There I was... in the Chukchi Sea, a desolate swath of ocean located off the N.W. Coast of Alaska. I was part of a diving crew providing underwater support for exploratory oilfield drilling operations aboard a Canadian drillship, leased by Gulf Petroleum for the 1989 drilling season ( May to October ).
Environmental regulations required the operator to impact the ocean environment as little as possible & this included a stipulation that no exploration apparatus could rise above the level of natural bottom. To satisfy this restriction, the driller would use a giant coring tool to dig a 10' dia., 40' deep hole in the bottom sediment, known as the "Glory Hole." From the bottom of this hole they would begin the exploratory well.
When "making hole" in the seafloor the driller begins with a 36" dia. hole to a predetermined depth, he then lines this hole with a steel liner or "casing" to give support to the hole in the surrounding sediment. Once the liner is run it is cemented in place. The "wellhead" is affixed to the top joint of 36"casing & is essentially an adapter, designed to accept the b.o.p. ( blowout preventer ) & later on, a production assembly if the hole is viable. Depending on the nature & depth of the sediment, a further series of ever-smaller diameter casings are run & cemented in down to bedrock.
Upon reaching bedrock the final hole bore begins ( about 7" dia. ) to t.d. ( terminal depth ). The drillstring is advanced downhole in 40' sections. Drilling mud is pumped from topside down through the drillpipe where it exits out holes in the heads of the drillbit. This mud is vital to the process as it performs a variety of functions including: cooling the drillbit, returning cuttings to the surface & providing hydrostatic pressure to counter ever increasing formation pressures downhole.
This concludes "Subsea Drilling 101...onto "Primer for Deepsea Diving..."
Built into the drillship in an enclosed area located midships on the main deck was our 1000' saturation diving system. System tankage included a living chamber to accomodate 4 divers, a transfer chamber containing a toilet & shower-head, and a submersible decompression chamber or "diving bell" that acted as our subsea elevator to the worksite. The bell was the only part of the system to enter the water. A "control van" contained all the electrics, electronics & pneumatic controls to operate the system. Additional system components included gas scrubbing, chamber environmental control, gas storage & bell handling winch system. The bell was supplied with power, breathing gases, hot water & communications via umbilical. The divers wore hot water suits for thermal protection & umbilical supplied hardhats for breathing & communications.
When the driller completes his "casing program" it is time to install the b.o.p.. To fascilitate this tricky operation a "guide base" is lowered over the wellhead & leveled at the bottom of the glory hole. From each corner of the square guide base rise the "guideposts". A diver will descend to drive a "spear" into the top of each post. From each spear runs a guide wire to surface which terminate to heave compensators on the drill floor. These compensators allow drilling to proceed in rough seas (up to a point).
The blowout preventer is essentially a series of hydraulically actuated rams. It stands about 40' tall & weighs about 25 tons. It is lowered to the wellhead by thick joints of 40' long pipe called "marine riser". Affixed to each corner of the b.o.p. are four posts. The bottom of these posts are flared in the shape of a funnel & act as centering guides for the tops of the guide base posts. When all is ready, the b.o.p. is lowered to the wellhead, 40' at a time, & is hydraulically latched.
When drilling to t.d. begins, the drillstring is advanced through the b.o.p., past the wellhead, down through the casing to bedrock. The primary function of the b.o.p. is to prevent down hole pressures from venting to surface ( "blowout" ) should this pressure overcome the hydrostatic pressure of the mud column in the hole. The driller can seal off the hole by activating "pipe rams" that will seal around the drillstring. If these fail to contain the pressure a "shear ram" can transect the string & block the hole.
Are ya with me?
Before drilling could commence the b.o.p. or "stack" had to be inspected & it was my good fortune that day to get the dive. Myself & another diver ( the "bellman" ) climbed into the bell, did our checks & prepared for launch. When all was ready, the bell would be "unmated" from the transfer chamber. A cover over the bell "moonpool" would be drawn back & the bell, at atmospheric pressure, would be lowered into the waiting sea. Natural bottom @ this location was 140', but my dive would take me to the bottom of the glory hole so our dive was planned for excursion to 180'. The bell's decent was halted 10' above natural bottom. Inside the bell we prepared for "blowdown." Fully dressed in my hot water suit, with hot water connected & bypassing, I sat perched on the edge of the "trunking" ( a 30" dia. access hole to the sea ) with helmet in hand & ready to go. We were conducting a "bounce dive" this day. I had to get out, get the job done, get back in the bell & begin ascending before our "bounce" bottom time expired. If We went overtime, we'd be committed to "saturation" & our decompression time would extend from 13 hrs. to 3 days.
