The Geological Potential of the Arabian Plate for CCS and CCUS - An Overview

Given allowable carbon emissions for reaching climate targets, CCS and CCUS are without alternatives to simultaneously maintain a supply of sufficient energy for the world and preventing stranded subsurface assets for hydrocarbon producing countries. Permanent storage of carbon dioxide (CO 2 ) in deep subsurface formations is acknowledged as a scalable and achievable technology to contribute to the ongoing efforts of limiting CO 2 emissions and possibly lead to the use of stored CO 2 for geothermal energy generation. The sequestration processes include entrapping CO 2 in saline aquifers and hydrocarbon reservoirs in its mobile phase and in basalts as carbonate minerals. So, what are then the geological subsurface opportunities in Arabia for CO 2 sequestration? A high level assessment has been conducted to identify geological formations suitable for storing and utilizing CO 2 on a large scale. Over the Arabian peninsula four significantly different geological terrains are likely suitable for CCS & CCUS: (1) An Eastern section of stacked Mesozoic aquifers along the coast and inland of the Arabian Gulf, (2) rift basins with deep saline aquifers along the Red Sea, (3) Cenozoic volcanic rocks inland of the Red Sea coast, and Proterozoic ultramafic rocks in the Arabian Shield, and (4) a fringe of Cretaceous obducted marine crust (ophiolites) in Northeastern Oman and the UAE. The potential of the North-Eastern section for retaining CO 2 in the subsurface is essentially manifested by the presence of many super giant oil reservoirs in stacked, layered limestone sequences of mainly Mesozoic age. During this time period the eastern part of the Arabian plate was at a passive continental margin in a near-equatorial location resulting in mainly limestone deposition over very large areas. The overall architecture of cyclic carbonate deposition, interrupted by the incursion of thick layers of evaporites (e.g. Tithonian Hith Anhydrite) and shales (e.g. Albian Nahr Umr FM), has produced an ideal combination of multiple stacked reservoirs/aquifers overlain by seals. Gentle folding has created numerous structures for the permanent entrapment of migrating hydrocarbons but also light fluids such as supercritical CO 2 . Aquifer porosity and permeability are typically around 20% and 10mD - 100mD respectively, but can reach up to 40% porosity and Darcy-scale permeability. Aquifer fluids are typically highly saline reaching concentrations of 5 times seawater or more. The favorable conditions of relatively high porosity and permeability can exist to several km depth at which the formation temperatures reach 150°C and sometimes beyond. This not only offers the possibility for CO 2 storage but also utilization as a geothermal source for electricity generation and other heat-energy utilization processes, such as desalination and district cooling. Similar favorable geological conditions for CCS and CCUS are likely present in the rift basins along the Red Sea Coast albeit at a smaller scale and less well explored. Rift basins reach 6km in depth and are filled with continental and marine clastic and carbonate sediments, salt and shale layers can provide seal capacity. Opportunities for CCUS and geothermal energy generation are likely to exist near the populated and industrialized centers along the Red Sea. Thick stacked basaltic lava flows inland of the Red Sea coast (Harrats) and ophiolites associated with seafloor obduction along the North-Eastern margin of the plate in Oman and the UAE offer opportunities for CO 2 sequestration in its solid phase.


