New Formulation for Sandstone Acidizing That Eliminates Sand Production Problems in Oil and Gas Sandstone Reservoirs

Abstract

The sandstone rocks' integrity and consolidation may be highly affected by the type and the strength of the stimulation fluids. Strong acids such as HF/HCl impair the rock consolidation. The reduction in the sandstone rock consolidation will trigger the sand production. Sand causes erosion of downhole and surface equipment especially when it is produced with high gas flow rates. In this study, gentle stimulation fluids for sandstone that consists of chelating agents and catalyst were proposed. The chelating agents are diethylene triamine penta acetic acid (DTPA) and ethylene diamine tetra acetic acid (EDTA). This is the first time to introduce a catalyst (potassium carbonate) in sandstone acidizing. Potassium carbonate was found to work as a clay stabilizer and catalyst that enhances the dissolution of chlorite clay mineral in the sandstone rock. The objective of introducing the catalyst is to enhance the solubility of the insoluble minerals such as chlorite clay minerals. The change in the mechanical properties of sandstone rocks (Bandera and Berea) was evaluated. The possibility of the formation damage after using seawater-based chelating agents was investigated and compared to HF/HCl mud acid. Coreflooding experiments were conducted to evaluate the effect of these fluids on the rock integrity. Computed tomography (CT) scanner was used to assess the formation damage. Different models were used to predict the sand production possibility after the stimulation with chelating agent/catalyst, and this was compared to the HF/HCl mud acid. The results showed that the permeability of sandstone core increased after acidizing. The reduction in CT-number after acidizing confirmed that no formation damage occurred. Rock mechanics evaluation showed no major changes occurred in the rock moduli and no sand production was observed. The model results showed that using chelating gents to stimulate Berea (BR) and Bandera (BN) sandstone cores did not cause sand production. Applying the same models for cores stimulated by HF/HCl acids indicated high possibility of sand production. The addition of potassium carbonate to DTPA chelating agents enhanced the chlorite clay mineral dissolution based on the inductively coupled plasma (ICP) analysis. Potassium carbonate as a catalyst did not affect the sandstone integrity because it only enhanced the dissolution of chlorite clay minerals (selective dissolution) and did not affect the solubility of carbonate minerals which are the primary cementing materials in the sandstone cores. A new dimensionless number was developed that describes the relation between the number of pore volumes (PVs) contacted the rock and the radial distance from the wellbore.