Surface Read-Out Of DST Data In Real Time
C. Macleod, S. Mitchell, A. Guimard, B. Glotin · Offshore Technology Conference · 1979
ABSTRACT A new testing technique allows surface monitoring of downhole pressures and temperatures, in real time, during an otherwise conventional drill stem test; the pressure and temperature data is measured at a point below the downhole test valve. This makes it possible, for the first time, to conduct the testing operation with optimum efficiency, according to the particular behaviour of the well being tested. The surface read-out capacity is achieved by using an electric wireline which can be latched on to a gauge located on top of the test tool. The, strain gauge type, pressure sensor used has an accuracy of ±0.04% of full scale (10,000 psi). and a resolution of 0.02 psi. The pressure and temperature data is available continuously, in real time, in the form of a print-out and a plot, in any co-ordinates. This data is also permanently recorded on magnetic tape. A computer which controls the data gathering operation, is also used for interpretation purposes. A description of the tools together with several case histories are given. INTRODUCTION For many years short time drill stem tests have been used to evaluate zones encountered while drilling exploratory wells and, less commonly, to quantify the potential of wells drilled into known reservoirs. The equipment used has evolved over the years, from the original packer and single shot downhole valves to the latest, relatively sophisticated annulus pressure controlled valves. The introduction of those annulus pressure controlled testing valves represented significant improvements in the safety and operational aspects of the testing procedure, but generally they still required retrieval of the test string to obtain the recorded downhole data. With a Full Bore testing valve it is possible to retrieve the downhole pressure and/or temperature recorders with 'slick? line, but this also involves considerable delay in the acquisition of the data. The present paper describes a technique which eliminates any delay between the generation of data downhole and its availability at surface. This new technique eliminates the necessity to pre-plan a drill stem test. Such 'pre-planning' is normally done essentially on the basis of rules of thumb, which stipulate shut-in times as a function of flow times. With a prolific well this can mean wasted rig time because wellbore pressure builds up close to or reaches reservoir pressure soon after shutting in. In these circumstances, a real time surface read-out of the downhole data would indicate early termination of the shut-in, with consequent savings of rig time. Conversely, many DST's of tighter zones often do not provide adequate information because shut-in time(s) were too short. With a surface read-out of the downhole data, in real time, every test can be engineered for maximum information thus avoiding costly retests or having to make major decisions with uncertain data.