Curtis Boney & Kazeem Adegbola, Schlumberger Oilfield Services
Dehydration and of the proppant crushing inside the fracture, are the two damage mechanisms mostly recognized as the main contributors to the overall reduction in fractured well productivity. Fracture face damage caused by the fracturing fluid loss through the four fracture faces also creates additional pressure drop that may further reduce the effective wellbore radius. The magnitude of the effect depends on reservoir characteristics, fracture geometry, extent of fluid leakoff into the reservoir, and the viscosity of the fracturing fluid filtrate. A step-by-step approach to predict the fluid loss through the fracture faces during the fracture treatment is explained in this paper. The depth of penetration through the fracture face and the resulting skin values for both the wall building and viscosity controlled leak-off model are determined. This study employs a simple approach that is based on the work of Cinco-Ley & Samaniego that assumes that damage through the fracture face is only caused by fluid saturation changes. The production-forecast simulator used to analyze the effect of various fracture face skin values on oil and gas well productivity agrees with Cinco-Ley and Samaniego study that shows the effect on the effective wellbore radius is negligible when skin value is less or equal to 0.1. In general, the study shows that fracture face damage has a negative effect on productivity only during the wellbore storage and fracture linear flow period. The magnitude of pressure drop increases with increase in reservoir permeability, damage ratio and fracturing fluid leakoff-viscosity.