Introduction
The countries of the Arabian Peninsula (Saudi Arabia, Kuwait, Qatar, Bahrain, United Arab Emirates, Oman and Yemen) are not only major hydrocarbon producers exporting vast quantities of gas and oil into the world, but also major consumers of energy derived almost completely from hydrocarbons.Most countries of this area exceed energy consumption and associated CO2 emissions on a per capita base compared the United States and European countries (3).In addition to normal electricity and transportation consumption this is owed basically to three factors: firstly, the need for cooling to cope with the excessive temperatures of Arabia, secondly, the dependency on desalinated water caused by the lack of rain and the depletion of groundwater resources and thirdly, the readily available hydrocarbon resources, which are produced inexpensively, and sold cheaply.Yet it is recognized that rising temperatures associated with anthropogenic climate change will have a significant negative impact on Arabian societies (4)(5)(6).Hence governments of the region have supported the Paris climate accord and are taking steps towards mitigating climate change through the development of non-hydrocarbon-based energy sources (7) and CCS and CCUS techniques (8).Recently, Saudi Arabia has initiated the Circular Carbon Economy (CCE), which is a comprehensive framework to address the dual challenge of energy and the environment by adopting four principles (4Rs), corresponding to Reduce, Reuse, Recycle, and Remove (9).However, Arabian societies will for the foreseeable future contribute significantly to world-wide CO2 emissions through internal hydrocarbon consumption and their dependency on the export of hydrocarbons to create income for their economies.This is likely to occur even if efficiencies improve (5) and alternative energy sources are developed.This paper evaluates this conundrum and looks at solutions to mitigate CO2 emissions without leaving hydrocarbon assets stranded in the subsurface.First, a simple overview is presented of carbon budgets based on hydrocarbon reserves and current annual production and consumption.Secondly, the geological potential for CCS and CCUS technologies is assessed for the Arabian Peninsula.Thirdly, a long-term holistic concept is proposed to utilize CO2 stored in the subsurface for electricity production using geothermal energy concepts.In addition to geothermal energy generation, subsurface storage of CO2 furthermore provides two additional major advantages: a secondary utilization loop for ultimately using the stored CO2 for large scale CO2-based enhanced oil recovery (CO2-EOR).

Definition of Carbon Capture & Sequestration (CCS) and Carbon Capture Utilization and Storage (CCUS)
We define CCS here as a terminal sequestration of CO2 in the subsurface in the form of carbonate mineralization (CO2 Sequestration in Basalt -CSB) or CO2 dissolution and dispersal in deep aquifers which are not in communication with the atmosphere over geological time spans (Fig. 1a).As a result, the injected CO2 is disposed of and is not usable as a resource anymore.Consequently, CCS is a negative cash operation and needs to be offset economically by another income.CCS in Arabia will most likely rely on saline water as a medium only (subsurface brines or ocean water) because fresh and even brackish water aquifers are scarce and of great value as a source for drinking water and agricultural irrigation.Technical criteria for subsurface sequestration are in the case of aquifer sequestration a minimum depth of 800m to keep CO2 in supercritical state, sufficient porosity and permeability to ensure storage and injectivity and the presence of seals to prevent leakage back to the surface.
CCUS technologies, on the other hand, consider CO2 as a resource that is captured, stored in the subsurface and reused for economic gain (Fig. 1b).Such technologies include, for example, geothermal energy extraction using supercritical CO2 stored in reservoirs at temperatures exceeding 100°C (9) or enhanced oil recovery using CO2 injection (10)(11)(12).Storage of CO2 and its reuse entail several main prerequisites: (1) geological structures are large enough and have sufficient pore space to accommodate the injected CO2, (2) seals of adequate strength can retain the CO2 in place and (3) permeabilities from matrix and/or fractures are large enough to allow an economic utilization of the stored CO2.Furthermore, while electricity generation from CO2-based geothermal is overall much more efficient compared to water-based processes it still requires temperatures in excess of about 100°C (13).While subsurface temperatures are a function of local geothermal gradient and lithology, this translates for most areas of the Arabian Peninsula into a minimum target depth of about 2500 m considering a geothermal gradient of 30-35°C/km and an average surface temperature of about 25°C.Potential for shallower depth will exist in areas of abnormally high gradient.A maximum target depth is dictated by the loss of porosity and permeability due to compaction and considered at about 4000 m albeit potential for deeper targets may also exist.

Data and Methods
Using published data, we provide an overview of reserves and current production of hydrocarbons from the Arabian Peninsula.A conversion of these data to CO2 provides insights into emission levels associated with the production of Arabian hydrocarbons and the internal consumption of countries from Arabia and a basis to compare to ongoing efforts to offset emissions.
A review of the geological potential of the Arabian Peninsula for potential sites of CO2 sequestration is the result of a review of published data.The aim of this effort is to collate all available surface and subsurface data into a common data base to produce a digital ArcGIS atlas of potential CCS and CCUS sites on the Arabian Peninsula.The progress of this work will be reported separately.
The industrial CO2 emissions database contains emissions from stationary points emitted across the country in 2015 and 2020, covering sectors of the economy such as desalination, steel, refinery & electricity production among others.

