Unconventional Gas for Increasing Security of Natural Gas Supply in Croatia
DSc Daria Karasalihović Sedlar
Associate Professor
University of Zagreb, Faculty of Mining, Geology & Petroleum Engineering,
Department of Petroleum Engineering,
Pierottijeva 6, Zagreb, Croatia
Abstract:
Security of oil and gas supply is the main goal of energy policy. Analysis of possibilities of primary
energy resources supply, related to natural gas due to its high share in energy consumption, and
particularly because of its strategic role in each country’s economy, so in Croatian, represents the
base of state security in natural gas supply. Unconventional gas could be step toward increase of
security of supply for Croatia. The development of unconventional reservoirs could enable the
reduction of overall European energy import dependence. Due to contemporary technology and gas
prices, gas production from unconventional reservoirs is much more complex comparing to gas
production from conventional reservoirs. Croatia as other European countries is facing necessity for
adoption of legislative framework for environmentally sustainable unconventional gas reservoirs
exploration and production. On the other hand, integration into Mediterranean energy circle could
diversify natural gas supply and increase security of supply.
Keywords: natural gas, security of supply, unconventional gas, energy security, gas market
Introduction
Global energy market trends and increasing role of geopolitics in energy supply, especially in
Europe, are reason why energy security becomes the main task of energy policy. Security of natural
gas supply in Croatia should be based on three main activities that should be introduced in natural
gas sector. Primarily, technology advances in enhanced oil recovery on mature fields and
unconventional gas production should be activated. Secondly, new exploration activities onshore
Panonian Basin and offshore Adriatic should be launched. Tertiary, analysis of critical energy
infrastructure and determination of system for continuous monitoring of security of gas supply
along with actions for preventing and eliminating disruptions of supply should be implemented.
Due to maturity of domestic oil and gas fields in the Republic of Croatia, gas production is
decreased and new exploration and discovery of new deposits is necessary. Many Croatian
geologists think that in the Croatian exploration area, particularly in the Pannonian Basin, there are
realistic prospects for economically viable exploration and commercial production of gas from
unconventional reservoirs. Croatia has a long history of hydrocarbon production, meaning oil and
natural gas and every year hydrocarbon reserves estimates are published officially.
Exploration of Unconventional Reservoirs
Like other countries, considering development of unconventional gas reservoirs, Croatia should
consider development of technically and economically recoverable gas reserves from
unconventional reservoirs. Without stimulation process like hydraulic fracturing is almost
impossible to exploit natural gas from this resources because of very low permeability. Therefore,
for creating faster and more effective fracturing processes, and for mitigating the impact of
fracturing on the environment, as many as possible realistic data related to the fracturing process
should be gathered. INA Plc. has started exploration of unconventional resources and found few
unconventional gas sources in Mura, Drava and Sava depression. Otherwise, unconventional
reservoirs are, for many years commercially exploited in the world.
Figure 1. Drava depression
Source: Malvić et al, 2003
The effective risk management at natural gas fields is feasible and therefore companies engaged in
unconventional gas projects development should use the best industry practices for promoting safe
business environment. During exploration of unconventional gas, development of reservoirs, well
completion and workover, natural gas should be used efficiently with sustainable environmental
protection meaning air and water quality protection, ecological impact minimization and land
impact remediation.
In table 1 there are comparative analysis of petrophisical characteristics of each Sava, Drava and
Mura geological depression which are considered as unconventional reservoirs in Croatia.
Table 1. Geological characteristics in different unconventional reservoirs in Croatia
Mura Depression
Drava Depression
Geographical situation
Northwest Croatia
Northern Croatia
Rock type
Silt, tight sandstones, shale, Mudstone,
marl,
silt,
marl
sandstones
Reservoir depth
3000-4000 m
3500-4500 m
Reservoir conditions
High temperature (190°C) High temperature (185°C)
and high pressure (570 bar)
and high pressure (790 bar)
Reservoir thickness
500 m
200-600 m
Porosity
3,2-19 %
3,2-19 %
Permeability
0,00017 mD (average)
0,0014 mD
Type of fluid
Thermogenic dry gas
Thermogenic dry gas
Source: Trogrlić et al., 2011
Some of the wells that have been drilled during exploration activities in Mura Depression are:
Murski Gost 6 (MG-6), Mursko Središće 5 (Msr-5), Zebanec 2 (Zb-2), Zebanec 3 (Zb-3), Zebanec 5
(Zb-5) and Peklenica 2 (Pek-2). Data analysis have shown that there are shale gas reservoirs and
tight sandstones gas reservoirs. Source rocks are between 3000 – 4000 m with average thickness
500 m mostly 250 m of tight sandstones and 258 m of shale. Reservoirs have high pressure tested at
562 bar on 3414m (gp= 1,66 bar/10m). Reservoir temperature on 3504 m is around 187 0C.
In table 2. there have been shown some estimated quantities of natural gas in Mura Depression. It is
predicted that shale contains 12% of total quantities and tight sandstones 30% of total quantities of
natural gas (Trogrlić et al., 2011).
Table 2. Estimated quantities of unconventional natural gas in Mura Depression
Tight sandstones
Shale fracture
Shale matrix
Shale total
Total
109 Sm3
109 Sm3
109 Sm3
109 Sm3
109 Sm3
39,194
88,212
8,256
96,469
135,663
Source: Trogrlić et all., 2011
In table 3. there are gas composition that is mostly 98.4% of methane and the rest are the other
components.
