--> --> Insights Into Reservoir Dynamics of the Montney Formation From Analysis of Flowback and Produced Fluids, Petrophysics, and Fluid Compatibility Modeling

2018 AAPG International Conference and Exhibition

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Insights Into Reservoir Dynamics of the Montney Formation From Analysis of Flowback and Produced Fluids, Petrophysics, and Fluid Compatibility Modeling

Abstract

Analysis of fluids and solids from flowback waters from forty Montney Formation horizontal well completions in Western Canada, when coupled with petrophysical analysis of core, provides insights into the dynamics of the reservoir and enables strategies for optimising well completions, production, and well surveillance. The chemistry and volume of flowback fluids following well completions is a complex product of mixing of connate water and fracturing fluid and fluid-rock interactions that includes precipitation and dissolution of minerals, ion exchange, imbibition, and diffusion/osmosis. The chemistry and volume of flowback waters varies with the completion program, reservoir geology, and hence geographically and stratigraphicially. In detail; however, the flowback volume and chemistry varies with a plethora of variables, many of which are multicollinear. The cumulative volume of flowback fluid is about 10% to 30% of the volume injected. The proportion of connate water in the flowback water, based on conserved element and isotope analyses, varies from about 10% to 60% and the ratio of connate water increases with time. The TDS values of Montney flowback fluids range up to 228 000 mg/L, with Cl and Na ions accounting for about 75% to 95% of the total dissolved solids. Other major ions are Ca, K, Mg Sr, and locally SO4. With cumulative flowback, the total dissolved solids (TDS) and most ions, for all studied Montney wells, increases linearly, although the rate of increase varies between wells, members, and geographic area. Deviation from the linear increase in TDS and conserved elements with cumulative flowback, reflects opening or closing of the fracture system(s) with declining pore pressure, variation in connate water chemistry/fluid rock interactions in the reservoir accessed in different completion stages, and/or fractures that have grown out of zone. Geochemical modeling suggests that the ions that deviate from the linear mixing model, predicted by the conserved elements and isotopes, are impacted by fluid-rock interactions including precipitation, dissolution, and/or ion exchange reactions. Analysis of connate water and fluid saturations indicate that most of the unconventional Montney Formation is below irreducible water saturation. The spontaneous and forced imbibition/osmosis of drilling and completion fluids results in significant fracture skin damage, resulting in a decreased relative matrix permeability by up to two orders of magnitude.