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Detection of Hydrocarbon Rich Reservoir Intervals Prior to Well Testing by Using Volatile and Semi-Volatile Organic Compounds in Drill Cuttings: Preliminary Results From Western Turkey

Abstract

Prior to well testing efforts of conventional reservoirs, detection of hydrocarbon rich intervals (HRIs), vertical continuity between the HRIs, hydrocarbon types and quality (oil versus gas) has long been done with the use of well log, core sample and drill stem test data. These approaches have been very expensive particularly in offshore areas and in basins where thin (HRIs < 2–5m) and multiple or stacked reservoirs are found such as in Gulf of Mexico in USA, South Caspian Basin in Azerbaijan and Bohai Bay Basin in China and Gediz graben in western Turkey. The purpose of this study is to introduce a method that helps to decrease the expense, shorten the decision time and accurate selection of test intervals prior to well testing. The method uses volatile organic compounds (VOCs) and semi-VOCs (SVOCs) present in collected drill cuttings. Each cutting sample is then subjected to passive treatment with a GORETM module that contains unique adsorbents to adsorb 45 different VOC and SVOCs within the range of n-C2 to n-C20. Each GORETM module is then analyzed by thermal destruction/gas chromatography/mass spectrometry (TD/GC-MS) to detect VOCs and SVOCs qualitative and quantitative manner (in a nanogram level). In this respect, a total of 333 drill cutting samples was cautiously collected along Sarikiz-2 (122) and Sarikiz-3 (211) wells from the Gediz graben of western Turkey and was treated with the method just described above. An assessment of the two data matrixes (122×45 and 211×45) using both conventional graphs and principle component score and loading plots allowed us to drive the following preliminary results: 1) Ten different HRIs below 1500m of Sarikiz-2 were determined in contrast Sarikiz-3 has no HRIs, 2) HRIs of Sarikiz-2 were ranked in terms of their VOC+VOCs concentration levels, 3) Extremely low concentration of VOCs and SVOCs were observed on top of the 1500m indicating an existing of very efficient seal in Sarikiz-2 whereas Sarikiz-3 presents disperse VOC and SVOCs along the well profile proving lack of efficient seal, 4) Vertical continuity between HRIs and hydrocarbon type and quality in the each HRI were successfully determined for Sarikiz-2. These conclusions were supported by well log and MLU data implying that the method just described in this study become more powerful if it is used together with well logs and MLU. The method is also applicable to unconventional shale-oil and shale-gas reservoirs when the core sample is not available.