SWELLING SHALE ZONE PREDICTION USING THE RELATIONSHIP OF CLAY MINERAL AND SHALE VOLUME OF FANG BASIN, THAILAND

Abstract

Stuck pipe of the drilling string by shale swelling is one of the problems for petroleum drilling wells, especially in the Fang oil field, Thailand. The research objectives are to study the shale volume using gamma ray log, and the variation of clay mineral and elemental composition of drill cuttings of FA-SS-35-04 well to identify minerals and predict the swelling shale zone. The FA-SS-35-04 well is in the San Sai oil field, Fang Basin. The lithology of the basin can be divided into two formations including Mae Fang formation (~450-2,600 ft) and Mae Sod formation (~2,600-9,200 ft) based on drill cutting. 39 samples in Mae Sod formation are analyzed using gamma ray log data, X-ray diffraction, and X-Ray fluorescence. The gamma-ray value shows a high content of shale volume in clay layers. The results of clay mineral consist of 18.0-82.2% quartz (avg. 51.26%), 5.1-37.7% kaolinite (avg. 17.68%,), 1.8-17.7% illite (avg. 9.97%), 0-2.0% chlorite (avg. 0.99%), 0-46.6% calcite (avg. 6.83%), 3.9-17.5% feldspar (avg. 9.27%), and 0.6-8.9% montmorillonite (avg. 3.99%). The montmorillonite in all units of Mae Sod formation impacts directly shale swelling according to the increased depth, Al2O3, Fe2O3, and MgO contents. The lower zone (unit C) of this formation (especially 7,110-9,150 ft) represents the highest montmorillonite content which can affect shale swelling. Based on this shale swelling zone study, it can lead to forewarning and select the appropriate method to reduce and prevent the risk of stuck drill string or logging tools or formation caving problems during drilling operations in Fang basin.