Table 3. Natural gas composition in Mura Depression
Source: Trogrlić et al. 2011
In Drava Depression the natural gas is in tight sandstone reservoirs and somewhere in shale
reservoirs. Matrix is middle Miocene mudstone. Source rocks are between 3500 – 4500 m with
average thickness of hydrocarbon reservoirs are from 200 m to 600 m. Reservoirs have high
pressure tested at 786 bar on 4178,5 m (gp= 1,88 bar/10m). Reservoir temperature on 4200 m is
around 184 0C.
In table 2. there have been shown some estimated quantities of natural gas in Mura Depression. It is
predicted that shale contains 12% of total quantities and tight sandstones 30% of total quantities of
natural gas. The average porosity is around 3.2% for matrix and up to 19% in fractures. The average
permeability is around 0.12 mD in fractures and 0.014 mD in matrix.
Hydrodynamic testing results have given gas reserves with similar characteristic to those in Mura
Depression. Estimated quantities of unconventional natural gas in Drava Depression is are around
363.565 ×109 Sm3 (Trogrlić et all. 2011).
Energy Policy
Therefore the role of unconventional gas development in Croatian national energy policy should be
clarified due to numerous stakeholders and public interested in unconventional gas development
process. Croatia has set national energy policy and national environmental goals according to
European Directives therefore policies for expanding unconventional gas development should be
consistent with it. Since there is geological potential of unconventional gas in Croatia, government
and industry should make sustained investment in associated capabilities for successful
unconventional gas production. The intention of unconventional gas development risks researching
was to establish a regulatory system in Croatia which is necessary to effectively govern
unconventional gas projects, including concessions and necessary permitting fees to support
required regulatory activities. This should be done in partnership with local community and
stakeholder participation. For environmental protection baseline conditions should be recorded and
monitoring of critical parameters should be introduced to detect any kind of environmental changes
resulting from development of unconventional gas.
Croatian platform on unconventional gas development should be established in order to interested
stakeholders, mainly upstream (INA Plc and potentially other new players on gas production market
side) and supply gas companies, local community and government bodies work together, share
specific technical knowledge, regulatory systems and community relationships, and help stimulate
continuous improvement. The success of unconventional gas projects in Croatia will depend on
different factors impacting market. For sustainable unconventional gas production strong political
support and local community cooperation is necessary. The challenge presents determination of the
fact in whose interest is development of unconventional gas projects in Croatia. Since Croatian
interest is assuring energy independence and security of energy supply it is necessary to define type
of governance systems for ensuring proper risk assessment and management. In order to make
proper decisions, prompt access to the best available information about technical, regulatory and
community practices is needed. The Faculty of Mining Geology and Petroleum Engineering at the
University of Zagreb, Croatia represents the neutral stakeholder in defining regulatory framework
for unconventional gas development to the government due to its scientific knowledge in the field
of natural gas engineering on one hand and has the council role for national energy policy on the
other. Base on the risk guidelines (JRC, 2012) (IRGC, 2013) the overall recommendations for
Croatian energy sector concerning development of unconventional gas reservoirs include:
A frac plan which will need to be constructed, submitted and approved by the Energy Department
of the Ministry of Economy of Croatia before any development activity can be initiated.
An Environmental Impact Assessment Study (EIA) should be mandatory for all operations
concerning development of unconventional reservoirs and involve the participation of local
communities through public debate. The EIA should assess risks and impacts across the entire life
cycle of unconventional reservoir gas exploration & production, including the disposal of wastes
and well abandonment. Seismic risks should also feature as part of the Study.
Transparency is required through overall process: all baseline monitoring data should be uploaded
on operators’ websites for public use.
Conclusion
By implementation of previously mentioned recommendations into contemporary Croatian
legislation and by introduction of new legislation framework concerning unconventional gas
development, Croatian Government can develop a much sustained legislation with greater
regulatory clarity and certainty for investors (operating and service companies), together with fiscal
system of concessions and taxes and also transparent legislation framework for environmental
protection.
Croatia has a more than a century long hydrocarbon production and therefore legitimacy of
unconventional gas development will be easier to accomplish. Economic crisis in Croatia and the
perceived need for industrial employment make opportune business environment. On the other hand
there have been previously failures and non-realization of a big energy projects (Pipeline
Brotherhood - Adria) due to negative perception of the nongovernmental organization.
Due to long petroleum history, local community opposition to unconventional gas development is
not very likely to be formed, but on the other hand regulatory system failure concerning
environmental protection during exploration of unconventional reservoirs could possible trigger
even the ban on unconventional gas projects in Croatia like in some other European Countries.
Therefore transparent legal framework with opportune fiscal regime will be prerequisite for further
development of unconventional gas projects in Croatia as tool for increasing security of natural gas
supply.
References:
Malvić, T., Cvetković, M. 2013. Lithostratigraphic units in the Drava Depression (Croatian and Hungarian
parts) – a correlation, Nafta, 64(1¸) 27-33
Trogrlić, S.; Cota, L.; Šikonja, Ž., 2011. „Nekonvencionalni izvori plina sjeverozapadnog djela Hrvatske i
mogućnost pridobivanja iz takvih rezervoara“, Opatija
Joint Research Centre, 2012. “Unconventional Gas: Potential Energy Market Impacts in the European
Union”, JRC, European Commission, Luxembourg.
doi: 10.2790/52499
International Risk Governance Council, 2013. “Risk Governance Guidelines for Unconventional Gas
Development”, IRGC, Lausanne.