Horizontal well bridge shooting combined operation method and device for avoiding casing coupling precision perforation

Abstract

A horizontal well bridge shooting combined operation method and device for avoiding casing coupling precise perforation. Mainly solve the problem that the existing bridge shooting combined operation construction perforation depth error is large and cannot avoid casing coupling precise perforation. Its characterized in that: determining the oil top depth, oil bottom depth, nearest casing coupling depth of each oil layer, perforation thickness and gun head length; comparing the corrected oil top depth and oil bottom depth with the nearest casing coupling depth, adjusting the perforation depth according to the comparison result, thereby determining the up value and ignition mark depth; after the well head is connected, the cable is lowered, the standard coupling depth is calibrated, the cable is lowered to the build-up section, pumping is started, the casing coupling data is verified during pumping, and the pumping is stopped 5m below the first standard coupling; the cable is lifted, the bridge plug is positioned and ignited and set; the first cluster, the second cluster and the remaining perforating gun are perforated in turn. The method has small perforation depth error, can avoid casing coupling perforation, and realizes precise fracturing of shale oil layer.

Description

Technical Field

[0001] The invention relates to the field of oil and gas well perforation, in particular to a device and method for precise perforation of a horizontal well by bridge-shot combination to avoid casing collars. Background Art

[0002] The cable-pumped bridge plug and perforation system uses a wellhead cable blowout preventer (BOP) to lower the bridge plug and perforating string to a predetermined depth (vertical or inclined) by weight. Using a wellhead cable blowout preventer, the bridge plug and perforating string are then lowered to the target formation by weight using a fracturing pump truck and logging winch, according to a planned pumping rate schedule. The bridge plug is then positioned and positioned, communicating with the downhole selective firing controller via the ground control system. Selective firing is then performed to complete the bridge plug setting. The perforating string is then raised, aligned with the designed perforation section, and intelligent selective firing is performed to complete the perforation. This process, a core technology for staged fracturing in unconventional reservoirs, has been applied in hundreds of wells in shale and tight oil fields in the Daqing Oilfield, and is gradually maturing and improving through large-scale application.

[0003] The depth of the bridge plug and perforation system is determined by measuring the number of pulley revolutions at the wellhead using a wellhead depth motor or Martindike. The cable's depth and speed are then calculated by multiplying the number of pulley revolutions by the pulley's circumference. This perforation depth does not include the cable's elongation downhole, resulting in a certain depth error, ranging from 0.5m to 1.0m or even greater. This makes it impossible to accurately avoid perforating the casing collar. If the perforation hits the collar, it will cause excessive abrasion of the perforation during the fracturing process, posing a risk to the long-term safety of the entire well. With the deepening of shale oil exploration and development, the need to narrow the perforation depth error and prohibit the perforation of the casing collar is increasing in order to accurately locate the "sweet spot." Existing depth measurement systems are no longer able to meet the needs of precise shale oil perforation. Summary of the Invention

[0004] In order to overcome the problem that the existing bridge-shooting combined operation has large perforation depth errors and cannot avoid casing couplings for accurate perforation, the present invention provides a horizontal well bridge-shooting combined operation method and device for accurate perforation by avoiding casing couplings. This method has a small perforation depth error and can avoid casing couplings for perforation, thereby achieving accurate fracturing of shale oil layers.

[0005] The technical solution of the present invention is: a horizontal well bridge shot-to-shot precise perforation method avoiding casing collars, comprising the following steps:

[0006] S1. Determine the oil top depth L of each oil layer a , oil bottom depth L b , the casing coupling depth L closest to the oil layer j , perforation thickness D, gun head length Q;

[0007] S2, the oil top depth L in step S1 a , oil bottom depth L b After correction, the depth L of the nearest casing collar j Compare and adjust the perforation depth according to the comparison results to determine the lifting value U and the ignition mark depth L f ;

[0008] S3. After the wellhead is docked, lower the cable, check the standard coupling depth, lower the cable to the deflection section, and start pumping. Verify the casing coupling data during pumping, and stop pumping when it reaches 5m below the first standard coupling.

[0009] S4. Lift the cable, position the bridge plug, ignite and seal it;

[0010] S5, perforating with the first cluster of perforating guns;

[0011] S6, perforating with the second cluster of perforating guns;

[0012] S7. Perforate with the remaining perforating guns.

