Method for quantitatively dividing vertical structure of metamorphic rock buried hill reservoir by using logging information

Abstract

The invention discloses a method for quantitatively dividing a vertical structure of a metamorphic rock buried hill reservoir by using logging information, which comprises the following steps of: selecting a research object according to comprehensive information; calculating a metamorphic rock buried hill feldspar weathering index by using element logging data; calculating a discriminant index of the buried hill reservoir of the metamorphic rock by comprehensively utilizing conventional logging information; establishing a metamorphic rock buried hill reservoir vertical structure unit division standard by using the feldspar mineral weathering degree index and the metamorphic rock buried hill reservoir discrimination index; and according to the standard, carrying out quantitative division on the vertical structure units of the metamorphic rock buried hill reservoir on the new well. According to the method, the metamorphic rock buried hill feldspar weathering index and the metamorphic rock buried hill reservoir discrimination index are calculated through the element logging data and the conventional logging data, the quantitative division standard is established, the reservoir vertical structure unit of the well drilling buried hill section is visually displayed, the reservoir vertical structure unit division efficiency is improved, and the reservoir vertical structure unit division efficiency is improved. And technical support is provided for subsequent development schemes and well location implementation.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field exploration and development, and particularly relates to a method for quantitatively dividing vertical structural units of metamorphic rock buried hill reservoirs by using recording and logging data. Background Art

[0002] Through a deeper understanding of the basic geology of various basins and the factors controlling oil and gas accumulation, China has achieved significant breakthroughs in offshore oil and gas exploration and development. In particular, the Bohai Sea has seen the discovery of numerous medium-to-large oil and gas fields within metamorphic buried hills, demonstrating enormous potential for exploration and development. Currently, the exploration and development of metamorphic buried hill reservoirs is still in its infancy, and understanding the development patterns of metamorphic buried hill reservoirs remains a challenge. Quantifying the vertical structural units of these reservoirs is one of the most pressing challenges.

[0003] In the past, the vertical structural units of metamorphic buried-hill reservoirs were primarily delineated using data from cores, wall cores, conventional well logs, and imaging logs. Qualitative delineation was performed based on the reservoir structure of cores and wall cores, or the extent of fracture development in imaging logs. These delineation methods, however, were incomplete due to the discontinuity of core and wall core data, the high cost of imaging logs, and the fact that retesting was typically limited to oil and gas-showing sections. These methods also relied on simple delineation based on conventional well log curve morphology, which often resulted in significant errors due to subjective judgment. Currently, no method for quantitatively delineating the vertical structural units of metamorphic buried-hill reservoirs has been established.

[0004] With the widespread adoption of PDC drill bits at drilling sites, drilling cuttings are often in powder form. This powder can be used for elemental logging. The theory behind this technique is that a single X-ray emitted by an X-ray tube excites the sample, causing the elements contained in the sample to emit fluorescent X-rays. The wavelength and intensity of these fluorescent X-rays allow for quantitative analysis of the elements in the sample. This technology enables rapid and accurate analysis of the chemical element content in rock cuttings samples at the drilling site. Because it uses continuous sampling, the variation of each element with depth can provide a powerful basis for chemical weathering in metamorphic buried hills. Furthermore, conventional logging curves, such as resistivity and acoustic transit time, are sensitive to metamorphic buried hill reservoirs. By establishing a discriminant index, these two types of logging data can be effectively combined.

[0005] The metamorphic buried-hill feldspar weathering index and metamorphic buried-hill reservoir discrimination factor were calculated by element logging data and conventional logging data, and a quantitative division standard for vertical structural units of metamorphic buried-hill reservoirs in the study area was established to guide the quantitative division of vertical structural units of metamorphic buried-hill reservoirs in subsequent drilling.

[0006] The existing method uses element logging and conventional logging measurement data to carry out work. Due to the influence of regional geological characteristics, the vertical structure of metamorphic rock buried hill reservoirs in different areas may be different, and the division criteria of area A cannot be applied to area B. Summary of the Invention

[0007] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for quantitatively dividing the vertical structure of metamorphic buried hill reservoirs by using well logging data.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for quantitatively dividing the vertical structure of a metamorphic buried-hill reservoir using well logging data comprises the following steps:

[0010] (I) Select research subjects based on comprehensive data;

[0011] (II) Calculation of feldspar weathering index of metamorphic rock buried hill using element logging data;

[0012] (III) Comprehensively utilizing the resistivity curve and acoustic transit time curve in conventional logging data, adopting the relative value method of eliminating trend background value and normalizing, the metamorphic buried hill reservoir discrimination index is calculated;

[0013] (IV) Using the feldspar mineral weathering index and metamorphic buried-hill reservoir discrimination index to establish a standard for the division of vertical structural units of metamorphic buried-hill reservoirs;

[0014] (V) Based on the vertical structural unit division standard of metamorphic buried-hill reservoir, the vertical structural units of metamorphic buried-hill reservoir are quantitatively divided for new wells.

