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OPEN-HOLE DRILLSTEM TESTING An Open Hole Drillstem Test is a short flow test of a well that is conducted before casing is run. The testing equipment is run into the well and the zone of interest is isolated using Inflate or Compression-Set packers. A down-hole valve is then opened, allowing the reservoir contents to flow into the pipe. Four independently operating Data Recorders record the down-hole pressures and a Bottom Hole Sampler collects reservoir samples. At surface, the flow rates are recorded using highly sensitive digital surface recorders and, if necessary, additional fluid samples are gathered while pulling out of the hole. Once the flow test is conducted, the down-hole valve is closed allowing the reservoir to build-up to its shut-in pressure. Pressures recorded during this build-up period are analyzed using standard techniques, providing pressure extrapolations and clues to reservoir characteristics, such as skin damage and permeability. The data recorded during a DST are a direct measurement of hydrocarbon production, and can be used to predict the commercial productivity of a well. Unlike log data, DST data can be used to classify reserves as proven. Inflate Inflate tests utilize a pair of strategically spaced packers which are inflated using annular fluid to isolate the formation of interest. This type of testing is adaptable to a wide range of conditions: Northstar Drillstem Testers’ Inflate equipment can operate in extremely deviated holes or holes experiencing up to 25 mm of washout. Inflate testing is the most time and cost effective method that can be used to isolate multiple formations since multiple zones can be analyzed during a single run in the hole. Compression Compression tests (sometimes referred to as Conventional tests) use compression set packers, which are positioned above the formation of interest. This type of DST is used when formations are susceptible to skidding, evaluation is required immediately upon zone penetration, or for wells which are deeper than 2,900 meters. The tools are put together with sufficient spacing below the packers to seal the zone of interest. The tool string is then run to total depth where weight is applied to the drill string causing compression of the packers and sealing of the formation. |
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