Method for identifying hydrocarbon reservoir by using deep and shallow resistivity

Abstract

The invention relates to a method for identifying a hydrocarbon reservoir by using deep and shallow resistivity, which comprises the following steps: S1, calculating formation resistivity under the condition of 100% water content, Rtw = Rxo * Rw / Rmf, Rtw is the formation resistivity under the condition of 100% water content, Rmf is the slurry filtrate resistivity, Rxo is the flushing zone resistivity, and Rw is the formation water resistivity; s2, calculating CRTW actual = Rt actual measurement / Rtw; s3, a hydrocarbon reservoir boundary CRTW hydrocarbon reservoir is calculated according to the Azier formula, and CRTW hydrocarbon reservoir = Rt / Rtw = (100 / Sw hydrocarbon reservoir) n; and S4, the actual CRTW is compared with the size of a hydrocarbon reservoir boundary CRTW hydrocarbon reservoir, if the actual CRTW is larger than or equal to the CRTW hydrocarbon reservoir, the stratum is the hydrocarbon reservoir, and if the actual CRTW is smaller than the CRTW hydrocarbon reservoir, the stratum is not the hydrocarbon reservoir. According to the method for identifying the hydrocarbon reservoir by using the deep and shallow resistivity, the problem that the hydrocarbon reservoir identification coincidence rate is not high due to the fact that the calculated hydrocarbon saturation is not accurate due to the fact that accurate data of parameters required by existing calculation of the hydrocarbon saturation is difficult to obtain is solved.

Description

Technical Field

[0001] The present invention relates to the exploration of oil and gas wells, and specifically to a method for identifying oil and gas layers by using deep and shallow resistivity. Background Art

[0002] Most of the conventional identification methods for clastic rock oil and gas layers adopt the method of calculating the oil and gas saturation (the ratio of the volume of oil in the effective pores of the oil layer to the volume of the effective pores of the rock), such as the method for identifying low-resistivity oil and gas layers by the porosity-resistivity-lithology matching relationship disclosed in the patent document with the patent number CN201810751552.4. This method requires good porosity measurement curves, rock electrical parameters from core experiments, and formation water data in this area. However, in actual logging, it is difficult to obtain these good data due to environmental influences. At the same time, many types of reservoirs are not cored, so rock electrical data cannot be obtained. Moreover, due to the influence of various complex factors in clastic rock oil and gas layers, the calculation of oil and gas saturation is inaccurate, and the coincidence rate of oil and gas identification is not high. Summary of the Invention

[0003] The present invention provides a method for identifying oil and gas layers by using deep and shallow resistivity, which overcomes the problem that accurate data of the parameters required for calculating the existing oil and gas saturation are difficult to obtain, so the calculated oil and gas saturation is inaccurate, resulting in a low coincidence rate of oil and gas layer identification.

[0004] The method for identifying oil and gas layers by using deep and shallow resistivity of the present invention includes the following steps:

[0005] S1. Calculate the formation resistivity under 100% water saturation, Rtw = Rxo × Rw / Rmf, where Rtw is the formation resistivity under 100% water saturation, Rmf is the resistivity of the mud filtrate, Rxo is the resistivity of the flushed zone, and Rw is the formation water resistivity;

[0006] S2. Calculate the ratio CRTW actual of the measured formation resistivity Rt measured to the formation resistivity Rtw of 100% water saturation, CRTW actual = Rt 实测 / Rtw;

[0007] S3. Calculate the oil and gas layer boundary CRTW 油气层 , and the calculation method is as follows,

[0008] The water saturation Sw of the water layer is 100%. According to Archie's formula,

[0009]

[0010] where a, b, m, and n are rock electrical parameters analyzed from the core,

[0011] The water saturation of the oil and gas layer is Sw 油气层 , according to Archie's formula,

[0012]

[0013] Dividing Equation 1 by Equation 2 gives:

[0014]

[0015] wherein, the value range of n is 1.6 to 2.0, Sw oil and gas reservoir = 100% - the lower limit of oil saturation in the oil and gas reservoir,

[0016] CRTW 油气层 = Rt / Rtw = (100 / Sw 油气层 )n

[0017] S4, compare CRTW 实际 with the oil and gas reservoir boundary CRTW 油气层 in terms of magnitude. If CRTW 实际 ≥CRTW 油气层 , then this formation is an oil and gas reservoir; if CRTW 实际 <CRTW 油气层 , then this formation is not an oil and gas reservoir.

