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Acquiring meaningful DFO data

Published:  29 April, 2015

A Stavanger-based provider of specialist well intervention services for the oil and gas industry - Ziebel AS - says for the first time in oil and gas history, a gravity-deployed slim carbon composite cable, was used to acquire meaningful Distributed Temperature and Distributed Acoustic fibre optic data during a commercial well intervention. ODEE reports.

ZIEBEL’s gravity-deployed slim carbon composite cable, the Z-Line made its first run for a major operator offshore Norway. The system accessed a platform well to a depth of 9684 ft with standard wireline-type gravity deployment and dry sealing pressure control equipment (no grease injection). All mechanical requirements of the line functioned successfully according to the company, and high quality Distributed Fibre Optic (DFO) data was acquired for the operator.

Successful performance

“We are very pleased with the Z-Line’s successful performance during its first commercial well intervention”, said Stig Hognestad, chief executive officer for Ziebel. He added: “It marks the culmination of a thorough process of development and rigorous testing by the Ziebel team. The real significance for us – and the industry – is that it proves that the system functions as intended in an actual live pressured well environment. With the success of this launch, the service is now available to all operators.”

Z-Line builds upon the Z-System carbon composite technology, which delivers critical decision-making well information to oil companies. The key difference between the two is that the Z-Line does so from a smaller wireline footprint, and, being gravity deployed, with a typically shorter intervention time per well.

The Z-Line is a 3/16” (4.8mm) diameter carbon composite line with embedded optical fibres at its core. This enables Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) to be performed along the full length of the line. In addition, Ziebel’s optical point pressure and temperature sensors are contained within the Bottom Hole Assembly (BHA), along with a connection to enable standard memory logging tools to be run below the BHA. The rig-up and footprint are similar to that of a standard wireline cased-hole setup, although the distributed measurement acquisition method does differ in that it is carried out with the line parked stationary in the well.

The carbon composite material enables the line to have an extremely high strength-to-weight ratio, with a breaking strength (6,600lbs/3,000kg) well in excess of what can be achieved with a similar diameter of steel wire or braided line. The smooth outer finish makes for effective sealing, and the low friction coefficient to steel plus the relative stiffness of the line gives it increased ability to reach into deviated wells. In addition, the low friction reduces the abrasion and tubing wear associated with standard wireline or slickline runs.

About Distributed Fibre Optics

DFO sensing makes it possible to continuously monitor the entire wellbore over extended periods of time. Unlike classical logging tools that can survey only a few inches of the well at a time, DFO provides a complete wellbore profile that is captured several times per second. As a result, dynamic events moving along the wellbore can be tracked, which provides a better insight into the wellbore dynamics and added confidence to well integrity decisions. For example, a gas leak migrating upwards can be followed and its speed measured, and intermittent events that would otherwise escape detection by traditional point measurement logging tools can be observed and diagnosed.

Z-Line applications

Applications that can be addressed with the service include:

• Well Integrity, producers: annular leak detection source and fluid migration behind casing detection.

• Well Integrity, injectors: verify that no unwanted injection occurs into the overburden. Decide, with confidence, whether remedial work is required or to resume injection.

• P&A: provide information to help optimise the number of plugs and to decide where they should be set, to determine where to safely cut casing strings, and to verify wellbore integrity.

• Production optimisation: determine gas lift settings required for a stable flow regime and the optimal gas injection volume/production ratio. Verify that GLVs operate in the right sequence and that dummy valves are not leaking. An optimised gas lift system can increase production by up to 15% and save gas injection costs.

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