A new, downlink drilling control system changes conventional drilling operations.

Halliburton's Sperry Sun product service line has developed the Geo-Pilot rotary steerable system and the Geo-Span downlink drilling control system, which make drilling operation less complicated and more efficient. The new technology not only saves drilling time and drills a better wellbore, but also thrusts drilling automation into the present. The following key features offer significant changes to conventional drilling operations:

• Simultaneous bi-directional communication between surface and downhole tools;
• Downlink control of multiple tools in the bottomhole assembly (BHA);
• Dual control option for downlink communication with the rotary steerable tool;
• Ultra smooth wellbore capability;
• Real time data exchange;
• Remote control operation; and
• Automated inclination control.
Basic Downlink Control System Hardware Configuration
The downlink control system includes the following hardware:
- Remote control computer
- Rig site computerized control system
- Surface transmitter skid
- Downhole receiver sensor
- Downhole tool control system
- Rotary steerable tool control system

Decisions for downlink commands are based on well planning information and measurement-while-drilling/logging-while-drilling (MWD/LWD) data. In order to transmit a downlink communication, a command is sent to the rigsite computerized control system. The rigsite computerized control system, activates the surface transmitter skid in order to create a proper sequence of negative pulses in the drillstring. Once the pressure pulses representing a certain instruction are generated on the surface and transmitted to the end of the drillstring, a downhole pressure sensor receives the signal and sends the command to the downhole tool control system. Each downlink command is encoded with an identifier that enables the downhole control system to send the command to the appropriate tool. The surface transmitter skid consist of an automatically controlled valve that bypasses a portion of the drilling fluid, going to the standpipe and back to the mud pump return line. The bypass procedure is automatically controlled by the rig site computerized control system.

The Control System's Advanced Communication Features

The new control system utilizes two-way communications. The downlink is achieved through mud pulses created by the surface transmitter skid. The uplink is achieved through normal MWD mud pulse telemetry. The uplink and downlink can be executed simultaneously without interference with each other while continuing to drill. This capability is achieved with dissimilar uplink and downlink transmission frequencies. Additionally, a combination of noise filtration and signal recognition firmware is used to ensure reliable downhole detection of the downlink signal. In order to provide real time confirmation of the successful reception of a downlink command, uplink verification is provided by the downhole tool control system.

The Geo-Pilot system is equipped with a dual-control option for downlink communication. The first is the downlink control and the second is a manual control mode. The two systems operate completely independent of each other, and control of the RST can be switched between the two modes as required. The manual mode involves pump cycling and rotation sequences of the drill string to send commands to the tool. The normal downlink mode is considered quite reliable. However, in the event of a downlink failure, the manual control provides a back-up method for controlling the tool. This back-up feature combination, which is unique in the industry, provides the ability to finish a job without tripping out of the hole in the event of a primary downlink failure. The net potential result would represent a significant cost saving particularly in offshore drilling operations.

The fast downlink data rate and comprehensive command base provide a way to very accurately control the toolface and deflection setting. The capability to accurately adjust the toolface and bend deflection, any number of times while drilling, enables the drilling of an extremely smooth well bore. This capability is in contrast to conventional motor drilling where the bend angle is fixed and setting of the tool face becomes extremely difficult in deep or extended reach well bores.

Tying it all together

Real-time graphics user interface capability is combined with real-time utilization of geophysical, petrophysical, and drilling engineering personnel. Using satellite and network technology, real time data exchange is now available to multiple personnel in remote locations via the Geo-Span service. MWD/LWD and directional drilling data, which are transmitted in real-time to the surface via uplink, can now be incorporated with mud log and well planning data, and reviewed real time by the geophysicist, petrophysicist, and drilling engineer both at the wellsite and in the office. All of the information can be integrated to make a decision for controlling the drilling operation. Downlink commands, based on this comprehensive review, can then be transmitted in real-time to control the downhole drilling tools.
The ability to exchange real-time data between rig site and remote personnel and then implement changes based on real-time decisions has completely changed the convention drilling operation. Additionally, the ability to integrate real-time drilling parameters and formation evaluation data with input from expert personnel in remote locations will reduce the decision-making cycle time and prevent costly mistakes.