Carbon Budgets of the Arabian Peninsula
Countries of the Arabian Peninsula are some of the major reserve holders and producers of hydrocarbons in the world.Hydrocarbon reserves of the Arabian Peninsula combined for all countries (Saudi Arabia, Kuwait, Qatar, Bahrain, United Arab Emirates, Oman, and Yemen) are estimated to amount to 754 billion barrels of oil equivalent (BOE) (Fig. 1; (14,15)).Annual production of hydrocarbons for export and internal consumption amount to about 9.5 billion BOE (14,15), with internal consumption amounting to an estimated 20%-25% of the total (Fig. 2).Assuming that all the hydrocarbon reserves and the annual production are converted to CO2 in one way or another this will amount to a production of respectively 324 gigatons of CO2 from utilizing all reserves and 4 gigatons of CO2 per year from annual production (16).A significant part of internal hydrocarbon consumption and associated CO2 emission is associated with fixed locations, which are power plants, desalination plants, cement and steel industries, refineries, petrochemical industry, etc. (Fig. 3).Most of the remaining consumptionan estimated 35-50% -is related to land and air mobility.will spend 44% of the worldwide remaining allowed CO2 emission to stay within a 2°C temperature rise, or 59% to stay within 1.5°C temperature rise.Assuming that the Paris accord will be met and only a smaller share of remaining CO2 emission will be available for Arabian derived CO2 this implies that the production of a substantial part of the Arabian hydrocarbon reserves should be combined with large-scale measures for CO2 removal.CCS and CCUS could offer such opportunities at the required scale.Alternatives can support but do not provide realistic offsets at scale (see offset by trees, column 9; (1, 2)) Climate models suggest that the allowed worldwide emission for CO2 is not to exceed more than 740 Gigatons of CO2 until the end of the 21 st century for a 90% chance of not increasing the world average temperature by more than 2°C ( 17)).For a 90% chance of staying within the 1.5°C temperature increase proposed by the Paris climate agreement, the remaining budget would have to be below an estimated 548 gigatons of CO2 (17).Hence, producing all reserves of Arabia and converting them to CO2 released into the atmosphere will consume respectively 44% or 59% of the remaining budget to have a 90% chance of not exceeding a worldwide temperature rise of 2°C or 1.5°C (Fig. 2).
Considering that other regions of this world have similar reserves and are emitting at similar rates and that coal emissions are not even considered, this is clearly an unsustainable scenario given that all countries of the Arabian Peninsula, except Yemen, have ratified the Paris climate agreement.
The clear support of governments for the Paris accord * has been substantiated by goals to lower emissions and increase the development of alternative energy sources.Since 2016 plans have been developed and projects have been initiated for large scale power generation from Solar PV plants and wind farms (18,19).There is a clear desire to further develop non-fossil fuel-related industries: renewable energy production, tourism, other industries (computing, space, etc.).However, the transition is expensive and will require long term substantial income from fossil fuel production and export.

Ongoing CCS and CCUS Efforts on the Arabian Peninsula
In order to produce and consume hydrocarbons and meet CO2 emission commitments, governments and national oil companies of the Arabian Peninsula are proposing and developing CCS and CCUS opportunities (20)(21)(22)(23).The main CCUS technology that is being investigated is CO2 injection into reservoirs for improving oil recovery (CO2 Fig. 3: KSA CO2 emission from stationary sources in million tons per year (mty) in 2020 (total: 568 mty with annual growth rate 0.65 %).Similar emissions patterns are expected for other countries of the Arabian Peninsula EOR).This results in about 60% of the injected CO2 remaining in the subsurface, while 40% is eventually reproduced as associated gas with the oil (24,25).Some laboratory experiments though suggest somewhat lower percentages as viscous fingering can cause CO2 bypass of much of the pore space (Van der Meer, 1995; Ennis-King and Paterson, 2001; Flett et al., 2005).So far two CO2 EOR pilots are ongoing in the region, one in Saudi Arabia and the other in the UAE with a CO2 injection of 800,000 t/a each (Fig. 1).Plans have been formulated to increase this to at least 5 million tons per year by 2030 (26).This amount of sequestered CO2 is equivalent to 0.12% of CO2 from the hydrocarbons produced in the Arabian Peninsula per or 0.4% of the CO2 generated within Arabia from hydrocarbon consumption per year.Furthermore, to reduce capture costs, the CO2 used for EOR is not from the conversion of hydrocarbons but almost exclusively associated CO2 gas separated as a byproduct from natural gas processing units.This CO2 is normally vented to air contributing to CO2 emissions.However, it is not offsetting any of the CO2 produced from utilizing hydrocarbons for energy generation or industrial products.
While CO2-EOR leads to the benefit of additional hydrocarbon reserves beyond those already booked, it is a complex technology with many subsurface challenges and substantial surface facilities costs (21,27).The cost of oil produced by CO2 EOR technology is reportedly to be around 35-40$/bbl.This is not an attractive economic solution considering the available reserves in Arabia that can be produced by much less expensive water floods.However, CO2-EOR will likely become economical at a later stage of reservoir depletion when secondary recovery methods such as water flooding have lost their economic efficiency.In any case, large scale, economically efficient CO2 EOR of super giant reservoirs common in Arabia will require enormous quantities of CO2.These exceed the volumes currently generated from point sources on an annual basis and will likely require large pools of stored CO2.

