Fracturing of horizontal wells is responsible for increasing rates and reserves from many reservoirs. Determining the optimum number of treatments, spacing, and eventual completion efficiency is critical to the success of a horizontal well development. This paper details the production analysis techniques required to evaluate the completion efficiency of multiply-fractured horizontal wells. Analytically modeled responses will be compared with actual horizontal well data to verify the technique.
Fracturing horizontal wells results in increased initial well rates and recoverable reserves. Determining the effectiveness and optimum number of fracture treatments to be placed in a horizontal section are critical questions that impact the economics of any play. Production analysis is routinely used to answer these questions, with the production from a horizontal well with associated fracture system modeled by a single fractured vertical well. Matching multiple fracture production with a single fracture model leads to different levels of confidence in the outputted parameters. An analytic model was designed to simulate the behavior of any number of fractures coupled to a single wellbore producing against a constant surface pressure. The model is equally applicable to vertically stacked fractures in discrete reservoirs and to multiple transverse fractures producing from a single reservoir with interference between adjacent fractures, when appropriate boundary conditions are applied. Output from the simulator was then analyzed in a single-phase production analysis package to determine the composite properties of the total reservoir system. The results of the production analysis are compared back to the original input properties to determine the accuracy and validity of the analysis results.
Simulator Model Setup
To assess the accuracy of the rate-transient production analysis model for multiple fractures, two cases were evaluated to investigate the response of multiple fractures draining independent volumetric reservoirs with no production interference. The basic properties that did not vary between simulator runs are listed in Table 1. Each individual fracture is assumed to have infinite conductivity with a closed rectangular drainage area. The simulator was run for two separate cases out to 10 years. Case 1 varied the formation permeability and height for each of the four fractures. Case 2 varied the fracture half-length.
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