Reviewed By
96 SECTION III: Wellsite Core Handling:
1. Introduction:
Coring is an expensive operation and, more importantly, provides valuable geological information to the Exploration Organization. Every part of the core is indispensable and should not be taken for granted. Only proper core handling by the wellsite geologist can ensure attaining the desired benefits and objectives of the core.
Core handling includes:
• Measuring the recovered core.
• Assigning the proper depths to the core tubes after it has been cut. • Assigning the proper orientation to the core tubes (top-bottom).
• Describing the core on location, if needed (lithology, and hydrocarbon shows). • Ensuring that the core tubes are properly stored and put into core boxes to be sent
to the core-lab store in Dhahran, unless otherwise instructed. • Filling out the core data sheet.
• Writing clearly and properly assigning core tags for each core tube.
Planning ahead, even before going to the rig location, ensures a successful core handling. Planning ahead requires acquiring general information regarding the core. Such
information, and more, can be obtained by reading the core-meeting minute and meeting the core proponent for further inquiries. Planning ahead will save you the troubles of going to the rig unprepared and lacking tools and information.
97 2. Conventional-Core Handling Procedures:
A. plan ahead:
A-1. Read the core meeting minute before leaving for the rig or meet the core proponent to find out about the following:
• Length of the core
• Formation compatibility. Fractures and faults that could possibly cause core jamming and you should be aware of possible jamming zones. • Significant change of rock hardness in the interval being cored. Change of
hardness of core from hard to soft could, sometimes, cause jamming if not carefully dealt with by the coring service company. Therefore, notifying the core hand of the zones of significant hardness change could help maintain better coring parameters.
• Best offset wells for correlations. Preferably an offset well that has a coring job done on the same section.
A-2. The following are tools needed to accomplish the job efficiently:
• Core tags and plastic straps that are provided by the Wellsite Geology Unit.
• A Hammer and a small chisel to take samples from the core. • Two screw drivers, to screw the caps clamps, to avoid wasting time
searching for them in the rig.
• A calculator will come in handy to calculate core tubes depths and other calculations.
98
B. When you get to the rig location, meet with the coring personnel and rig foreman to make sure they are aware of the core requirements.
Also, as soon as you get to the rig location, make sure that the core shipping- boxes are available.
C. Pulling out of hole for possible jamming is definitely not your decision. However, when cutting a core, Rate of Penetration (ROP) might significantly slow down. This could indicate a possible core jam that requires pulling out of hole. The core hand will definitely come to ask you if you think the slow down is due to a change of the formation hardness. Answer him in the light of your meeting with the core proponent. Also, review the offset wells for any significant slow down. Sometimes, offset wells’ trends are not accurate enough and do not apply to your well, especially when coring in Unayzah, which is one of the highly cored sections, because of its random sandstone-siltstone spatial distribution (facies change).
ROP slow down is only one indication of jamming. The core hand has other indications of jamming such as change of pressure and torque. He is the expert in the coring operation. You just provide him with the geological consultations that might help him make better decisions.
D. When the core barrels come out to the surface, make sure you know the order of the inner core barrels: the number of inner tubes in each run depends on the planned length of core cut. Usually, each coring run will include two inner core barrels. In that case it is easy to distinguish the top core barrel from the bottom barrel, because the bottom core barrel will have the shoe attached to it (Figure 3.1). When there are three core barrels, you should pay attention to distinguish between the second and third core barrels. To distinguish between the second and third core barrels be on the rig floor when the core barrels are being brought out to
99
the surface. The first core barrel to come out of the hole is the very top inner barrel. The second barrel is the middle barrel. And, of course, the last barrel to come out is the very bottom barrel.
E. Write down your notes and measurements clearly on a piece of paper while working on the cat walk, so you can use it later to fill out the “Core Data Sheet”. DO NOT count on your memory to fill out the core data.
F. Only when all core barrels are being laid down on the cat walk, can you start making your measurements and markings.
G. First measure the length of missing core from the top side of the core by inserting the measuring tape inside the top core barrel. Also measure the missing core from the shoe. Subtracting the total missing length from the total length of the core assembly (core barrels, shoe, and bearing joints between core barrels) gives you the recovered core length. See (Diagram 3.1), to identify the different parts of the inner core barrels.
H. Before starting to make markings on the core tubes, it is recommended that you clean the mud off the core barrels using water and cloths. Cleaning the core barrels will make it easier to write on the core barrels and will ensure that your writings do not come off later.
I. Now, the core barrels are ready to be marked. Give yourself all the time you need for marking and numbering the core tubes. Do not rush.
• Marking: make a mark every 3 feet on the core barrels. These marks indicate where the core barrels are cut to make the 3 feet core tubes. The core in the shoe stays in a separate core tube (~ 1.5’). So, start making the 3 feet marks from the end of the shoe to the end of the first core barrel. Then the core in the bearing joint between barrels, if present, stays also in a separate core tube (~ 1
100
foot). Next, continue making the 3 feet marks on the second barrel to the end of core barrels. If the end of the top core barrel is empty, then, use this extra amount of core barrel to make 2 core tubes. One for the core in the shoe and the other for the core in the bearing. (Diagram 3.2)
• Numbering: start numbering the core tubes with the shoe being core tube #1 and increase numbers going upward. (Diagram 3.2).
• Orientation: indicate by writing on the core tubes at the bottom end and top end. In one core tube, the bottom end is the end that is closer to the bottom of the hole, or closer the shoe (Diagram 3.2). Also, draw the black and red stripes to indicate the bottom from top, as shown in (Diagram 3.3).
