2.6 Overlying and adjacent aquifers

Generally, the degree of mineralisationIs a natural form of geologically storing CO2Carbon dioxide  by the very slow reaction between CO2Carbon dioxide  and naturally occurring minerals, such as magnesium silicate, to form the corresponding mineral carbonateNatural minerals (e.g. calcite, dolomite, siderite, limestone) composed of various anions bonded to a CO32- cation of formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it waters increases with increasing depth, although locally other settings may occur, e.g. in deep karst or in arid and coastal environments. Hence, overlying and adjacent Aauifers may comprise saline and/or freshwaters. Measuring the geochemical evolution of subsurface formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it waters is one tool to directly detect the potential impact of leaking CO2Carbon dioxide, brine or other fluids into overlying or adjacent aquifers. These measurements require fluid sampling on a regular basis. monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions could be undertaken in boreholes that penetrate the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids or in monitoringMeasurement and surveillance activities necessary for ensuring safe and reliable operation of a CGS project (storage integrity), and for estimating emission reductions wells that penetrate overlying formations. Measurements could include parameters, such as: pH, alkalinity, HCO₃^-, dissolved gases, hydrocarbons, major and minor elements, TIC, TOC, stable isotopes, redoxReduction-oxidisation reaction potential, specific conductance, TDS, density, natural and introduced tracers. It is important to design the sample retrieval system that will conserve the properties that are required for analysis. Fluid mixtures (CO2Carbon dioxide, brine plus any other relevant fluid or hydrocarbons) will density-separate in the wellboreThe physical hole that makes up the wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids, it can be cased, open, or a combination of both; open means open for fluid migrationThe movement of fluids in reservoir rocks laterally between the wellbore and surrounding formations; cased means closing of the wellbore to avoid such migrationThe movement of fluids in reservoir rocks, and this fractionation will increase as fluids move upward through tubing and gases expand and become less dense. Temperature and solubility relationships will also change, for example gas in solution will evolve. If needed, several techniques can be used to reduce these complications.

Extraction of fluids is labour-intensive, requiring a gas lift or pumping system except where pressure or gas saturation are high enough to lift fluids to the surface. Commercial downhole sampler systems can be deployed on wireline or slickline to collect samples at reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids pressure and temperature and then conserve this volume during transport to the surface. WellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids drilling and completion(well) Refers to the cementing and perforating of casingA pipe which is inserted to stabilise the borehole of a well after it is drilled and stimulation to connect a well bore to reservoir may cause contamination of the near wellboreThe physical hole that makes up the wellManmade hole drilled into the earth to produce liquids or gases, or to allow the injectionThe process of using pressure to force fluids down wells of fluids, it can be cased, open, or a combination of both; open means open for fluid migrationThe movement of fluids in reservoir rocks laterally between the wellbore and surrounding formations; cased means closing of the wellbore to avoid such migrationThe movement of fluids in reservoir rocks environment with allochthonous fluids that must be reduced and corrected for.

A U-tube sampler was designed for the Frio Project that allows samples to be returned to surface at near reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids pressures (Freifeld and Trautz, 20062006 - Barry M Freifeld, Robert C TrautzReal‐time quadrupole mass spectrometer analysis of gas in borehole fluid samples acquired using the U‐tube sampling methodologysee more). The U-tube is composed of a double length of high pressure stainless steel tubing with a check valve open to the reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids. FormationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluid is collected in the U-Tube, driven at reservoirA subsurface body of rock with sufficient porosityMeasure for the amount of pore spaceSpace between rock or sediment grains that can contain fluids in a rock and permeabilityAbility to flow or transmit fluids through a porous solid such as rock to store and transmit fluids pressure into evacuated sample cylinders at the surface by high pressure, ultra-pure nitrogen. Free gas in the sample and gases coming out of solution are pumped from the top of the gas separator through a quadrupole mass spectrometer analyser and a landfill gas analyser to measure changes in gas composition in the field (Fig. 2-18). Geochemical analysis must also be matched to the analysis requirements, which may require measurement of gas and liquid fractions at known pressure and temperature, collection of field parameters, filtration, stabilisation, labelling, storing, and shipping of samples.

Investigating aqueous geochemistry provides detailed information needed to confirm model predictions on CO2Carbon dioxide migrationThe movement of fluids in reservoir rocks and potential leakage(in CO2Carbon dioxide storage) The escape of injected fluid from the storage formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it to the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) or water column pathways. In particular, it is the only technique available that has promise to document dissolution and mineral trapping(CO2Carbon dioxide) ContainmentRestriction of the movement of a fluid to a designated volume (e.g. reservoir) or immobilisation of CO2Carbon dioxide, there are four main trapping mechanisms: structural or stratigraphicThe order and relative position of geological strata trapping; residual CO2Carbon dioxide trapping (capillary trappingImmobilisation of a fraction of in-situ fluids by capillary forces) by capillary forces; solubility trappingA process in which fluids are retained by dissolution in liquids naturally present by dissolution of CO2Carbon dioxide in resident formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it fluids forming a non-buoyant fluid; and mineral trapping where CO2Carbon dioxide is absorbed by solid minerals present in the storage(CO2Carbon dioxide) A process for retaining captured CO2Carbon dioxide, so that it does not reach the atmosphereThe layer of gases surrounding the earth; the gases are mainly nitrogen (78%) and oxygen (around 21%) volume or, conversely, any geochemical interactions that may lead to increased riskConcept that denotes the product of the probability of a hazard and the subsequent consequence of the associated event (e.g. damage to formationA body of rock of considerable extent with distinctive characteristics that allow geologists to map, describe, and name it, confining zone, or engineered system).