Numerous conveyance options exist for deploying wireline tools, each tailored to address specific challenges encountered within wells and to fulfill data acquisition needs. Below, we offer a brief overview of each option, outlining their fundamental components and suggesting scenarios where they might be most applicable.
Wireline (e-line)
Wireline refers to a system used for lowering equipment or measurement tools into a wellbore using a cable, or “wireline,” to perform various tasks related to well logging, maintenance, and completion. The term “wireline” covers a broad range of operations and tools that can be classified into two main categories: electric line (e-line*) and slickline.
*Note: During the composition of this article, it became clear that the terms “wireline” and “e-line” are often used interchangeably in the industry today, with “e-line” considered a specific category of “wireline,” which also includes “slickline.” A brief review of OnePetro journal articles reveals that “wireline” has been mentioned in the context of cased-hole and open-hole data acquisition as far back as 1941 (ref), while references to “e-line” begin to surface in the literature starting from the mid-2000s. For the purposes of this discussion, we will use the term “wireline” to specifically refer to “e-line.”
Components of a wireline system
Cable: The wireline itself is a cable that can vary in construction depending on its use and typically includes:
- Electrical conductors for power delivery and data transmission between the surface and the downhole tools
- Insulation to prevent electrical leakage and contact with the other conductors
- Armors to provide mechanical protection against the wellbore environment whilst adding tensile strength to the cable, helping to bear the weight of the downhole tool and the cable itself
Typically wireline cables are either monocable (single conductor), bi-cables (two conductors), and multiconductor cables, selection dependent on the needs of the operation with more conductors allow for more data transmission capabilities.
Surface Equipment: This includes the winch that spools the wireline and controls its movement in and out of the well, as well as data acquisition systems (in the case of wireline operations) that monitor and record the data being sent from the downhole tools.
Capstan (optional): The purpose of a capstan is hinted at by the word’s nautical origin – dating back to the days of sailing ships. It refers to a vertical-axled rotating machine used to enable sailors to more easily perform tasks that required significant force, such as hoisting sails, raising the anchor, or pulling in heavy ropes or cables.
For wireline operations a capstan is employed to achieve high tension on the cable within the well, whilst simultaneously ensuring that the tension on the winch drum remains safely controlled during spooling. This setup combined with modern high strength cables enabling tensions of 26,000lbs to be reached in the GOM (ref).
Slickline
Fundamentally wireline, e-line and slickline system all aim to convey downhole tools into a wellbore via a cable. The key differences between slickline and wireline (e-line) have historically included:
Cable Type: The most significant difference lies in the cable used; wireline units use electric cables for power and data transmission, while slickline units use a single, solid strand of wire for mechanical tasks.
Operational Capabilities: Wireline units can perform a wider range of operations, including complex logging and interventions requiring electrical power, whereas slickline units are suited for mechanical interventions and maintenance tasks and the conveyance of memory logging/setting/activating tools powered by downhole batteries
Data Transmission: Wireline units can provide real-time data from the wellbore, essential for detailed formation evaluation and precise operations, whereas slickline operations are conducted ‘blind’ without real-time data, relying on surface measurements and operator experience. Digital Slickline is a relativley new technology which changes the game here slightlyly, incorporating real-time digital communication capabilities into the otherwise mechanical slickline process. While traditional slickline is a single-strand wire used for mechanical tasks within a wellbore without the ability to transmit data, digital slickline enhances this by integrating digital technology, allowing for data transmission and real-time control of downhole tools.
Note:
Braided line refers to a multi-strand wireline variant employed in slickline tasks where increased tension handling or load-bearing capacity is essential (braided line | Energy Glossary (slb.com))
Through Drillpipe Logging
Through drillpipe logging conveyance refers to a method used to deploy wireline tools and equipment downhole through the interior of the drill pipe rather than directly into the wellbore. Weatherford’s Compact Shuttle (ref) and Schlumberger’s (SLB) ThruBit (ref) Wireline technology are both variations on this innovation which can be especially useful in challenging well environments.
