Changes

==Conventional coring systems==

==Conventional coring systems==

Designed to recover core from consolidated formations, conventional coring systems consist of an inner core barrel with a core catcher, suspended by a swivel assembly inside of an outer core barrel that is attached to the drill string, and a core bit (Figure 1). As mentioned previously, the final selection of a particular system depends upon the formation, location, and objectives of the coring program.

[[file:conventional-coring_fig1.png|thumb|{{figure number|1}}Conventional core barrel. © Eastman Christensen, Technical Data Sheet C-105.]]

[[file:conventional-coring_fig1.png|thumb|{{figure number|1}}Conventional core barrel. © Eastman Christensen, Technical Data Sheet C-105.]]

Designed to recover core from consolidated formations, conventional coring systems consist of an inner core barrel with a core catcher, suspended by a swivel assembly inside of an outer core barrel that is attached to the drill string, and a core bit ([[:file:conventional-coring_fig1.png|Figure 1]]). As mentioned previously, the final selection of a particular system depends upon the formation, location, and objectives of the coring program.

Types of inner barrels are summarized in Table 1. Core diameter can vary from 1.75 to 5.25 in. Core length can range from [[length::1.5 ft]] for short radius horizontal wells to greater than [[length::400 ft]] for vertical holes.

Types of inner barrels are summarized in Table 1. Core diameter can vary from 1.75 to 5.25 in. Core length can range from [[length::1.5 ft]] for short radius horizontal wells to greater than [[length::400 ft]] for vertical holes.

Attempts have been made to use core barrel liners to cut naturally fractured rock. Unfortunately, shards of core often cut into the relatively soft liner material, causing the core barrel to jam.

Attempts have been made to use core barrel liners to cut naturally fractured rock. Unfortunately, shards of core often cut into the relatively soft liner material, causing the core barrel to jam.

===Sponge-lined coring system===

===Sponge-lined coring system===

The sponge-lined coring system was developed to improve the accuracy of core-based oil saturation data. This is very important information to have when evaluating the merits of a secondary or tertiary oil recovery program.

The sponge-lined coring system was developed to improve the accuracy of core-based oil saturation data. This is very important information to have when evaluating the merits of a secondary or tertiary oil recovery program.

The sponge coring system consists of a conventional core barrel fitted with a series of sponge-lined aluminum inserts (Figure 2). The system cuts a relatively small core, 2.5 or 3.25 in. wide and [[length::30 ft]] long. The sponge liner catches oil that “bleeds” out of the rock as the core is pulled (tripped) from the hole. The oil-wet sponge holds oil tightly, while allowing water and gas to move through the sponge and out vent holes drilled in the aluminum liner. Sponge and conventional cores may be cut one after another without making special trips to open the hole, so it is possible to “spot” a sponge core and still acquire larger diameter cores for other analyses.

The sponge coring system consists of a conventional core barrel fitted with a series of sponge-lined aluminum inserts ([[:file:conventional-coring_fig2.png|Figure 2]]). The system cuts a relatively small core, 2.5 or 3.25 in. wide and [[length::30 ft]] long. The sponge liner catches oil that “bleeds” out of the rock as the core is pulled (tripped) from the hole. The oil-wet sponge holds oil tightly, while allowing water and gas to move through the sponge and out vent holes drilled in the aluminum liner. Sponge and conventional cores may be cut one after another without making special trips to open the hole, so it is possible to “spot” a sponge core and still acquire larger diameter cores for other analyses.

[[file:conventional-coring_fig2.png|thumb|{{figure number|2}}Sponge-lined coring system. © DBS, a Baroid Company.]]

[[file:conventional-coring_fig3.png|thumb|{{figure number|3}}Full-closure core catcher. (From <ref name=pt03r49>Whitebay, L. E., 1986, Improved coring and core-handling procedures for the unconsolidated sands of the Green Canyon area, Gulf of Mexico: SPE Paper 15385, 61st Annual Technical Conference and Exhibition, New Orleans, LA, Oct. 5–8.</ref>.)]]

===Full-closure coring systems===

===Full-closure coring systems===

Full-closure coring systems were developed for coring unconsolidated formations. They use disposable inner barrels or inner barrel liners and a special core-catching system to retrieve soft cores successfully. Currently, full-closure coring systems cut [[length::30 ft]] of 3- to 5-in.-diameter core. Systems are being developed to cut larger diameter and longer cores.

Full-closure coring systems were developed for coring unconsolidated formations. They use disposable inner barrels or inner barrel liners and a special core-catching system to retrieve soft cores successfully. Currently, full-closure coring systems cut [[length::30 ft]] of 3- to 5-in.-diameter core. Systems are being developed to cut larger diameter and longer cores.

The difference between full-closure and other coring systems is that the core catcher is not exposed during coring. This allows the inner core barrel to slip over the soft core with a minimum of disturbance. After coring, a ball is pumped downhole activating the core catcher and sealing off the bottom of the barrel (Figure 3).

The difference between full-closure and other coring systems is that the core catcher is not exposed during coring. This allows the inner core barrel to slip over the soft core with a minimum of disturbance. After coring, a ball is pumped downhole activating the core catcher and sealing off the bottom of the barrel ([[:file:conventional-coring_fig3.png|Figure 3]]).

 

[[file:conventional-coring_fig3.png|thumb|{{figure number|3}}Full-closure core catcher. (From <ref name=pt03r49>Whitebay, L. E., 1986, Improved coring and core-handling procedures for the unconsolidated sands of the Green Canyon area, Gulf of Mexico: SPE Paper 15385, 61st Annual Technical Conference and Exhibition, New Orleans, LA, Oct. 5–8.</ref>.)]]

The hidden core catcher is both the major asset and major liability of this coring system. Since the core catcher is not exposed during coring, coming off bottom is likely to result in lost core. If the catcher is not activated after coring, the core will be lost during tripping. Against these risks, the benefits are a longer length and larger diameter core than is possible with a rubber sleeve core barrel and a less disturbed core than one cut with a conventional coring system.

The hidden core catcher is both the major asset and major liability of this coring system. Since the core catcher is not exposed during coring, coming off bottom is likely to result in lost core. If the catcher is not activated after coring, the core will be lost during tripping. Against these risks, the benefits are a longer length and larger diameter core than is possible with a rubber sleeve core barrel and a less disturbed core than one cut with a conventional coring system.