A target prediction method under variable azimuth conditions in horizontal well geosteering

Abstract

The application discloses a target point prediction method under variable azimuth conditions in horizontal well geosteering, and the method comprises the following steps: identifying rock and electricity mark layers before entering the target, and calculating vertical distances of the mark layers to the center line of the target window of the horizontal section; calculating the apparent dip angle of the stratum according to the vertical depth difference, the plane distance and the vertical thickness between the two mark layers of the actual drilling and the adjacent well or pilot well; reading the plane position points of any two mark layers, connecting and extending the plane position points of the two mark layers, and intersecting the contour line formed by the target point position to obtain the equivalent position of the target point, and measuring the straight line distance between the plane position point of one mark layer and the equivalent target point; and based on the equal-thickness geological model, the vertical depth of the mark layer, the apparent dip angle of the stratum, the plane distance between the intersection point and the selected plane position point are used to complete the prediction of the vertical depth of the target point. Through the application, the target point prediction accuracy can be improved, the smoothness of the horizontal well borehole is effectively improved, and the accurate landing of the subsequent horizontal well and the control of the horizontal section are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas exploration and development, and particularly relates to a target point prediction method under variable azimuth conditions in horizontal well geosteering. BACKGROUND

[0002] In a relatively low degree of exploration area, due to the complex underground geological conditions and the limited accuracy of seismic data interpretation, there is a certain error in the design of target point depth, which needs to be adjusted in time according to the real drilling data. Due to the successful application of high build-up rate tools, most horizontal wells are drilled near the target point, and the azimuth is constantly changing before entering the target, which will lead to the fact that the target vertical depth cannot be accurately predicted according to the real drilling data during the real drilling process.

[0003] At present, there are generally two methods for target point prediction under variable azimuth conditions during drilling at home and abroad. One is to obtain the average velocity curve of a single well through fine well-seismic calibration, establish a three-dimensional average velocity field, and obtain the depth structure map of the target layer through time-depth conversion to predict the target vertical depth. The other is to identify the rock-electricity marker layer before entering the target in the adjacent well or pilot hole, and then calculate the deviation range of each rock-electricity marker layer drilled by combining the designed well trajectory and the build-up capacity of the directional tool. In the real drilling process, the trajectory is controlled in sections according to the pre-calculated deviation range of each rock-electricity marker layer to achieve the target. Both of the above methods have certain limitations in practical application. The former requires higher quality of the curve and seismic data, and the target prediction accuracy is difficult to meet the production demand. The latter inevitably causes poor well trajectory smoothness due to the segmented control, which causes certain risk to the subsequent engineering construction. SUMMARY

[0004] The present application relates to a target point prediction method under variable azimuth conditions in horizontal well geosteering. It can guide the effective prediction of the target point under variable azimuth conditions in the horizontal well drilling process, improve the target prediction accuracy, and effectively improve the well trajectory smoothness of the horizontal well, which provides a guarantee for the subsequent accurate landing and horizontal section control of the horizontal well.

[0005] The present application adopts the following technical scheme: a target point prediction method under variable azimuth conditions in horizontal well geosteering, comprising:

[0006] S1, identifying the rock-electricity marker layer before entering the target based on the analysis and comparison of adjacent wells or pilot holes, and calculating the vertical distance of each marker layer from the center line of the target window of the horizontal section;

[0007] S2, calculating the apparent dip angle of the stratum according to the vertical depth difference of the two marker layers, the planar distance and the vertical thickness of the two marker layers of the adjacent wells or pilot holes;

[0008] S3, read the planar position points of any two marker layers, connect the planar position points of the two marker layers and extend, intersect with the contour line formed by the target point position, and measure the straight line distance between the planar position point of one of the marker layers and the intersection point;

[0009] S4, based on the equal-thickness geological model, the vertical depth of the selected marker layer planar position point, the apparent dip angle of the stratum, and the planar distance between the intersection point and the selected planar position point are used to complete the prediction of the vertical depth of the target point.

[0010] Further, according to the drilled marker layer, the first to fourth steps are repeated to predict the depth of the target point.

[0011] Further, the calculation formula of the apparent dip angle of the stratum is:

[0012]

[0013] Wherein, h is the vertical thickness of the two marker layers of the pilot well or the adjacent well; h1 is the vertical depth difference of the two marker layers; L is the planar distance of the two marker layers.

[0014] Further, the formula of the vertical depth of the target point is:

[0015]

[0016] Wherein, H1 is the vertical depth of the selected planar position point of one of the selected two marker layers, h0 is the vertical distance from the target center of the adjacent well or the pilot well, and S is the planar distance between the intersection point and the selected planar position point.

[0017] The beneficial effects of the present application are that the prediction accuracy of the target point can be improved, and the smoothness of the horizontal well borehole can be effectively improved, which provides guarantee for the subsequent accurate landing and horizontal section control of the horizontal well. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flowchart of a target point prediction method in horizontal well geosteering under variable azimuth conditions is provided.

[0019] Figure 2 A schematic diagram of the position of the well rock and electricity marker layer and the distance from the target center in the target point prediction method in horizontal well geosteering under variable azimuth conditions is provided.

[0020] Figure 3 A schematic diagram of the apparent dip angle of the stratum calculated by different strata in the target point prediction method in horizontal well geosteering under variable azimuth conditions is provided.

[0021] Figure 4The position setting schematic diagram of the two-layer marker layer plane position points, the intersection points and the target point in a target point prediction method under variable azimuth conditions in horizontal well geosteering provided by the application is shown. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0023] Figure 1 The target point prediction method under variable azimuth conditions in horizontal well geosteering provided by the application comprises the following steps.

