(46b) Superstructure-Based Shale Play Water Management Optimization

Water use makes up approximately 10% of the overall shale gas drilling and completion costs.  Even though the Marcellus Shale Play overlies a water-rich region, regulatory restrictions pose considerable logistics challenges that demand sophisticated management strategies.  There are four key aspects for water use in hydraulic fracturing, including source water acquisition, wastewater production, reuse and recycle, and subsequent transportation, storage, and disposal.  The difficulty with surface water acquisition is that withdrawal is only permitted if the minimum flowrate requirement is met.  Once a well is fractured, there is considerable flowback water.  The total dissolved solids (TDS) concentration in the flowback water is the key criterion for determining the volume of freshwater to be blended to make up the source water used for the next fracture.  However, flowback concentration and flowrate profiles exhibit nonlinear behavior.  The flowback water can be reused directly, recycle reused, or disposed.  Of these options, disposal is not economically viable since it requires transporting wastewater to Ohio.  In addition, transportation is a major expense since ninety percent of the trucks required for the completion of a well pad are associated with the fracturing process.  Alternatively, permanent or temporary piping could be considered.  Finally, storage of freshwater and wastewater is also heavily regulated, making storage of wastewater undesirable. 

This presentation optimizes water use life cycle for well pads through a mixed-integer linear programming (MILP) discrete-time representation.  The objective is to minimize transportation cost, treatment cost, freshwater cost, and additional infrastructure cost while maximizing the number of stages to be completed within the time frame.  Assuming freshwater sources, river withdrawal data, location of well pads and treatment facilities are given, the goal is to determine an optimal fracturing schedule, recycling ratio, additional impoundment capacity, and treatment unit installation.  The formulation involves a large number of binary variables mainly due to the long time horizon under consideration.  A case study will be presented to illustrate the effectiveness of the formulation and to identify additional optimization opportunities that can improve the economics of water use.   

References

[1] Horner, P., Halldorson, B., and Slutz, J. 2011. Shale Gas Water Treatment Value Chain - A Review of Technologies, including Case Studies. SPE.

[2] Integrated Pollution Prevention and Control Reference Document on Available Techniques in Common Waste Water and Waste Gas Treatment/Management Systems in the Chemical Sector. European Commission, 2011.

[3] Mendez, C.A., Cerda, J., Grossmann, I.E., Harjunkoski, I., and Fahl, M. 2006. State-of-the-art review of optimization methods for short-term scheduling of batch processes. Computers and Chemical Engineering, 30, 913-946.

[4] Slutz, J., Anderson, J., Broderick, R., and Horner, P. 2012. Key Shale Gas Water Management Strategies: An Economic Assessment Tool. SPE.