A method for selecting a low-risk drilling target area under salt based on a main controlling factor of well drilling complexity

Abstract

The application discloses a method for optimizing a low-risk drilling target area under salt based on a main control factor of drilling complexity, relates to the field of oil and gas exploration, and comprises the following analysis processes: (1) collecting research area data systematically, and counting drilling complexity types and prone sections; (2) extracting relevant seismic data, establishing a corresponding relationship between drilling complexity and a fracture-fissure development area and lithological distribution characteristics, and determining deep geological main control factors of drilling complexity; (3) based on the corresponding relationship between drilling complexity and the fracture-fissure development area and the lithological distribution characteristics, the planar distribution of a high-risk area of drilling complexity in the research area is described; and (4) based on the above distribution law, a low-risk drilling target area of a salted structure group is optimized in the research area by taking avoiding high-risk strata as a constraint condition. The application realizes the rapid optimization of the low-risk drilling target area, and effectively reduces the drilling engineering risk.

Description

[0001] This invention belongs to the field of oil and gas resource exploration, specifically relating to a method for selecting low-risk drilling target areas of sub-salt structural groups based on the planar distribution characteristics of complex formations during drilling. Background Technology

[0002] As oil and gas exploration continues to deepen, the exploration of deep and ultra-deep oil and gas resources is becoming increasingly important. Meanwhile, drilling is the core of oil and gas exploration, and the speed and quality of drilling directly affect the economic benefits of exploration and development.

[0003] In the process of deep and ultra-deep oil and gas exploration, various complex drilling situations are often encountered, such as lost circulation, stuck pipe, and drilling fluid contamination. These complex drilling situations not only seriously delay the project schedule, but also cause certain wear and tear on drilling equipment, resulting in a large amount of economic losses.

[0004] Currently, in traditional drilling engineering, the solutions to the impact of the aforementioned complex drilling conditions on the drilling process typically rely on single "engineering methods," such as replacing the drill bit or adjusting the drilling fluid properties. These existing solutions disconnect the "engineering problem" from the "geological essence," lacking a mindset that integrates the actual engineering problems in production with the deep geological controlling factors. Existing exploration techniques struggle to accurately characterize the planar distribution of these potential engineering risks, often resulting in a "blind men and the elephant" approach in drilling engineering, making it impossible to proactively avoid these high-risk areas.

[0005] In summary, the industry urgently needs a method that combines drilling engineering problems with essential geological factors to analyze the main geological controlling factors and spatial distribution characteristics of complex drilling situations from a geological perspective, and to select low-risk drilling target areas to achieve the drilling target requirements of high exploration potential and low geological risk. Summary of the Invention

[0006] This invention provides a method for selecting low-risk drilling target areas of pre-salt structural groups based on the main geological control factors and planar distribution characteristics of strata with high incidence of drilling complexities. It selects low-risk drilling target areas based on the main geological control factors and planar distribution characteristics of strata with high incidence of drilling complexities, thus providing a foundation for oil and gas exploration.

[0007] The method mainly includes the following steps: (1) Collect drilling and seismic data in the study area, statistically analyze the types of drilling complexities and the frequency of occurrence of each type, and identify the strata prone to major drilling complexities.

[0008] (2) Extract the seismic coherence attributes and absolute amplitude attributes of the study area, and use the parameters to establish the correspondence between the drilling complexity and the fracture-fracture development zone and lithological distribution characteristics, so as to determine the deep geological control factors of the drilling complexity.

[0009] (3) Based on the correspondence between drilling complexity and fracture-fracture development zone and lithological distribution characteristics, the attribute parameters are plotted on a three-dimensional seismic data volume to generate a planar distribution map of drilling complexity risk in the study area, thereby characterizing the high-risk areas of drilling complexity in the study area.

[0010] (4) Based on the high-risk area plan of the drilling complex situation in the study area, and with the constraint of avoiding high-risk strata, the low-risk drilling target area of ​​the subsalt structural group is selected in the study area.