Weatherford Compact Shuttle (ref)
The Compact™ Well Shuttle is designed to encase logging tools within the drillpipe for protection during tripping and to release them into the open hole upon reaching Total Depth (TD). This method allows for the drillpipe to be rotated, reciprocated, and circulated as necessary to meet the demands of specific well conditions enabling wireline tools to get to bottom, where otherwise they may not. Utilising the Compact well shuttle for logging is especially beneficial in extended-reach wells, enabling the collection of data in a single trip, compared to the multiple trips that traditional pipe-conveyed logging methods may require.
Once the bottomhole assembly (BHA) arrives at TD, the logging tools are deployed into the open hole. As the drillpipe is withdrawn, the logging tools begin data collection, with the gathered information being ready for analysis after the tools are retrieved to the surface. During the removal of the drillpipe, data is continuously recorded and later correlated with time to produce standard depth logs. This system can also be run on wireline (as opposed to memory based data recording).
SLB ThruBit (ref)
SLB’s ThruBit wireline technology is designed to convey logging tools through the drill bit into the wellbore. A proprietary ”Portal Bit” is used to ream to to prepare the borehole for logging. The slim-hole wireline toolstring is then pushed through the Portal Bit, and the wireline disconnected. Data collection is then acquired in memory mode, whilst pulling out of hole to casing, at which point the toolstring is retrieved via a wireline latch.
Drillpipe conveyed logging
Drillpipe conveyed logging is a system that was originally introduced to make possible data acquisition with standard wireline tools in horizontal and highly deviated boreholes (ref). At higher angles conveyance by wireline under the force of gravity alone becomes challenging and drill-pipe conveyance is one option available to overcome this. Different vendor systems are named differently but fundamentally they all follow the same principles and commonly use the same pieces of equipment:
Baker Hughes – PCL (Pipe Conveyed Logging)
SLB – TLC or TLCS (Tough Logging Conditions / System)
Halliburton – TPL (Toolpusher Logging)
Weatherford – PCL (Pipe Conveyed Logging)
The basic equipment for pipe-conveyed logging includes a downhole connector head for mechanical connection of the wireline logging tools to the drill pipe, a pump down wireline head which is connected to the end of the wireline cable and latches into the downhole connector head to make connection with the wireline tools once they are at an appropriate depth. A side door entry sub is inserted into the drill string once the tools are at depth which facilitates continuous wireline tool data acquisition and can also hold pressure enabling some circulation if the cable is not present. It is also required that a downhole compression and tension sub is run to monitor downhole forces on the tool as the risk of tool damage downhole due to the wirght of drill pipe above is high.
The basic procedure for pipe-conveyed operations include (note specific values would be required based on vendor equipment specifications and this is presented as an overview only):
Make Up Tool String:
- Assemble the wireline tool string, including the necessary downhole connection heads, following standard operating procedures.
- Perform surface checks on the wireline tool and measure cable resistances.
- Attach the downhole connector head to the first stand of drillpipe using appropriate torque.
- Ensure all pipes and crossovers meet minimum diameter requirements. Cross check pipe tally depths.
Running in Hole (RIH):
- Avoid rotating the drill pipe; keep the rotary locked.
- Apply minimal pipe dope to the pins only.
- Maintain a consistent RIH speed, pausing at an agreed number of stands to circulate the mud and clean out the downhole connector.
- Keep the pipe filled, carefully handle the string in the slips, and avoid sudden movements.
- Monitor for any hang-ups and stop at the predetermined latch depth for circulation and checks.
Rig-up the side door entry sub and latch the wireline cable downhole
- Set up the wireline and install slotted bushings.
- Lift the side entry sub and feed the cable into the top stand of the drill pipe, proceeding with RIH wireline.
- Connect the side entry sub and add one stand on top for the pump-down cable wet connect to make the latch at the downhole connect head.
- Ensure latching pressure is appropriately adjusted.
- Confirm successful tool power-up and perform a pull-test on the cable.
- Reset tool depth to match the drill floor level.
- Establish good comms between rig floor and wireline unit.
- Perform logging operations whilst maintaining a consistent tension in the cable, allowing for additional cable weight as the cable is lowered into the well.
- Once logging is complete, unlatch, pull out of hole (POOH) wireline, remove side entry sub and trip out of hole with pipe at recommended speeds.