[0013] Further, in step S2,

[0014] U=L j +QL a -P

[0015] L f =L a +PQ

[0016] Where: P is the correction value;

[0017] Further, the step S2 includes:

[0018] S2.1, when L b +P <L j hour,

[0019] ① If L j -L b -P<0.5m, adjust the perforation depth as follows:

[0020] L b =L j -0.5mP

[0021] L a =L j -D

[0022] ②If L j -L b -P≥0.5m, no perforation depth adjustment is performed;

[0023] S2.2, when La +P>L j hour,

[0024] ① If L a +PL j <0.5m, make the following perforation depth adjustments:

[0025] L a =L j +0.5mP

[0026] L b =L a +D

[0027] ②If L a +PL j ≥0.5m, no perforation depth adjustment is performed;

[0028] S2.3, when L a +P≤L j ≤(L a +P+L b +P) / 2, make the following perforation depth adjustments:

[0029] L a =L j +0.5mP

[0030] L b =L a +D

[0031] S2.4, when (L a +P+L b +P) / 2 <L j ≤L b When +P, make the following perforation depth adjustments:

[0032] L b =L j -0.5mP

[0033] L a =L j -D.

[0034] Furthermore, in step S4, when the difference between the last oil top depth and the first standard coupling depth is not less than 5m:

[0035] If the first standard coupling is identified and the depth L of the casing coupling is the same as that in step S1 j The difference should not exceed 3m, and the seal will be set after the upward lift value U is raised;

[0036] If the first standard coupling is identified but the depth L of the casing coupling is different from that in step S1 jIf the difference is greater than 3m, use the standard collar for positioning and then ignite and seal;

[0037] If the first standard coupling is not identified but the coupling curve has a shape, determine whether it is the first standard coupling. If it is the first standard coupling, use the method of identifying and positioning the standard coupling for construction, and then ignite and set the coupling.

[0038] If the first standard coupling is not identified and the coupling curve has no shape, align the real-time depth with the ignition mark depth in the calculation report, and then ignite and seal.

[0039] Furthermore, in step S4, when the difference between the last oil top depth and the first standard coupling depth is less than 5m, the real-time depth is aligned with the ignition mark depth in the calculation report, and ignition is started.

[0040] Furthermore, in step S5, if the first cluster of perforating guns and the bridge plug share the second standard coupling, ignite and perforate;

[0041] If the first cluster of perforating guns and the bridge plug are not a standard coupling, proceed to step S6.

[0042] Furthermore, in step S6, after the first cluster of perforating guns perforate,

[0043] If the third standard collar is identified, it is lifted by a lifting value U and then ignited and perforated;

[0044] If the third standard coupling is identified but the depth difference with the theoretical third standard coupling is greater than 3m, the standard coupling shall be positioned using the method of identification. After identification, the ignition strip will appear and then ignition and perforation will be carried out.

[0045] Furthermore, in step S6, after the first cluster of perforating guns perforate,

[0046] If the third standard coupling is not identified but the coupling curve has a shape, determine whether it is a standard coupling. If it is a standard coupling, use the method of pointing and locating the standard coupling for construction, and then ignite and perforate;

[0047] If the standard coupling is not identified and has no shape, use the continuous lifting value to track the lifting positioning, and ignite and perforate after accurate positioning.

[0048] Furthermore, in step S6, the continuous withdrawal value L h It is the distance between the depth of the current ignition mark and the depth of the next ignition mark, that is:

[0049] L h = L f1 -L f2 =(L a1 +P-Q1)-(L a2 +P-Q2)

[0050] Where: L f1The depth of the ignition mark for the current stop; L f2 The depth of the ignition mark for the next parking; L a1 is the current oil layer top depth; L a2 is the oil top depth of the next oil layer, Q1 is the length of the current blast head, and Q2 is the length of the next blast head.

[0051] A horizontal well bridge-shooting combined operation precise perforating device that avoids casing couplings includes a wellhead device, the lower part of which is connected to a magnetic locator, the lower end of which is sequentially connected to a counterweight rod, a perforating gun, a bridge plug setting tool, and a bridge plug, the magnetic locator is connected to a cable, which passes through a top pulley and a ground pulley and then is connected to a numerical control device.