Geological Terrains of the Arabian Peninsula for CCS and CCUS
Four geological terrains are recognized for their potential of CO2 sequestration and/or storage (Fig. 3) and discussed separately below:

Stacked sedimentary layers of the Eastern Plate Margin
The eastern section of the Arabian Plate contains some of the largest oil reservoirs of the world in stacked, layered limestone sequences of mainly Jurassic to late Cretaceous age (Fig. 4-6).During this time period the Arabian plate was at a passive continental margin in a near equatorial location resulting in predominantly carbonate sediment deposition over very large areas (28).The bulk of the sediments were deposited in a vast shallow marine lagoon behind a platform margin that was aggrading and prograding over time from a plate interior position towards the plate margin in the East.The stacking of the sedimentary units within the area of the lagoon is rather simple with sediments having been deposited in an overall layer-cake architecture.Platform margin and slope deposits towards the Tethys Ocean are more complex in architecture.The overall architecture is of cyclic carbonate deposition and was interrupted several times by the incursion of thick evaporite (e.g.Tithonian Hith; Eocene Rus FM) and siliciclastic shale /argillaceous limestone sequences (e.g.Albian Nahr Umr FM).This has created an ideal combination of multiple stacked sequences of porous rock and overlying seals (Fig. 6).Gentle folding of the strata during the latest Cretaceous / Early Tertiary has created numerous structures ideal for the permanent entrapment of migrating hydrocarbons in the porous sequences beneath the seals (Fig. 4; (28, 29)) However, not all structures are filled with hydrocarbonsmany only contain saline waters of regional subsurface aquifers and could become the target for injecting and trapping light fluids such as hypercritical CO2.
Aquifer porosity and permeability is variable in aquifers, typically around 20% and 10mD -100mD respectively, but can reach values of up to 40% porosity and Darcy-scale permeability.Aquifer fluids are typically highly saline reaching concentrations of up to 5-7 times seawater or even more (30).The favorable conditions of relatively high porosity and permeability can exist to several km depth at which the formation temperatures reach 150 o C and more.
The occurrence and extend of the aquifers, reservoirs, traps, seals and their properties are generally well understood and documented in many publications (e.g. ( 28)).However, detailed data required for locating and evaluating potential targets for CO2 sequestration and/or storage pilots are proprietary and reside in the data bases of the National Oil Companies.

Rift Basins of the Western Plate Margin
The African and Arabian plates started splitting and drifting apart during the Late Oligocene (31).As a consequence, up to 6 km deep rift basins developed along the continental margins facing the spreading center (Fig. 7; (32,33)).These rift basins were filled initially with continental clastic sediments (Red Beds) followed after a marine transgression by a thick succession of carbonates and evaporites.
Incursions of siliciclastics shed from the rift margins add additional complexity to the stratigraphy (32).Sandstones, limestone and dolomites likely contain favorable porosity and permeability.Salt and shale layers provide seal capacity (33).However, the Neogene section and rift basins are characterized by significant lithologic diversity and architectural complexity as a consequence of both rift and salt tectonics (e.g. ( 33)).Little data has been published on geothermal temperature gradients along the western plate margin.However, gradients of 32°C/km are to be expected with significantly higher ones in areas of geothermal springs, for example Al Lith and Jizzan in the south of the KSA Red Sea coastline (Fig. 3).This underlines the potential of these basins not only for CCS but also for CCUS and geothermal energy generation especially near populated and industrialized centers along the Red Sea (Jizzan, Al Lith, Jeddah, Rabigh, Yanbu) with large CO2 point sources (Fig. 2).Yet, detailed mapping of suitable targets has not been done as data are not publically available for initial assessments.

