Method for releasing gas from the shallow bottom layer at a site for exploratory drilling
Patent Information
- Application Number
- CN202311189207.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-15
- Publication Date
- 2026-09-11
- Estimated Expiration
- 2043-09-15
AI Technical Summary
[0002]海上油气开发通过自升式平台进行勘探井作业作为探明主力油层和重大油藏的有效手段，在自升式平台钻井作业前，要进行钻前井场调查，由于地层沉积等原因，经常发现地层中有浅层气，浅层气是影响自升式平台插桩就位以及后续钻井作业安全的重要因素，如果井位中心正好位于浅层气气区范围内，且强度特别大，在自升式插桩时会发生气涌现象，对自升式平台、人员安全及财产造成重大影响，并且在钻井期间会发生溢流、井涌、井喷等复杂钻井事故，不仅对钻井设施和人员造成巨大危害，甚至危及海洋生态
[0046] 2. It is beneficial to the safety of jacking-up platforms for pile driving and drilling operations;
Smart Images
Figure CN117489307B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of jack-up platform installation operations in offshore oil fields, and more specifically to a method for releasing shallow bottom gas at exploration well sites. Background Technology
[0002] Offshore oil and gas development utilizes jack-up platforms for exploration well operations as an effective means of identifying key oil layers and major reservoirs. Before drilling operations on a jack-up platform, a pre-drilling site survey must be conducted. Due to geological sedimentation and other factors, shallow gas is often found in the formation. Shallow gas is a significant factor affecting the safety of jack-up platform installation and subsequent drilling operations. If the well site is located within a shallow gas zone with particularly high intensity, a gas surge can occur during jack-up installation, posing a significant threat to the jack-up platform, personnel safety, and property. Furthermore, complex drilling accidents such as overflows, well kicks, and blowouts can occur during drilling, causing immense damage to drilling facilities and personnel, and even endangering the marine ecosystem.
[0003] The conventional method used in current technology involves moving the wellhead out of the shallow gas zone and then drilling directional wells to explore the target formation. While this ensures the safe placement of the jack-up platform, it increases drilling difficulty and cost, and the risks of overflows and blowouts during drilling remain. Therefore, shallow gas poses significant safety hazards to personnel and large facilities, impacting the progress of oilfield exploration and development. Summary of the Invention
[0004] This invention overcomes the shortcomings of the prior art and provides a method for releasing gas in the shallow bottom layer of an exploration well site.
[0005] The objective of this invention is achieved through the following technical solution.
[0006] The purpose of the invention is achieved through the following technical solution.
[0007] The method for releasing shallow subsurface gas at exploration well sites includes the following specific steps:
[0008] S1. Conduct geophysical surveys of exploration well sites and determine gas zones;
[0009] Centered on the well site, a 2000m x 2000m square is defined as the engineering geophysical survey area. The engineering geophysical survey uses simulation survey methods to obtain the distribution range, intensity, stratification, and thickness of gas in the shallow formation within 100 meters below the mud surface.
[0010] Gas zone identification involves obtaining the distribution range, intensity, stratification, and thickness of shallow subsurface gases at depths of 100 to 1000 meters below the mud surface through seismic surveys.
[0011] Digital seismic surveys were used to obtain the distribution range, intensity, stratification, and thickness of shallow formation gases at depths of 100 to 1000 meters below the mudline.
[0012] S2. Conduct engineering geological surveys and tests at the well sites of exploration wells;
[0013] Geological surveys of exploration wells involve obtaining soil samples through drilling and recording the shallow gas leakage during the sampling process.
[0014] The tests included on-site shipboard laboratory tests and land laboratory tests to obtain soil parameters at the well site, and to calculate the planned drilling platform pile driving depth curve based on the soil parameters.
[0015] S3. Design the drilling platform positioning plan and determine the hull position;
[0016] The design of the drilling platform positioning scheme includes the positioning center point, heading and heading deviation, and positioning radius;
[0017] The hull position includes the coordinates of the hull center point, the bow direction, and the coordinates of the center of the legs or shoe to determine the hull position and the relative positional relationship between the drilling platform hull and the shoe and the shallow gas.
[0018] S4. Analyze the interference between the location and mud penetration depth of the drilling platform's pile legs and the gas zone;
[0019] When the depth of the pile driving into the mud overlaps with the top burial depth of the gas zone, the strength of the shallow gas zone is analyzed. If the strength is not high, the pile is driven into the original position. If the strength is high, it needs to be moved out of the gas zone.