[0011] This invention provides a method for selecting low-risk drilling target areas for the subsalt tectonic group in eastern Sichuan based on the main geological control factors and spatial distribution characteristics of formations prone to complex drilling conditions. This method offers the following advantages: 1. This invention pioneers a method that combines practical engineering problems with geological factor analysis, enabling the tracing of the main controlling factors of complex drilling situations from a geological perspective.

[0012] 2. Based on clarifying the main geological controlling factors of strata with high incidence of complex drilling situations, this invention can accurately depict the distribution characteristics of engineering risks in the plane and effectively guide the design and deployment of drilling trajectories.

[0013] 3. By avoiding high-risk areas (such as areas prone to stuck drills due to the development of fracture-fracture systems and areas prone to stuck drills due to thick layers of gypsum-cloud / gypsum-sand interlayers), this invention can effectively improve drilling safety and significantly reduce engineering losses and economic costs. Attached Figure Description

[0014] Figure 1 The method technical route and comprehensive analysis flowchart provided for the examples of this invention; Figure 2 This is a schematic diagram of the main geological controlling factors (fracture-fracture system) of well leakage in an example of the present invention; Figure 3 This is a schematic diagram of the main geological factors controlling the stuck drill in an example of the present invention (thick gypsum-cloud / gypsum-sand interlayer); Figure 4 This diagram illustrates the mechanical / mechanical principle of interlayered rock causing stuck drill bit (anhydrite expansion and overlying rock collapse and diameter reduction) in an example of the present invention. Figure 5 This is a predicted plan view of the main stratigraphic bottom interface faults / fractures in the study area of ​​this invention example; Figure 6This is a predicted distribution map of the gypsum salt in the Gaotai Formation in an example of the present invention; Figure 7 This is a schematic diagram of the distribution of high-quality traps in the study area in an example of the present invention; Figure 8 This is a plan view of the fracture and gypsum-salt distribution in the target area of ​​the No. 1 high-speed drilling well, which was finally selected in the example of this invention. Figure 9 This is a plan view of the fracture and gypsum-salt distribution in the target area of ​​the No. 2 high-speed drilling well, which was ultimately selected in the example of this invention. Detailed Implementation

[0015] like Figure 1 As shown, this invention provides a method for selecting low-risk drilling target areas for sub-salt structural groups based on the main geological control factors of formations prone to complex drilling conditions and their planar distribution characteristics. The method includes the following main steps: (1) Data collection and preliminary preparation: Taking the Sinian-Cambrian subsalt system in eastern Sichuan as an example, drilling data and seismic data of the study area were systematically collected; (2) Analysis of the main geological controlling factors of drilling complexities: Statistical analysis of the main types of drilling complexities revealed that the main types in this area include lost circulation, drilling fluid contamination, and stuck pipe, with lost circulation being the most prevalent. Further analysis and verification of drilling information confirmed that the strata with a high incidence of drilling complexities are the Gaotai Formation. Subsequently, seismic coherence attributes and absolute seismic amplitude attributes of the study area were extracted. Using these attribute parameters, a correspondence between drilling complexities and fracture-fracture development zones and lithological distribution characteristics was established, and the main geological controlling factors corresponding to various complexities were summarized, such as... Figure 2 As shown, the main geological controlling factor for well leakage is the development of the fracture-fracture system, such as... Figure 3 As shown, the main geological factors controlling drill bit stuck are thick gypsum-cloud interbedded layers or thick gypsum-sand interbedded layers, which are more likely to cause drill bit stuck. Figure 4 The mechanical mechanism of stuck drill pipe caused by thick gypsum-salt interbedded layers and gypsum-sand interbedded layers is explained in detail: the expansion of the gypsum-salt layer due to water absorption leads to the reduction of the wellbore diameter, while the overlying dolomite or sandstone collapses due to the loss of effective support. The combined effect of the reduction of diameter and the collapse of the wellbore ultimately induces stuck drill pipe.