J. Now the core barrels are ready to be cut into 3 feet long tubes by the core saw. Conventional core tubes are suppose to be cut in an angle with water. It does not matter if you start cutting from top to bottom or vise versa as long you have made the right marking, numbering, and orientation on the core barrels.
K. When cutting the core tubes, pieces of the core might fall out. Place back these fallen core pieces in the right orientation.
L. Vibrations of the core saw eject loose core parts outside the core barrel. Therefore, cap the open ends to prevent losing pieces of the core.
M. Before capping the bottom end, take a sample for examination. The samples description goes to the strip log. Each sample is used to describe the top 3 feet.
N. Now that the core barrels are cut into 3 feet tubes, make sure each tube is capped from both ends and secured by the metal clamps around the plastic caps. Place a plastic strap at the bottom end to be used later for hanging the core tags (Figure 3.2).
101
O. Now, you should be ready to fill out the core data sheet, and make the core tags. Also, this is a good time to add the lengths of all the core tubes to calculate the length of the recovered core. Compare the result with your initial calculation from step G.
P. Place the core tags on the proper tubes. Also, write the core number and well name on every tube (Figure 3.3, and 3.4). Core number indicates the core run number. If there were 2 core runs in Arab-D formation, for example, then the first core number in Unayzah, for example, will be core number 3.
Q. Make a final check up on your work and, then, place the core tubes inside the designated core boxes in the order of their numbers. Then, ensure that the box’ covers are properly attached. Use duck tape or straps to close the covers, if necessary.
R. Make sure that all received foam beds are placed back inside the core shipment boxes, if not used.
S. Make sure that the rig foreman places an order to transport all the core boxes to the core store in Dhahran (DPC-155, BLDG-3170) as soon as the coring job is done. Core boxes are supposed to be transported on a truck separately, and not with other rig materials, to avoid any damage to the cores.
102 3. Preserved-Core Handling Procedures:
Conventional core handling procedures apply for preserved cores, provided that you strictly meet the following requirements:
• Do not use water to cut the core tubes. Instead cut dry.
• Do not use the steel clamps to seal the plastic caps. Instead use the silver duck tape. Also, use the silver duck tape to attach the core tags. (Figure 3.5)
• Place the tubes in the ProtecCore and seal it immediately. Make sure that the ProtecCore is not damaged.
• Then, wrap the tube with bubble-wrap at least twice to protect the ProtecCore from being damaged during handling and transportation. Also, it is necessary to ensure that the tube ends are covered with bubble-wrap. (Figure 3.6)
• Write on the bubble-wrap the well number, core number, and tube number. Also, label the top and bottom for orientation.
• Core boxes should be transported immediately to the Saudi Aramco core store, unless directed to a different location.
103 4. Exploration Wells’ Core Handling Procedures:
Conventional core handling procedures apply for exploration wells’ cores. However, cores that are cut in exploration wells require a complete description of the core on location.
Therefore;
• The cores are taken out of the core tubes and placed in the 3 feet core trays to be examined on location.
• The red and black stripes are labeled on the core directly.
• All information and labels (well number, core number, and tray number) are placed on the bottom side of the core trays. (Diagram 3.4)
• After examination a wooden cover is used to seal the core trays and then strapped to secure the core inside the core tray.
• NOTE: foam beds are not sent with the core boxes to exploration wells, because they are not used with the core trays.
104 5. Safety Precautions:
1. Wear your safety gear at all time, including ear plugs.
2. Make sure that everyone who works with you on the cat walk understands the nature of has role. Stop at any time you feel someone is confused and might cause an accident, especially if it is his first time working on the cat-walk and cutting core barrels.
3. Do not start marking the core tubes until all core tubes are laid down. Keep the worst in mind, i.e. the cables carrying the core tubes from the rig floor to the cat walk might snap in the air and crash down. Keep an eye also on the crane and its operator when moving the core cradle around the cat walk. Better yet, stay at the far end of the cat walk until all core barrels are laid down.
4. Be aware of scattering pieces of rock when you take samples by a hammer. It could cause serious damage if they hit your face or the person holding core tubes. Make sure that the person’s face holding the tube is not at the same level with the core tube end where you take a sample and that he is looking the other direction. This is a time where everyone around should be wearing their safety goggles.
5. Also, be aware of fine pieces of aluminum that could fly behind and in front of the core saw when core barrels are being cut.
6. Be gentle when you lift core tubes from the ground, to avoid back injuries.
7. Be extra cautious if you are operating at the end of a crew shift. People tend to be fatigued and slow in reaction.
105
Figure 1: The shoe: it prevents the core from slipping out of the core barrel.
106
Figure 3: write the well name, core number, and tube number clearly.
Figure 4: The Necessary labels (well name, core number, tube number, and top-bottom) on one side and the red and black stripes on the other side
107
Figure 5: Preserved core, sliver duck tape is used to seal caps and attach core tags (photo is a courtesy of AbdulHafiz Masri, Cores Coordinator)
Figure 6: Persevered core wrapped inside bubble-wrap (Photo Courtesy of AbdulHafiz Masri)
108 2. 23 TO 2. C O RE B ARR EL 26.00 1.12 CO R E HE A D STABI L IZER 4.00 2. 23 STA B IL IZ ER 4. 0 0 STA B IL IZ E R 4. 00 2. 2 3 CO RE BA RR E L 26.00 LD AD J U STI N G SY T E M O . TU BE 3. 74 Sta n d a rd P ilo t Sho e As se mbl y 1. 38 30. 00 3 0 .00 1. 00 1. 00 Inne r Tube Inne r Tube Inne r Tube Stab . Inne r Tube Ext. L. D. A d ju st ing Sy st e m