[0018] Preferably, calculate the oil-water zone boundary CRTW 油水同层 , CRTW 油水同层 = (100 / Sw 油水同层 )n, where Sw 油水同层 = 100% - the lower limit of oil saturation in the oil-water zone.

[0019] Compare the magnitude of CRTW 实际 with CRTW 油水同层 . If CRTW 油气层 >CRTW 实际 ≥CRTW 油水同层 , then this formation is an oil-water zone; if CRTW 实际 <CRTW 油水同层 , then this formation is in the range from an oil-bearing water zone to a water zone.

[0020] Preferably, the method for obtaining Rtw in S1 = Rxo×Rw / Rmf is as follows: According to Archie's formula, assuming that the virgin formation has no oil and gas and is a water zone, then the water saturation is 100%, that is, calculate the water saturation Sw of the virgin formation zone,

[0021]

[0022] where: φ is the formation porosity, Rw is the resistivity of the virgin formation water, Rtw is the resistivity of the virgin formation at 100% water saturation, and a, b, m, n are rock electrical parameters obtained from core analysis,

[0023] For a general flushed zone, if there is oil and gas, it will be displaced completely due to continuous flushing, and its water saturation is 100%. Calculate the water saturation Sxo of the flushed zone.

[0024]

[0025] Where: φ is the formation porosity, Rmf is the resistivity of the mud filtrate in the flushed zone, Rxo is the resistivity of the flushed zone, and a, b, m, n are the petrophysical parameters obtained from core analysis.

[0026] Equating Equation 3 and Equation 4, i.e., Sw = Sxo = 100%, then we have:

[0027]

[0028] After simplifying the above equation, we get: Rtw = Rxo × Rw / Rmf.

[0029] Preferably, Rxo is obtained by actual downhole measurement using logging instruments.

[0030] Preferably, Rw is obtained by the logging spontaneous potential method and the back-calculation method for pure water layers.

[0031] Preferably, Rmf, the resistivity of the mud filtrate, is obtained by measurement and conversion using actual drilling mud data. The formula is as follows:

[0032] R mf = C × R m 1.07 Equation 5

[0033] In the formula, Rm is the resistivity of the drilling fluid measured by logging, and C is a coefficient related to the density of the drilling fluid.

[0034] Compared with the prior art, the present invention has the following beneficial effects: By the method of identifying oil and gas layers using deep and shallow resistivities of the present invention, it is not necessary to obtain data such as in-layer lithology curves, in-layer porosity curves, and in-layer resistivity curves. According to the three parameters of the resistivity of the mud filtrate Rmf, the resistivity of the flushed zone Rxo, and the resistivity of the formation water Rw, the formation resistivity under 100% water saturation can be calculated, and then the ratio CRTW of the measured formation resistivity to the formation resistivity of 100% water saturation is calculated 实际 and the oil and gas layer boundary CRTW 油气层 , and by comparing the magnitudes of CRTW 实际 and CRTW 油气层 , it can be determined whether the formation is an oil and gas layer. The method for obtaining data is simpler and the data is not affected by the environment, so it is more accurate. Therefore, the identification of oil and gas layers is also more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1Flowchart of a method for identifying hydrocarbon-bearing formations using deep and shallow resistivity according to an embodiment of the present invention.

