A calculation method for wettability reversal degree of tight sandstone

Abstract

The present invention relates to the technical field of oil and gas field development, and specifically to a method for calculating the degree of wettability reversal of tight sandstone. The method comprises obtaining the spontaneous imbibition time, spontaneous imbibition volume, displacement pressure difference, and displacement volume of a tight sandstone core sample before immersion in a silica nanofluid; obtaining the spontaneous imbibition time, spontaneous imbibition volume, displacement pressure difference, and displacement volume of the tight sandstone core sample after immersion in a silica nanofluid; and then calculating the degree of wettability reversal based on the obtained spontaneous imbibition weight and displacement weight. The present invention establishes a method for calculating the degree of wettability reversal of tight sandstone. The method relies solely on the results obtained from spontaneous imbibition and displacement experiments, and can achieve quantitative evaluation of wettability reversal without destroying the core. This method provides a theoretical reference for improving the recovery rate of tight sandstone gas reservoirs and is of great value for achieving efficient development.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a method for calculating the wettability inversion degree of tight sandstone. Background Art

[0002] The wettability of a rock represents the ability of a liquid to spread on the surface of the rock core and is usually expressed by the size of the contact angle. The strength of the wettability is inversely proportional to the size of the contact angle: the smaller the contact angle, the stronger the wettability, and the larger the contact angle, the weaker the wettability. Tight sandstone gas reservoirs rely on elastic energy extraction, with natural gas and formation water exhibiting two-phase flow in the rock pores and throats. Since the wettability of the rock surface is generally strong, the natural recovery rate of tight sandstone gas reservoirs is generally low. Acidizing treatment and carbon dioxide injection can effectively improve the seepage conditions of the gas reservoir and thus increase the recovery rate. However, the recovery enhancement mechanisms of acidizing treatment and carbon dioxide injection include not only changing the wettability of the rock, but also other recovery enhancement mechanisms such as unblocking and energy replenishment. Relatively little research has been conducted specifically on the wettability of rocks in tight sandstone gas reservoirs.

[0003] Existing research has shown that soaking cores with silica nanofluids can significantly reduce wettability. Methods for evaluating the degree of wettability changes before and after soaking include static wettability measurements, spontaneous imbibition experiments, and displacement experiments. Static wettability measurements offer the most intuitive results, but require core slices. Spontaneous imbibition and displacement experiments, conducted directly on cores, offer the advantage of not destroying the cores. Furthermore, spontaneous imbibition and displacement occur simultaneously within rock pore throats. Therefore, developing a method to calculate the degree of wettability reversal in tight sandstones based on the results of spontaneous imbibition and displacement experiments would be crucial for developing technical strategies to enhance oil recovery in tight sandstone gas reservoirs. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes a method for calculating the wettability inversion degree of tight sandstone.

[0005] The principle of the present invention is:

[0006] According to the experimental principle of spontaneous imbibition experiment, the imbibition amount increases with the increase of imbibition time, but when the imbibition time increases to a certain time, the imbibition amount tends to be stable and no longer changes. The data of the change of imbibition amount with imbibition time is recorded, and the imbibition time at this time is taken as the spontaneous imbibition time, and the imbibition amount corresponding to the spontaneous imbibition time is taken as the spontaneous imbibition amount.

[0007] Therefore, the spontaneous imbibition time of the silica nanofluid before immersion can be obtained by conducting a spontaneous imbibition experiment before immersion. t (0) , and the spontaneous imbibition of silica nanofluids before immersion qimb (0) Similarly, the spontaneous imbibition time of the silica nanofluid after immersion can be obtained by conducting a spontaneous imbibition experiment after immersion. t (1) , and the spontaneous absorption of silica nanofluid after immersion q imb (1) .

[0008] q imb (0) / t (0) represents the spontaneous imbibition rate before immersion, q imb (1) / t (1) Represents the spontaneous imbibition rate after immersion. For spontaneous imbibition experiments, the wettability is proportional to the spontaneous imbibition rate. The stronger the wettability, the faster the spontaneous imbibition rate, and the weaker the wettability, the slower the spontaneous imbibition rate. Since immersion weakens the wettability of dense sandstone, q imb (1) / t (1) < q imb (0) / t (0) , ( q imb (1) / t (1) ) / ( q imb (0) / t (0) ) is smaller, the more obvious the weakening of wettability caused by immersion is.

