Browsing by Subject "Acid Stimulation"
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Item Evaluation of Perforated Carbonate Cores Under Acid Stimulation(2011-10-21) Diaz, Nerwing JoseAlthough it has been shown that clean perforation tunnels facilitate the evolution of a single, deeper-penetrating wormhole, there are no reported applications of reactive shaped charges in carbonates prior to acid stimulation. The present study was instigated to evaluate the impact of reactive charges on acid wormholing in representative carbonate cores. A set of oil-saturated Indiana limestone and cream chalk cores have been perforated under simulated downhole conditions using either a conventional or a reactive shaped charge of equal explosive load. After CT scanning to eliminate outlying perforations affected by rock property anomalies, the set of cores were subjected to identical acid injection treatments representative of typical carbonate reservoir stimulations. Time to breakthrough and effluent chemistry were both analyzed and recorded. Finally, post-stimulation CT scans were used to evaluate wormhole morphology. The laboratory experiments showed that reactive charges provide wider perforation tunnels with higher injectivity, which is beneficial for any type of stimulation job. Higher injectivity tunnels help to propagate more dominant and straighter wormholes resulting in less acid to break through the cores. This technology has a significant potential when perforating tight formations or heterogeneous intervals, where obtaining clean tunnels with conventional perforators is most challenging. Further research work needs to be done to evaluate if the difference in acid volume to breakthrough observed in the experiments would have a major impact in the field.Item Tracer Fluid Flow through Porous Media: Theory Applied to Acid Stimulation Treatments in Carbonate Rocks(2014-07-29) Zakaria Mohamed Reda, AhmedMost carbonate rocks are heterogeneous at multiple length scales. These heterogeneities strongly influence the outcome of the acid stimulation treatments which are routinely performed to improve well productivity. At the pore scale, carbonate rocks are very complex and exhibit a wide variety of pore classes. However, most of the previous studies reported in the literature have focused on the injection rate, temperature, and fluid properties. This study focused primarily on the effect of carbonate pore structure on the acid stimulation treatments. The objective of this study were to: 1) understand the effect of carbonate pore structure on the acid fluid flow through porous media by the use of thin section analysis, electrical measurements, nuclear magnetic resonance (NMR) and mercury injection capillary pressure (MICP) measurements, and tracer tests; 2) correlate the parameters that govern the tracer fluid flow through porous media to the acid fluid flow through the porous media of the carbonate rocks; 3) quantify the heterogeneity of the carbonate rocks at the pore scale so that the response of the carbonate rock to acid treatments in terms of acid volume needed to propagate the wormhole beyond the damaged zone, the wormhole fractal dimension, and the skin factor evolution during the treatment, can be correlated to the magnitude of pore scale heterogeneity; 4) find correlations between the flowing fraction obtained from tracer tests and the petrophysical parameters obtained from MICP and NMR measurements so that the response of the carbonate rocks to acid treatments can be connected to the basic petrophysical parameters; and 5) build a new methodology to predict the performance of acid stimulation treatments in carbonate rocks using non-destructive tracer tests. In order to achieve the objectives of the study, a carbonate characterization study was conducted first on different carbonate rock types using thin section analysis, electrical measurements, NMR, and MICP measurements. Then, tracer tests were conducted on these carbonates using two different tracer fluids. Following the tracer tests, coreflood experiments using two different acid systems (15 wt% HCl, and emulsified acid formulated at 1 vol% emulsifier and 0.7 acid volume fraction) were conducted at field conditions. The results reveal that the pore scale heterogeneity has a significant effect on the acid stimulation treatments. It was also found that the response of carbonate rocks to acid treatments is correlated to the basic petrophysical parameters and the tracer fluid flow through porous media. A tracer fluid can be injected into a core, or on a field scale, between two wells, or injected into a single well configuration and then flow it back. The analysis of the tracer flowback samples can be then used to predict the acid stimulation treatments in carbonate rocks. This approach helps to optimize the acidizing job to get the ultimate benefit of the treatment.