Recovery of fracturing fluid is considered a critical aspect for achieving production performance that meets the expectations of fracture treatment designs. Fluid recovery is often described simply as a percentage of load recovery on a volume basis, without consideration of the composition of the recovered water. Some of this water may in fact be formation water and not original load water at all. Analysis of the ionic composition of the water can determine whether the recovered water is formation water or treatment water. This paper describes a new model that embodies the physics of flow during back-production of a fracturing treatment and incorporates a chemistry “layer” that allows for matching fracturing fluid flowback compositions. The model accommodates formation water having a separate composition from the fracturing fluid. The movements of sodium, potassium, chloride, sulfate, carbohydrate, boron, etc. are modeled during shut-in and production. The compositions of the produced water calculated by the simulator were compared to field production samples. The process of matching the produced water analyses after the fracturing treatment first required a good match of the produced water rates as a function of both time and the produced gas rates. Reservoir and fracture properties were optimized to match the water production. The ionic composition of the flowback water was then matched by adjusting various parameters that might affect how the water was recovered from the reservoir. The information obtained by adjusting these parameters includes relative permeability curves, capillary pressure curves, and some fracture structure details. Deviations of the model from the observed return profiles indicated areas where the understanding of fluid chemistry and physics of flow might be improved.
展开▼
