Mud pulse telemetry (MPT) is the core real-time data transmission technology in the upstream oil and gas industry. The need for reliable high-speed MPT (HSMPT) has grown as the amount of real-time data required while drilling has increased, and it is now used across many regions of the globe. Yet the changing requirements for MPT and the environment in which it must operate have raised complications that have threatened the reliability of existing HSMPT systems to the point where a very high level of user interaction from offshore field service engineers and remote operations support personnel is required.

A new automated HSMPT system from Baker Hughes combines higher automation levels and advanced signal processing to increase both speed and reliability of data transmission. The aXcelerate PLUS system has performed successfully in complex bottomhole assemblies (BHAs) in many ultradeepwater drilling environments, with many LWD services and with outstanding data density and no reduction in ROP. The impressive results demonstrate the ability of an automated HSMPT to expand the technical limit for safe and economically viable drilling operations.

Growing challenges
Initially seen as the real-time data transmission provider for all required formation evaluation (FE) information, HSMPT usage has expanded to provide the enabling data transmission for drilling automation and optimization services and advanced wellbore positioning and pressure-while-drilling services in extreme downhole conditions such as HP/HT wells and high-viscosity drilling mud environments. New FE measurements have been incorporated into BHAs. Some traditional FE measurements have moved from wireline to LWD, and additional drilling optimization data are now transmitted in real time. Improvements in bit technology and overall drilling procedures have increased average ROP, requiring additional transmission speed to maintain the same data density per meter drilled. Often, the full complement of downhole processes that can be provided by HSMPT is critical for HSE compliance and for technical risk reductions. These changes have significantly raised the amount of real-time data required while drilling.

At the same time, additional challenges have emerged that complicate MPT in general and high- transmission speeds in particular. As wells are drilled deeper, the mud column that attenuates the MPT signal increases. More challenging mud systems with high density, high plastic viscosity (PV) or high solids content are used in applications that demand a high transmission speed. Additional drilling optimization tools (e.g., agitators) have been added to BHAs and create superimposed noise to the HSMPT channel.

As drilling, MWD and FE tools have become more reliable and able to withstand higher levels of vibration and stick/slip (VSS), acceptable VSS levels during drilling have risen. These high VSS levels negatively affect decoding performance. Additionally, extended-reach applications, which are now much more common than previously, experience high surface torque and drilling VSS that compromises MPT.

Strong variations in rigs, equipment, mud and piping lead to changing environments for the MPT system downhole as well as at surface. This situation increases the complexity of the required system to overcome the difference in operating environments.

The reliability issues that often result from the changing requirements and more challenging environments in which HSMPT must function have elevated required user interaction levels, frequently forcing field engineers to redirect their focus from delivering answers to maintaining highly complex tools.

Finding a solution
Although HSMPT data rates of 10 bits per second (bps) or more have been recorded in the field for about a decade, lack of reliability forced a thorough analysis of existing problems. The conclusion was that significant improvement can be achieved through the automation of manual processes and advanced signal processing.

The new HSMPT system applies automation in every field operation to simplify operations, save time and eliminate error-prone tasks such as manually reentering data. When a transmission parameter already is configured in one system, this information is automatically distributed. Additionally, conditional data such as flow rate, depths and other information measured are gathered during field operations and saved with the transmission parameters.

The simplified HSMPT system consists of a downhole transmitter (the pulser), the mud channel and the receiver on the surface side, which usually has one or more pressure transducers. The main distortion sources for MPT data transmission are the mud channel and additional variable distortions. To reduce distortion and improve signal processing, special signal sequences automatically adjust adaptive filters. The pulser sends out the sequences regularly, enabling the surface system to tune the adaptive filters for changing channel conditions. The filter performance is tested and saved into a database with quality indicators, which enable field personnel to optimize decoding quality through better decision-making (Figure 1). Enhanced signal processing algorithms on the surface significantly increase the success rate of the automated system and improve the decoding quality and reliability.

Successful field performance
The new HSMPT system has enjoyed 100% success rates in many ultradeepwater drilling regions in a wide range of applications, all of which require a significant amount of real-time data to enable accurate decision-making. The technology has been used in more than 60 runs, with more than 5,000 circulating hours and more than 3,000 drilling hours. Physical data rates higher than 10 bps were reliably achieved while drilling in every job. The technology was deployed in both oil-based and water-based mud environments with measured depth of up to 8,000 m (26,247 ft). Different mud systems were used, with PV higher than 20 centipoise (cP) in 40 runs and higher than 40 cP in 10 runs.

Among successful applications of the new HSMPT system was its deployment in one of the longest and most sophisticated BHAs worldwide, in the North Sea. The system’s ability to reliably transmit more real-time data enabled the operator to deploy a BHA incorporating numerous drilling and LWD services to provide more answers in real time (Figure 2). The new system provided up to 15 bps data rate in a challenging oil-based mud system with a PV of 34 cP. The drilled section, from 4,635 m to 6,611 m (15,207 ft to 21,690 ft) measured depth, was drilled in one run with 184 circulating hours.

Increasing HSMPT data rates and reliability means that the technology can now be run in complex drilling environments—including ultradeepwater wells and rigs with demanding mud conditions—that previously required significant manual effort and a potential fallback to data rates below 10 bps. Automation and ease of use expand operating limits for HSMPT activities and reduce unnecessary workloads from technical support centers and field engineers. Allowing field service engineers to concentrate on delivering more answers to the operator improves efficiency and safety while drilling and reduces overall drilling cost.

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