[0015] In the above technical solution, the comprehensive data includes geological data, well logging data and well logging data.

[0016] In the above technical solution, the research object is a well with a vertical unit type similar to that of a standard well buried hill reservoir.

[0017] In the above technical solution, the calculation formula of the feldspar mineral weathering index is:

[0018]

[0019] Where: C is the weathering degree index of feldspar minerals, dimensionless; M Al is the molar percentage of Al in the element logging sample; M K is the molar percentage of K element in the element logging sample; M Na is the molar percentage of Na in the element logging sample; M Ca is the molar percentage of Ca in the element logging sample.

[0020] In the above technical solution, the calculation formula for the metamorphic buried hill reservoir discrimination index is:

[0021] P=1-(1-P1)(1-P2)

[0022] in:

[0023]

[0024]

[0025] In the above formula: P is the discriminant index of metamorphic buried hill reservoir, dimensionless; P1 is the discriminant index of resistivity, dimensionless; P2 is the discriminant index of acoustic wave time difference, dimensionless; Rt i h i Ideal resistivity at depth, in Ω·m; Rt is h i The actual resistivity at depth, in Ω·m; ΔRt is the difference between the actual resistivity value and the trend value, in Ω·m; DT i h i The ideal acoustic time difference at depth, in μs / m; DT is h i The actual acoustic time difference at depth, in μs / m; ΔDT is the difference between the actual acoustic time difference and the trend value, in μs / m; Rt2 is the actual resistivity at the end depth of the buried hill section, in Ω·m; Rt1 is the actual resistivity at the starting depth of the buried hill section, in Ω·m; h2 is the end depth of the buried hill section, in m; h1 is the starting depth of the buried hill section, in m; DT2 is the actual acoustic time difference at the end depth of the buried hill section, in μs / m; DT1 is the actual acoustic time difference at the starting depth of the buried hill section, in μs / m; h i is the depth of any point in the buried hill section, in m.

[0026] In the above technical solution, the step (IV) specifically comprises intersecting the feldspar mineral weathering degree index and the metamorphic buried-hill reservoir discrimination index to obtain a quantitative division chart of the vertical structural units of the metamorphic buried-hill, identifying from the chart that different vertical structural units of the metamorphic buried-hill reservoir occupy different zones in the intersection chart, and obtaining a quantitative division standard for the vertical structural units of the metamorphic buried-hill reservoir.

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

[0028] The present invention provides a method for quantitatively dividing the vertical structural units of metamorphic buried-hill reservoirs using logging and well logging data. The method calculates the metamorphic buried-hill feldspar weathering index and the metamorphic buried-hill reservoir discrimination index through element logging data and conventional logging data, establishes a quantitative division standard, and intuitively displays the vertical structural units of the reservoir in the drilling buried-hill section, thereby improving the efficiency of the reservoir vertical structural unit division and providing technical support for subsequent development plans and well location implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is an overall flow chart of an embodiment of the present invention;

[0030] Figure 2 This is a comprehensive evaluation diagram of vertical structural units of the buried hill zone of the exploration well in Example 1 of the present invention;

[0031] Figure 3 Graph showing the resistivity and acoustic wave transit time curves of the buried hill zone of the exploration well in Example 1 of the present invention as a function of depth;

[0032] Figure 4 A quantitative division chart of vertical structural units of the buried hill zone of the exploration well in Example 1 of the present invention;

[0033] Figure 5 This is a quantitative division diagram of vertical structural units of the newly drilled buried hill zone in Example 1 of the present invention.

[0034] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0036] like Figure 1 As shown, a method for quantitatively dividing the vertical structure of metamorphic buried-hill reservoirs using well logging data includes the following steps:

[0037] (I) Comprehensive geological, logging and well logging data to select research objects

[0038] When selecting research objects, the influence of the geological background of metamorphic buried-hill in the study area was taken into consideration. The vertical unit types and thicknesses of metamorphic buried-hill reservoirs in different geological backgrounds are different. The vertical structural unit types of metamorphic buried-hill reservoirs in standard wells in the study area were determined based on drilling, logging and well logging data, and wells with vertical unit types similar to those of standard buried-hill reservoirs were selected as research objects.

