Increasing overall permeability of organic shale is the key to increase its hydrocarbon recovery. The nano-darcy permeability of organic shale currently precludes the field application of all proposed methods to increase hydrocarbon recovery by gas or liquid flooding. A new technique developed by the authors and named "Optimized Modified Zipper Frac" (OMZF) avoids this limitation by using stress shadowing to lessen the magnitude difference between horizontal stresses in the stimulated reservoir volume (SRV) before it gets fractured, thereby maximizing the SRV's complexity and overall permeability.
When OMZF is used to recover hydrocarbons from shale, a stage of hydraulic fractures (preferably fat-propped fractures) are first created near the toe of a horizontal well. A second stage is then created and ballooned on the same well at a designed distance from the first stage. Then, a third stage is created along an adjacent well midway and staggered between stages one and two. This operational sequence is then repeated. The first two stages (along the first well) are ballooned to produce a stress shadow strong enough to maximize the complexity of the third stage (along the second well) when it is fractured. A detailed design process is presented and includes different scenarios to optimize zipper fracturing.
Reservoir simulations and field applications confirm that Texas Two-Step and Modified Zipper Frac will in fact increase the complexity and permeability of nearby fractured zones. Optimized Modified Zipper Frac will maximize these increases by optimizing the net pressure and fracture dimensions, thereby strengthen the stress shadow on zones before fractured. This will increase near wellbore complexity, overall permeability, hydrocarbon recovery, and may also allow gas injection as an EOR application. These simulations strongly suggest that unlike experimental methods that propose flooding shale cores with different fluids, OMZF is field applicable. Any increased production resulting from this work will help the petroleum industry to meet its ever-increasing demand.