sample, the above method of the present invention and the existing "inversion back stripping method" are used to obtain the antiquities of the rock sample. Sexual results see Figure 5 , in the figure, the paleo-porosity obtained by the method for determining the physical properties of the sandstone reservoir before cementation proposed by the present invention is φ 1 , the ancient permeability is K 1 , the paleoporosity calculated by the existing "inversion back-stripping method" is φ 2 , the ancient permeability is K 2. Depend on Figure 5 It can be seen that for the same rock sample, the paleo-porosity and paleo-permeability obtained by the two methods are significantly different. The method for determining the physical properties of the sandstone reservoir before the occurrence of cementation proposed in the present invention directly measures the physical properties of the sandstone before the occurrence of cementation, effectively avoiding the artificial influence in the process of statistics and calculation, and the overall porosity is relatively high, or carbon in fine pores It is obtained by melting the salt cement, which is in good agreement with the actual geological situation, and the result is more accurate.
[0053] The above-mentioned embodiments are used to explain the present invention rather than limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims all fall into the protection scope of the present invention.
