In the present work, the stratigraphic distribution of the Muerto Formation was evaluated, with the objective of identifying the lithological facies, using petrography studies through thin sections and gamma ray analysis for an elevation. The section under study crops out on the eastern margin of the Amotape Mountains. Stratigraphic, facies, and sedimentological analyzes are methods of vital importance to evaluate the potential of an unconventional reservoir. These studies make it possible to predict the spatial distribution of facies, as well as to identify the areas with the most favorable petrophysical properties for the prospecting and exploitation of hydrocarbons, in addition to being able to estimate with greater certainty the volume of hydrocarbons in situ and the optimal completion of a well.
Top1. Introduction
Stratigraphic, facies and sedimentological analyzes are methods of vital importance to evaluate the potential of an unconventional reservoir. These studies make it possible to predict the spatial distribution of facies, as well as to identify the areas with the most favorable petrophysical properties for the prospecting and exploitation of hydrocarbons, in addition to being able to estimate with greater certainty the volume of hydrocarbons in situ and the optimal completion of a well. (Kietzmann & Vennari, 2013). Unconventional deposits have been commercially exploited for approximately 20 years in various basins around the world, but in recent years they have sparked renewed interest. (Barreriro & Masarik, 2011) Because total gas production figures will likely increase as new unconventional gas reserves are discovered and quantified and extraction methods improved. Furthermore, it is very possible that unconventional gas reserves greatly exceed conventional gas reserves. The potential that is beginning to be glimpsed in unconventional hydrocarbons, and particularly in unconventional gas, is generating the conviction that the world is on the verge of a true energy revolution. (Luis & Moncayo, 2013)
In Peru there are 18 sedimentary basins with potential for hydrocarbon exploration. All these basins are related, to a greater or lesser degree, to the processes of plate tectonics and uplift of the Peruvian Andes.(Ministerio de Energia y Minas, 2001) 8 of the 18 basins are totally or partially offshore, they are: Tumbes Progreso, Talara, Sechura, Salaverry, Trujillo, Lima, Pisco and Mollendo. The remaining 10 basins are located on the mainland: Lancones, Moquegua, Santiago, Bagua, Huallaga, Ene, Titicaca, Marañón, Ucayali and Madre de Dios. (Ministerio de Energia y Minas, 2001) 4 of these basins concentrate 98% of Peru's exploratory wells, which are the Talara, Sechura, Marañón and Ucayali basins. (Perúpetro, 2017)
In the North of Peru, in the department of Piura, is the Lancones basin, which is the study basin for this project, where favorable conditions exist for a thick sequence of Cretaceous sediments, with diverse horizons rich in organic matter, potential reservoirs in the basal sandstones (Gigantal formation) and attractive folding structures for hydrocarbon exploration. However, it is estimated that the presence of nearby igneous bodies and associated hypoabyssal volcanism may be a risk factor for exploration.(Villar & Pardo, 2010a)
Within the Lancones Basin is the Muerto Formation, which is presumed to be the main source rock of the Lancones Basin, Northwestern Peru. (Álvarez P., 1987), and it is also considered the First Non-Conventional Play Reservoir in this country. (Morales et al., 2018b) The Muerto Formation is of Albian age (Cruzado, 1985), related to a regional marine transgression (Uyen & Valencia, 2002). The Muerto Formation is characterized by the deposition of black clayey fossiliferous limestones with a strong smell of petroleum in the fractures and with pelagic foraminifera. (Fernández et al., 2005)
Petroleum geochemistry is a fundamental factor in understanding the properties of the source rock, such as its productive and non-productive zones, oil migration and oil field development. For this, parameters such as Total Organic Carbon (TOC) were used, which indicates the total amount of organic matter; S1 (mgHC/g rock) records the free hydrocarbons that are released from the rock sample without separating the kerogen during the first heating stage at a temperature of 300°C, and S2 (mgHC/g rock) records the hydrocarbons that are released from the sample during the second stage of programmed heat application of the pyrolysis process that represents the milligrams of residual hydrocarbons contained in one gram of rock, therefore indicating the potential amount of hydrocarbons that the source rock could continue to produce if the thermal maturation process continued. (McCarthy et al., 2011) Previous studies have shown that the geochemistry of the Muerto Formation acts as an excellent source rock. This source rock has a TOC of 0.8 to 4.0 wt.% in calcareous lithology, S1 of 0.05 to 1.56 (mg/g) and S2 of 0.8 to 0.09 to 64.8 (mg /g) (Morales, Porlles, Rodriguez, Taipe, & Arguedas, 2018) which indicates that the organic matter is autochthonous, behaving as a good source rock with type III kerogen and capable of generating gas. By thermally maturing, the rock in the Muerto Formation is mature and located in the oil window. (Morales et al., 2018b)