[0016] (3) Characterization of high-risk areas with complex drilling conditions: Based on the seismic coherence and amplitude data collected in the early stage, the overall regional structural characteristics and lithological distribution of the Sinian-Cambrian subsalt strata in eastern Sichuan were analyzed to clarify their distribution patterns. Then, combined with the fault-fracture system and thick gypsum-salt distribution characteristics identified in step (2), the planar distribution characteristics of strata with high incidence of complex drilling conditions in the Sinian-Cambrian subsalt strata in eastern Sichuan were characterized. Among them, the regional structural characteristics are as follows: Figure 5 As shown, the fault-fracture system is highly developed in the thrust zone on the southeast side, and Figure 6The distribution prediction of gypsum and salt in the Gaotai Formation is shown, and the overlapping area of ​​the two is the area where drilling complications are frequent.

[0017] (4) Optimal drilling target area selection: Based on the clear distribution pattern of high-risk areas in complex drilling situations, selection criteria are set, combined with the study area, such as Figure 7 The high-quality traps shown were designed to avoid the high-platform formations where complex drilling conditions frequently occur during well site deployment and trajectory design, ultimately selecting the best traps. Figure 8 and Figure 9 The area shown is a low-risk drilling target area with high exploration potential and low geological risk.

Claims

1. A method for selecting low-risk sub-salt drilling target areas based on complex drilling control factors, characterized in that, The specific analysis steps include the following: (1) Collect drilling and seismic data in the study area, statistically analyze the main types of drilling complexities and the frequency of occurrence of each type, and identify the strata where various major drilling complexities are prone to occur; (2) Extract the seismic coherence attributes and absolute seismic amplitude attributes of the study area, and use the parameters to establish the correspondence between the drilling complexity situation and the fracture-fracture development zone and lithological distribution characteristics, so as to determine the deep geological main control factors of the drilling complexity situation and establish the drilling complexity risk level; (3) Based on the correspondence between drilling complexity and fracture-fracture development zones and lithological distribution characteristics, high-risk areas of drilling complexity in the study area are characterized; (4) Based on the complex drilling situation and high-risk area distribution in the study area, and with the constraint of avoiding high-risk strata, low-risk drilling target areas of the subsalt structural group are selected in the study area.

2. The method according to claim 1, characterized in that: The study area is the Sinian-Cambrian subsalt formation in eastern Sichuan. The main drilling complications include lost circulation, drilling fluid contamination, and stuck pipe. The Gaotai Formation is the most prone to these issues.

3. The method according to claim 1, characterized in that: The fracture-fracture development zone is identified by extracting the coherence properties of seismic data, and areas with abnormally high coherence property values ​​are marked as high-risk areas for well leakage.

4. The method according to claim 1, characterized in that: The lithological distribution features are thick gypsum-cloud interbedded and gypsum-sand interbedded sections within the Gaotai Formation. The thick interbedded sections exhibit continuous medium to strong parallel reflection characteristics on seismic profiles. These thick gypsum-cloud interbedded and gypsum-sand interbedded sections are high-risk areas for stuck drill bits.

5. The method according to claim 1, characterized in that: The Gaotai Formation gypsum-salt rocks were identified by their absolute seismic amplitude attributes. Areas with high absolute seismic amplitude values ​​represent areas where the Gaotai Formation gypsum-salt rocks are developed, and these areas are concentrated in structurally high locations.

6. The method according to claim 3, characterized in that: The southeastern part of the study area is a subsalt layer thrust tectonic zone with significant coherence properties and well-developed internal faults and fractures; the northwestern part of the study area is a stable tectonic zone with few faults and weak coherence properties.

7. The method according to claim 1, characterized in that: The constraint of "avoiding high-risk strata" refers to avoiding areas with abnormally high seismic coherence properties and areas with abnormally high gypsum-salt rock accumulations.

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