[0009] According to the experimental principle of the core displacement experiment, the experimental pressure difference increases with the continuous increase of the injection volume. However, when the injection volume increases to a certain extent, the experimental pressure difference tends to be stable and no longer changes. The data of the change of the experimental pressure difference with the injection volume are recorded. The experimental pressure difference at this time is used as the displacement pressure difference, and the injection volume corresponding to the displacement pressure difference is used as the displacement volume.

[0010] Therefore, the core displacement experiment of silica nanofluid was carried out before immersion, and the displacement pressure difference Δ before immersion of silica nanofluid was obtained. p (0) , and the displacement amount of silica nanofluid before immersion q dis (0)Similarly, the core displacement experiment was carried out after the silica nanofluid was soaked, and the displacement pressure difference after the silica nanofluid was obtained. p (1) , and the displacement of silica nanofluid after immersion q dis (1) .

[0011] q dis (0) / Δ p (0) represents the displacement per unit pressure difference before immersion, q dis (1) / Δ p (1) Represents the displacement per unit pressure difference after soaking. For core displacement experiments, the wettability is inversely proportional to the displacement per unit pressure difference. The stronger the wettability, the smaller the displacement per unit pressure difference, and the weaker the wettability, the larger the displacement per unit pressure difference. Since soaking weakens the wettability of tight sandstone, q dis (1) / Δ p (1) > q dis (0) / Δ p (0) , ( q dis (1) / Δ p (1) ) / ( q dis (0) / Δ p (0) ) is larger, the more obvious the weakening of wettability caused by immersion is.

[0012] Spontaneous imbibition experiment ( q imb (1) / t (1) ) / ( q imb (0) / t (0) ) and core flooding experiments ( q dis (1) / Δ p (1) ) / ( q dis (0) / Δ p(0) ) all reflect the degree of wettability weakening caused by immersion. q imb (1) / t (1) ) / ( q imb (0) / t (0) ) is smaller, which means the wettability is weakened more obviously. q dis (1) / Δ p (1) ) / ( q dis (0) / Δ p (0) ) is larger, the more obvious the wettability is weakened.

[0013] During the development of tight sandstone gas reservoirs, spontaneous imbibition and displacement phenomena coexist. If silica nanofluid is used to treat the pore throats of tight sandstone gas reservoir cores, the wettability is weakened, resulting in a decrease in the spontaneous imbibition rate and an increase in the displacement per unit pressure difference. Since the spontaneous imbibition rate is inversely proportional to the recovery factor, and the displacement per unit pressure difference is directly proportional to the recovery factor, the combined effect of the two results in an increase in the recovery factor of tight sandstone gas reservoirs.

[0014] When wettability changes from strong to weak, it means that the wettability has reversed. The greater the degree of wettability reversal, the smaller the spontaneous imbibition rate, the larger the displacement per unit pressure difference, and the greater the increase in recovery rate. Therefore, the degree of wettability reversal determines the degree of recovery improvement. Since the degree of wettability reversal is determined by both the spontaneous imbibition rate and the displacement per unit pressure difference, a calculation formula for the degree of wettability reversal can be established:

[0015] DWR = ω dis ×( q dis (1) ×Δ p (0) ) / ( q dis (0) ×Δ p (1) )- ω imb ×( q imb (1) × t (0) ) / ( q imb(0) × t (1) ) (1)

[0016] Where: DWR is the degree of wettability reversal, dimensionless;

[0017] ω dis is the displacement weight, dimensionless; ω imb is the spontaneous imbibition weight, dimensionless;

[0018] q dis (0) is the displacement before immersion, PV; q dis (1) is the displacement volume after immersion, PV;

[0019] Δ p (0) is the displacement pressure difference before immersion, MPa; Δ p (1) is the displacement pressure difference after immersion, MPa;

[0020] t (0) is the spontaneous imbibition time before immersion, min; t (1) is the spontaneous imbibition time after immersion, min;

[0021] q imb (0) is the spontaneous imbibition volume before immersion, PV; q imb (1) is the spontaneous imbibition volume after immersion, PV.

[0022] According to formula (1), the wettability reversal degree DWR It is determined by spontaneous imbibition and displacement. q dis (1) , Δ p (0) 、 q dis (0) , Δ p (1) 、 q imb (1) 、 t (0) 、 q imb (0) and t(1) are known parameters, ω dis and ω imb is an unknown parameter. According to the spontaneous imbibition experiment, wettability is weakened after soaking, and the spontaneous imbibition amount is reduced after soaking. Therefore, the degree of reduction in spontaneous imbibition amount before and after soaking ( q imb (0) - q imb (1) ) / q imb (0) Represents the degree of wettability reversal due to spontaneous imbibition DWR According to the core displacement experiment, the wettability is weakened after soaking, and the displacement pressure difference is reduced after soaking. Therefore, the degree of reduction in the displacement pressure difference before and after soaking (Δ p (0) -Δ p (1) ) / Δ p (0) Represents the degree of wettability reversal caused by displacement DWR The size of the contribution.

