Reducing Carbon Footprint of Matrix Acidizing in Carbonate Formations. How Much Acid Do We Really Need to Pump?

Abstract

Abstract With uncertain global economic conditions and calls for lowering carbon footprint, optimizing carbonate matrix acidizing along with other operations is crucial for operators and services companies. Accurate modeling of wormhole growth is inevitable to optimize acid placement in the field. In this study, a field-scale carbonate acidizing model tuned and validated against 600+ linear and radial experiments is presented to optimize/improve field treatments. Unlike previous semi-empirical models, this model presents the wormhole velocity as a function of Darcy's velocity. This model was validated against a huge number of linear HCl experiments with various temperatures, acid concentrations, rock types, and core dimensions. Both internal and published data were used. The upscaling from linear to radial flow was based on changing the flow area and the number of wormholes as a function of acid progression in the formation. The upscaled model was validated against radial experiments and field observations. The results show that the model can accurately predict acid performance under field conditions. The results of this model have revealed that limestone and dolomite formations can be stimulated using HCl acid volumes as low as 50 gal/ft. For limestone formations, low volume acidizing operations (50 gal/ft.) can result in skin as low as −3.1 (well-flow efficiency (WFE) of 1.6). On the other hand, moderate-high volume acidizing operations (100 gal/ft.) will result in skin of −3.7 (WFE of 1.8). The effect of temperature on the performance increases as the volume of the injected acid increased. At very low injection rates (long horizontals/ low Kh zones), pumping 100 gal/ft. will create 5 ft. long and 2 ft. long wormhole at 100°F and 300°F, respectively. For the dolomite formations, pumping 50 gal/ft. of 15% HCl at 150°F will result in skin of −2.7 (WFE of 1.5), while pumping 100 gal/ft. will result in skin of −3.1 (WFE of 1.6). At 75°F, the injection of 100 gal/ft. will create short wormhole (2.8 ft.) in dolomite and long wormhole (12.6) in limestone. This is because the acidizing process is reaction rate limited at low temperature dolomite. This paper presents a new carbonate matrix acidizing model to optimize carbonate acidizing field treatments. Carbonate wells can be stimulated using low acid volumes with little effect on well performance. That will reduce both the cost and the carbon footprint of those operations.