Abstract

This study presents the successful application of the advanced cuttings characterization (ACC) together with the Advanced Mass Spectrometer (AMS) on the campaign in Bolivia within a complex geology in HPHT environment. The Huamampampa Formation is in a duplex structure on the upper block, and in a structural high in the down-dropped block of the fault. Interbedded sandstones with different petrophysical characteristics make conventional drilling challenging. Drilling through this rock requires the use of a downhole motor in the BHA, which generates rock powder make the drilling, making geological characterization impossible. Due to this constraint, geological mapping relies on the old technique of Palynology. This technique has several limitations and drawbacks leading to ambiguity around identifying tops of drilled formations. Moreover, this technique is time-consuming, i.e., results are available several months after the end of the drilling. However, valuable information can be obtained from mudlogging to predict reservoir quality, fluid contact and reservoirs permeability. The evaluation came from mudlogging ACC, which provided:

• Mineralogy and total organic carbon (TOC) from cuttings through Diffuse reflectance infrared Fourier transform spectroscopy technique DRIFTS.

• Geochemical ratio and Gamma Ray via X-Ray Fluorescence (XRF): this provided better quantitative assessment of different rock-facies and provide a better control on the geological model.

• Hydrocarbons C1-C10, and inorganic species like CO2, He, and H2 to understand the reservoir. Formation gas is considered the first indication of zones of interest and so it needed deeper evaluation (AMS).

The analysis and study of the ACC data confirmed that these techniques are very valuable for reservoir evaluation while drilling in HPHT development fields and are not affected by the downhole motor, being the greatest technological in this area today. ACC was able to differentiate different geological unit within the Paleozoic, by measuring and identifying markers in quartz, feldspars, chlorite, and illite, and Zr/SiO2 and SiO2/Al2O3 ratios. Moreover, the AMS exhibited fluid grading from top to bottom of the Huamampampa Formation. ACC and AMS were utilized for the first time in Bolivia in real-time while drilling.

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