3...2...1..Blowdown! The bellman would actuate a spring-loaded valve & compressed air would roar into the bell. On gauges inside the bell & in the control van our decent to depth would be monitored. Upon reaching depth, internal bell pressure equalized with external ambient water pressure & the hatch to the sea would swing silently open. I would don my helmet, switch my hot water to dive mode & slip through the trunking space into the cold, black ocean. Powerfull external bell lighting would illuminate the blackness enough to guide me to the lip of the glory hole.
So there I was, trying to see past the swirling clouds of mud that continuously cloud the glory hole as I squeezed between the wall of the hole & the side of the b.o.p.. My job was to inspect the stack for damage, leaks & anything out of the ordinary. Working blind, I would feel my way around & down the device, occassionally updating topside as to my progress. The last job on my list was to check the "indicator pin", a small steel rod that would retract into a hole in the base of the b.o.p. where it connects with the wellhead when ( & if ) the base of the stack latches properly to the wellhead. If you slide your hand along the surface of the base, you can just feel the head of the pin protruding if the latch was good; if it wasn't, the pin would be extended from the hole about 4". To get at the area of the pin required one to lay on their side on the bottom of the glory hole & reach into the base area of the stack...
Fully stretched out on my side, I'm reaching way in to locate the pin when I feel something moving under me, no, SQUIRMING under me! Wait a minute! There are lots of things moving under me! Its so tight between the wall of the hole & the stack that my movement was limited but now my need to move was urgent so that I might escape the clutches of whatever ungodly prehistoric mutant organisms the cursed coring tool had unearthed!!
"Topside! there is something moving under me!" I reported in a hoarse rasp. " Probably just your bowels Dan, Carry on with the inspection" the Supervisor answered. "I said under me, not in me fer chrissakes!"
Collecting all my courage, I forced my arm beneath me & felt for the abominations, fully expecting my arm to be ripped from its' socket any moment. Getting ahold of something, I raised it up in front of my helmet-mounted dive light to see...a crab! Good heavens, I've got crabs everywhere! The bottom of the hole was crawling with the critters!
Turns out the mindless drones were on a seasonal migratory march & some of them managed to stumble upon the glory hole & fall in! What to do? OPERATION "CRAB RESCUE" of course!
When the rescue was complete we had several bags of crabs on deck with no where to go. Not having the heart to toss them back into the merciless sea, forever seperated from their fellow crabs, we tossed em' into the pot instead!
Best damn crabs ya ever tasted.
D.S.D.
Environmental regulations required the operator to impact the ocean environment as little as possible & this included a stipulation that no exploration apparatus could rise above the level of natural bottom. To satisfy this restriction, the driller would use a giant coring tool to dig a 10' dia., 40' deep hole in the bottom sediment, known as the "Glory Hole." From the bottom of this hole they would begin the exploratory well.
When "making hole" in the seafloor the driller begins with a 36" dia. hole to a predetermined depth, he then lines this hole with a steel liner or "casing" to give support to the hole in the surrounding sediment. Once the liner is run it is cemented in place. The "wellhead" is affixed to the top joint of 36"casing & is essentially an adapter, designed to accept the b.o.p. ( blowout preventer ) & later on, a production assembly if the hole is viable. Depending on the nature & depth of the sediment, a further series of ever-smaller diameter casings are run & cemented in down to bedrock.
Upon reaching bedrock the final hole bore begins ( about 7" dia. ) to t.d. ( terminal depth ). The drillstring is advanced downhole in 40' sections. Drilling mud is pumped from topside down through the drillpipe where it exits out holes in the heads of the drillbit. This mud is vital to the process as it performs a variety of functions including: cooling the drillbit, returning cuttings to the surface & providing hydrostatic pressure to counter ever increasing formation pressures downhole.
This concludes "Subsea Drilling 101...onto "Primer for Deepsea Diving..."
Built into the drillship in an enclosed area located midships on the main deck was our 1000' saturation diving system. System tankage included a living chamber to accomodate 4 divers, a transfer chamber containing a toilet & shower-head, and a submersible decompression chamber or "diving bell" that acted as our subsea elevator to the worksite. The bell was the only part of the system to enter the water. A "control van" contained all the electrics, electronics & pneumatic controls to operate the system. Additional system components included gas scrubbing, chamber environmental control, gas storage & bell handling winch system. The bell was supplied with power, breathing gases, hot water & communications via umbilical. The divers wore hot water suits for thermal protection & umbilical supplied hardhats for breathing & communications.