[0023] The reduction degree of spontaneous imbibition before and after immersion ( q imb (0) - q imb (1) ) / q imb (0) and the degree of reduction in displacement pressure difference (Δ p (0) -Δ p (1) ) / Δ p (0) Both represent the contribution size, due to the degree of wettability reversal DWR It is determined by the combination of spontaneous imbibition and displacement. Therefore, the degree of reduction of spontaneous imbibition and the degree of reduction of displacement pressure difference can be normalized to establish the spontaneous imbibition weight. ω imb The calculation formula and displacement weight ω dis The calculation formula is:

[0024] ω imb =(( q imb (0) - q imb (1) ) / qimb (0) ) / (( q imb (0) - q imb (1) ) / q imb (0) +(Δ p (0) -Δ p (1) ) / Δ p (0) ) (2)

[0025] ω dis =((Δ p (0) -Δ p (1) ) / Δ p (0) ) / (( q imb (0) - q imb (1) ) / q imb (0) +(Δ p (0) -Δ p (1) ) / Δ p (0) ) (3)

[0026] According to the experimental results of spontaneous imbibition experiment and core displacement experiment, the wettability reversal degree can be calculated by substituting them into formula (2), formula (3) and formula (1) respectively: DWR , wettability reversal degree DWR The larger it is, the greater the degree to which the recovery rate can be improved.

[0027] The technical effects of the present invention are:

[0028] The present invention establishes a calculation method for the degree of wettability reversal in tight sandstone. Relying solely on the results of spontaneous imbibition and displacement experiments, the method can achieve quantitative evaluation of wettability reversal without destroying the core. This provides a theoretical reference for improving the recovery rate of tight sandstone gas reservoirs and is of great value for achieving efficient development. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Figure 2 shows the recovery factor distribution of tight sandstone core sample 1 before and after immersion in silica nanofluid.

[0030] Figure 2 Figure 2 shows the recovery factor distribution of tight sandstone core sample 2 before and after immersion in silica nanofluid. DETAILED DESCRIPTION

[0031] A method for calculating the wettability reversal degree of tight sandstone is as follows:

[0032] Step 1: Before soaking the dense sandstone core sample in silica nanofluid, a spontaneous imbibition experiment was conducted to obtain the data on the change of imbibition amount with imbibition time. When the imbibition amount no longer changes with the imbibition time, the imbibition time at this time is taken as the spontaneous imbibition time before soaking. t (0) , spontaneous imbibition time before immersion t (0) The corresponding imbibition volume is the spontaneous imbibition volume before immersion q imb (0) ;

[0033] Step 2: After the dense sandstone core sample is soaked in silica nanofluid, a spontaneous imbibition experiment is carried out to obtain the data on the change of imbibition amount with imbibition time. When the imbibition amount no longer changes with the imbibition time, the imbibition time at this time is taken as the spontaneous imbibition time after soaking t (1) , spontaneous imbibition time after immersion t (1) The corresponding imbibition volume is the spontaneous imbibition volume after immersion q imb (1) ;

[0034] Step 3: Conduct a core displacement experiment before soaking the tight sandstone core sample in silica nanofluid to obtain the experimental pressure difference change data with the injection volume. When the experimental pressure difference no longer changes with the injection volume, the experimental pressure difference at this time is used as the displacement pressure difference before soaking Δ p (0) , displacement pressure difference before immersion Δ p (0) The corresponding injection volume is the displacement volume before immersion q dis (0) ;

[0035] Step 4: After the tight sandstone core sample is soaked in silica nanofluid, a core displacement experiment is carried out to obtain the experimental pressure difference change data with the injection volume. When the experimental pressure difference no longer changes with the injection volume, the experimental pressure difference at this time is used as the displacement pressure difference after soaking Δ p (1) , displacement pressure difference after immersion Δ p (1) The corresponding injection volume is the displacement volume after immersionq dis (1) ;

[0036] Step 5: Calculate the spontaneous imbibition weight according to formula (2) ω imb , calculate the displacement weight according to formula (3) ω dis ; Then calculate the wettability reversal degree according to formula (1) DWR .

