Sandstone acidizing of the region surrounding perforations

The objective of this project is to develop a sandstone acidizing model that explicitly considers the flow geometry around perforations. The effect of diverting agent upon the acid injection along the perforation boundary is also modelled.;Assuming the perforation to be ellipsoidal in geometry, we derived a two-dimensional numerical model which describes the single-phase flow of hydrofluoric acid through a perforated sandstone that contains two pseudochemical minerals (representing quartz and aluminosilicates) dissolving at different rates. Different types of formation damage with various levels of permeability reduction are assigned to the corresponding zones surrounding the perforation to account for the effect of the near-wellbore damage on the acid penetration. The pressure distribution, flow rate, and concentration distributions over the regions of interest are obtained by solving the system of governing equations in ellipsoidal coordinates.;Diverting agents composed of finely ground, oil-soluble resin particles are commonly employed in the acidization of vertically heterogeneous reservoirs. They build up a layer of filter cake at the perforation surface during the acid treatment. Using filtration theory, the flow resistance across a layer of diverting agent cake may be quantified, and the flow distribution along the perforation can be formulated as a set of ordinary differential equations.;An approximation of the downhole-multiperforation system is also made in the model. Each perforation takes a paraboloidal section of the formation to account for the more restrictive flow region near the wellbore. The stimulation results calculated from the numerical model are then converted to well productivity as an indication of the acidizing efficiency.;The single-perforation model shows two important findings: the most detrimental damage to the flow capacity of perforations is perforation-crushed zone damage; and, diverting agents play an insignificant role in improving the flow capacity of individual perforations of a well undergoing acid treatment.;The downhole-perforation model shows that the optimum acid treatment for a perforated well depends greatly on the origin of the existing damage and the condition of the perforations. Severe damage detected from a well test may come from a thin crushed zone which requires only a small acid job. Deep penetrating perforations can tolerate shallow drilling damage to some degree and allow the injected acid to achieve full penetration in a deeply damaged zone at a smaller acid volume.