[0052] The present invention has the following beneficial effects: due to the adoption of the above-mentioned scheme, the perforation method can accurately avoid casing joints, greatly reduce the perforation depth error, realize accurate fracturing of shale oil layers, avoid excessive abrasion of the perforation holes on the couplings during the fracturing process, and make the operation of the entire well safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a structural schematic diagram of the present invention;

[0054] Figure 2 It is a schematic diagram of the relationship between standard coupling depth and oil layer position.

[0055] In the figure, 1- overhead pulley, 2- grease injection control head, 3- blowout preventer riser, 4- cable blowout preventer, 5- wellhead assembly, 6- magnetic positioner, 7- counterweight rod, 8- perforating gun, 9- bridge plug setting tool, 10- bridge plug, 11- cable, 12- high-pressure grease injection pump, 13- depth motor, 14- ground pulley, 15- numerical control device. DETAILED DESCRIPTION

[0056] The present invention will be further described below in conjunction with the accompanying drawings:

[0057] Depend on Figure 1 、 Figure 2 As shown, a method for precise perforation in a horizontal well by bridge-shot combined operation to avoid casing collars includes the following steps:

[0058] S1. Determine the oil top depth L of each oil layer a , oil bottom depth L b , the casing coupling depth L closest to the oil layer j , perforation thickness D, gun head length Q.

[0059] S2, the oil top depth L in step S1 a , oil bottom depth L b After correction, the depth L of the nearest casing collar jBy comparing the results, we can judge whether it is necessary to adjust the perforation depth and the bridge plug setting depth so that the perforation holes avoid the casing collar. According to the comparison results, the perforation depth is adjusted to determine the lifting value U and the ignition mark depth L. f ;in

[0060] U=L j +QL a -P (1)

[0061] L f =L a +PQ (2)

[0062] Where: P is the correction value.

[0063] From formula (1) and (2), we can see that the upper value U and the ignition mark depth L f and oil top depth L a and oil bottom depth L b Therefore, the depth of the oil top and the oil bottom can be used to determine the depth of the lift U and the ignition mark.

[0064] According to the different positional relationships between the oil layer and the standard coupling, it can be divided into the following situations:

[0065] S2.1. If the sum of the oil bottom depth and the correction value is shallower than the nearest coupling, that is, L b +P <L j When, see Figure 2 Figure a in

[0066] ① If L j -L b -P<0.5m, adjust the perforation depth as follows:

[0067] L b =L j -0.5mP

[0068] L a =L j -D

[0069] ②If L j -L b -P≥0.5m, no perforation depth adjustment is performed;

[0070] S2.2. If the sum of the oil bottom depth and the correction value is deeper than the nearest coupling depth, that is, L a +P>L j

[0071] When, see Figure 2 Figure b in the figure,

[0072] ① If L a +PL j<0.5m, make the following perforation depth adjustments:

[0073] L a =L j +0.5mP

[0074] L b =L a +D

[0075] ②If L a +PL j ≥0.5m, no perforation depth adjustment is performed;

[0076] S2.3, when L a +P≤L j ≤(L a +P+L b +P) / 2, see Figure 2 In Figure c, make the following perforation depth adjustments:

[0077] L a =L j +0.5mP

[0078] L b =L a +D

[0079] S2.4, when (L a +P+L b +P) / 2 <L j ≤L b +P, see Figure 2 In Figure d, make the following perforation depth adjustments:

[0080] L b =L j -0.5mP

[0081] L a =L j -D.

[0082] Since readjusting the depth requires analyzing and calculating a large amount of coupling data, especially during shale oil operations, which require 24-hour operation, fatigued workers are prone to making mistakes. To reduce the workload and avoid manual calculation errors, a coupling-free perforation depth adjustment program was developed. This program uses a graphical control design. After reading the top and bottom oil depths, it automatically analyzes and selects the casing coupling as the standard coupling. The depth positions of the top oil, bottom oil, and casing coupling are graphically displayed on the computer screen, allowing the operator to clearly understand the relative depth relationships among the three.