[0039] The study area of this example is located in the Bohai Sea area of the Bohai Bay Basin. The regional structure is the middle section of the metamorphic buried hill belt of the Bonan low uplift. Its reservoir is the Archean metamorphic buried hill, which is greatly affected by tectonic evolution. It experienced near SN compression during the Indosinian period, forming a NWW-near EW paleo-uplift; it experienced strong NWW compression during the Yanshan period, further cutting the paleo-uplift along the NEE fault into different blocks; it began to stretch during the Himalayan period and entered the deep burial stage of depression. The lithology of the metamorphic buried hill reservoir is mainly granite gneiss and mixed granite, and the reservoir space has obvious stratification in the vertical direction ( Figure 2), according to the degree of weathering and the development of fractures and pores, it can be divided into two primary structural units: the weathering crust and the inner part of the buried hill. The weathering crust is further divided into three secondary structural units: the sandstone zone, the strong weathering zone, and the weak weathering zone. The inner part of the buried hill is not further subdivided because it basically has no reservoir and only sporadic fracture sections.

[0040] Different reservoir structural units have different production capacities due to their different reservoir types, as shown in Table 1.

[0041] Table 1: Division of vertical structural units in the buried hill section of Bozhong 26-6 oilfield

[0042]

[0043] Wells with vertical unit types similar to those of standard wells in the study area were selected as research objects.

[0044] Specifically, the reservoir lithology in the study area is Archean metamorphic buried hill. Due to tectonic influences, the reservoir is primarily fractured, while the top is affected by weathering, denudation, and leaching, resulting in relatively well-developed porosity. Vertically, from top to bottom, the reservoir exhibits fracture-pore, pore-fracture, and fracture patterns.

[0045] (II) Calculation of Feldspar Mineral Weathering Index in Metamorphic Buried Hills Using Elemental Mud Logging Data

[0046] Metamorphic rock buried hill reservoirs are rich in feldspar minerals, which are easily weathered into clay minerals. Since Al is enriched and K / Na / Ca is lost during the weathering process, the feldspar mineral weathering degree index can be calculated using elemental logging data.

[0047] The calculation formula of the feldspar mineral weathering index is:

[0048]

[0049] Where: C is the weathering degree index of feldspar minerals, dimensionless; M Al is the molar percentage of Al in the element logging sample; M K is the molar percentage of K element in the element logging sample; M Na is the molar percentage of Na in the element logging sample; M Ca is the molar percentage of Ca element in the element logging sample;

[0050] The element logging values are directly obtained at the drilling site. The feldspar mineral weathering index C is calculated according to the calculation formula of the feldspar mineral weathering index, as shown in Table 2. Due to the large amount of data, only part of the data is shown.

[0051] Table 2: Element logging and weathering index data for the buried hill section of Well BZ26-6-2

[0052]

[0053]

[0054] (III) Comprehensively utilizing the resistivity curve and acoustic time difference curve in conventional logging data, the relative value method of eliminating trend background value and normalizing is adopted to calculate the metamorphic buried hill reservoir discrimination index P

[0055] The metamorphic buried-hill reservoirs in the study area have been drilled to a depth of more than 3500m. The overlying strata have high pressure. Due to the compaction effect of the strata, the baselines of the resistivity curve and the acoustic transit time curve will gradually increase or decrease with increasing depth. Therefore, when using the resistivity curve and the acoustic transit time curve to study metamorphic buried-hill reservoirs, the influence of the background value must be eliminated first.

[0056] Assuming that the starting and ending points of the buried hill section of a well are h1 and h2, the corresponding resistivities are Rt1 and Rt2, and the corresponding acoustic transit times are DT1 and DT2, respectively. Based on the linear correlation between resistivity, acoustic transit time and depth, the ideal trend background line of resistivity and acoustic transit time in the metamorphic rock buried hill section is obtained ( Figure 3 ), any depth point h between the starting point and the end point in the buried hill section i , the corresponding ideal resistivity Rt i Time difference DT from ideal sound wave i The calculation formula is:

[0057]

[0058] Where: Rt i h i The ideal resistivity at depth is expressed in Ω·m. Rt2 is the actual resistivity at the end point of the buried hill section, in Ω·m. Rt1 is the actual resistivity at the starting point of the buried hill section, in Ω·m. h2 is the end point depth of the buried hill section, in m. h1 is the starting point depth of the buried hill section, in m. DT i h i The ideal acoustic time difference at depth, in μs / m; DT2 is the actual acoustic time difference at the end point of the buried hill section, in μs / m; DT1 is the actual acoustic time difference at the starting point of the buried hill section, in μs / m;