The Harrats of Saudi Arabia
Mafic rocks composed mainly of alkali olivine basalts are abundant in the volcanic areas (Harrats) of western and northern Saudi Arabia where at least 14 young volcanic fields have been mapped (Fig. 8a; (34)).They consist mainly of sequences of flat lying basaltic lava flows that mantle the underlying topography, and a few felsic lava domes (trachyte, phonolite).The basaltic lavas erupted mainly from fissures and small monogenetic volcanoes (cinder and spatter cones) that are aligned along structural lineation parallel to the Red Sea.The Harrats are of Oligocene to Recent age (30-0 MY) and are associated with the onset of continental rifting and a later phase with the opening of the Red Sea.The basaltic fields vary in thickness from 0 to hundreds of meters with most being less than 100 m thick but exceeding in places several hundred meters.
The suitability of an area for CO2 storage in basalts can be evaluated against the following parameters: geology/rock reactivity, thickness/volume of reactive rocks, sufficient effective porosity and permeability, proximity to major CO2 sources from industrial facilities, height of the groundwater column, and availability and proximity to water.Since freshwater aquifers are reserved for other purposes this implies proximity to seawater as a source.Furthermore, a potential reservoir must possess sufficient thickness of >500m, with at least 400 m saturated with groundwater (41).To maximize the efficiency of the mineralization process, CO2 has to be co-injected with sufficient water downhole so that the gas is completely dissolved at the depth of its release into the target subsurface basalt.A similar requirement has been proposed by the Carbfix process (35).With some of the Saudi Arabian harrats being close to the coast and major industrial centers (Figs. 3, 8; Jizzan, Jeddah, Rabigh, Yanbu) significant potential likely exists for CO2 storage in basalts.

The Obducted Ocean Crust of Oman and the UAE
During the Late Cretaceous the northeastern continental margin of the Arabian plate started to collide with relatively young and hot oceanic crust that was converging from the northern Neo-Tethys towards Arabia (36) The continental margin was subducted and oceanic ophiolite crust obducted onto the continental crust (37,38).Subsequent uplift in the Tertiary exposed thick sequences of ophiolite along the northeastern margin of the Arabian Peninsula in Oman and the UAE (Fig. 3, 9).The ophiolite is composed of gabbros and ultramafic rocks and reaches a thickness of more than 4 km (37).Paukert et al (2012) (39) calculated a high efficiency of CO2 sequestration at 90°C and an associated injection depth of 2km.The suitability for CCS in the Oman ophiolite has been evaluated by Kelemen et al. (2018) (40) who identified potential but also many uncertainties whether the process could work technically and economically.

CCS Opportunities
CCS opportunities are associated either with injection of CO2 into basalt or ultramafic rocks to bind the CO2 in the form of carbonate mineral precipitates (dolomite, huntite, calcite) or into saline aquifers in the eastern and western margin areas for dispersal in the subsurface.Technical criteria help in assessing subsurface potential of different geological settings such as minimum depth.
Mafic basalts and ultramafics rocks are located in the Saudi Arabian Harrats and the Oman ophiolites (Figs. 3, 8, 9).However, the process of mineralizing CO2 into carbonate minerals requires substantial amounts of water to carry the CO2 to the reaction sites at depth and to promote reactions underground.A ratio of 20:1 has been proposed for the water/CO2 volume (41).This requires initially the sourcing of large amount of water to injection sites.In order to prevent development of overpressure at the injection level, the fluids have to be reproduced after the CO2 has reacted with the host rock.Produced water can be re-used for enrichment with CO2 and re-injected.Eventually, however, the disposal of some reproduced waters may have to be considered as well.These criteria are fulfilled with the proximity of some KSA harrats and the Oman/UAE ophiolites to nearby coasts with easy access to seawater as well as CO2 point sources from desalination and electricity plants and other industrial facilities frequently found in coastal areas.
Shallow aquifers and geological structures for suitable CO2 sequestration can be found in both the stacked sedimentary units of Eastern Arabia and the Western rift basins.Examples in the East are the aquifer/seal pairs of the Aruma and Umr Er Rhaduma limestones / Rus Evaporites of the KSA and UAE, the Shilaif/Natih Limestones and Fiqa shales of the UAE and Oman and several other deeper aquifer/seal pairs (Fig. 6).Injection into aquifers below the regional more extensive major seal units of the Nahr Umr shales and the Hith and Khuff D anhydrites might also be possible even without lateral confinement such as 4-way dip structures as seals and aquitards are so extensive and of proven quality that leakage is highly unlikely.More proximal to the Arabian shield, the Nahr Umr Fm of the Wasia Group, transitions from a major seal composed of shales and argillaceous limestone into a sandstone aquifer potentially suitable for large scale CO2 injection and sequestration.With a total area of more than 4.8E+5 km 2 , an average thickness of between 200 -500 m and porosities of 3% to 29% (42), the Wasia aquifer corresponds to a major potential target area for CCS.
On the west coast along the Red Sea, aquifer/seal pairs are less well defined but could be developed relatively shallow in the Early/Middle Miocene sandstones and limestones of the Burqan, Wadi Waqb and Umm Luj Formations with overlying Middle Miocene salt units of the Mansiyah Formation acting as seals.