[0083] The downhole tool string includes a magnetic locator, counterweight, perforating gun, bridge plug setting tool, and bridge plug. The magnetic locator measures the casing collar signal. The principle is that when the tool moves through the casing collar, the thickening of the casing at the collar changes the magnetic field distribution around the magnet, causing the magnetic flux through the coil to change, generating an induced electromotive force. The magnitude of the induced current is recorded. Simultaneously, a wellhead depth counter motor measures the length of the downhole cable to measure the collar depth, thereby generating a casing collar curve. The casing collar curve, combined with radioactive logging, can accurately determine the perforation locations in the well. The counterweight increases the weight of the tool string for easier running. The perforating gun is loaded with perforating charges, detonating cord, and detonators, and then ignites and detonates to open the formation. When the bridge plug setting tool is powered on from the surface, the cable detonates the igniter inside the setting tool, igniting the slow-burning pyrotechnics. The gas generated by the slow-burning pyrotechnics propels the setting tool relative to the bridge plug, enabling the setting and release of the bridge plug. The bridge plug is delivered to the desired wellbore location via a cable. Pressure generated by explosives, hydraulic setting, or mechanical setting tools acts on the upper slips, which in turn exerts tension on the tension rod. This tension, applied through the upper and lower cones, applies both upward and downward forces to the sealing rubber sleeve. When the tension reaches a certain value, the tension rod breaks, and the setting tool detaches from the bridge plug. At this point, the locking device on the bridge plug's center tube activates, breaking the upper and lower slips and embedding them in the inner wall of the casing. The rubber sleeve expands and seals, completing the setting process.

[0084] S3. Slowly and evenly raise the cable until the tension increases by 0.5kN-1.0kN. Then lower the cable until the tension is restored. The operating engineer places the cable at depth "0." Upon receiving the command, the winch station begins lowering the cable. When the lowered casing string is 50m above the short casing marking the vertical section, measurement begins. After measuring the short casing, the cable is raised. The depth and length of the short casing coupling are measured, and the operation is stopped. The operating engineer compares the actual measured casing depth data with the short casing depth data from the post-casing magnetic map. The measured short casing is corrected and the pulley error is verified for accuracy. Error control range: coupling depth ±3.0m, casing length ±0.1m. After depth calibration, the cable is lowered. During the entire lowering and pumping process, the casing coupling automatic recognition program automatically identifies the casing couplings and counts the coupling numbers, ensuring a one-to-one correspondence between the measured couplings and the couplings on the magnetic discharge curve. If any casing shorts occur during pumping, the short casing depths are verified, and the standard casing coupling configuration selected for this section is observed to ensure normal operation. The tool string stops when it reaches the first standard coupling at a depth of 5m.

[0085] S4. The operating engineer directs the winch to lift. The winch post pays close attention to the tension during the lifting process. After the tension is normal, the speed is quickly increased to 1000m / h-1200m / h; then the bridge plug positioning and ignition procedure is carried out.

[0086] When the bridge plug is positioned and ignited, the following situations are included:

[0087] (1) When the difference between the last oil top depth and the first standard coupling depth is not less than 5m:

[0088] If the first standard coupling is identified and the depth L of the casing coupling is the same as that in step S1 j If the difference does not exceed 3m, the tool string will be lifted by the standard coupling, and the lifting distance is the lifting value U. The lifting count adopts a graphical design. After the lifting is zero, the operator clicks the "Make Ignition Mark" button to perform the ignition operation, and clicks the "Next" button after normal ignition.

[0089] If the first standard coupling is identified but the depth L of the casing coupling is different from that in step S1 j If the difference is greater than 3m, the winch will stop immediately to avoid over-lifting. The operator will use the method of pointing and marking to construct. After pointing, the ignition bar will appear when the cable is slightly moved. The remaining operations are the same as above.

[0090] If the first standard coupling is not recognized but the coupling curve is present, stop the winch immediately to prevent over-lifting. The operator can determine whether it is a standard coupling by changing the display scale, shape, and depth. If it is a standard coupling, use the standard coupling identification method. After identification, the ignition bar will appear on the micro-cable. The remaining operations are the same as above.

[0091] If the first standard coupling is not recognized and the coupling curve has no shape, align the real-time depth with the ignition mark depth in the calculation report, press the "Make Ignition Mark" button at the operator's post, perform the ignition operation, and press the "Next" button after normal ignition.

[0092] (2) When the difference between the last oil top depth and the first standard coupling depth is less than 5m, the real-time depth is aligned with the ignition mark depth in the calculation report. The operator presses the "Make ignition mark" button to perform the ignition operation. Wait until the bridge plug is completely seated and release it before pressing the "Next" button.