When the driller completes his "casing program" it is time to install the b.o.p.. To fascilitate this tricky operation a "guide base" is lowered over the wellhead & leveled at the bottom of the glory hole. From each corner of the square guide base rise the "guideposts". A diver will descend to drive a "spear" into the top of each post. From each spear runs a guide wire to surface which terminate to heave compensators on the drill floor. These compensators allow drilling to proceed in rough seas (up to a point).
The blowout preventer is essentially a series of hydraulically actuated rams. It stands about 40' tall & weighs about 25 tons. It is lowered to the wellhead by thick joints of 40' long pipe called "marine riser". Affixed to each corner of the b.o.p. are four posts. The bottom of these posts are flared in the shape of a funnel & act as centering guides for the tops of the guide base posts. When all is ready, the b.o.p. is lowered to the wellhead, 40' at a time, & is hydraulically latched.
When drilling to t.d. begins, the drillstring is advanced through the b.o.p., past the wellhead, down through the casing to bedrock. The primary function of the b.o.p. is to prevent down hole pressures from venting to surface ( "blowout" ) should this pressure overcome the hydrostatic pressure of the mud column in the hole. The driller can seal off the hole by activating "pipe rams" that will seal around the drillstring. If these fail to contain the pressure a "shear ram" can transect the string & block the hole.
Are ya with me?
Before drilling could commence the b.o.p. or "stack" had to be inspected & it was my good fortune that day to get the dive. Myself & another diver ( the "bellman" ) climbed into the bell, did our checks & prepared for launch. When all was ready, the bell would be "unmated" from the transfer chamber. A cover over the bell "moonpool" would be drawn back & the bell, at atmospheric pressure, would be lowered into the waiting sea. Natural bottom @ this location was 140', but my dive would take me to the bottom of the glory hole so our dive was planned for excursion to 180'. The bell's decent was halted 10' above natural bottom. Inside the bell we prepared for "blowdown." Fully dressed in my hot water suit, with hot water connected & bypassing, I sat perched on the edge of the "trunking" ( a 30" dia. access hole to the sea ) with helmet in hand & ready to go. We were conducting a "bounce dive" this day. I had to get out, get the job done, get back in the bell & begin ascending before our "bounce" bottom time expired. If We went overtime, we'd be committed to "saturation" & our decompression time would extend from 13 hrs. to 3 days.
3...2...1..Blowdown! The bellman would actuate a spring-loaded valve & compressed air would roar into the bell. On gauges inside the bell & in the control van our decent to depth would be monitored. Upon reaching depth, internal bell pressure equalized with external ambient water pressure & the hatch to the sea would swing silently open. I would don my helmet, switch my hot water to dive mode & slip through the trunking space into the cold, black ocean. Powerfull external bell lighting would illuminate the blackness enough to guide me to the lip of the glory hole.
So there I was, trying to see past the swirling clouds of mud that continuously cloud the glory hole as I squeezed between the wall of the hole & the side of the b.o.p.. My job was to inspect the stack for damage, leaks & anything out of the ordinary. Working blind, I would feel my way around & down the device, occassionally updating topside as to my progress. The last job on my list was to check the "indicator pin", a small steel rod that would retract into a hole in the base of the b.o.p. where it connects with the wellhead when ( & if ) the base of the stack latches properly to the wellhead. If you slide your hand along the surface of the base, you can just feel the head of the pin protruding if the latch was good; if it wasn't, the pin would be extended from the hole about 4". To get at the area of the pin required one to lay on their side on the bottom of the glory hole & reach into the base area of the stack...
Fully stretched out on my side, I'm reaching way in to locate the pin when I feel something moving under me, no, SQUIRMING under me! Wait a minute! There are lots of things moving under me! Its so tight between the wall of the hole & the stack that my movement was limited but now my need to move was urgent so that I might escape the clutches of whatever ungodly prehistoric mutant organisms the cursed coring tool had unearthed!!
"Topside! there is something moving under me!" I reported in a hoarse rasp. " Probably just your bowels Dan, Carry on with the inspection" the Supervisor answered. "I said under me, not in me fer chrissakes!"
Collecting all my courage, I forced my arm beneath me & felt for the abominations, fully expecting my arm to be ripped from its' socket any moment. Getting ahold of something, I raised it up in front of my helmet-mounted dive light to see...a crab! Good heavens, I've got crabs everywhere! The bottom of the hole was crawling with the critters!
Turns out the mindless drones were on a seasonal migratory march & some of them managed to stumble upon the glory hole & fall in! What to do? OPERATION "CRAB RESCUE" of course!
When the rescue was complete we had several bags of crabs on deck with no where to go. Not having the heart to toss them back into the merciless sea, forever seperated from their fellow crabs, we tossed em' into the pot instead!
Best damn crabs ya ever tasted.
D.S.D.