[0037] Specific experimental cases

[0038] Two tight sandstone core samples were selected. Pre-immersion spontaneous imbibition experiments and core displacement experiments were carried out according to GB / T 28912-2012 Determination of relative permeability of two-phase fluids in rocks and SY / T 5153-2017 Determination of wettability of reservoir rocks. After immersion in 0.4% silica nanofluid for 24 hours, spontaneous imbibition experiments and core displacement experiments were carried out after immersion.

[0039] (1) A spontaneous imbibition experiment was conducted on the tight sandstone core sample 1 before immersion, and a spontaneous imbibition experiment was conducted after immersion in silica nanofluid. The experimental results are shown in Table 1.

[0040] Table 1 Spontaneous imbibition test results of tight sandstone core sample 1

[0041] ;

[0042] It can be seen from Table 1 that the imbibition amount increases with the increase of imbibition time. In the spontaneous imbibition experiment before immersion, when the imbibition time increases to 70 min, the imbibition amount is 0.62 PV. As the imbibition time continues to increase, the imbibition amount no longer changes. That is, the spontaneous imbibition time before immersion of tight sandstone core sample 1 is t (0) =70min, corresponding to the spontaneous absorption before immersion q imb (0) =0.62PV;

[0043] In the spontaneous imbibition experiment after immersion, when the imbibition time increases to 30 min, the imbibition amount is 0.07 PV. As the imbibition time continues to increase, the imbibition amount no longer changes. That is, the spontaneous imbibition time of the tight sandstone core sample 1 after immersion is t (1) =30min, corresponding to the spontaneous absorption after immersion q imb (1) =0.07PV.

[0044] A core flooding experiment was conducted on the tight sandstone core sample 1 before immersion, and a core flooding experiment was conducted after immersion in silica nanofluid. The experimental results are shown in Table 2.

[0045] Table 2 Core flooding test results of tight sandstone core sample 1

[0046] ;

[0047] It can be seen from Table 2 that the experimental pressure difference increases with the increase of injection volume. In the core displacement experiment before immersion, when the injection volume increases to 1.3 PV, the experimental pressure difference is 0.252 MPa. As the injection volume continues to increase, the experimental pressure difference does not change. Therefore, the displacement pressure difference Δ before immersion of the tight sandstone core sample 1 is obtained. p (0) =0.252 MPa, corresponding displacement before immersion q dis (0) =1.3 PV;

[0048] In the core displacement experiment after immersion, when the injection volume increased to 0.9PV, the experimental pressure difference was 0.075MPa. As the injection volume continued to increase, the experimental pressure difference did not change. Therefore, the displacement pressure difference Δ after immersion of the tight sandstone core sample 1 was obtained. p (1) =0.075 MPa, corresponding displacement after immersion q dis (1) =0.9 PV.

[0049] The spontaneous imbibition weight of tight sandstone core sample 1 is calculated according to formula (2): ω imb = 55.82%. The displacement weight of tight sandstone core sample 1 is calculated according to formula (3): ω dis = 44.18%; then, the wettability reversal degree of tight sandstone core sample 1 was calculated according to formula (1): DWR= 0.88.

[0050] (2) A spontaneous imbibition experiment was conducted on the tight sandstone core sample 2 before immersion, and a spontaneous imbibition experiment was conducted after immersion in silica nanofluid. The experimental results are shown in Table 3.

[0051] Table 3 Spontaneous imbibition test results of tight sandstone core sample 2

[0052] ;

[0053] The spontaneous imbibition time before immersion of tight sandstone core sample 2 was obtained t (0)=50min, corresponding to the spontaneous absorption before immersion q imb (0) =0.68 PV, spontaneous imbibition time after immersion t (1) =40min, corresponding to the spontaneous absorption after immersion q imb (1) =0.17PV.

[0054] A core flooding experiment was conducted on the tight sandstone core sample 2 before immersion, and a core flooding experiment was conducted after immersion in silica nanofluid. The experimental results are shown in Table 4.

[0055] Table 4 Core flooding test results of tight sandstone core sample 2

[0056] ;

[0057] The displacement pressure difference Δ before immersion of tight sandstone core sample 2 is obtained p (0) =0.296 MPa, corresponding displacement before immersion q dis (0) =1.0 PV, displacement pressure difference after immersion Δ p (1) =0.174 MPa, corresponding displacement before immersion q dis (0) =0.9 PV.