[0093] S5. The first cluster of perforating guns perforates. Since the first cluster of guns is closer to the bridge plug, normally the first cluster of perforating guns and the bridge plug will share a standard connection, namely the second standard coupling. After the operator clicks the "Next" button, a new ignition bar will appear. After lifting it to zero, the normal operation can be carried out.

[0094] If the first cluster of perforating guns and the bridge plug are not a standard coupling, proceed to step S6.

[0095] S6. The second cluster of perforating guns performs perforating, including the following situations:

[0096] (1) After the operator clicks the "Next" button, the winch post closely monitors the tension. Depending on the equipment conditions, when the tension is normal, the speed is quickly increased to 1000-1200m / h. If the third standard coupling is identified and the ignition bar appears, the upper value U is raised to zero. The operator clicks the "Make Ignition Mark" button to perform the ignition operation. After normal ignition, click the "Next" button.

[0097] (2) If the third standard coupling is identified but the depth difference with the theoretical third standard coupling is greater than 3m, the winch will stop immediately to avoid over-lifting. The operator will use the method of pointing and positioning the coupling for construction. After identification, the ignition bar will appear on the micro-cable. After the upper value U is raised to zero, the operator will click the "make ignition mark" button to perform the ignition operation. After normal ignition, click the "next time" button.

[0098] (3) If the third standard coupling is not identified but the shape is present, the winch will be stopped immediately to avoid over-lifting. The operator will judge whether it is a standard connection by changing the display ratio, shape and depth. If it is a standard connection, the standard connection will be identified and the ignition bar will appear after the identification of the cable. The operator will press the "make ignition mark" button to ignite the connection. After normal ignition, press the "next" button.

[0099] (4) If the third standard coupling is not identified and there is no shape, use the continuous value L h Track and lift positioning. After the countdown tracking reaches zero, make an ignition mark, click next time, and the continuous lift value will be automatically refreshed. The continuous lift value is the distance between the depth of the current parking ignition mark and the depth of the next parking ignition mark, that is, the difference between the two ignition mark depths:

[0100] L h = L f1 -L f2 =(L a1 +P-Q1)-(L a2 +P-Q2),

[0101] Where: L f1 The depth of the ignition mark for the current stop; L f2 The depth of the ignition mark for the next parking; L a1 is the current oil layer top depth; L a2 is the oil top depth of the next oil layer; Q1 is the length of the current blast head, and Q2 is the length of the next blast head.

[0102] S7. Perforating with the remaining perforating guns. During the positioning and firing process of the remaining perforating guns, if the corresponding standard coupling can be identified, then proceed to step S6 (1); if the third standard coupling is not identified but has a shape, then proceed to step S6 (3); if the third standard coupling is not identified and has no shape, then proceed to step S6 (4).

[0103] A horizontal well bridge-shot precision perforating device for avoiding casing couplings comprises a cable 11 and a wellhead assembly 5. A cable blowout preventer 4 is fixed to the wellhead assembly 5. A blowout preventer riser 3 is fixed to the upper portion of the cable blowout preventer 4. A grease injection head 2 is connected to the blowout preventer riser 3. After passing through the wellhead assembly 5, the cable 11 is connected to a magnetic locator 6. The lower end of the magnetic locator 6 is sequentially connected to a counterweight rod 7, a perforating gun 8, a bridge plug setting tool 9, and a bridge plug 10. After passing through a top pulley 1 and a ground pulley 14, the cable 11 is connected to a numerical control device 15. The ground pulley 14 is connected to a depth motor 13. During operation, the numerical control device 15 can execute various construction procedures, including a perforating depth adjustment program for avoiding couplings, a perforating depth measurement system, an automatic casing coupling identification program, and a bridge-shot positioning and ignition program, to ensure accurate perforating depth.

