When well testing is conducted, the reservoir response during the initial surge to stable drawdown and pressure buildup will define productivity expectations for a new well. The quality of the reservoir fluid samples further defines the value of the reservoir assets. To ensure that operations will be conducted safely, rig-time efficiency will be maximized, and the overall well test objectives will be met, several critical well testing decisions must be made. This paper describes the value of real-time access to reservoir information and tools to control well testing operations. Also described is a system that has been used to provide immediate access to the reservoir through the use of wireless downhole telemetry, data acquisition and control, and instantaneous visibility of data from any location around the world. While the idea of providing access to some reservoir information in near real time is not a new concept, the system described is not dependent on formation geology and is the only one with the capability to provide access to all reservoir information in real time, perform analysis using this information, and control well testing operations remotely with the click of a mouse button. Case histories will be presented to demonstrate the capabilities of the system described.
Electronic gas measurement has evolved from providing a simple replacement for circular chart recorders to including requirements for instantaneous remote access of flow information. Coupled with this capability is the need to have access to this same information in multiple locations simultaneously. With existing equipment unavailable to meet these requirements, one operator and manufacturer allied themselves to develop a new flow computer. This new flow computer incorporates features to meet not only the specific and unique requirements of the operator's communication system, but also provides adaptation for future requirements. Installation of this new flow computer has resulted in significant operating cost reductions for the operator by requiring fewer trips to offshore locations and providing instantaneous flow information for engineers, technicians, and gas accounting personnel. Introduction Electronic Gas Measurement (EGM) systems have grown in popularity in recent years due in large part to their ability to provide both on-site viewing of real-time data and historical recording of the same data. The typical EGM system (Fig. 1) has been used to replace two- and three-pin chart recorders. hese systems were required to input physical parameters such as differential pressure, static pressure, and temperature to produce a volume total and calculated instantaneous flow rate. In addition, EGMs were capable of recording flow information to be retrieved at a later time. However, EGM systems have been increasingly required to contain many additional features normally associated with remote terminal units (RTUs) and programmable logic controllers (PLCs). Requirements related to communication within a wide area network are often weighted evenly with measurement and recording capabilities when evaluating new EGM systems. These systems must be configurable, both with regard to normal EGM functions and expanded communication system functions, yet easy to operate. These requirements, brought about by the increase in use of Supervisory Control and Data Acquisition (SCADA) computer systems, has shifted the role of the EGM device from simple chart recorder replacement to full-featured communication equipment. In addition, the SCADA systems themselves have advanced to include a multitude of communication media options ranging from simple hardwire to microwave. Prior to the introduction of flow computers, differential pressure, static pressure, temperature, and flow-rate data was interfaced to SCADA systems by connecting analog voltage or current outputs from a transmitter to analog inputs in a PLC or RTU, which was then connected to the SCADA system. Even with the introduction of flow computers, volume totals were often interfaced to a SCADA system by connecting a pulsed digital output, with the number of pulses corresponding to a scaled version of the total volume, to a pulse input in the PLC or RTU. This setup tends to be both costly to install and difficult to maintain. In addition to the added SCADA support requirements, new EGM devices are expected to incorporate features that allow their use in many more varied applications than the early flow computers. New EGM devices are expected to retain the key features of traditional EGMs but allow for applications such as liquid measurement and storage in order to incorporate them Into well test and allocation applications.
This paper was prepared for presentation at the 1999 SPE Latin American and Caribbean Petroleum Engineering Conference held in Caracas, Venezuela, 21–23 April 1999.
Drill stem testing (DST) provides reservoir information that helps evaluate the potential of a new field. The data includes permeability, total skin (damage) and formation pressure, but these calculations are possible only if the build-up period is sufficiently long to attain middle time regime. The best technique for determining the length of flowing and build-up periods required is to monitor real-time bottomhole pressure (BHP) at surface. Traditionally, BHP and temperature data have been recorded using downhole memory gauges, but the data could only be retrieved after the test had concluded and the DST bottomhole assembly (BHA) was pulled out of hole. Wireline surface read-out (SRO) was used in the next evolution of the applicable technology. This method lowered a wireline retrieval tool into the BHA during the build-up periods to retrieve real-time data from downhole gauges. This technique worked satisfactorily during build-up periods but was difficult to achieve during flowing periods, especially at high rates and with sand or solid production. Now, a real-time downhole data acquisition solution that uses the newest generation of an acoustic wireless telemetry system has been developed. This system allows data transmission by the tubular wall using acoustic energy during flowing and build-up periods, thus providing real-time SRO throughout the test to facilitate quick decisions and troubleshooting solutions. With the acoustic wireless telemetry system, wireline intervention during DST is not required, thus eliminating inherent risks and costs of such operations. A project undertaken by PETRONAS and a major service company using this system was successfully implemented on jack-up rigs in Malaysia. This paper discusses the challenges and step-by-step improvements made to enable these jobs to successfully meet the sought-after goals.
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