Performance Report: Romania: FloThru Cures Total Losses, Enables Instant Gas Production on Workover

Challenge: Laslău Mare is a highly depleted gas field in the Transylvania Basin of central Romania. The operator partnered with Schlumberger IPM to execute well interventions to improve field production. The main challenges in this field are total losses and induced damage, which contribute to an extended time for well clean-up before full production can be initiated. The targeted workover recompletion well had sustained production decline that required replacing the production tubing and perforating the interval extension. One of the main challenges was the very low reservoir pressure, creating a high overbalance on the formation during workover (190 bar / 2755 psi or 0.74 SG / 6.14 lb/gal EMW). M-I SWACO and SLB IPM discussed the job requirements with the aim of selecting a workover fluid capable of killing the well while withstanding losses and protecting the reservoir, thus eliminating the long post-job clean-up time.

Solution: M-I SWACO proposed the FLOTHRU system, comprising organophilic components which eliminates the need for filter cake cleanup. This system could be used both as a kill and fluid. Since it forms a very impermeable and thin filter-cake. FLOTHRU is ideal for perforations as well. The FLOTHRU system included optimized bridging agent particle size distribution (PSD) engineered to seal the pore openings. The PSD was based on OPTIBRIDGE software simulations and designed to prevent invasion into the formation while not exceeding the fracture gradient. In this case, the fracture gradient was 110% above the bottom hole pressure that the FLOTHRU hydrostatic column generated, thereby making losses easily avoided.

The engineered solution included not only the fluid itself, but the all-inclusive planning, delivery and execution process, with continuous contact and collaboration between M-I SWACO and IPM representatives.

Result: The FLOTHRU system delivered all anticipated results. The well was killed in one circulation without any formation losses, tubing was replaced and new interval perforated with no losses encountered.

At the end of the job, production commenced immediately once the well was underbalanced with nitrogen. No remedial filter cake removal operation was required. Good collaboration between M-I SWACO and IPM enabled a flawless operation with optimum safety and logistic results.

Offset wells were killed using filtered formation brine and encountered severe losses. In those earlier wells, 50 m3 to 130 m3 (315 to 819 bbl) of fluid was lost regularly to the formation. Those wells required up to six months to recover the lost fluid and ramp up gas production.

The FLOTHRU system was mixed at the rig site and circulated through the shakers to eliminate polymer “fish eyes.” Fish eyes usually result from poor mixing facilities on small workover rigs. Nonetheless, after circulation and homogenization the fluid had superb properties.

The well was killed in one circulation by pumping the FLOTHRU system through the production tubing. No formation losses occurred. After 48 days of workover operations, which included fishing production tubing and milling operations, an additional interval was perforated with the FLOTHRU system. Afterwards, a production packer was set and the well completed. Once the FLOTHRU fluid was flushed out above the perforated interval using nitrogen, immediate and full gas production started. No stimulation was necessary and no additional time was required for well cleanup before starting full production. In addition to achieving production several months earlier than usual, the system also delivered formation protection, no losses as well as the ability to handle and treat fluids recovered during production. Consequently, the system was requested for the next similar operation on the field.

Download: Romania: FLOTHRU Cures Total Losses, Enables Instant Gas Production on Workover (0.20 MB PDF)

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“The FLOTHRU system once again proved its capabilities to protect the reservoir, avoid losses and yield instant production at the end of the job. No filtercake cleanup was necessary, thus eliminating risks and costs of cleanup operations.”
Paulin Vlăsceanu
M-I SWACO Wellbore Productivity Senior Project Engineer