Core Barrels

Outer Barrel

The outer barrel assembly is unique in terms of dimensional characteristics. The barrels are designed to combine in sections of twenty foot lengths which provide improved stabilization. This is critical to counteract vibrations and buckling forces applied to the bottom hole assembly (BHA) while cutting the core.

Chart shows Core barrel resistance to buckling

Starting at the core head, integral blade stabilizers are placed in the first two ten-foot intervals and then between every twenty foot outer barrel thereafter. The BHA becomes a packed-hole assembly compared to traditional assemblies which are limited to thirty foot placements where bending and buckling forces are destructively transferred to the core itself.

In addition to the barrel length and stabilizer placement, Corpro utilizes larger diameter barrels. The increased diameter provides better hydraulics, improves the pulling capacity and torque profile of the connections, and increases the stiffness rating. A stiffer assembly mitigates core damage caused by BHA dynamics while acquiring the core. The proper engineering of dimensional data maximizes mechanical integrity to the benefit of both drilling and core quality.

Upper Head Assembly

The upper head assembly is comprised of a bearing system from which the Thin Sleeve System is suspended. The bearing system is required to maintain rotational independence between the inner and outer barrel assemblies. Additionally, the upper head contains the means to divert flow to the inner barrel or the annulus of the inner and outer barrel. While tripping in the hole, a portion of the flow is directed to the inside to ensure cuttings do not accumulate within the core liner. Once on bottom, a ball is dropped and flow is diverted to the annulus to ensure the core is not washed as it enters the liner.

A sealed bearing unit is available to maximize rotational independence in more challenging applications such as high deviation, poor mud conditions, or extra long barrel assemblies. With a sealed bearing, the efficiency of the bearing is maximized as the bearings themselves are not exposed to the hostile drilling fluids of traditional systems. As such, the rotation of the outer barrel is not transferred to the inner tube as is common in other systems. This allows for longer core lengths and improved core quality.

Corpro’s Thin Sleeve System is fundamental in terms of design which improves the efficiency of rig operations and focuses on the quality of the core. With TSS comes a platform for advanced coring services including core visualization at the rig site and the ability to trap escaping gas and fluids.

Inner Barrel Thin Sleeve System (TSS)

With Corpro’s Thin Sleeve System (TSS), the core is cut and retained by a system of three concentric tubulars including the outer barrel, a thin sleeve inner tube, and an interchangeable/disposable core liner. The Thin Sleeve System is packaged within an upper and lower bearing assembly which provides ultimate protection of the core while maximizing coring performance. The TSS also employs the core catcher which is available in standard spring catcher and full closure configurations.

TSS focuses on core usability. With a standard inner/outer barrel configuration, torsional forces are induced in the core when breaking the joints of the inner tube at surface. The friction forces, acting on the core, can break the core into a chevron pattern as much as three feet above and below the connection which results in unusable core. TSS eliminates this problem as the core is independent from the inner barrel and not in direct contact with the jointed connection. At the rig floor, the TSS connection is disassembled while the core is protected by a core liner. By maintaining the integrity of the core during the retrieval process, TSS delivers up to 20% more usable core.

The Thin Sleeve System is comprised of twenty foot sections which can be combined to the desired barrel length. In keeping with a focus on the quality of the core, the TSS is configured with a pin-up/box-down connection to properly support the core while cutting the core at the rig floor. The liners are installed within the TSS inner tubes to accept the core as it is cut. At surface, the TSS joints are exposed once the outer barrel connection is broken. Once the core is sheared, a lifting sub is easily attached to the bottom section of core without damaging the core itself.

An upper and lower bearing assembly ensures proper support and exact spacing between the core liner and the throat of the core head. Corpro’s TSS provides a system that is not affected by the difference in thermal expansion between the inner and outer barrels. TSS damage to the core is encountered if the inner barrel is allowed to impart stress on the core itself. With TSS, radial and thrust bearings provide the support required at either end of the inner barrel. Along the barrel, each box connector contains six ribs which keep the inner tubes centrally positioned within the outer barrel. The inner tube and core is fully supported along its length.

On-Ice Half Moon Coring

'On Ice' is an innovative technology designed to improve efficiency and combat the problem of core barrel jamming. Jamming is the primary problem associated with coring cost and the degradation of core quality.

It occurs primarily in unconsolidated formations, fractured formations, and in areas of swelling clays. In general, jamming is more likely to occur where the core is unstable or can no longer support its own weight and the downward forces exerted as it enters the inner tube.

