This week we wanted to highlight and share a paper we think everyone in tight unconventionals should read, namely URTeC 2118, “Rate Transient Analysis of Fracture Swarm Fractal Networks” by Jorge Acuna. The paper is a few years old now, exemplifies how RTA can be formed on wells with complex fracture networks.
Fractal techniques are used to create networks with fracture swarm geometry that resembles that observed in exploratory cores in the literature. These networks have desired total pore volume, maximum and minimum fracture spacing, and fractional dimension, and their hydraulic behavior is controlled by these properties and fracture conductivity. Numerical simulation of individual fragments and total production is shown to be consistent with simulations of the entire network when fracture conductivity is high, leading to sub-linear flow (pressure derivative slope between 0.5 and 1). When fracture conductivity is low, the network exhibits sub-radial flow (pressure derivative slope between 0 and 0.5) at early times, with a transition to sub-linear or boundary-dominated flow (BDF) at later times. The duration of sub-radial flow can be extended by reducing fracture conductivity. These types of flow behavior cover the entire range seen in unconventional wells and demonstrate how the power-law behavior frequently observed in diagnostic plots can be produced by the combined effect of matrix fragments that individually can only show linear, bi-linear, or BDF flow. The relatively simple geometry of fracture swarms also allows for the calculation of properties for sub-radial flow, providing new insights into the production mechanisms of unconventional wells.
More info can be found here in the whitson+ manual: https://manual.whitson.com/modules/well-performance/numerical-rta/#7-numerical-rta-accounting-for-uneven-frac-spacing
Want to learn more? Download the paper →→→here←←←.
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Curtis Hays Whitson
Mathias Lia Carlsen
whitson supports energy companies, oil services companies, investors and government organizations with expertise and expansive analysis within PVT, gas condensate reservoirs and gas-based EOR. Our coverage ranges from R&D based industry studies to detailed due diligence, transaction or court case projects. We help our clients find the best possible answers to complex questions and assist them in the successful decision-making on technical challenges. We do this through a continuous, transparent dialog with our clients – before, during and after our engagement. The company was founded by Dr. Curtis Hays Whitson in 1988 and is a Norwegian corporation located in Trondheim, Norway, with local presence in USA, Middle East, India and Indonesia.