[0020] When the depth of the pile driven into the mud is less than the burial depth of the top of the gas zone, only the influence of the gas zone during drilling is considered.
[0021] The gas zone overlaps with the pile driving depth because the three pile legs of the drilling platform occupy a large space, and the range and area of the gas zone must be considered.
[0022] S5. Analyze the overlap between the drilling well trajectory and the gas zone;
[0023] The coordinates of the drilling wellbore are recorded every 30 meters. When the wellbore is a vertical well, the coordinates of the wellhead are recorded.
[0024] The key nodes of the wellbore trajectory are superimposed with the shallow gas profile to show the relationship between the wellbore trajectory and the shallow gas before and after entering the shallow gas, and to record the coordinates of the wellbore trajectory when it is about to enter the shallow gas.
[0025] Once the wellbore trajectory enters shallow gas, record the initial depth of the wellbore trajectory segment with particularly high shallow gas intensity:
[0026] S6. Based on the analysis results of S4 and S5, determine the number, location, depth, and diameter of the vent holes;
[0027] There are 5 vent holes.
[0028] There is one well center, and the other four are distributed on a circle with a radius of 20 meters centered on the well center, respectively set at 0°, 90°, 180° and 270° of the circle;
[0029] The drilling depth is 120-200 meters below the mud surface;
[0030] The borehole diameter is 1066.8m;
[0031] S7. Design an implementation plan for offshore venting operations;
[0032] S8. Gas release operations are carried out at sea.
[0033] Step S1: The gas zone is determined by a combination of simulation survey and digital seismic survey results, including the boundary, intensity, top burial depth, bottom burial depth, and the extent of both.
[0034] Step S2: When the drilling depth is greater than 120 meters, determine whether there is a high-intensity gas or a high-intensity gas zone. If so, install a diverter on the venting drill.
[0035] In step S5, the wellbore trajectory and shallow gas zone are analyzed by interweaving the trajectory lines with the gas zone range in three-dimensional space.
[0036] During the drilling process, data on the total amount of gas spilled and the depth of major gas inrushes were recorded.
[0037] The drilling vessel uses a dynamic positioning system.
[0038] The drilling depth is determined by the overlap depth between the shallow gas layer and the wellbore trajectory. The borehole at the center of the well location is 30-50 meters deeper than the other four boreholes.
[0039] In step S2, the drilling depth for the exploration well engineering geological survey is 40 meters.
[0040] Step S7, the construction plan design, includes the design and basis for the location coordinates of the vent holes, the design and basis for the drilling specifications, on-site operations and observations, and safety and emergency measures.
[0041] Sea state requirements include wind force and wave height;
[0042] The selection of exploration vessels includes factors such as water depth adaptability, drilling equipment capabilities, anchoring and positioning, and dynamic positioning.
[0043] Establishment of positioning operation procedures for survey vessels.
[0044] The beneficial effects of this invention specifically include the following three points:
[0045] 1. By releasing gas from shallow formations, the impact and hazards of shallow gas can be minimized;
[0046] 2. It is beneficial to the safety of jacking-up platforms for pile driving and drilling operations;
[0047] 3. It ensured the safety of large-scale offshore facilities and personnel.
[0048] In summary, this method helps reduce the impact of shallow formation gas on jack-up platforms during placement and drilling operations, ensuring the safety of jack-up platform placement and drilling operations, and also protecting the safety of large facilities and personnel, thus promoting offshore oilfield exploration and development. Attached Figure Description
[0049] Figure 1 This is a logic step diagram of the present invention;
[0050] Figure 2 This is a shallow gas characteristic map obtained from a geophysical simulation survey of the well site.
[0051] Figure 3 It is a high-resolution digital display of the highlight profile - A09 image;
[0052] Figure 4 This is a high-resolution digital display of highlights profile - Image B07;
[0053] Figure 5 It is a digital seismic shallow gas feature map;
[0054] Figure 6 It is a design drawing of the drilling platform positioning scheme;
[0055] Figure 7 It is a graph showing the relationship between the ultimate pile corner load and the depth of the pile tip into the mud.