[0036] Figure 2 Curve graph of parameter CRTW used in the method for identifying hydrocarbon-bearing formations using deep and shallow resistivity according to an embodiment of the present invention. Detailed implementation manners

[0037] The present invention provides a method for identifying hydrocarbon-bearing formations using deep and shallow resistivity, including the following steps:

[0038] S1. Calculate the formation resistivity under 100% water saturation, \(R_{tw}=R_{xo}\times R_w / R_{mf}\), where \(R_{tw}\) is the formation resistivity under 100% water saturation, \(R_{xo}\) is the resistivity of the formation at a depth away from the wellbore, called deep resistivity, \(R_{mf}\) is the resistivity of the mud filtrate, \(R_{xo}\) is the resistivity of the flushed zone, called shallow resistivity, and \(R_w\) is the resistivity of the formation water. During the drilling process, generally the mud column pressure is greater than the formation pressure. This pressure difference causes the mud to infiltrate into the formation in permeable formations and displace the original fluids in the reservoir. This phenomenon is called mud invasion. Due to mud invasion, the fluids in the pores near the wellbore are continuously displaced and almost entirely replaced by the invaded mud filtrate. This part is called the flushed zone. Slightly farther away from the wellbore is the place where the invaded mud filtrate mixes with the formation fluids, called the transition zone. Farther away from the wellbore, there is no invasion by the mud filtrate and the original fluids remain unchanged, called the virgin formation. The above \(R_{xo}\) is obtained by actual downhole measurement using logging instruments, and \(R_w\) is obtained by the logging spontaneous potential method or the back-calculation method for a pure water layer. Both of these methods are well-known, and the results obtained by the two can be mutually verified or one result can be used to correct the other. \(R_{mf}\) is the resistivity of the mud filtrate, which is measured and converted using actual drilling mud data. The formula is as follows:

[0039] R mf =C×R m 1.07 Equation 5

[0040] In Equation 5, \(R_m\) - the resistivity of the drilling fluid measured by logging, unit is \(\Omega\cdot m\); C - the coefficient related to the density of the drilling fluid, as shown in Table 1 specifically:

[0041] Table 1 Corresponding relationship table of C value and drilling fluid density

[0042] <![CDATA[Drilling fluid density (g / cm 3 )]]> 1.2 1.32 1.44 1.56 1.68 1.92 2.16 C 0.847 0.706 0.584 0.488 0.412 0.380 0.350

[0043] The obtaining method of \(R_{tw}=R_{xo}\times R_w / R_{mf}\) in S1 is: According to Archie's formula, assuming that the virgin formation has no oil and gas and is a water layer, then the water saturation is 100%, that is, calculate the water saturation \(S_w\) of the virgin formation zone,

[0044]

[0045] Wherein: φ is the formation porosity, Rw is the resistivity of the virgin formation water, Rtw is the resistivity of the virgin formation at 100% water saturation, and a, b, m, and n are the petrophysical parameters analyzed from the core.

[0046] Generally, if there is oil and gas in the flushed zone, it will be displaced completely due to continuous flushing, and its water saturation is 100%. Calculate the water saturation Sxo of the flushed zone.

[0047]

[0048] Wherein: φ is the formation porosity, Rmf is the resistivity of the mud filtrate in the flushed zone, Rxo is the resistivity of the flushed zone, and a, b, m, and n are the petrophysical parameters analyzed from the core.

[0049] Equation 3 is equal to Equation 4, that is, Sw = Sxo = 100%. Then there is:

[0050]

[0051] After canceling out the above formula, we can get: Rtw = Rxo × Rw / Rmf.

[0052] S2, calculate the measured formation resistivity Rt 实测 The ratio CRTW of the measured formation resistivity Rt to the resistivity Rtw of the 100% water-bearing formation 实际 = Rt 实测 / Rtw;

[0053] S3, calculate the oil and gas layer boundary CRTW according to Archie's formula 油气层 , the calculation method is as follows,[[]]

[0054] The water saturation Sw of the water layer is 100%. According to Archie's formula,[[]]

[0055]

[0056] Wherein, a, b, m, and n are the petrophysical parameters analyzed from the core.[[]]

[0057] The water saturation of the oil and gas layer is Sw of the oil and gas layer. According to Archie's formula,[[]]

[0058]

