In horizontal-well, plug-and-perforate completions, various studies have shown that not all perforation clusters are stimulated equally. To increase perforation cluster treatment efficiency, engineers attempt to move the perforations of each stage to similarly-stressed rock. Most of these efforts have not included predictions quantifying efficiency improvements. This paper outlines a methodology for predicting improvements of perforation cluster treatment efficiency and includes a case study verifying the results of the model using pre-treatment diagnostics.
In four Western Anadarko Basin wells, the operator measured mechanical rock properties using drill bit geomechanics. These properties were used to calculate the changes in minimum horizontal stress along each ~5,000-ft horizontal well. Within each treatment stage, the engineers chose perforation locations to minimize the difference in minimum horizontal stress. Using offset vertical logs and the geosteering interpretations, the engineers built a high-resolution fracture simulation model for each well. The model included the measured mechanical properties along the wellbore path. Comparing results from a geometric perforation model and the stress-balanced perforation model, the engineers predicted increased perforation cluster efficiencies between 10 and 20%.
The four wells were completed using the stress-balanced perforation designs. Like all previous wells in the area, the operator performed step-down rate tests on these wells before each stimulation treatment. The step-down rate test is a common hydraulic fracturing diagnostic to quantify the number of open perforations taking treatment fluid. Compared to the operator's previous geometrically-perforated wells, the wells with the stress-balanced perforation designs showed more open perforations. A higher number of open perforations suggests a greater perforation cluster treatment efficiency. The increase in efficiency measured by the step-down rate tests was consistent with the model predictions.
By understanding how stress-balancing perforation clusters will affect perforation cluster treatment efficiency, operators can optimize stimulations. The industry has not widely adopted stress-balanced perforation designs or other ‘engineered’ completion strategies. The results of ‘engineered’ completion studies have often been inconclusive, likely due to small sample sizes and reliance on production results. By combining affordable measurement of rock properties, modeled perforation cluster efficiency, and an affordable measurement of perforation efficiency, this paper provides a methodology for economically optimizing multi-stage stimulations in horizontal wells.