Vaca muerta

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Vaca Muerta is a geologic formation located at Neuquen Basin in central west Argentina.Prior to 2010, It was a well-known basin for conventional reservoirs. In recent years, it has been a place of great interest for major oil and gas companies for its unconventional resource potential.The shales at the Vaca Muerta formation were deposited in the Jurassic-Cretaceous period and are known as a world-class source rock [1]. As a recent decline in production of the conventional reservoirs this shale has become very important. Today with the technological development of shale tight oil and shale gas this formation has become one of the world’s largest shale plays in the world.

Figure 1. Prospective Shale Basins in Argentina

Formation

The Vaca Muerta shale of Jurassic and cretaceous age is considered the primary source rock of conventional oil production in the Neuquen Basin.The formation consists of marine black shales, fine-grained mudstones, marls and limestones that were deposited in an anoxic environments[2]. The formation is a highly organic rich shale that has a total organic carbón (TOC) levels from 1.0 to 8.0 (wt%)[3].The depth of Vaca Muerta ranges from 3,000 to 10,000 feet and contains an overpressure condition of 0.6 to 1.0 psi/ft [3]. These characteristic make Vaca Muerta a well-known productive unconventional play. As discussed by Converse-Gomez in 2017,the depositional system that is part of the Vaca Muerta formation is called Quintuco-Vaca Muerta from the early Tithonian which started due to a marine transgression from the pacific ocean[3]. Vaca Muerta represents deep marine deposits and Quintuco represents shallow marine deposits. In seismic data the top of the Quintuco formation is well defined and easy to identify while the top of the Vaca Formation is harder to identified as it grades over the carbonates in the Quintuco formation[3].

Stratigraphy

The Neuquen is a retroact foreland basin located in west central Argentina[4]. It spreads over an area of 66,900mi2[5].It was driven by extensional forces during the late Triassic and early Jurassic from the Permian-Triassic orogenic belt[4]. The shales found in the Vaca Muerta are from deep marine sediments that were deposited in a period of early post rift and sea level highstands. These led to the preservation of organic rich shales which are the primary source rocks in the basin. They consist of mudstones, marls and limestones[6] .

The Neuquen basin is surrounded by the Andes Mountains on the west and on the east and southeast by the Colorado Basin and North Patagonian Massif[7].The western part of the basin is more complex and has several thrust features, where the most proliferous part of the basin resides. The Vaca Muerta formation thickens from east to west and is composed of three main sections – the lower, middle and upper members[6] .The main differences between the sections are the changes in lithology, sedimentary structures and depositional environment[6]. The lower member represents the most important part of the formation because it has major accumulation of hydrocarbons[6].

Figure 2. Neuquen Basin Stratigraphy

Production

The Vaca Muerta formation is a petroliferous formation, with recoverable reserves estimated at 16.22 billion barrels of oil[8].Today with the technological development the Vaca Muerta has become a potential productive unconventional play [8]. The vaca muerta once considered too tight to produce viable oil has awaken interest by numerous important oil and gas companies which have exploited the productivity of the basin through horizontal and hydraulic fracturing completion techniques[8]. In 2018, Argentina’s Vaca Muerta production can reach 113,000 boe/d.
figure 3. Argentina Production

Seismic

As discussed by Lipinski in the year 2014, the Vaca Muerta formation based on regional 2D and 3D seismic data shows transgressive and regressive cycles of 2nd order and they are built up by 5 higher frequency 3rd order depositional sequences[9]. The clinoform topsets, foreset and bottomsets found at the Vaca Muerta are marked by a high amplitude reflector that is interpreted as the maximum flooding surface, they are followed by low angle and low amplitude regressive seismic facies that correspond to a prograding clinorform [9]. The clinoforms show a medium amplitude which correlate to different stratigraphic patterns in various parts of the basin. As a result, facies distribution can give insight on the prediction of a reservoir and it can also be useful to delineate an Unconventional sweet spot [9]. In addition, Vaca Muerta formation internal reflectors have very low impedance making seismic geomorphology limited [9]. However, it has been possible to identify aeolian sand dunes, oyster banks, and clinoform slope-break progradation trends that are captured on (Figure4). These images provide invaluable information that define the depositional systems that help understand the lithology distribution of the Vaca Muerta[9].