CCUS Opportunities
Arabia probably offers the most promising geological potential for utilizing sequestered CO2 for desalination, district cooling and electricity production via geothermal heat extraction.This CCUS technology proposes the recycling of CO2 stored in intermediate depth reservoirs at temperatures between 100 -150°C.The multiple stacked aquifers, the presence of suitable seals and the favourable setting of gentle anticlinal structures combined with large numbers of point sources on the peninsula for capturing CO2 and utilizing it for optimized geothermal heat extraction, constitute a unique scenario for the successful development and large-scale deployment of CCUS technology.Successful development not only promises a steady revenue stream from stored CO2 but also provides CO2 reservoirs for a late- stage CO2 EOR phase to improve recovery from hydrocarbon reservoirs in the future.Simple boundary conditions for exploration have been set for geothermal CCUS at depth of more than 2000 m and less than 4000 m (Fig. 5).Deeper targets give higher temperatures but drilling is more expensive and productivity usually diminishes because of decreasing porosity and permeability with depth.Using these simple criteria for a first screening identifies many potential targets for in-depth studies, exploration and eventually piloting.

Status, Potential and the Way Forward
Massive efforts of CCS and CCUS are required quickly in order to keep emissions of CO2 derived from the production of Arabian hydrocarbons (exported and consumed within Arabia) below levels leading to severe adverse climate change specifically in Arabia but also elsewhere.A real danger exists that subsurface hydrocarbon assets become stranded if carbon emissions are curbed worldwide to meet climate targets.On the other hand, geological conditions are diverse and excellent for the sequestration of CO2 and storage-for-reuse at the scale of gigatons that is required to offset the large emission levels.Point-sources of CO2 are many.Technology of capturing CO2 at point source is available and being optimized to increase efficiency and decrease costs.However, despite the massive need and the high potential for CCS/CCUS, little concrete efforts are ongoing to reduce uncertainties for sequestering or storing CO2 in the subsurface at large scale.Two small CO2 EOR pilot projects executed by National Oil Companies are the only concrete efforts.
A major roadblock to effectively research the potential for CCS and CCUS and prepare the way forward for pilots and economic developments is the lack of publicly available subsurface data.A vast quantity of subsurface data has been acquired over the last 50 years in pursuit of hydrocarbon exploration and production.The availability of this data to the research communities and investors will allow faster development of CSS and CCUS.Considering that large scale CCS and CCUS projects will take years to develop and that the world emits some 35-40 Gt/y CO2 against a remaining budget of about 550 Gt, time is running out quickly to prevent either catastrophic climate change or energy shortage and stranded hydrocarbon assets.