[0056] Figure 8 This is a schematic diagram of the wellbore trajectory;
[0057] Figure 9 It is a three-dimensional diagram of the intersection / overlap of wellbore trajectory and shallow gas;
[0058] Figure 10 It is a cross-sectional view of the intersection / overlap of the wellbore trajectory and shallow gas;
[0059] Figure 11 It is a wellbore trajectory diagram;
[0060] Figure 12 This is a schematic diagram of bubble observation. Detailed Implementation
[0061] The technical solution of the present invention will be further described below through specific embodiments.
[0062] Example
[0063] like Figure 1 As shown, taking well A, a exploratory well located in a certain block of offshore LD, as an example, the specific steps are as follows:
[0064] In this embodiment, according to step S1, a square survey area of 2000m × 2000m is set with the center of well A as the center, and a marine engineering geophysical simulation survey is conducted using an engineering survey vessel. The simulation survey results revealed the presence of shallow gas, and a shallow gas characteristic map of the shallow layer (0m below the mud surface to 100m below the mud surface) was obtained. Figure 2 .
[0065] The simulated shallow gas survey is described as follows: An anomalous reflection zone related to shallow gas, named A1, was discovered in the shallow to intermediate stratigraphic profile data (i.e., stratigraphic data from the seabed to within 100m below the seabed) within the survey area. Anomalous reflection zone A1 has a relatively large distribution area within the survey area, with the top of most of A1 buried at a depth of approximately 16m. The planned well location is located outside of anomalous reflection zone A1, with the closest distance to its edge being approximately 14m.
[0066] Digital seismic surveys to obtain digital seismic profiles Figure 3 Characteristic map of shallow gas at depths of 100 to 1000 meters below the mud surface. Figure 4 ;
[0067] Figure 3 and Figure 4 The light-colored areas represent areas of stronger gas, while the dark-colored areas represent diffused gas. The stronger gas areas are shaped like chimneys. This diagram is used as a basis for determining whether there is a strong gas or a strong gas region.
[0068] Digital seismic analysis describes the shallow gas characteristics as follows: at the predetermined well location, the top of the shallow gas layer is buried at a depth of 15-18 meters. Diffuse shallow gas exists in most areas within a 160ms / 100m range at depths of 15-100m below the seabed in the shallow strata. It is inferred that the intensity and pressure of the shallow gas within this depth are relatively low. Figure 2 As shown, ground-reflected waves exhibit chaotic reflection or are partially shielded; within a depth range of 100m-890m (430ms-1000ms) below the seabed, most anomalous reflection zones show blank reflections, such as... Figure 3 As shown, the analysis suggests that the shallow gas content increases in this depth region, enhancing the shielding effect of reflected waves.
[0069] like Figure 5As shown, shallow gas exists to varying degrees in the strata 76-890m below the seabed at the predetermined well location.
[0070] In step S2, based on the borehole sampling information of well A, the shallow soil conditions within a depth of 40m in this area can be determined: the soil layer from 0 to 19.8m is mainly cohesive soil, which has a trapping effect on the shallow gas below; the soil layer from 19.8 to 40m is mainly granular soil, which can play a role in storing shallow gas.
[0071] During the drilling process, due to the borehole diameter being only 15cm, only a small number of bubbles were observed emerging from the sea surface.
[0072] In step S3, as Figure 6 As shown, based on the seasonal heading and the main current direction of the block, the positioning center point is the well site center point, with a positioning heading of 10° and a deviation of ±1°. The positions of the three pile legs were calculated based on the well site center coordinates. All three pile legs interfere with the shallow gas layer, especially the bow pile, which is completely located within the shallow gas layer. The coordinates are as follows:
[0073] Table 1 shows the coordinates of the pile leg positions.
[0074] 1# XX°XX′XX"N,XXX°XX′XX"E 2# YY°YY'YY"N,YYY°YY'YY"E 3# ZZ°ZZ'ZZ"N,ZZZ°ZZ'ZZ"E
[0075] In step S4, the drilling platform is planned to be used to drive the pile into the mud at well A, as shown in the following curve: Figure 7 As shown.
[0076] In this embodiment, it can be seen from the shallow gas feature map that the top of the shallow gas at the predetermined well location is buried at a depth of 15-18 meters, which is deeper than the depth of the drilling platform pile insertion. The drilling platform pile shoe cannot touch the top of the shallow gas, that is, the pile insertion is safe, and it is concluded that there is no need to drill holes to release gas at the three pile leg insertion positions.