Figure 4. Seismic geomorphic techniques [9].


Microseismic Monitoring

Microseismic monitoring is an important key for shale exploration. Vaca Muerta formation use of microseismic monitoring has helped to understand the completions of the reservoir[10]. The Microsesimic Monitoring informs horizontal wellbore direction, stage spacing and landing depth[10]. Furthermore, focal mechanisms have been important to understand the distribution of stress at the Vaca Muerta to refine completions in the future[10].

External Links

  1. Editors, OGJ.(2017, May4) WoodMac: Argentina's Vaca Muerta Production to Reach 113,000 Boe/d by 2018. Oil & Gas Journal
  2. Olmos, Sebastian.(2017, Feb 20)Challenges in Vaca Muerta: Tecpetrol Experience in the Exploration and Appraisal of the Play
  3. Mosse, Laurent, et al.(2016, January) Vaca Muerta Shale - Taming a Giant. Slb.com
  4. The Neuquén Basin: Sequence Stratigraphy of Vaca Muerta Formation.Seal Capacity of Different Rock Types - AAPG Wiki

References

  1. Fantin, E.A. (2014,Aug25) “Vaca Muerta Stratigraphy in Central Neuquén Basin: Impact on Emergent Unconventional Project.” Drilling Fluids Design and Management for Extended Reach Drilling - OnePetro, Society of Petroleum Engineers, 25 Aug. 2014, www.onepetro.org/conference-paper/URTEC-1923793-MS
  2. Dominguez, E.A.(n.d). “Organic-Rich Stratigraphic Units in the Vaca Muerta Formation, and Their Distribution and Characterization in the Neuquén Basin (Argentina).” Proceedings of the 4th Unconventional Resources Technology Conference, 2016, doi:10.15530/urtec-2016-2456851.
  3. 3.0 3.1 3.2 3.3 Convers-Gomez (2017).“Prediction of Reservoir Properties for Geomechanical Analysis Using 3-D Seismic Data and Rock Physics Modeling in the Vaca Muerta Formation”. Colorado School of Mines, ProQuest Dissertations Publishing, 2017. 10269482.
  4. 4.0 4.1 Rainoldi, A. L., E.A.(2014) “Large-Scale Bleaching of Red Beds Related To Upward Migration of Hydrocarbons: Los Chihuidos High, Neuquen Basin, Argentina.” Journal of Sedimentary Research, vol. 84, no. 5, 2014, pp. 373–393., doi:10.2110/jsr.2014.31.
  5. “Technically Recoverable Shale Oil and Shale Gas Resources: Argentina.” Eia U.S. Energy Information Administration, (Sept. 2015), www.eia.gov/analysis/studies/worldshalegas/pdf/Argentina_2013.pdf.
  6. 6.0 6.1 6.2 6.3 Garcia,N. E.A.(2013) “Vaca Muerta Shale Reservoir Characterization and Description: The Starting Point for Development of a Shale Play with Very Good Possibilities for a Successful Project.” Unconventional Resources Technology Conference, Denver, Colorado, 12-14 August 2013, 2013, doi:10.1190/urtec2013-090.
  7. “Technically Recoverable Shale Oil and Shale Gas Resources: Argentina.” Eia U.S. Energy Information Administration, (Sept. 2015), www.eia.gov/analysis/studies/worldshalegas/pdf/Argentina_2013.pdf.
  8. 8.0 8.1 8.2 Bilbao,(2016). High-Resolution Chemostratigraphy, Sequence Stratigraphic Correlation, Porosity and Fracture Characterization of the Vaca Muerta Formation, Neuquen Basin, Argentina. 2016, dspace.library.colostate.edu/bitstream/handle/11124/170104/HernandezBilbao_mines_0052E_10991.pdf?sequence=1.
  9. 9.0 9.1 9.2 9.3 9.4 9.5 Lipinski E.A.(2014). “Vaca Muerta Seismic Stratigraphy and Geomorphology:Regional Architectural Trends for Unconventional Exploration.”
  10. 10.0 10.1 10.2 Curia, David, E.A.(2018). “Microseismic Monitoring of Vaca Muerta Completions in the Neuquén Basin, Argentina.” Micro Seismic, Apr. 2018, www.microseismic.com/wp-content/uploads/2018/04/3704_TSS_Curia1-1.pdf.