Novel, Multistage Stimulation Processes Can Help Achieve and Control Branch Fracturing and Increase Stimulated Reservoir Volume for Unconventional Reservoirs

摘要

This is largely related to recent success in exploiting unconventional reservoirs and successful development and implementation of innovative technologies. In Europe, unconventional reservoirs (in particular shale gas) are receiving considerable attention. Basins with potential shale-gas plays exist, as does the infrastructure to transport gas to the end user. In addition, the gas-price scenario is favorable as well. It will be critical to find US analogs and transfer technologies/processes that will facilitate European shale-play developments into economically successful projects. However, the market and challenges in Europe are significantly different from those in the US. The population density is much higher and environmental regulations will play a different role. In addition, the entire industry is set up different with a lot less drilling rigs and other service providers. For different reasons, costs are somewhat higher than in the US as well. This demands optimization from Day 1. Directional drilling of horizontal wells needs to progress toward sweet spots, and the completion and fracturing process must be optimized starting at the first well. Therefore, it is important to understand the technologies that were game changers in the US, identify their applicability in Europe, and implement them properly. This paper discusses two recently developed hydraulic-fracturing processes and a hybrid unit that might have considerable impact on advancing economic recovery of unconventional reservoirs. The first new process is designed for high-pumping-rate, multistage fracturing treatments with low proppant concentration. Highly concentrated proppant slurries are pumped down the coiled tubing (CT), jointed tubing (JT), or combination string, and nonabrasive, clean fluid is pumped down the annulus. In such pumping scenarios, the permanent well tubulars are saved from erosion. The pumping rate can be manipulated in real time to customize the placement and downhole-proppant concentration instantly. In case of premature screenout, a well could be easily reverse circulated and cleaned for the next stage. The combination of downhole mixing and microseismic fracture mapping provides unprecedented control of fracture execution to facilitate branch fracturing. The second new process is a combination of mechanically activated sleeve completions and fracturing of individual intervals, but with a change in the sequence in which the intervals are stimulated. This new method is proposed with a goal of altering the stress in the rock to facilitate (or enhance) branch fracturing and connect to induced stress-relief fractures in a single, horizontal well.