[0077] In step S5, the wellbore trajectory is determined in relation to shallow layers and the depth of intersection / overlap. The wellbore trajectory is as follows: Figure 8 As shown.
[0078] The purpose of this step is to determine the depth at which the wellbore trajectory begins to intersect / overlap with the shallow gas layer.
[0079] like Figure 9 The wellbore trajectory shown mainly includes parameters such as depth nodes, vertical well section transition to directional drilling, vertical projection coordinate points, and directional drilling angle to characterize the three-dimensional trajectory.
[0080] like Figure 10 As shown, through the cross-sectional diagram and 3D diagram of the intersection / overlap of the well trajectory and the shallow gas, the relationship between the well trajectory and the shallow gas before and after entering the shallow gas is obtained. The shallow gas encountered is 165 meters below the mud surface.
[0081] In this embodiment, step 6 is as follows: Figure 11 As shown, one vent hole is arranged at the center of the well site, with a depth of 165 + 30 = 195 meters. The other four are distributed on a circle with a radius of 20 meters centered on the well site, located at 0°, 90°, 180° and 270° of the circle, respectively, with a depth of 165 meters and a borehole diameter of 1066.8 mm.
[0082] In step 7, the implementation plan for offshore venting operations specifically includes:
[0083] (1) Determine the location of the vent holes BH1 to BH5:
[0084] BH1 552740.49 4367127.41 BH2 552760.49 4367127.41 BH3 552720.49 4367127.41 BH4 552740.49 4367147.41 BH5 552740.49 4367107.41
[0085] The basis for arranging five vent holes at the center of the predetermined well location and within 20m in four directions in Well A is mainly based on engineering geophysical data. The location was selected to be more likely to be affected by shallow gas than the original predetermined well location, so that a more obvious venting phenomenon could be observed on site.
[0086] (2) Depth of vent hole
[0087] The depth of the five venting holes is 165m-200m, and the specific drilling depth will be determined on-site based on safe operation and venting conditions.
[0088] The main basis is that, according to the geophysical data, the boreholes should be drilled as far as possible to or near the top of the stronger gas zone, which will help to better observe and judge the influence of shallow gas in the area.
[0089] (3) On-site operations and observation
[0090] Operating vessel: Haiyang Shiyou 7XX vessel, equipped with both DP2 dynamic positioning and four-anchor positioning.
[0091] Sea conditions required: wind force 5 or below, wave height below 1.5m, and a 3-day consecutive operating window.
[0092] After anchoring and positioning, the water depth was measured, drilling began, and two people were assigned to each of the port and starboard sides of the ship to observe the bubbles on the sea surface and record video, while another person was assigned to record the drilling and mud conditions in real time and record video, etc.
[0093] (4) Safety and emergency measures
[0094] Based on the HSE policy of the operating company, this embodiment refines the emergency plan and JSA analysis in detail before the operation, and holds a discussion meeting to finally determine the safety emergency measures applicable to this project.
[0095] The specific process of implementing the gas release operation at sea in step 8 is as follows:
[0096] The implementation process is as follows: weather forecast - vessel sails to the work area - anchoring at the predetermined drilling location - drilling location positioning - drilling operation - bubble observation and drilling status recording - operation completion.
[0097] In this embodiment, the HYSY7XX vessel drilled a shallow gas venting hole BH1 with a depth of 170m at well site A in XX year. During the operation, the HYSY7XX vessel used DP2 positioning to keep the vessel stable at the borehole position, while the observation vessel conducted vertical observations from 30-50 meters away.
[0098] The sea conditions at the site were: southwest wind force 2-3, wave height 0.1-0.5m. At the site, the area where bubbles appear is mainly determined by the direction and speed of the ocean current. When positioning with DP2, maintain a certain angle between the bow and the direction of the ocean current to facilitate observation of the bubbles; adjust the bow as needed as the current changes.
[0099] like Figure 12 As shown in the table below, during drilling operations, air bubbles are observed and drilling conditions are recorded.
[0100] The table below is a record of the drilling of shallow gas venting holes at well location A.
[0101]
[0102] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.