A real-time drilling display combined with a comprehensive graphics user interface (GUI) has been implemented in the new drilling control system. The GUI, includes the following:

- Well planning profile
- Real time drilling profile
- 3-D views of the profiles
- Anti-collision data
- Drilling parameters settings
- Surface automated features
- Down hole automated features
- Command communications status
- Control of downlink commands.

Remote Control Operation

The Geo-Span system is equipped with remote control capability. For example, personnel in Houston can operate a rotary steerable tool on a job in Norway. Cost is not the only issue. There are instances in which it is desirable to have a highly experienced directional driller on more than one job at the same time. The only way to achieve this capability is through remote control operation. Furthermore, in complicated offshore drilling situations, a significant amount of communication can be required between the directional driller and several personnel in the onshore office. By having the directional driller work directly with the onshore personnel, a reduction in decision/rig time can be realized.

Automated Inclination Control and Automated Surface Functions

Currently, directional drilling decisions are primarily based on the driller's experience. Different directional drillers will adjust drilling parameters differently for a given drilling condition. In addition, different formations in various locations will yield unique drilling results. The challenge is to work toward drilling decisions based on knowledge as opposed to relying solely on experience. One solution is automated drilling functions that control tools based on actual formation characteristics. The new downlink drilling control system includes an inclination "cruise control" function that provides automated inclination control of the rotary steerable tool. A cruise command, which includes the specified inclination angle, tolerance, and sensitivity is sent via the downlink system to the tool. After the rotary steerable tool's control processor receives the command, it will monitor the at bit inclination (ABI) sensor periodically. When wellbore inclination or change rate of the inclination deviates from the specified value, the control processor will automatically adjust to the proper toolface and deflection in order to maintain the preset inclination in its defined tolerance. Even though this is not a fully automated drilling system, this feature has moved toward knowledge-based drilling. This function utilizes knowledge of inclination at the bit to accurately control the rotary steerable system.

In regard to control of the wellbore profile, automatic inclination control will make the wellbore smoother because of the real-time parameter adjustment. The automatic function can detect minute fluctuations much earlier than the directional driller can. Therefore, the inclination adjustments will be much smaller than those made by a directional driller. An added benefit will be increased rate of penetration due to the smoother wellbore and better weight-on-bit transference.

Future Developments

There are two major future developments: 1) completely automated drilling and 2) automated drilling using artificial intelligence.

In regard to completely automated drilling, this technology will utilize automated 3-D drilling to drill a well based on a predetermined well plan. This system utilizes real-time surface automated controls and has the option of including preprogrammed automated downhole controls. The downhole automated controls can be updated or mode switched real time via the downlink control system. The vision for this technology is straightforward: to be able to load the well planning profile in the remote or rig site surface control computer and let the computer automatically set the proper drilling parameters for the rotary steerable tool based on the prescribed well plan. A directional driller is then only needed to monitor the well, or multiple wells, from a central onshore location.

The significance of this technology is that today the industry has a downlink system that is fast enough to allow for the steering calculations to be done on surface instead of downhole. Several advantages will come into play because of this breakthrough, including the ability to fully understand what the automated steering control system wants to do before it executes the commands. This is significant because instead of finding out what the rotary steerable tool did after the fact, when perhaps it is too late to correct the well trajectory back onto the plan, one can see what the intention of the system is and assess whether the plan should be overruled, just like one does with the cruise control in a car.

By combining the 3-D automated drilling control function with formation evaluation information, a level of artificial intelligence can be achieved in the automated drilling system. The system can be further enhanced by including formation evaluation information from offset wells. The new technology is called automatic geosteering. Much development has taken place in regard to software for formation evaluation and 3-D automated drilling control. The challenge lies in how to best integrate the two technologies into one comprehensive automated system. This type of integration is technically achievable. When such a system will be available is strongly dependent on the demand for this type of technology. The new downlink drilling control service will grow as more rotary steerable tools with evolving technologies become available in the market.