Throughout the last decade the oil industry has searched for alternatives to balance reservoir understanding with the costs involved in exploration and development of oil and gas fields. The use of the Rez-Connect real-time telemetry system (Figure 1) during exploration drillstem testing (DST) helps ensure well testing objectives by providing flexibility to the predetermined well testing program. This flexibility is based on access to reservoir data, real-time control of DST tools and real-time analysis of well productivity parameters, thus increasing efficiency and the quality of information gathered during well testing operations. Traditional real-time systems have ranged from deploying wire downhole to using acoustic telemetry technology.

Acoustic telemetry communication systems apply the concept of compressional waves as a way to establish communication between tools. These longitudinal waves can be more easily visualized through observation of spring vibrations, as shown in Figure 2, assuming that a long spring is held in the hand and, as it is moved downward, a section of the spring is compressed. When the hand is moved upward, a section of the spring is stretched. These sections of compression and tension travel through the entire length of the spring. When the compressional waves reach the end of the spring, they reflect and travel back in the opposite direction. This is very similar to the way that acoustic waves propagate in acoustic telemetry systems.

The stiffness and density of the spring influence the speed at which these compressional waves travel. The tubing or drillpipe is very stiff, and the wave speed in the tubing is very high, on the order of 5,121 m/sec (16,800 ft/sec). As a result, the human eye is unable to see the acoustic waves propagate through the tubing. The waves can, however, be heard with the use of Halliburton’s DynaLink Telemetry System, which powers the RezConnect System, allowing tool communication.

Wireless telemetry
The new wireless telemetry system was designed for services in the cased-hole environment and has been fully proven in the field. The system can reduce risks and provide dynamic real-time control, measurement and analysis of well productivity parameters to deliver accurate, real-time reservoir characterization. RezConnect is powered by the telemetry system, which is a wireless sensor and acoustic transmitter that enables bi-directional communication between downhole tools and the surface.
The system also provides real-time data, allowing operators to make more informed and quicker decisions and enabling them to more accurately characterize reservoir formations through pressure and temperature measurements and acoustic control of downhole valves, sample collection and analysis.

The system is a battery-powered wireless system designed to be deployed during DST operations. It is the platform that supports the RezConnect System operation. It distinguishes itself from conventional surface readout systems by generating acoustic energy to transmit real-time data to the surface through the tubing wall. Gauges are equipped with quartz crystal sensors that provide accurate pressure and temperature measurement downhole. These gauges operate in both memory and in real-time modes. The DynaLink system also enables activation of and communication with downhole samplers and tester/circulating valves and other downhole tools.

Dynamic real-time control
Initial development and application of the acoustic system was for data acquisition. Later developments allowed the telemetry system to be used as a downhole network communication to actuate downhole devices such as valves and samplers. Discoveries and developments in deepwater and deep formations with higher downhole pressures required the use of higher hydrostatics using high-density drilling muds, which caused pressure transmissibility issues. Associated solids created challenges during the use of annulus pressure-operated tools. The application of wireless telemetry to control the downhole DST assembly provided the solution, reducing or even eliminating the need for pressure activation of downhole tools. Additional benefits include less concern from casing pressure limitations, and the need for wireline operation during DST was minimized or eliminated, thus reducing safety concerns, particularly during the development of deepwater operations. Additionally, the system can be used to diagnose tool behavior and provide feedback at the surface about downhole tool status and completion of downhole tasks, allowing confirmation of downhole tool events. This is critical during deepwater operations, allowing reduction of uncertainties, creating operational efficiencies, optimizing testing procedures and allowing time reductions.

Measurement, analysis of well productivity
The system has been deployed during well-testing operations worldwide, facilitating decisions because of its capability to provide real-time downhole data using downhole quartz gauges in addition to allowing qualitative determination of the basic fluid composition of samples collected downhole and the number of collected samples. These two capabilities further reduce testing uncertainties and provide valuable information to reservoir engineers. Reservoir information is the essence and key objective of any testing operation and provides a powerful collaboration and decision-making tool to engineers for the entire testing operation to facilitate and optimize the testing process. Before the use of current real-time systems, data were acquired through the deployment of electronic memory gauges that were retrieved at the end of testing operations for reservoir interpretation.

A similar concept was applicable during development of downhole sampling operations since sampling was performed with no assurance of samples being collected or what fluid was collected in the samplers. The quality of data and samples collected only could be confirmed at the end of the entire operation, when samples were transferred and validated after the testing operation. In the event of inconclusive test results, the ability to repeat well testing operations is limited and, in most of the cases, impossible because of the cost and operational requirements involved.

The development of downhole wireless acoustic technology has helped achieve the objective of accurately characterizing reservoirs and production potential in real time. The technology is capable of accurately acquiring dynamic reservoir data, efficiently controlling downhole tools and fluid samplers and operating in a collaborative environment, allowing optimization of the well test. The improvement in terms of efficiency is achieved through immediate and accurate decisions to reach planned well testing objectives with less rig time and improved safety conditions during DST operations.

Hydrostatic pressure can pose significant limitations and restrict well testing operations since the applied annulus pressure cannot exceed the maximum allowable casing pressure. The use of wireless acoustic technology helped eliminate this limitation with its capability to activate multiple DST tools without the use of annulus pressure. The operator can operate downhole tools and fluid samplers in a low casing-pressure testing environment.

The well testing system provides full acoustic actuation and control of downhole test tools and pressure-volumetemperature
fluid samplers and delivers their operational status along with bottomhole pressure and temperature data in real time. The system allows real-time verification and monitoring of complete downhole testing operations, reducing uncertainties and enabling operators to meet or exceed well testing objectives. This is achieved through the use of advanced wireless telemetry
technology that provides acoustic activation and control of downhole testing tools. Downhole sensors and acoustic repeaters are spaced along the work string with full bi-directional communication and control capacity to monitor formation behavior, tool activation and operational status during the entire testing operation.

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