[0059] Dividing Equation 1 by Equation 2, we get:[[]]

[0060] Rt is the resistivity of the virgin formation, called the deep resistivity.[[]]

[0061] Among them, the value range of n is 1.6 to 2.0, and in this embodiment, the average value of 1.8 of 827 clastic rock samples in the whole Tahe Oilfield is selected. The water saturation Sw of the oil and gas layer 油气层 = 100% - the lower limit of the oil saturation of the oil and gas layer. If there is a lower limit of the oil saturation established by core analysis in this area, then the lower limit of the regional oil saturation shall prevail. If there is no such data, the general oil saturation of 50% (water saturation of 50%) can be used as the lower limit of the oil and gas layer, while the lower limit of the oil saturation of the low-resistivity oil and gas layer is 40% (water saturation of 60%) according to core analysis. In this embodiment, the lower limit value of the oil saturation is 40%, then Sw 油气层 is 60.

[0062] CRTW 油气层 = Rt / Rtw = (100 / Sw 油气层 ) n , in this embodiment, the relationship between CRTW and the oil saturation is shown in Figure 2 , where CRTW 油气层 = 1.667 1.8 = 2.50.

[0063] S4, compare the size of CRTW 实际 with the oil and gas layer boundary CRTW 油气层 . If CRTW 实际 ≥CRTW 油气层 , in this embodiment, CRTW 油气层 = 2.50, then this formation is an oil and gas layer. If CRTW 实际 <CRTW 油气层 , then this formation is not an oil and gas layer.

[0064] The method for identifying oil and gas layers by using deep and shallow resistivity of the present invention further includes: calculating the oil-water transition zone boundary CRTW 油水同层 , in this embodiment, Therefore, CRTW 油水同层 = (100 / Sw 油水同层 ) n , Sw 油水同层 = 100% - the lower limit of the oil saturation of the oil-water transition zone. In this embodiment, Sw 油水同层 is 75,

[0065]

[0066] see Figure 2 , CRTW 油水同层 = 1.34 1.8 = 1.69.

[0067] Compare CRTW 实际With CRTW 油水同层 in size, CRTW 油气层 > CRTW 实际 ≥CRTW 油水同层 , then this formation is an oil - water co - layer. If CRTW 实际 <CRTW 油水同层 , then this formation is in the range from an oil - bearing water layer to a water layer.

[0068] Through the method for identifying oil and gas layers by using deep and shallow resistivity of the present invention, it is not necessary to obtain data such as in - layer lithology curves, in - layer porosity curves, and in - layer resistivity curves, nor is it necessary to perform complex operations such as coring. According to three parameters: mud filtrate resistivity Rmf, flushed zone resistivity Rxo, and formation water resistivity Rw, the formation resistivity under 100% water - bearing conditions can be calculated, and then the ratio CRTW 实际 and the oil and gas layer boundary CRTW 油气层 can be obtained. By comparing the sizes of CRTW 实际 and CRTW 油气层 , it can be determined whether this formation is an oil and gas layer. This method is more convenient for obtaining data, and the data is not affected by the environment and thus more accurate. Therefore, the identification of oil and gas layers is also more accurate.

[0069] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art make various modifications or equivalent replacements within the essence and protection scope of the present invention, which also fall within the protection scope of the present invention.

Claims

1. A method for identifying oil and gas layers using deep and shallow resistivity, characterized in that Including the following steps: S1. Calculate the formation resistivity Rtw under 100% water saturation; S2, calculate the measured formation resistivity Rt 实测 and the ratio CRTW of the resistivity Rtw of a 100% water-bearing formation 实际 = Rt 实测 / Rtw; S3. Calculate the oil and gas reservoir boundary CRTW 油气层 ; S4, compare CRTW 实际 with the oil and gas reservoir boundary CRTW 油气层 in terms of size. If CRTW 实际 ≥CRTW 油气层 , then this formation is an oil and gas reservoir. If CRTW 实际 <CRTW 油气层 , then this formation is a non - oil and gas reservoir.