[0024] Based on the analysis and comparison of adjacent wells or pilot wells, the rock and electricity marker layers before entering the target are identified, and the vertical distances of the marker layers from the center line of the target window of the horizontal section are calculated respectively. Figure 2 As shown in the figure, the positions of the rock and electricity marker layers of the well under different stratum attitudes and the distances from the target center are given. In the subsequent calculation process, the values in the figure can be directly used for calculation.

[0025] The apparent dip angle of the stratum is calculated according to the vertical depth difference, the plane distance and the vertical thickness of the two marker layers of the actual drilling.

[0026] The plane position points of any two marker layers are read, the plane position points of the two marker layers are connected and extended, the contour line formed by the target point position is intersected, and the straight line distance between the plane position point of one of the marker layers and the intersection point is measured.

[0027] Based on the equal-thickness geological model, the vertical depth of the target point is predicted by using the vertical depth of the selected marker layer plane position point, the apparent dip angle of the stratum and the plane distance between the selected plane position point and the intersection point.

[0028] The pilot well is a well drilled under the condition that the geological conditions of the well site are not clear, in order to obtain accurate data, determine the accurate layer position and lay the foundation for the construction of the horizontal section. The purpose is to understand the lithology, physical property, electrical property, oil-bearing property, oil-water relationship of the oil and gas reservoir, structure and its change of the target layer, so as to determine the A, B… target point parameters of the horizontal well, and play the role of correcting the design target point. But its main role is still to correct the position of the A target point (the A target point is the starting point of the horizontal section of the horizontal well). The pilot well can be a straight pilot well or an inclined pilot well. The distance between the straight pilot well and the target A is far, and in the case that the geological conditions are relatively complex, the straight pilot well cannot meet the requirements, and the inclined pilot well needs to be drilled.

[0029] Further, the target point depth is predicted by repeating the first to fourth steps in turn according to the drilled marker layers.

[0030] Furthermore, the formula for calculating the apparent dip angle of a stratum is as follows:

[0031]

[0032] Where h is the vertical thickness between two marker layers in the pilot well or adjacent well; h1 is the vertical depth difference between two actual drilled marker layers; and L is the horizontal distance between two actual drilled marker layers.

[0033] like Figure 3 As shown, under actual formation conditions, the interlayer vertical thickness of any two marker layers in a pilot well or adjacent well, and the vertical depth of the two drilled marker layers are uncertain. Figure 3 In the topography on the left and right sides, the vertical thickness between any two marker layers of the pilot well or adjacent well in the left diagram is greater than the vertical depth of the two actual drilled marker layers. In the right diagram, the vertical thickness between any two marker layers of the pilot well or adjacent well in the left diagram is less than the vertical depth of the two actual drilled marker layers. When actually calculating the apparent dip angle of the formation, the absolute value of the difference between the vertical thickness between any two marker layers of the pilot well or adjacent well and the vertical depth of the two actual drilled marker layers is used for calculation.

[0034] like Figure 4 As shown, the two selected marker layers are denoted as B1 and B2. Connecting B1 and B2, the extended line intersects the contour line constructed at the target point location, and the intersection point is set as A'. The straight-line distance between the marker layer where the measured plane location point B2 is located and the intersection point A' is set as S. Based on the isopyroge geological model, the vertical depth of target point A is predicted using the vertical depth of point B2, the apparent dip angle of the strata, and the plane distance between the intersection point A' and point B2.

[0035] Furthermore, the target depth formula is expressed as:

[0036]

[0037] Where H1 is the vertical depth of the selected planar location point of one of the two selected marker layers, h0 is the vertical distance of the adjacent well or pilot well from the target center, and S is the planar distance between the intersection point and the selected planar location point.

[0038] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A method for target prediction under varying azimuth conditions in geological steering of horizontal wells, characterized in that, include: S1. Based on the analysis and comparison of adjacent wells or pilot wells, identify the rock electrical marker layers before the target is entered, and calculate the vertical distance of each marker layer from the center line of the horizontal target window. S2. Calculate the apparent dip angle of the formation based on the vertical depth difference, horizontal distance, and vertical thickness between two marker layers in adjacent wells or pilot wells; S3. Read the planar position points of any two marker layers, connect the planar position points of the two marker layers and extend them to intersect the contour lines constructed with the target point as the equivalent target point, and measure the straight-line distance between the planar position point of one of the marker layers and the equivalent target point. S4. Based on the isopyrophyre geological model, the vertical depth of the target point is predicted using the vertical depth of the selected marker layer planar location point, the apparent dip angle of the strata, and the straight-line distance between the equivalent target point and the selected planar location point. The target point vertical depth formula is expressed as: Where H1 is the vertical depth of the selected planar location point of one of the two selected marker layers, h0 is the vertical distance of the adjacent well or pilot well from the target center, S is the straight-line distance between the equivalent target point and the selected planar location point, and a is the apparent dip angle of the formation.

2. The target prediction method for horizontal well geological steering under varying azimuth conditions according to claim 1, characterized in that, Based on the marker layers encountered during drilling, repeat steps one through four to predict the target depth in a rolling manner.

3. The target prediction method for horizontal well geological steering under varying azimuth conditions according to claim 1, characterized in that, The formula for calculating the apparent dip angle of a stratum is: Where h is the vertical thickness between two marker layers in the pilot well or adjacent well; h1 is the vertical depth difference between two actual drilled marker layers; and L is the horizontal distance between two actual drilled marker layers.

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