The deep and hard limestones found off-shore Brazil are being extensively evaluated, and some of them would require stimulation to enable commercial development. The main objective of this paper is to discuss the feasibility of acid fracturing stimulation in hard carbonates. Laboratory test are performed to verify whether an acid-induced fracture can withstand the high effective normal stresses expected during the exploitation stage of pre-salt development, keeping an acceptable conductivity. There is no agreement in the technical community regarding the survival of an acid fracture at closure stress greater than 5,000 psi. However, the experience that leads to this controversy is mainly based on: (1) wells on land and, (2) few published tests on rocks with mechanical properties compatible with those depths. An experimental program has been designed to evaluate these chances of acid fracture survival. A few initial essays with samples of these carbonate rocks have shown significantly higher rock strength than those commonly found in the literature. Initially, the Nierode & Kruk correlation (1973) is used to predict fracture conductivity behavior. Both mechanical strength and dissolved rock equivalent conductivity are measured from outcrops, and from soft and hard offshore carbonates samples. This work reports the results with outcrops and reservoir samples, in order to assess whether the adopted experimental methodology is consistent and reproducible. Some topics about acid fracture conductivity prediction are also addressed. Further research should be performed with pre-salt rock samples using the same procedures. Copyright 2012, Society of Petroleum Engineers. 361372Schlumberger,Coiled Tubing and Fracturing Energy Services, Inc.,Baker Hughes,Dorf Ketal,Mission Well ServicesAbass, H.H., Acid fracturing or proppant fracturing in carbonate formation? A rock mechanic's view SPE Technical Conference and Exhibition. San Antonio, TX, 24-27 Set 2006, , SPE 102590Alkattan, M., An experimental study of calcite and limestone dissolution rates as a function of pH from -1 to 3 and temperature from 25° to 80°C (1998) Chemical Geology, 151, pp. 199-214Recommended practices for evaluating short term proppant pack conductivity (1989) API Recommended Practice, 61. , American Petroleum Institute. Washington, DCAntelo, L.F., Surface Characterization and its Effect on Fracture Conductivity in Acid Fracturing SPE Hydraulic Fracturing Technology Conference, The Woodlands, TX, USA, 2009, , SPE119743Azevedo, C.T., Rosolen, M.A., Neumann, L.F., Challenges Faced to Execute Hydraulic Fracturing in Brazilian Pre-Salt Wells ARMA 10-212. 44 th US Rock Mechanics Symposium and 5 th U.S.-Canada Rock Mechanics Symposium, Held in Salt Lake City, UT June 27-30, 2010Bale, A., Smith, M.B., Klein, H.H., Stimulation of carbonates combining acid fracturing with proppant (CAPF): A revolutionary approach for enhancement of sustained conductivity and effective fracture half-length SPE Annual Technical Conference and Exhibition, Florença, Italia. Setembro 2010, , Paper SPE 134307Barron, A.N., Hendrickson, A.R., Wieland, D.R., The Effect of Flow on Acid Reactivity in a Carbonate Fracture (1962) J. Pet. Tech., 22 (5), pp. 409-418Beatty, C.V., Characterization of Small Scale Heterogeneity to Predict Acid Fracture Performance SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, EUA. Janeiro 2011, , SPE 140336. DOI 10.2118/140336-MSBeltrão, R.L.C., Challenges and new technologies for the development of pré-salt cluster, Santos basin, Brazil OTC - Offshore Technology Conference, 2009, Texas (U.S.A.), , Houston: OTC 19880Broaddus, G.C., Knox, J.A., Fredrickson, S.E., Dynamic Etching Tests and Their Use in Planning Acid Treatments SPE Oklahoma Regional Meeting, Oklahoma (U.S.A.), 1968, , SPE 2362Carminatti, M., Dias, J.L., Wolff, B., From turbidites to carbonates: Breaking paradigms in deep waters OTC - Offshore Technology Conference, 2009, Texas (U.S.A.), , Houston: OTC 20124Daneshy, A., Valkó, P., Norman, L., Well Stimulation (1998) Petroleum Well Construction, p. 506. , Chapter 17 Edited by M. Economides WileyDarin, S.R., Huitt, J.L., Effect of a partial monolayer of propping agent on fracture flow capacity (1960) Trans. AIME, 219, pp. 31-37Deng, J., Zhu, D., Hill, A.D., A Theoretical Study of Acid Fracture Conductivity under Closure Stress SPE Annual Technical Conference and Exhibition, Nova