Abstract
The full potential of a well cannot be ascertained if the proppant is not cleaned up properly after a fracture treatment, particularly in tight gas formations. This paper makes an in-depth evaluation of the impact of fracturing water that remains trapped and unproduced within the proppant pack. This water must be differentiated from the condensed water or water from the reservoir that may be produced. The paper studies some of the main fracturing and reservoir characteristics and identifies variables that have a major impact in reducing the proppant pack conductivity and well production. The major variables studied and analyzed are the fracture fluid and broken gel viscosity, the proppant material, closure stress, fracture conductivity, reservoir pressure, and formation permeability. The paper presents an approach to evaluate and correlate different fracture and reservoir variables to the post-fracture sustained production rate. The study was conducted in two steps; first is a sensitivity study using a full scale numerical simulator and using important reservoir properties from a particular gas field in Saudi Arabia along with the characteristics of typical fluids and proppants pumped during a multistage fracturing treatment in horizontal wells in a low permeability sandstone reservoir. The second step consisted of analyzing the actual post-frac water recovery, test gas rate, and long-term production performance. Comparisons are drawn to establish the variables that impact well productivity the most.
The paper presents important plots to illustrate the flow back behavior and well productivity under different fracturing fluids scenarios. There have been practical steps taken to minimize fracture damage, thereby maximizing well deliverability. The factor impairing deliverability the most is the unbroken gel viscosity. The early time production behavior is a function of broken gel and fracture conductivity. With the improved treatment scheduling, use of better fluids and proppants, and application of novel completion methods, the well performances have been significantly improved in challenging, heterogeneous, and low permeability reservoirs.