[0058] The spontaneous imbibition weight of tight sandstone core sample 2 is calculated according to formula (2): ω imb = 64.66%, and the displacement weight of tight sandstone core sample 2 is calculated according to formula (3): ω dis =35.34%; then, the wettability reversal degree of tight sandstone core sample 2 was calculated according to formula (1): DWR= 0.34.

[0059] The recovery factor distribution of tight sandstone core sample 1 before and after immersion in silica nanofluid is shown in Figure 2. Figure 1 As shown in Figure 2, the recovery factor distribution of tight sandstone core sample 2 before and after silica nanofluid immersion is as follows: Figure 2As shown in Figure 2, it can be seen that the recovery rates of tight sandstone core sample 1 and tight sandstone core sample 2 are significantly improved after soaking. Since the wettability reversal degree of tight sandstone core sample 1 is greater than that of tight sandstone core sample 2, and the recovery rate increase of tight sandstone core sample 1 is significantly higher than that of tight sandstone core sample 2, it is confirmed that the wettability reversal degree DWR The larger it is, the greater the degree to which the recovery rate can be improved.

Claims

1. A method for calculating the wettability inversion degree of tight sandstone, characterized in that: Here’s how: Obtain the spontaneous imbibition time of tight sandstone core samples before immersion in silica nanofluid t (0) , spontaneous absorption before immersion q imb (0) , displacement pressure difference before immersion Δ p (0) and displacement before immersion q dis (0) ; Obtaining the spontaneous imbibition time of tight sandstone core samples after being soaked in silica nanofluid t (1) , spontaneous absorption after immersion q imb (1) , displacement pressure difference after immersion Δ p (1) and displacement after immersion q dis (1) ; The spontaneous imbibition weight is calculated according to the following formula (2): ω imb , calculate the displacement weight according to the following formula (3): ω dis : ω imb =(( q imb (0) - q imb (1) ) / q imb (0) ) / (( q imb (0) - q imb (1) ) / q imb (0) +(D p (0) -D p (1) ) / D p (0) ) (2) ω dis =((D p (0) -D p (1) ) / D p (0) ) / (( q imb (0) - q imb (1) ) / q imb (0) +(D p (0) -D p (1) ) / D p (0) ) (3) The wettability reversal degree is calculated according to the following formula (1): DWR : DWR = ω dis ×( q dis (1) ×Δ p (0) ) / ( q dis (0) ×Δ p (1) )- ω imb ×( q imb (1) × t (0) ) / ( q imb (0) × t (1) ) (1)。 2. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: Spontaneous imbibition time before immersion t (0) The specific acquisition process is as follows: the dense sandstone core sample is subjected to a spontaneous imbibition experiment before being soaked in silica nanofluid. The imbibition time corresponding to the time when the imbibition amount does not change with the imbibition time is the spontaneous imbibition time before soaking. t (0) .

3. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: Spontaneous imbibition time after immersion t (1) The specific acquisition process is as follows: the dense sandstone core sample is soaked in silica nanofluid and then the spontaneous imbibition experiment is carried out. The imbibition time corresponding to the time when the imbibition amount does not change with the imbibition time is the spontaneous imbibition time after soaking. t (1) .

4. The method for calculating the wettability inversion degree of tight sandstone according to claim 1, characterized in that: The spontaneous absorption before immersion q imb (0) Spontaneous imbibition time before immersion t (0) The corresponding absorption amount.

5. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: The spontaneous absorption capacity after immersion q imb (1) Spontaneous imbibition time after immersion t (1) The corresponding absorption amount.

6. The method for calculating the wettability inversion degree of tight sandstone according to claim 1, characterized in that: The displacement pressure difference before soaking Δ p (0) The specific process of obtaining Δ is as follows: the core displacement experiment before soaking the tight sandstone core sample is carried out before soaking with silica nanofluid. The experimental pressure difference when the experimental pressure difference does not change with the injection volume is the displacement pressure difference before soaking Δ p (0) .

7. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: The displacement pressure difference after soaking Δ p (1) The specific process of obtaining Δ is as follows: the tight sandstone core sample is soaked in silica nanofluid and then the core displacement experiment is carried out. The experimental pressure difference corresponding to the experimental pressure difference when the experimental pressure difference does not change with the injection volume is the displacement pressure difference after soaking Δ p (1) .

8. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: The displacement amount before soaking q dis (0) is the displacement pressure difference before immersion Δ p (0) The corresponding injection volume.

9. The method for calculating the wettability reversal degree of tight sandstone according to claim 1, characterized in that: The displacement amount after soaking q dis (1) is the displacement pressure difference after immersion Δ p (1) The corresponding injection volume.

Images