Volumetric Fracture Stage Spacing Optimization in Shale Reservoirs Using Rate Transient Analytics – Haynesville, Eagle Ford and Permian Applications
Authors: Aniemena Chigozie , Hailu Thomas , LaBryer Allen , Suter Kirke , Churchwell Nathan 
Published: January 2024

Abstract
This paper addresses the problem of volumetric fracture stage spacing optimization using multi-well rate transient analytics with explicit semi-analytical consideration of stress shadows. A permeability contrast description of the stimulated reservoir volume (SRV) is presented and supported by dual porosity reservoir simulation and RNP diagnostic of late life Haynesville shale production data. The k-contrast drainage volume is characterized by a depth of stimulation Xd adjacent to the hydraulic fracture face in which effective permeability is significantly enhanced relative to unstimulated matrix permeability A key implication of k-contrast SRV in shales is that significant hydrocarbon volumes may remain unrecovered under initial reservoir pressure even in depleted late life wells due to sub optimal fracture stage spacing. Reduced order models (ROM) enable deconvolution of the k-contrast SRV to quantify the effect of stress shadows in terms of fracture stage efficiency. The process also enables estimation of effective stage spacing and effective permeability in the stimulated zone. In the process of ROM parameter estimation, the Boussinesq solution for deformation and stress distribution in a linear elastic half space under load is used to estimate the critical stage length at which stress shadow effect is negligible. SRV deconvolution results enable generation of spacing performance curves for well specific performance sensitivity studies across variations of stage lengths and stress shadow severity. Results from workflow deployment in Permian, Eagle Ford and Haynesville shale plays indicate that wells across all vintages are predominantly in volumetrically suboptimal states. Fracture stage efficiency in company operated Permian, Eagle Ford and Haynesville, is estimated at ∼40% at 200 ft stage spacing. The implication is that at 200 ft, the effective stage spacing in the stimulated reservoir volume is more than twice the designed stage spacing at the surface leaving significant hydrocarbon volumes stranded by stress shadows. Spacing performance curves indicate that tighter stage present recovery upside, however, stress shadows significantly dampen performance scaling thereby increasing the economic burden of achieving volumetrically optimized fracture stage spacing. In Eagle Ford dry (gas window) stage tightening from 250 ft to 150 ft is estimated to yield an EUR uplift of ∼26%. Without stress shadow effects, EUR uplift is estimated at ∼190%. The workflow is extended to perforation cluster level analysis and reveals a maximum cluster efficiency of 10-13% in Eagle Ford and Haynesville and 25% in Permian. Therefore, in this work, tighter stage spacing, and lower perforation density is considered the preferred well performance optimization pathway in line with the findings of a joint industry surveillance project (Hydraulic Fracture Test Site 1- Phase 3). Multi-Pass completions and responsive refracs are proposed to mitigate or compensate for drainage limitations from stress shadows towards transformational uplift in shale well performance.