2. The method for identifying an oil and gas layer by using deep and shallow resistivity according to claim 1, characterized in that, The formation resistivity Rtw under 100% water saturation = Rxo×Rw / Rmf, where Rtw is the formation resistivity under 100% water saturation, Rmf is the resistivity of the mud filtrate, Rxo is the resistivity of the flushed zone, and Rw is the resistivity of the formation water.

3. The method for identifying an oil and gas layer by using deep and shallow resistivity according to claim 2, wherein Oil and gas reservoir boundary CRTW 油气层 The calculation method is as follows, CRTW 油气层 =(100 / Sw 油气层 ) n , where the value range of n is 1.6 - 2.0, Sw 油气层 = 100% - the lower limit of oil saturation in the oil and gas reservoir.

4. The method for identifying hydrocarbon reservoirs by using deep and shallow resistivity according to claim 3, characterized in that, Calculating the oil-water zone boundary CRTW 油水同层 , CRTW 油水同层 =(100 / Sw 油水同层 ) n , Sw 油水同层 = 100% - the lower limit of oil saturation in the oil-water zone.

5. The method for identifying hydrocarbon-bearing formations using deep and shallow resistivity according to claim 4, characterized in that, Compare CRTW 实际 with CRTW 油水同层 . If CRTW 油气层 > CRTW 实际 ≥CRTW 油水同层 , then this formation is an oil-water zone. If CRTW 实际 < CRTW 油水同层 , then this formation is within the range from an oil-bearing water zone to a water zone.

6. The method for identifying oil and gas layers by using deep and shallow resistivity according to claim 2, characterized in that, The method for obtaining Rtw = Rxo×Rw / Rmf in S1 is as follows: According to Archie's formula, assuming that the virgin formation has no oil and gas and is a water layer, then the water saturation is 100%, that is, calculate the water saturation Sw of the virgin formation zone. Where: Φ is the formation porosity, Rw is the resistivity of the virgin formation water, Rtw is the resistivity of the virgin formation under 100% water saturation, and a, b, m, n are the petrophysical parameters analyzed from the core. Generally, if there is oil and gas in the flushed zone, it will be displaced completely due to continuous flushing, and its water saturation is 100%. Calculate the water saturation Sxo of the flushed zone. Where: φ is the formation porosity, Rmf is the resistivity of the mud filtrate in the flushed zone, Rxo is the resistivity of the flushed zone, and a, b, m, n are the petrophysical parameters analyzed from the core. Equation 3 is equal to Equation 4, that is, Sw = Sxo = 100%, then there is: After simplifying the above formula, we can get: Rtw = Rxo×Rw / Rmf.

7. The method for identifying hydrocarbon reservoirs by using deep and shallow resistivity according to claim 2, characterized in that, Rxo is obtained by actual downhole measurement with logging tools.

8. The method for identifying oil and gas layers by using deep and shallow resistivity according to claim 2, characterized in that, Rw is obtained by the logging spontaneous potential method and the back-calculation method for pure water layers.

9. The method for identifying oil and gas layers by using deep and shallow resistivity according to claim 2, characterized in that, Rmf, the resistivity of the mud filtrate, is obtained by measurement and conversion using actual drilling mud data. The formula is as follows: R mf = C × R m 1.07 Equation 5 In the formula, Rm is the resistivity of the drilling fluid measured by logging, and C is a coefficient related to the density of the drilling fluid.

10. The method for identifying oil and gas layers by using deep and shallow resistivity according to claim 3, characterized in that, CRTW 油气层 =(100 / Sw 油气层 ) n The method for obtaining The water saturation Sw of the water layer is 100%. According to Archie's formula, Where, a, b, m, n are the petrophysical parameters analyzed from the core. The water saturation of the oil and gas layer is Sw of the oil and gas layer. According to Archie's formula, Where, Rt is the resistivity of the virgin formation. Dividing Equation 1 by Equation 2, we get: Obtain CRTW 油气层 = Rt / Rtw = (100 / Sw 油气层 ) n .

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