Orleans, LA, EUA. Outubro 2009. DPlot Graph Software, HydeSoft Computing, 2001-2011, Vicksburg, Mississippi, , SPE 124755Economides, M.J., Nolte, K.G., (2000) Reservoir Stimulation, pp. 5-10. , 3 ed., Londres, UK, John Wiley & SonsFormigli, J.M., (2008) O Pólo Pré-sal Da Bacia de Santos: Desafios Tecnológicos para A Área de Engenharia, , www.dep.fem.unicamp.br/arquivos, Site internet 11/06/2008. Acessado em 26/09/2009Fredrickson, S.E., Stimulating Carbonate Formations Using a Closed Fracture Acidizing Technique SPE East Texas Regional Meeting, 21-22 April 1986, Tyler, Texas, , SPE 14654 inGong, M., Lacote, S., Hill, A.D., A new model of acid fracture conductivity based on deformation of surface asperities (1999) SPE Journal, 4 (3), pp. 206-214. , SetembroLiu, E., Effects of fracture aperture and roughness on hydraulic and mechanical properties of rocks: Implication of seismic characterization of fractured reservoirs (2005) J. Geophys. Eng., 2, pp. 38-47. , DOI 10.1088/1742-2132/2/1/006Lu, C., Some notes on the study of fractals, in fracture 5th Australasian Congress on Applied Mechanics, ACAM, Brisbane, Australia, 2007Malagon, C., Pournik, M., Hill, A.D., The texture of acidized fracture surfaces: Implications for acid fracture conductivity (2008) SPE Production & Operations, 23 (3), pp. 343-352McGlothlin, B.B., Huitt, J.L., Relation of Formation Rock Strength to Propping Agent Strength in Hydraulic Fracturing SPE Petroleum Conference, Tulsa, Oklahoma, 1965, , SPE 1131Mou, J., Zhu, C., Hill, A.D., Acid-Etched Channels in Heterogeneous Carbonates - A Newly Discovered Mechanism for Creating Acid-Fracture Conductivity (2009) SPE Journal, 15 (12), pp. 440-1416Mumallah, N.A., Reaction rates of hydrochloric acid with chalks (1998) Journal of Petroleum Science and Engineering, 21, pp. 165-177. , abrilNavarrete, R.C., Miller, M.J., Gordon, J.E., Laboratory and theoretical studies for acid fracture stimulation optimization 1998 Permian Base Oil and Gas Recovery Conferency, Midland, Texas, Março 1998, , SPE 39776Neumann, L.F., Case study of multiple hydraulic fracture completion in a subsea well, Campos basin (2010) SPE Drilling & Completion, 25 (1), pp. 113-122. , SPE 98277-PA. Março DOI 10.2118/98277-PANeumann, L.F., De Oliveira E Sousa, J.L.A., Brandão, E.M., Acid Fracturing: New insigths on acid etching patterns from experimental investigation SPE Hydraulic Fracturing Technology Conference, The Woodlands, TX, Feb. 2012, , SPE 151481 inNeumann, L.F., (2011) Experimental Investigation on Generation, Visualization, and Evaluation of Conductivity of Acid Fractures on Microbial Carbonates, p. 242. , MS thesis. Universidade Estadual de Campinas, Campinas, SP, Brasil, 2011 in portugueseNierode, D.E., Kruk, K.F., An evaluation of acid fluid Loss Additives, Retarded Acids, and Acidized Fracture Conductivity SPE Annual Metting of AIME, Las Vegas, NE, 1973, , SPE 4549Pournik, M., Zou, C., Small-scale fracture conductivity created by modern acid-fracture fluids SPE Hydraulic Fracturing Technology Conference, College Station, TX, EUA. Janeiro 2007, , SPE 106272Pournik, M., Zhu, D., Hill, A.D., Acid-Fracture Conductivity Correlation Development Based on Acid-Fracture Characterization 8th European Formation Damage Conference, Scheveningen, Holanda, 2009, , SPE122333 inRoberts, L.D., Guin, J.A., The effect of surface kinetics in fracture acidizing (1974) Soc. Pet. Eng. J., pp. 385-395. , AgostoRoberts, L.D., Guin, J.A., A new method for predicting acid penetration distance (1975) Soc. Pet. Eng. J., pp. 277-286. , AgostoRuffet, C., Fery, J.J., Onaisi, A., Acid Fracturing Treatment: A Surface-Topography Analysis of Acid-Etched Fractures to Determine Residual Conductivity (1998) SPE Journal, 3 (2), pp. 155-162Van Domselaar, H.R., Shols, R.S., Visser, W., An analysis of acidizing process in acid fracturing (1973) Soc. Pet. Eng. J., 255, pp. 239-250Verberg, R., Ladd, A.J.C., Simulation of chemical erosion in rough fractures (2002) Physical Review E, 65. , DOI: 10.1103/PhysRevE.65.056311Williams, B.B., Characterization of liquid/solid reactions - The hydrochloric acid/calcium carbonate reaction (1970) I. and E. C. Fund, 9, pp. 589-596. , novWilliams, B.B., Nierode, D.E., Design of Acid Fracturing Treatments (1972) J. Pet. Tech., 24, pp. 849-859. , JulhoWilliams, B.B., Nierode, D.E., Characteristics of acid reaction in limestones formations (1971) Soc. Pet. Eng. J., pp. 406-418. , Dez