Cost-effective removal of sand from wells is achievable, according to Welltec’s Farzad Farzadnia technical sales manager, Middle East & North Africa.
Recent operations involving new technology has clearly demonstrated how part of the problem with sand clogging wells can be prevented. Compared to more traditional intervention solutions this new technology offers a lightweight and more cost-effective approach.
This is becoming increasingly important as wells are drilled on still deep water and being developed subsea.
Sand accumulation in high angle wellbores inhibits production, plugs completions, erodes hardware and blocks access to downhole jewellery.
Bailing on slick line wire is the preferred, low cost method to clean sand and debris in vertical wells but slick line cannot often reach sand buildup in high inclinations. Conventional remediation methods for high angles use either coiled tubing or an expensive rig to remove sand and debris.
The industry is experiencing a demand for well intervention technology that can operate efficiently and cost effectively under these conditions while also optimising recovery rates.
Rigless well intervention technology is generally preferred due to the high cost associated with rig rates especially in subsea well interventions.
A rigless alternative to sand or debris removal from wells is the utilisation of a new vacuum/bailer system conveyed on electric wireline and can be run in combination with a wireline tractor technology for access into a high angle well.
The solution is based on the field proven wireline tractor run in conjunction with a newly developed wireline cleaner tool).
Combining a tractor with a well cleaning system provides a means of accessing and removing debris either selectively in one run or over a general area in multiple runs. Experience has shown that it sometimes is small bridges or sand dunes hindering access to the wellbore with wireline.
Cleaning system for well maintenance
At the core of this new system is a device called the Power Suction Tool which basically is a cleaning system designed to work in a liquid environment.
The main driving mechanism in the tool consists of a basic rotational unit that includes electronics, pressure compensator and electrical motor sections and below this there is a fluid pump.
The unit drives an impeller which circulates well bore fluid and creates a fluid flow through the fluid pump. The fluid pump in turn creates a magnified vacuum flow to circulate through the tool ‘dragging’ sand through the shoe and check valve into the debris collector bailer.
Filtered fluid from the bailer will then be re-circulated back into the well bore while sand/debris will be trapped in the bailer. Any length of bailer sections can be run, limited by available rig up height, lubricator length, cable safe working load and cable head weak point rating.
These electric wireline powered tools can be mobilised quickly with small crews, and for far less cost than a coiled tubing mobilisation. Following the sand removal, evaluation of the source of sanding problem can then be performed with electric wireline inspection services during the same rig up.
In vertical wells, the wireline cleaner can be deployed and run standalone whereas, in highly deviated or horisontal wells, the tool can be run in conjunction with the wireline tractor.
In this instance, the wireline tractor is mainly for conveyance to depth while the wireline cleaner performs the sand removal operation independently.
Picking up sand from the top of a bridge plug
An operator was experiencing problems with sand build-up in one of their production wells along the perforated zone and needed to gain knowledge of whether it was sand production or mechanical issues that had disturbed the well.
An increased gas to oil ratio had indicated that a 5-1/2” bridge plug had moved up by 26 ft in the middle of a perforated zone. However, the operator doubted that the bridge plug had moved but sand could possibly have settled on top of the bridge plug.
The wireline cleaner was subsequently then run in hole with an original objective for fact finding and also to determine if a section of the sand screen above the bridge plug has punctured thus causing sand settlement above the bridge plug.
After three runs and the removal of 54 liters of sand, the problem was determined to be a hole in the sand screen above the bridge plug. The wireline cleaner was pulling sand through the hole in the sand screen thus confirming mechanical anomaly in the well.
This resulted in improved understanding of the well condition by the operator which allowed planning for future remedial work and made it safe to continue the production.
Cleaning the isolation valve
An operator was not able to open a full ball isolation valve as planned offshore.
The provider of the wireline tractor was contacted for a contingency plan that involved cleaning the valve with a wireline cleaner and opening the isolation valve with the wireline tractor and wireline stroker.
In the first run, the wireline cleaner was run in hole configured with two bailer sections. Upon return to surface, the 12 ft of bailers proved to be 25% full of pipegrease, barite mud and other debris fill.
A second run with the wireline cleaner was performed where the bailers returned empty to surface, which confirmed that all debris on top of the valve had been retrieved in the first run.
Free of debris, the valve was then successfully opened with the wireline tractor/wireline stroker combination.
Removing 250 litres of sand
The wireline cleaner PST was mobilised to remove a large amount of sand that had built up in the wellbore. This was done in order to establish access to logging zones below with the purpose of establishing new production.
Over the course of 16 runs, a total of 250 liters of sand were removed from the well. This cleanup operation was executed inside a 9 5/8” casing at an inclination of 90 degrees with 4 inches diameter bailer tubes. Cleaning was performed while tractoring. Access to the lower zones was established and logging services was performed.
With the introduction of this new technology or cleaning system concept a substantial step has been achieved in accommodating industries requirements.