Claims

1. A horizontal well bridge-shot joint operation to avoid casing collars and achieve precise perforation, characterized by The following steps are involved: S1. Determine the oil top depth L of each oil layer a , oil bottom depth L b , the casing coupling depth L closest to the oil layer j , perforation thickness D, gun head length Q; S2, the oil top depth L in step S1 a , oil bottom depth L b After correction, the depth L of the nearest casing collar j Compare and adjust the perforation depth according to the comparison results to determine the lifting value U and the ignition mark depth L f ;in, U=L j +Q-L a -P L f =L a +P-Q Where: P is the correction value; The step S2 comprises: S2.1, when L b +P <L j hour, ① If L j -L b -P<0.5m, adjust the perforation depth as follows: IT b =L j -0.5mP L a =L j -D ②If L j -L b -P≥0.5m, no perforation depth adjustment is performed; S2.2, when L a +P>L j hour, ① If L a +PL j <0.5m, make the following perforation depth adjustments: IT a =L j +0.5mP L b =L a +D ②If L a +PL j ≥0.5m, no perforation depth adjustment is performed; S2.3, when L a +P≤L j ≤(L a +P+L b +P) / 2, make the following perforation depth adjustments: IT a =L j +0.5mP L b =L a +D S2.4, when (L a +P+L b +P) / 2 <L j ≤L b When +P, make the following perforation depth adjustments: IT b =L j -0.5mP L a =L j -D; S3. After the wellhead is docked, lower the cable, check the standard coupling depth, lower the cable to the deflection section, and start pumping. Verify the casing coupling data during pumping, and stop pumping when it reaches 5m below the first standard coupling. S4. Lift the cable, position the bridge plug, ignite and seal it; S5, perforating with the first cluster of perforating guns; S6, perforating with the second cluster of perforating guns; S7. Perforate with the remaining perforating guns.

2. The horizontal well bridge-shot precision perforating method according to claim 1, characterized in that: In step S4, when the difference between the last oil top depth and the first standard coupling depth is not less than 5m: If the first standard coupling is identified and the depth L of the casing coupling is the same as that in step S1 j The difference should not exceed 3m, and the seal will be set after the upward lift value U is raised; If the first standard coupling is identified but the depth L of the casing coupling is different from that in step S1 j If the difference is greater than 3m, use the standard collar for positioning and then ignite and seal; If the first standard coupling is not identified but the coupling curve has a shape, determine whether it is the first standard coupling. If it is the first standard coupling, use the method of identifying and positioning the standard coupling for construction, and then ignite and set the coupling. If the first standard coupling is not identified and the coupling curve has no shape, align the real-time depth with the ignition mark depth in the calculation report, and then ignite and seal.

3. The horizontal well bridge-shot precision perforating method according to claim 2 is characterized by: In step S4, when the difference between the last oil top depth and the first standard coupling depth is less than 5m, the real-time depth is aligned with the ignition mark depth in the calculation report, and ignition is started.

4. The horizontal well bridge-shot precision perforating method according to claim 3 is characterized by: In step S5, if the first cluster perforating gun and the bridge plug share the second standard coupling, ignite and perforate; If the first cluster of perforating guns and the bridge plug are not a standard coupling, proceed to step S6.

5. The horizontal well bridge-shot precision perforating method according to claim 4 is characterized by: In step S6, after the first cluster of perforating guns perforate, If the third standard collar is identified, it is lifted by a lifting value U and then ignited and perforated; If the third standard coupling is identified but the depth difference with the theoretical third standard coupling is greater than 3m, the standard coupling shall be positioned using the method of identification. After identification, the ignition strip will appear and then ignition and perforation will be carried out.

6. The horizontal well bridge-shot precision perforating method according to claim 5 is characterized by: In step S6, after the first cluster of perforating guns perforate, If the third standard coupling is not identified but the coupling curve has a shape, determine whether it is a standard coupling. If it is a standard coupling, use the method of pointing and locating the standard coupling for construction, and then ignite and perforate; If the standard coupling is not identified and has no shape, use the continuous lifting value to track the lifting positioning, and ignite and perforate after accurate positioning.

7. The horizontal well bridge-shot precision perforating method according to claim 6 is characterized by: In step S6, the continuous withdrawal value L h It is the distance between the depth of the current ignition mark and the depth of the next ignition mark, that is: L h = L f1 - L f2 =(L a1 +P-Q1)-(L a2 +P-Q2) Where: L f1 The depth of the ignition mark for the current stop; L f2 The depth of the ignition mark for the next parking; L a1 is the current oil layer top depth; L a2 is the oil top depth of the next oil layer; Q1 is the length of the current blast head, and Q2 is the length of the next blast head.

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