Analysis of Multi-Well and Stage-by-Stage Flowback from Multi-Fractured Horizontal Wells

Abstract

Abstract As a result of low gas prices and recent reductions in natural gas liquids prices, unconventional light oil reservoirs remain a primary target for exploration and development in North America. Due to the low permeability of such reservoirs, well-life tends to be dominated by transient linear flow from the matrix to the fractures which may last several years. This flow period is affected by hydraulic fracture properties, therefore operators are looking for new methods to characterize hydraulic fractures, particularly early in the well life. In previous studies by the authors it has been shown that high-frequency flowback flow rates and flowing pressures can be modeled to obtain key hydraulic fracture parameters (i.e. half-length and conductivity). Although commingled data is commonly gathered, technology exists to collect individual stage data. In this work, we advance the analytical procedure presented by Clarkson and Williams-Kovacs (2013b) and Williams-Kovacs and Clarkson (2013c) for analyzing pre- and post-breakthrough of formation fluid during flowback of light tight oil wells by investigating multi-well and stage-by-stage flowback. Studies have shown that there may be significant communication both between stages and between wells on a given pad (or beyond) during the flowback period but not during long-term production. In order to accurately model the flowback period this communication must be accounted for in order to properly assess individual well hydraulic fracture properties. Building upon the analytical models developed previously for single well flowback from unconventional light tight oil wells, we employ the "communicating tanks" concept to account for stage (or inter-well) interaction. Proper allocation and transfer of fluids between stages, if they are communicating, is necessary to ensure that the fracture volume assigned to each stage/well is correct. Our work demonstrates that if individual stage/well flowback data is analyzed without accounting for communication, derived reservoir properties (i.e. fracture halflength) are in significant error. As a result, future well performance predictions, and attempts to optimize fracture stimulations, will also be in error. Our new methods are tested against both simulated and field examples. Stage-by-stage flowback is demonstrated using simulated data, while multi-well flowback will be demonstrated using field data from a multi-well pad.