The mechanics of jamming must be understood in order to minimize the problem. Jamming occurs when the compressive strength of the core is less than the combined weight of the core and friction forces acting downward as it enters the inner tube. The only solution is to reduce the friction forces or limit the length of core cut. Operationally, the mud properties must be such that unnecessary friction is not created by swelling clays or thick mud cakes. From this starting point, a focus must be placed on reducing the internal friction properties of the inner barrel.

Embarking on a comprehensive research program, Corpro developed the breakthrough ‘On Ice’ inner tube system, supported by the Thin Sleeve System. ‘On Ice’ uses a proprietary technology and is a significant step towards reducing the friction forces that inhibit smooth entry of core. The ‘On Ice’ development focused on reducing the frictional forces between the inner barrel and the core, achieving the lowest friction coefficient in the industry.

A thorough experiment of lab tests was performed in order to measure the friction coefficient of industry standard disposable inner tube systems in comparison with the proprietary ‘On Ice’ system. The ‘On Ice’ system results in a 61% reduction in resistance to core entry over the next best available system. This is demonstrated in the following table.

Half Moon Liner

Half Moon liner technology provides a safe, efficient, and non-damaging means to visualize the core at the rig site. By viewing the core at the rig site, real time decisions can be made concerning subsequent operations associated with coring, drilling ahead, core preservation, and future analysis. As well, surface processing services such as plugging and waxing are expedited.

In the absence of Half Moon liners, the only means to view the core include manually sliding the core out of the inner tube or cutting the entire length of the inner tube with a longitudinal saw. These techniques are destructive and expose the core to damage. The exposure could disrupt the quality of the core and/or alter its downhole characteristics. The methods also expose personnel to unnecessary safety risks in trying to free the core or operating the saw itself. The Half Moon Tube™ safely provides a quick and easy way to visually examine the core on the rig site without affecting the quality and characteristics of the core.

A quick visual of the core provides many advantages. It provides a conclusive decision on whether the reservoir is completely cored and could reduce the number of coring runs. An inspection of the core between runs provides valuable information as to any alterations which may be needed on subsequent runs in terms of core head selection, barrel lengths, and operating parameters to optimize the process. In terms of core handling, the ability to see the core provides valuable information in terms of cutting the core for preservation and transport. Well site personnel are able to ensure a cut is not performed in a critical section of the core such as at a fracture where damage would be possibly induced into the core itself.

The Half Moon Tube™ is used in conjunction with the Thin Sleeve System (TSS) where the Half Moon Tube is used as the liner. The Half Moon Tube™ is extracted from the steel inner barrel like a normal liner and clipped together. Once the core is positioned on the cradle, the upper portion of the Half-Moon is removed and the core is available for inspection.

Expendable Inner Liner

The TSS inner barrel assembly includes disposable liners which house the core. The liners are made of aluminum or fiberglass and can be upgraded for enhanced coring services. The liners ease the ability of the core to enter due to lower friction compared to conventional steel inner barrels. Each material contains a compromise between structural integrity, temperature rating, friction coefficients, and cost. Corpro provides the following liner options :

• Aluminum Liners
• Fiberglass Liners
• Half-Moon Liners for core visualization
• On-Ice Half-Moon Liners for reduced jamming and core visualization

Aluminum Liners

Aluminum is the most widely used disposable liner in that it provides ample benefit at an economical value. Most importantly, it offers a lower friction coefficient compared to steel while maintaining integrity to avoid structural damage. The aluminum liner can be dry cut with the use of special blades to avoid unnecessary core contamination.

Fiberglass Liners

Fiberglas liners are made from fibrous strand roving, which are impregnated with epoxy resin and helically wound, under tension, onto a polished mandrel. The combination of material and manufacture provide a polished internal wall with a low coefficient of friction which allows smooth transfer of core into the inner tube. Core jamming is reduced and higher core recovery can theoretically be achieved. Fiberglass has limitations in that it is limited in its structural integrity while acquiring the core, cannot be used above 180C, and cannot be used in all drilling fluids.

A safety hazard exists in that the fiberglass and resin can be toxic while cutting the core at surface and require special care and PPE equipment.

Lower Bearing

The lower bearing assembly is located within the body of the Corpro core head and is provided to minimize friction caused by the rotation of the outer barrel. The bearing assembly assists in rotational independence, particularly in highly deviated wellbores where the inner assembly needs additional support without contacting the outer barrel.