Roller standoff assembly installed adjacent to the single probe sampler.

The risks associated with the conveyance of downhole instruments are an important aspect to consider during the design, construction, and productive life of a well. These risks are associated with acquiring formation evaluation data while the hole is being drilled and during subsequent well intervention operations while monitoring or servicing a completed well. With an increase in the drilling of long, deep, and tortuous wells (mainly in high-cost operating environments), these risks have become more acute.

The Deployment Risk Management (DRM) methodology, based on modeling of wireline forces and best practices gathered for several decades, has been developed to take advantage of new conveyance technologies that are intended to alleviate or eliminate these risks. The DRM methodology is primarily designed to help operating and service companies reduce the overall cost and risks associated with wireline well interventions in long, deep, and tortuous wells. Over the last five years, new conveyance and risk-reduction technologies have been introduced into “complex-well” markets, significantly reducing the costs and risks associated with wireline operations.

A wireline fluid sampling job successfully completed in a well with 75° deviation demonstrates the merits of the DRM methodology.

The targeted offshore platform is located in the North Sea, 250 ft (76 m) above the sea floor and easily accessible from a large oil and gas service support center where most conveyance technologies are readily available.

A failure with a competitor’s directional drilling assembly had led to the deviation being 75° instead of the planned 55°. The reservoir characterization instrument
(RCI) had never attempted a sampling job in such a highly deviated well, but it was deemed possible with low-friction roller standoffs (flywheels) attached to the toolstring adjacent to the single probe sampler.

The cost of not being able to perform this sampling operation using unassisted wireline would result in a pipe-conveyed logging operation lasting 2.5 days (costing the project an additional US $5 million in deferred production from this well).

Initial strategy
The initial strategy proposed the use of the wireline readily available on the platform
(0.472 in. outer diameter and 23,000 lb breaking strength), a 10,000-lb weakpoint, and four sets of clamp-on metal standoffs mounted on the toolstring.

The main hazards identified (in order of importance) include:
• High risk of the toolstring not getting below this point (almost no tension on the wireline);
• Insufficient overpull capacity (2,000 lb at surface) to free a stuck toolstring;
• Wireline damage by spooling wireline at 9,000 lb over a section spooled only at 1,500 lb; and
• A 10,000-lb weakpoint that cannot be safely broken below 3,000 ft (915 m).

Final strategy
The “Best Practices” database contains a collection of hazard-type records with engineering criteria and policies, proven risk control mechanisms/actions/procedures, and contingency plans. The following counter-measures and contingency plans were selected from the database for the final strategy:
• Install low-friction roller standoffs to mitigate differential sticking and increase the net pulling-down force while helping the toolstring ride over borehole imperfections and debris. Use a high-strength wireline and insert multiconductor jars on top of the toolstring to ensure a large overpull capacity would be available if needed;
• Select a crush-resistant wireline; if not available, use a powered capstan designed to be inserted between the wellhead access point and the wireline unit to take up the burden of high tensions needed on the well side while maintaining a pre-selected spooling tension on the wireline unit side; and
• Use a releasable cablehead to avoid pulling extreme tensions while trying to free a stuck toolstring and include a 10,000-lb weakpoint as a contingency.

Results
The operation was completed in one day. Twelve high-quality fluid samples were obtained in two separate runs, saving the operating company $1.3 million and 1.5 days of rig time.

The results of using risk-reduction technologies on the model and the actual operation were:
• The minimum wireline tension while running in hole (RIH) was 500 lb more than the compression limit;
• More than 5,000 lb of surface overpull capacity was available to maximize the jar’s tensile strike;
• The pulling out of hole (POOH)/RIH spooling tension ratio was less than three using a crush-resistant wireline; and
• It was not possible to break the 10,000-lb weakpoint below 5,000 ft (1,524 m). However, the releasable cablehead was the primary contingency, and the toolstring did not need to be fished.

The “+” and “x” marks in Figure 3 depict actual tensions measured at the surface during the second run. The marks clearly match the modeled RIH and POOH tension curves, with the only noticeable exception being the 13,000-lb pull at 14,300 ft (4,358 m), which was necessary to fire the wireline jars and free up the toolstring after being stationary and sampling for 3.5 hours.

Applications
The strategy applied in this case study has been successfully used in 12 separate fluid sampling jobs in the North Sea, where customers saved $1.1 million on average per job by avoiding the use of less-efficient pipe-conveyed logging operations.

The roller standoffs ensured minimum area of contact with the borehole wall, which greatly reduced the differential sticking force and allowed the toolstring to roll out of the overbalanced permeable formation with minimum wireline overpull. These devices also allowed toolstring deployment in this highly deviated well by riding over debris and well imperfections with minimum friction forces.

The application of the DRM methodology and modern wireline risk-reduction technologies has resulted in a significant reduction of rig time dedicated to wireline well interventions, the number of fishing jobs, and lost equipment in particular while taking formation-fluid samples.

This methodology is equally applicable to cased-hole wireline operations (logging, monitoring, perforating, and remedial interventions) using alternative conveyance systems and risk-reduction technologies in some cases, i.e., downhole tractors or releasable tools.

The effective use of the DRM methodology and the intelligent use of modern risk-reduction technologies have significantly expanded the operational envelope of wireline. Some examples of how this contributes to the economics of modern challenging projects include:
• Reducing the number of logging runs by being able to convey multisensory heavy toolstrings safely;
• Allowing high-resolution, high-accuracy formation evaluation data and fluid samples to be safely acquired in wells with lengths in excess of 30,000 ft (9,144 m);
• Reducing stuck-tool events, fishing jobs, and the replacement costs of lost equipment; and
• Avoiding costly and time-consuming pipe-conveyed logging operations in wells with deviations up to 75°.