Claims
1. A method for releasing gas from the shallow subsurface layer of an exploration well site, characterized in that, The specific steps include: S1. Conduct geophysical surveys of exploration well sites and determine gas zones; Centered on the well site, a 2000m x 2000m square is defined as the engineering geophysical survey area. The engineering geophysical survey uses simulation survey methods to obtain the distribution range, intensity, stratification, and thickness of gas in the shallow formation within 100 meters below the mud surface. Gas zone identification involves obtaining the distribution range, intensity, stratification, and thickness of shallow subsurface gases at depths of 100 to 1000 meters below the mud surface through seismic surveys. Digital seismic surveys were used to obtain the distribution range, intensity, stratification, and thickness of shallow formation gases at depths of 100 to 1000 meters below the mudline. S2. Conduct engineering geological surveys and tests at the well sites of exploration wells; Geological surveys of exploration wells involve obtaining soil samples through drilling and recording the shallow gas leakage during the sampling process. The tests included on-site shipboard laboratory tests and land laboratory tests to obtain soil parameters at the well site, and to calculate the planned drilling platform pile driving depth curve based on the soil parameters. S3. Design the drilling platform positioning plan and determine the hull position; The design of the drilling platform positioning scheme includes the positioning center point, heading and heading deviation, and positioning radius; The hull position includes the coordinates of the hull center point, the bow direction, and the coordinates of the center of the legs or shoe to determine the hull position and the relative positional relationship between the drilling platform hull and the shoe and the shallow gas. S4. Analyze the interference between the location and mud penetration depth of the drilling platform's pile legs and the gas zone; When the depth of the pile driven into the mud overlaps with the top burial depth of the gas zone, the strength of the shallow gas zone is analyzed. The strength of the gas zone is judged based on the shallow stratum profile. When the strength of the gas zone is judged to be too great, the pile needs to be moved out of the gas zone. When the depth of the pile into the mud is less than the top burial depth of the gas zone, the pile depth overlaps with the gas zone; when the pile depth is greater than the top burial depth of the gas zone, observe the overflow of sea surface bubbles at the pile leg during the pile insertion process. S5. Analyze the overlap between the drilling well trajectory and the gas zone; The coordinates of the drilling wellbore are recorded every 30 meters. When the wellbore is a vertical well, the coordinates of the wellhead are recorded. The key nodes of the wellbore trajectory are superimposed with the shallow gas profile to show the relationship between the wellbore trajectory and the shallow gas before and after entering the shallow gas, and to record the coordinates of the wellbore trajectory when it is about to enter the shallow gas. Once the wellbore trajectory enters shallow gas, the initial depth of the wellbore trajectory segment with high shallow gas intensity is recorded based on the gas zone structure in the shallow formation profile: S6. Based on the analysis results of S4 and S5, determine the number, location, depth, and diameter of the vent holes; Five vent holes are used. The vent holes are located as follows: one at the center of the well site, and the other four are distributed on a circle with a radius of 20 meters centered on the well site, at positions of 0°, 90°, 180° and 270° of the circle, respectively. The drilling depth is 120-200 meters below the mud surface; The borehole diameter is 1066.8m; S7. Design an implementation plan for offshore venting operations; S8. Gas release operations are carried out at sea; The drilling depth is determined by the overlap depth between the shallow gas layer and the wellbore trajectory. The borehole at the center of the well location is 30-50 meters deeper than the other four boreholes.
2. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: In step S1, the gas zone is determined by a combination of simulation survey and digital seismic survey results, which determines the boundary, intensity, top burial depth, and bottom burial depth of the gas zone, as well as the range of both.
3. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: In step S2, when the drilling depth is greater than 120 meters, it is determined whether there is a high-intensity gas or a high-intensity gas zone. If so, a diverter is installed on the venting drill.
4. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: In step S5, both the wellbore trajectory and the shallow gas zone are analyzed by interweaving the trajectory lines with the gas zone range in three-dimensional space.
5. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: During drilling, record the total amount of gas that overflows and the depth of the gas surge.
6. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: The drilling vessel uses a dynamic positioning system.
7. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: In step S2, the drilling depth for the exploration well engineering geological survey is 40 meters.
8. The method for releasing shallow bottom gas at an exploration well site according to claim 1, characterized in that: The construction plan design content of step S7 includes the design and basis of the location coordinates of the vent hole, the design and basis of the drilling specifications, the on-site operation and observation, and the content of safety and emergency measures. Sea state requirements include wind force and wave height; The selection of exploration vessels includes considerations such as water depth suitability, drilling equipment capabilities, anchoring and dynamic positioning; and the development of positioning procedures for exploration vessels.