Rock-On-A-Chip Approach Provides New Insight for Well Interferences in Liquids-Rich Shale Plays

Abstract As infill drilling practices become more widely used, operators have observed increased well interference or "bashing" in various shale plays wherein the production of mature wells has been significantly impaired by new infilling wells. Notably, some wells have experienced production decrease of approximately 80% as a result of bashing. One possible explanation is the occurrence of hydraulic communication between the old and new wells because they are most likely connected by the newly created or reactivated natural fractures. However, the mechanisms in which hydraulic communication influences production have not been fundamentally studied. Current technologies, such as pressure-transient analysis or production data mining, do not explicitly provide a physical understanding of the bashing phenomena. This paper discusses a study wherein "Rock-on-a-chip" (ROC) devices were used to investigate hydraulic fracturing fluid invasion and flowback processes. A homogeneous porous network based on the Voronoi tessellation method was patterned on a ROC device. To simulate one aspect of well interference (the impact of an offset well's fracturing fluid entering an existing well's fracture network), two fluid invasion-flowback cycles were performed. It was hypothesized that if the fracturing fluid injected through the new infill enters the fracture networks of existing wells, fracturing fluid would again be forced into the matrix, inflicting damage to the fracture-matrix interface and impairing production. Test results revealed that water saturations in the ROC after the second flowback were higher than those after the first invasion-flowback cycle, suggesting that the second invasion-flowback cycle could indeed damage the matrix and reduce the relative permeability of the oil. Additionally, surfactant clearly improved the displacement efficiencies in the matrix. One experiment shows that surfactant used in the second invasion-flowback cycle even reduced the damage incurred by the first invasion-flowback cycle. The benefit of surfactant has been observed from field results from the Wolfcamp shale, where it was discovered that the EURs (estimated ultimate recoverys) of wells bashed by surfactant-stimulated offset wells were higher than those bashed by non-surfactant-stimulated offset wells. This study shows that fracturing fluid from offset wells can, in fact, damage the productivity of existing wells through connected fractures. In addition, surfactant, when properly selected, can potentially be used to help reduce damage, or even repair previous damage, caused by well bashing.