ABSTRACT

Understanding the properties of fluids in hydrocarbon reservoirs requires measurements on fluid samples. Focused sampling techniques for wireline formation testers, represent an important breakthrough in downhole fluid sampling since it has enabled the capture of clean and representative reservoir fluid samples much faster than with conventional sampling methods.

In this contribution we describe techniques to monitor focused fluid sampling and methods to determine the efficiency of focused sampling by utilizing the dynamic responses of reservoir fluid flow in a dual flowline formation testing system during fluid sampling operations. The method requires for the integration of downhole fluid analysis measurements which are acquired simultaneously in both the sample and guard flowlines during sampling operations.

Multiple fluid property measurements are available to monitor both flowlines during formation testing and sampling operations. The dual flowline optical spectroscopy measurements are acquired simultaneously with the same hardware including the light source, optical filter arrays, photo detectors, and electronics used on both flowlines. This configuration limits any system bias between the fluid property measurements, which now enables direct and real-time comparisons of fluid properties and contamination levels in each flowline with better accuracy.

The method also allows monitoring and controlling the efficiency of focused sampling and testing operations while adjusting the flow rate ratios and pressure drawdowns for the sampling pump modules. These techniques can also be combined with the application of three dimensional (3D) multi-drain focused sampling probes, which further expand the operating envelope for fluid sampling and sampling measurements in reservoirs with wider ranges of permeability and reservoir fluid type.

In this paper, we provide two case studies to illustrate the method, together with examples to show the practical utility for quality control and monitoring of the efficiency of focused sampling. The integration and analysis of dual flowline sampling measurements provides new insights to improve the assessment of dynamic behaviour and responses during sample cleanup. We also propose the use of new indicators for determining contamination which can be used for input to better decision making for reservoir fluid sampling and formation testing operations.

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