Pre-Salt Carbonate Reservoir Analog Selection for Stimulation Optimization

Abstract

Hydrocarbon production optimization in Pre-Salt carbonate reservoirs is a main focus for oil and gas research in Brazil. Stimulation treatment design optimization requires good knowledge of the reservoir properties and excellent understanding of the interaction between rock formation and treating fluid. This paper investigates these interactions through laboratory tests determining the compatibility of fluids used in matrix stimulation with different Pre-Salt carbonate rock types. The objective of this work is to relate the geology, petrophysics, and geomechanics of the Pre-Salt reservoirs to their expected stimulation response. Because of the difficulty in obtaining downhole cores and the destructive nature of most tests, the study focused on samples collected from a Pre-Salt carbonate analog: the Coquinas formation (Schafer 1973) from the Sao Miguel quarry, northeast Brazil (Chagas de Azambuja Filho et al. 1998). A thorough geology-based study of the Coquinas formation, including routine core analysis (FZI) microtomography, and thin section study was conducted. Usually these grain-supported carbonates show different amounts and types of primary porosity, closed and reopened by multiple diagenetic phases. Throughout the 25-m thick Coquinas reservoir, five rock types in 13 layers with permeability ranging from microdarcy to almost 1 darcy were identified. All rock types were subjected to routine mineralogy evaluation and various petrophysical, geomechanical, and spectroscopic measurements. Six of the thirteen layers were selected to perform core flow tests with a viscoelastic surfactant technology based diverting acid fluid (Al-Mutawa et al. 2005; Chang et al. 2001; Samuel et al. 1997). This is the first extensive study reporting the efficiency of a viscoelastic diverting acid system in the Pre-Salt analogue Coquinas carbonate formation outcrop cores. Spectroscopic measurement showed wormhole creation and, in some cases, rock texture alteration or fine migration. Through the study we identified the flow units and characterized the rock behavior when chemically stimulated. The conclusions from this study will enable us to tailor and optimize stimulation treatments of Pre-Salt carbonate reservoirs. Introduction The offshore Pre-Salt in Brazil comprises a group of recently discovered fields with promising oil reserves in the Coquinas formation or the above the microbialites section. For example, Lula (ex-Tupi) field, the lead field of the Santos cluster, is believed to hold between 5 to 8 billions barrels of oil equivalent (Beltrao et al. 2009). The Pre-Salt reservoirs are currently the focus of research in Brazil; however, the scarceness of downhole samples collected makes destructive tests very difficult to perform, and so analysis must be performed on analogues. The onshore Coquinas formation from northeast Brazil is taken here as analogue of the Pre-Salt carbonates.

Evaluation of fluid–fluid and rock–fluid interfacial interactions using silica nanofluids and crude oil for a deepwater carbonate pre-salt field

“…The Brazilian Pre-Salt fields are among the biggest oil discoveries in recent decades. For example, the Lula Field in the Santos Basin contains 8.3 billion barrels of oil equivalent reserves [13] with 28°API oil and high salinity brine (23%) [14]. Most chemicals used in chemical EOR processes tend to degrade and lose their effectiveness under extreme conditions.…”

Experimental study of the effect of carbonated brine on wettability and oil displacement for EOR application in the Brazilian Pre-Salt reservoirs

“…The Brazilian carbonate Pre-Salt fields, which are among the greatest oil discoveries of the last decades, are natural offshore candidates for the application of EOR/CCS. Lula Field in Santos Basin contains 8.3 billion barrels of oil equivalent reserves (Formigli, Pinto, and Almeida 2009) with 28 °API oil, high salinity (23%) brine and gas to oil ratios (GOR) of up to 27 scf/stb with CO 2 concentration up to 12% (Pepin et al 2014;Pizarro, De Santanna, and Branco 2012). The main features for the application of CCS in Lula Pre-Salt field were presented elsewhere (de Almeida et al 2010).…”

Investigation of the Key Parameters Affecting Wettability of a Brazilian Pre-Salt Crude Oil and Brine on Pure Minerals Through Statistical Analysis

“…According to the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), the fields in the Campos and Santos basins have aided in the 25% increase of Brazil's oil production representing over 50% of the total production at the present time (ANP, 2018). However, these reservoirs consist of complex heterogeneous carbonate rocks, light and medium oils, and brine salinities over 200,000 ppm (Pepin et al, 2014;Pizarro & Branco, 2012). This unique environment represents a challenge in terms of wettability assessment and reservoir modeling.…”

“…This unique environment represents a challenge in terms of wettability assessment and reservoir modeling. While there are descriptions of the Pre-Salt rocks in the literature (Pepin et al, 2014;Teles et al, 2016), there is no detailed data describing their wettability.…”

“…However, none of these included brines of salinity and hardness as high as that of the Pre-Salt reservoirs. Also, none of them focused on the minerals which are the major components of Pre-Salt rocks (Pepin et al, 2014). A recent study (Al-Khafaji & Wen, 2019) considered the wettability of different crudes on limestone and dolomite rocks as a function of brine salinity.…”