Evaluation of Multistage Hydraulic Fracturing Techniques for Production Optimization in Naturally Fractured Reservoirs Using Coupled Geomechanics Fracture and Flow Model
Authors: Suppachoknirun Theerapat , Tutuncu Azra N. , Kazemi Hossein 
Published: November 2016

Over the past decade, significant improvements have been made in the stimulation treatment strategy to deal with the unique characteristics and complexities in naturally fractured shale reservoirs. Several well placement patterns have been developed to promote the fracture complexity and reduce the undesirable impacts of in-situ stress alteration in prevention of unfavorable fracture orientation. However, most traditional approaches used to evaluate the fracturing techniques usually relied on the production predicted using fracture model with the fracture geometry pre-determined or pre-established as a fixed pattern. Without a proper model representing the accurate reservoir characteristics, the validity of the evaluation could be significantly undermined.

Operation parameters and the important considerations on fracture propagation - which include the interactions between natural fractures and approaching hydraulic fractures, the impacts of rock properties on fracture growth, the stress shadow due to in-situ stress alteration, and the fluid and proppant transport - are among the critical aspects known to enhance accurate representation of the fracture network geometry and its associated properties. Although an accurate production forecasting tool might be created by integrating the actual fracture geometry in the fluid flow model, having the precise characterization of the reservoir and all parameters are nearly impossible in practice. With availability of reliable data, we used the workflow engineered to develop the fracture network model with the enhanced capability to represent the behavior of the formation. With the grid specifically generated for the modeled DFN, more reliable production forecasting was attainable with reasonable computational and data requirements. Introduced approach and model developed were validated against the field data from a well pad in the Eagle Ford shale formation.

Various hydraulic fracturing patterns were evaluated based on the production analysis. The study case based on the information used indicates that greater initial production rate and total oil recovery could be anticipated when each well in a pad has been fractured in alternating pattern, compared to the others. However, its relatively high decline rate might prevent the alternating technique to be the best option in long-term production. Conventional consecutive pattern appears to be less preferable in terms of production rate and volume recovered. The advantages of the zipper technique include late-time production rate and its relatively larger drainage area.

The recommendations based on the analysis and evaluation performed using the approach presented in this study can be beneficial to the operators in terms of optimizing fracturing design and production. The approach itself can also be efficiently used to evaluate a design for any shale reservoir since a simulated fracture network is inclusive of formation characteristics in the area. This could help to prevent an unexpected adverse circumstance pertaining to the unsuitable design, avoiding both CAPEX and operation expenses.