[0059] After eliminating the interference of burial depth, the metamorphic rock buried hill reservoir discrimination index is calculated by homogenization. The calculation formula of the metamorphic rock buried hill reservoir discrimination index is:

[0060] P=1-(1-P1)(1-P2)

[0061]

[0062]

[0063] Where: P is the discriminant index of metamorphic buried hill reservoir, dimensionless; P1 is the resistivity discriminant index; Rt i is the ideal resistivity at a certain depth, in Ω·m; Rt is the actual resistivity at a certain depth, in Ω·m; ΔRt is the difference between the actual resistivity value and the trend value, in Ω·m; P2 is the acoustic time difference discrimination index; DT i is the ideal acoustic time difference at a certain depth, in μs / m; DT is the actual acoustic time difference at a certain depth, in μs / m; ΔDT is the difference between the actual value and the trend value of the acoustic time difference, in μs / m;

[0064] Conventional logging values are directly obtained at the drilling site. The metamorphic buried-hill reservoir discrimination index P is calculated according to the calculation formula of the metamorphic buried-hill reservoir discrimination index, as shown in Table 3. Due to the large amount of data, only part of the data is shown.

[0065] Table 3: Conventional logging and discriminant factor data for the buried hill section of Well BZ26-6-2

[0066] depth DT24 Rt Ideal Rt ΔRt P1 Ideal DT ΔDT P2 P-factor 3808 65.566 -2.291 1.877 4.168 0.341 52.484 13.082 0.544 0.699 3809 64.901 -0.792 1.877 2.669 0.218 52.484 12.417 0.516 0.622 3810 64.144 0.349 1.878 1.529 0.125 52.483 11.661 0.485 0.549 3811 63.434 1.370 1.878 0.508 0.042 52.483 10.951 0.455 0.478 3812 63.007 2.269 1.879 0.390 0.032 52.482 10.525 0.437 0.455 3813 62.828 2.898 1.879 1.019 0.083 52.481 10.346 0.430 0.478 3814 63.344 3.305 1.880 1.426 0.117 52.481 10.864 0.452 0.516 3815 64.268 3.558 1.880 1.678 0.137 52.480 11.787 0.490 0.560 3816 65.555 3.639 1.881 1.759 0.144 52.480 13.075 0.543 0.609 3817 67.165 3.591 1.881 1.710 0.140 52.479 14.686 0.610 0.665 3818 68.705 3.520 1.881 1.639 0.134 52.479 16.226 0.674 0.718 3819 70.169 3.443 1.882 1.561 0.128 52.478 17.691 0.735 0.769 3820 71.265 3.392 1.882 1.510 0.124 52.477 18.788 0.781 0.808 3821 72.117 3.387 1.883 1.504 0.123 52.477 19.641 0.816 0.839 3822 72.672 3.406 1.883 1.523 0.125 52.476 20.196 0.839 0.859 3823 72.855 3.442 1.884 1.559 0.128 52.476 20.380 0.847 0.867 3824 72.854 3.495 1.884 1.611 0.132 52.475 20.380 0.847 0.867 3825 72.620 3.556 1.885 1.671 0.137 52.474 20.145 0.837 0.860 3826 72.343 3.608 1.885 1.723 0.141 52.474 19.869 0.826 0.850 3827 72.092 3.637 1.886 1.751 0.143 52.473 19.618 0.815 0.842 3828 71.904 3.628 1.886 1.742 0.143 52.473 19.431 0.808 0.835 3829 71.664 3.598 1.886 1.712 0.140 52.472 19.192 0.798 0.826 3830 71.280 3.567 1.887 1.680 0.137 52.471 18.808 0.782 0.812 3831 70.568 3.551 1.887 1.664 0.136 52.471 18.097 0.752 0.786 3832 69.439 3.564 1.888 1.676 0.137 52.470 16.968 0.705 0.746 3833 68.093 3.606 1.888 1.717 0.141 52.470 15.624 0.649 0.699 3834 66.473 3.655 1.889 1.767 0.145 52.469 14.004 0.582 0.642 3835 64.917 3.683 1.889 1.794 0.147 52.469 12.448 0.517 0.588 3836 63.430 3.681 1.890 1.792 0.147 52.468 10.962 0.456 0.535

[0067] (IV) Using the feldspar mineral weathering index C and the metamorphic buried hill reservoir discrimination index P to intersect, the quantitative division chart of the vertical structural units of the metamorphic buried hill is obtained ( Figure 4 ), it can be seen from the figure that different vertical structural units of metamorphic buried-hill reservoirs occupy different zones in the intersection plate. Therefore, the quantitative division standard of vertical structural units of metamorphic buried-hill reservoirs is obtained. According to the standard, the vertical structural units of metamorphic buried-hill reservoirs are quantitatively divided into two primary vertical structural units: weathering crust and buried-hill interior. The weathering crust is further divided into three secondary vertical structural units: sandstone zone, strong weathering zone and secondary weathering zone, as shown in Table 4.