Conclusions
Countries of the Arabian Peninsula have reported so far only a couple of pilot projects towards CCS and CCUS despite being main contributors to CO2 production worldwide.Fast development of CCS and CCUS contributes to the success of the ambition and goals of Arabian countries to combat the negative impact of CO2 emissions on climate (e.g.Vision 2030 of KSA).Furthermore, mitigating CO2 produced from hydrocarbon utilization is crucial to maintain the viability of hydrocarbon assets to stay competitive with alternative energy sources and avoid catastrophic climate change.These hydrocarbon assets are expected to remain the main contributor to the GDP of Arabian countries, and therefore promoting CCS and CCUS is an urgent need.
Arabia is blessed with excellent opportunities for large scale CCS and CCUS in a variety of geological settings:  The eastern plate margin along the Arabian Gulf offers multiple stacked aquifers with seals and suitable structures for safe long-term CO2 storage.Notably, Mesozoic carbonate aquifers are extremely well known in their extent, depth, composition and petrophysical properties through the extensive exploration and production of hydrocarbons.Seals of proven capacity and extent are well known (e.g.Hith anhydrite, Nahr Umr shales); others exist too. The western plate margin contains deep rift basins which are less explored but are likely to contain significant aquifers in the synrift clastics and patchy carbonate platforms.Shales and thick evaporites are likely to provide excellent seals to safely store CO2. Thick basalt flows of Western Arabia and basalt, gabbro and peridotite sequences of Eastern Arabia (the Semail Ophiolite of Oman and UAE) provide opportunities for CCS using mineral alteration processes and CarbFix technologies.
Arabia probably offers some of the most promising potential for utilizing sequestered CO2 for desalination, district cooling and electricity production via geothermal heat extraction.The multiple stacked aquifers, the presence of suitable seals and the favorable setting of gentle anticlinal structures combined with large numbers of CO2 point sources are all ideal for optimized geothermal heat extraction.The development and large-scale deployment of CCUS technology promise a steady revenue stream from stored CO2 and also provides CO2 reservoirs for a late-stage CO2 EOR phase to improve recovery from hydrocarbon reservoirs in the future.
Finally, a major roadblock to effectively research the potential for CCS and CCUS and prepare the way for pilots and economic development is the lack of publicly available subsurface data.The availability of data that has been acquired over the last 50 years from hydrocarbon exploration and production will be crucial to the development of geological-based solutions to reduce, recover, reuse, and recycle" CO2.

Fig. 1 :
Fig. 1: Two main concepts for CCS/CCUS in Arabia.CCS technology removes CO2 using injection into saline aquifers or dispersal into mafic/ultramafic rocks to form carbonate minerals (a).CCUS targets sealed geological structures at intermediate depth (2000m+) and temperatures in excess of 100°C (b).Reuse of the stored CO2 allows geothermal energy extraction and electricity generation.CO2 based enhanced oil recovery (EOR) is a secondary CCUS loop when water-flood recovery in oil fields becomes less economical in comparison.Inherently, CCUS is preferred because it follows a "reduce, recover, reuse, recycle" strategy.

Fig. 2 :
Fig.2: Production of all booked hydrocarbon reserves of the Arabian Peninsula (Saudi Arabia, Kuwait, Qatar, UAE, Oman, Bahrain & Yemen) will spend 44% of the worldwide remaining allowed CO2 emission to stay within a 2°C temperature rise, or 59% to stay within 1.5°C temperature rise.Assuming that the Paris accord will be met and only a smaller share of remaining CO2 emission will be available for Arabian derived CO2 this implies that the production of a substantial part of the Arabian hydrocarbon reserves should be combined with large-scale measures for CO2 removal.CCS and CCUS could offer such opportunities at the required scale.Alternatives can support but do not provide realistic offsets at scale (see offset by trees, column 9; (1, 2))

Fig. 5 :
Fig. 5: CCS and CCUS opportunities in sedimentary sequences of the Eastern Arabian Peninsula.Many stacked aquifer/seal pairs offer opportunities of varying properties and qualities.CCS requires a depth of at least 800m to keep the CO2 in supercritical state.Geothermal CCUS based on circulation of stored CO2 requires a minimum temperature of 100°C.Late Mesozoic and Early Cenozoic deformation resulted in many gentle structures fit for carbon storage and utilization at targeted depth & temperature ranges.Similar depositional and structural architectures exist in Kuwait, the UAE and northern Oman (modified from 32).

Fig. 6 :
Fig. 6: The Paleozoic to Tertiary stratigraphy of the Eastern Arabian Peninsulaexample from KSA. Known aquifers marked by a red arrow, seals by a blue (modified from 43).

Fig. 8 .
Fig. 8. Map showing in the distribution and ages of Cenozoic volcanic fields in KSA (39).

Fig. 9 :
Fig. 9: Location and thickness of the Oman ophiolite and associated ultramafic rocks.Numbers above bars in (C) correspond to the location of the measured ophiolites shown in B (Fig. 1 of 43).