Tractor logging
A wireline tractor is a specialised downhole tool used in wireline operations to transport logging and intervention equipment within a wellbore, especially in conditions where gravity alone is insufficient for moving the tools to the desired location. This technology is particularly useful in horizontal or highly deviated wells where traditional wireline methods struggle due to the lack of gravitational pull on the tools.
How wireline tractors work:
Propulsion: Wireline tractors are equipped with an electric or hydraulic drive mechanism that allows them to “crawl” along the wellbore. The tractor extends arms or wheels that press against the wellbore walls, creating the friction required for movement.
Directional Control: Operators can control the tractor’s movement from the surface, directing it to move down the wellbore or pulling up as needed to position logging or intervention tools accurately.
Tool Conveyance: The tractor is attached to the wireline above the toolstring. As it moves through the wellbore, it pulls the wireline and attached tools along with it.
Advantages of Using Wireline Tractors:
Access: Tractors enable access to parts of the wellbore that would otherwise be inaccessible due to well architecture or gravity limitations, such as horizontal sections.
Efficient Data Acquisition: They facilitate comprehensive logging in challenging well conditions, allowing for better data acquisition and interpretation.
Operational Efficiency: Tractors can significantly reduce the time and cost associated with well interventions by enabling direct access to target zones
Enhanced Tool Performance: By ensuring tools reach the exact location needed for measurements or interventions, tractors enhance the performance and accuracy of downhole operations.
Wireline tractors have become an useful option in wireline operations, expanding the capabilities of wireline logging and intervention in complex well environments and a potentially quicker alternative to pipe-conveyed logging for open-hole operations.
Coiled Tubing
Coiled tubing (CT) refers to a continuous length of steel or composite tubing that is wound on a large reel and used in oil and gas operations for interventions in wells and for pipeline maintenance.
Key Features of Coiled Tubing:
Continuous Length: Coiled tubing is manufactured in long, continuous lengths to avoid the need for connections during deployment, allowing for quicker and smoother operations.
Diameter: The diameter of coiled tubing can vary, with sizes typically ranging from about 1 inch to 4.5 inches, to suit different wellbore sizes and operational requirements. Coiled tubing maximum pull rating can be up to ~135,000lbs (ref) which is considerably more than can be achieved with wireline cables (40,000lbs ref) and significantly lower for those cables which can be effectively operated within pressure control equipment and the constrains of specific operating parameters (pressure/fluid type etc).
Flexibility: The flexibility of coiled tubing makes it particularly useful for navigating through tight spots, deviations, and horizontal sections of wells.
Reel-Mounted: The tubing is spooled on a large reel mounted on a truck, trailer, or skid, making it easily transportable to and operable at the well site.
Basic wireline tools have traditionally been deployed on coiled tubing as early as 1987 in France and Germany, with the wireline placed inside of the coiled tubing (ref). These systems allowed the use of larger perforating gun systems at higher angles without having to kill the well. Atlernatively, wireline tools can be powered downhole using batteries and a memory module to store the data which can then be downloaded and depth/time matched. Today, real-time (ref) and hybrid fibre optic technologies provide systems which can deliver both data and power to downhole tools (ref) (ref) eliminating the requirement for downhole batteries or traditional wireline cables.
Technical Advisory
When planning operations for data acquisition in wells, understanding the range of conveyance options available for wireline tools is crucial. Each method has been developed to address specific well challenges and data acquisition needs.
Technical advice for planning these operations should focus on:
- Well Geometry and Conditions: Choose the conveyance method that best suits the well’s directional and geological challenges.
- Data Acquisition Needs: Consider the type of data required and select a conveyance method that can provide accurate and comprehensive data.
- Operational Efficiency and Safety: Evaluate the efficiency and safety benefits of each method to ensure operations are conducted smoothly and without undue risk.
- Equipment Compatibility: Ensure the selected conveyance method is compatible with the existing well infrastructure and the tools intended for use.
- Time and cost – each of these conveyance solutions can potentially save time and money when used in the correct way for the right application.
Conclusion
A good understanding of the when, why and how different conveyence types can be effetively utilised is key to determining which is the most approprite for any application. Well modelling along with a comprehensive data acquisition strategy can help with this process. one&zero as a a group have extensive experience with all conveyance types presented – get in touch if you think we can help. [email protected]
