Maximizing well construction return on investment is essential in unconventional shale formations, it is therefore important to have consistent key performance indicators, which enable optimization of completion and fracturing design parameters. To this end, PIs (Productivity Index) and the SRVs (Stimulated Reservoir Volumes) were measured on over sixty MFHW (Multi-Fractured Horizontal Wells) in Bakken shales, thereby quantifying the impact of horizontal lateral length, fracture spacing and volume of fluid pumped in each perforation cluster.
The PI was measured during BDF (boundary dominated flow) and in undersaturated conditions, thereby eliminating the effect of free gas on inflow productivity. To eliminate the dependence on fluid properties (e.g. formation volume factor), the downhole flowrate was measured directly utilizing ESP (Electrical Submersible Pump) properties. This method had the additional benefit of providing the required data frequency, resolution and repeatability to analyze bilinear and linear reservoir flow regimes. This technique also eliminates the time lag between downhole pressure measurements and surface rate metering.
The downhole real-time flowrate measurement proved to be a consistently reliable method for visualizing when the well was in bilinear, linear and boundary dominated flow regimes. This real time data and workflow also enabled calculation of the real-time average SRV static pressure, which therefore made calculation of the PI and SRV relatively simple using physics-based workflows as opposed to correlations. As expected, the length of the horizontal drain had a quantifiable positive impact on both the SRV and the fracture flow PI, which was compared to the known analytical expressions for both these performance indicators to provide a forecasting tool. The SRV also showed an increase when the volume of proppant pumped per perforation cluster was also increased. The PI, on the other hand, showed an increase when the spacing between perforation cluster was reduced, which effectively increased the number of induced fractures for a given length of horizontal drain. Finally, the trends in rates of depletion and PI established a database of production profiles for known completion parameters, which enabled production forecasting using analytical tools as opposed to empirical decline curve models.
The availability of high-quality real time downhole pressure and liquid rates enabled rapid well performance measurement, which not only enabled optimization of future completion designs, but also provides a means of evaluating well placement and completion and fracturing execution practices by comparing achieved well performance against a known historical base line. This data collection and measurement techniques is key to both maintaining and improving the ROI of well construction in unconventional wells.
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