[0068] Table 4: Quantitative classification standards for vertical structural units of the buried hill reservoir in Well BZ26-6-2

[0069]

[0070] (V) Quantitatively classify the vertical structural units of metamorphic buried-hill reservoirs in new wells according to the standards

[0071] The feldspar weathering index and reservoir identification index were calculated based on the element logging data and conventional logging data of the new well. The newly drilled buried hill section was quantitatively divided according to the quantitative division standard. The vertical depth of the newly drilled buried hill section is 3747-3791m as the sandstone conglomerate zone, 3791-3826m as the strong weathering zone, 3826-3934m as the weak weathering zone, and 3934-4052m as the buried hill inner zone ( Figure 5 ).

[0072] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data, characterized by: The following steps are involved: (I) Select research subjects based on comprehensive data; (II) Calculation of feldspar weathering index of metamorphic rock buried hill using element logging data; (III) Comprehensively utilizing the resistivity curve and acoustic transit time curve in conventional logging data, adopting the relative value method of eliminating trend background value and normalizing, the metamorphic buried hill reservoir discrimination index is calculated; (IV) Using the feldspar mineral weathering index and metamorphic buried-hill reservoir discrimination index to establish a standard for the division of vertical structural units of metamorphic buried-hill reservoirs; (V) Based on the vertical structural unit division standard of metamorphic buried-hill reservoir, the vertical structural units of metamorphic buried-hill reservoir are quantitatively divided for new wells.

2. The method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data according to claim 1, characterized in that: The comprehensive data includes geological data, well logging data and well logging data.

3. The method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data according to claim 1, characterized in that: The research object is a well with a vertical unit type similar to that of a standard well buried hill reservoir.

4. The method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data according to claim 1, characterized in that: The calculation formula of the feldspar mineral weathering index is: Where: C is the weathering degree index of feldspar minerals, dimensionless; M Al is the molar percentage of Al in the element logging sample; M K is the molar percentage of K element in the element logging sample; M Na is the molar percentage of Na in the element logging sample; M Ca is the molar percentage of Ca in the element logging sample.

5. The method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data according to claim 1, characterized in that: The calculation formula of the metamorphic rock buried hill reservoir discrimination index is: P=1-(1-P1)(1-P2) in: In the above formula: P is the discriminant index of metamorphic buried hill reservoir, dimensionless; P1 is the discriminant index of resistivity, dimensionless; P2 is the discriminant index of acoustic wave time difference, dimensionless; Rt i h i Ideal resistivity at depth, in Ω·m; Rt is h i The actual resistivity at depth, in Ω·m; ΔRt is the difference between the actual resistivity value and the trend value, in Ω·m; DT i h i The ideal acoustic time difference at depth, in μs / m; DT is h i The actual acoustic time difference at depth, in μs / m; ΔDT is the difference between the actual acoustic time difference and the trend value, in μs / m; Rt2 is the actual resistivity at the end depth of the buried hill section, in Ω·m; Rt1 is the actual resistivity at the starting depth of the buried hill section, in Ω·m; h2 is the end depth of the buried hill section, in m; h1 is the starting depth of the buried hill section, in m; DT2 is the actual acoustic time difference at the end depth of the buried hill section, in μs / m; DT1 is the actual acoustic time difference at the starting depth of the buried hill section, in μs / m; h i is the depth of any point in the buried hill section, in m.

6. The method for quantitatively classifying the vertical structure of metamorphic buried-hill reservoirs using well logging data according to claim 1, characterized in that: The step (IV) specifically comprises intersecting the feldspar mineral weathering degree index and the metamorphic buried-hill reservoir discrimination index to obtain a quantitative division chart of the vertical structural units of the metamorphic buried-hill, identifying from the chart that different vertical structural units of the metamorphic buried-hill reservoir occupy different zones in the intersection chart, and obtaining a quantitative division standard for the vertical structural units of the metamorphic buried-hill reservoir.

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