In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

The flow of homogeneous fluids through porous media: analogies with other physical problems

With the decline in oil discoveries during the last decades it is believed that EOR technologies will play a key role to meet the energy demand in years to come. This paper presents a comprehensive review of EOR status and opportunities to increase final recovery factors in reservoirs ranging from extra heavy oil to gas condensate. Specifically, the paper discusses EOR status and opportunities organized by reservoir lithology (sandstone and carbonates formations and turbiditic reservoirs to a lesser extent) and offshore and onshore fields. Risk and rewards of EOR methods including growing trends in recent years such as CO2 injection, high pressure air injection (HPAI) and chemical flooding are addressed including a brief overview of CO2-EOR project economics.

Enhanced Oil Recovery: An Update Review

The Intergovernmental Panel on Climate Change assumes the warming of the climate system, associating the increase of global average temperature to the observed increase of the anthropogenic greenhouse gas (GHG) concentrations in the atmosphere. Carbon dioxide (CO 2 ) is considered the most important GHG, due to the dependence of world economies on fossil fuels, since their combustion processes are the most important sources of this gas. CO 2 concentrations are increasing in the last decades mainly due to the increase of anthropogenic emissions. The processes involving CO 2 capture and storage is gaining attention on the scientific community as an alternative for decreasing CO 2 emission, reducing its concentration in ambient air. However, several technological, economical and environmental issues as well as safety problems remain to be solved, such as the following needs: increase of CO 2 capture efficiency, reduction of process costs, and verification of environmental sustainability of CO 2 storage. This paper aims to review the recent developments (from 2006 until now) on the carbon capture and storage (CCS) methodologies. Special attention was focused on the basic findings achieved in CCS operational projects.

Recent developments on carbon capture and storage: An overview

The rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low-temperature alteration can be enhanced to develop a significant sink for atmospheric CO2. Natural carbonation of peridotite in the Samail ophiolite, an uplifted slice of oceanic crust and upper mantle in the Sultanate of Oman, is surprisingly rapid. Carbonate veins in mantle peridotite in Oman have an average 14C age of ≈26,000 years, and are not 30–95 million years old as previously believed. These data and reconnaissance mapping show that ≈104 to 105 tons per year of atmospheric CO2 are converted to solid carbonate minerals via peridotite weathering in Oman. Peridotite carbonation can be accelerated via drilling, hydraulic fracture, input of purified CO2 at elevated pressure, and, in particular, increased temperature at depth. After an initial heating step, CO2 pumped at 25 or 30 °C can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy. In situ carbonation of peridotite could consume >1 billion tons of CO2 per year in Oman alone, affording a low-cost, safe, and permanent method to capture and store atmospheric CO2.

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In situ carbonation of peridotite for CO2 storage

The matrix treatment of a subterranean formation is adjusted in real time to minimize formation damage as indicated by the skin factor. The process comprises initial injecting an inert fluid into the formation and observing the variation in injection pressure over time. During the matrix treatment with a treatment fluid, the pressure is again observed over time and, by comparison with the pressure variation noted in the inert fluid injection phase, the skin factor is determined. The treatment parameters are then adjusted in real time to minimize the skin factor thereby minimizing formation damage.

Matrix treatment process for oil extraction applications

Real-time evaluation of matrix acidizing treatments

Application of Pressure-Transient and Production-Data Analysis for Hydraulic-Fracture-Treatment Evaluation

A horizontal well test in a large reservoir and with small wellbore storage should produce certain distinct flow regimes These should lead to the estimation of three permeabilities (along, normal and vertical to the well trajectory) the total well skin effect and, perhaps, the effective (open) well length The objective of this work is to optimize well test design to obtain the desired flow regimes It is shown that the important early-time flow regimes can be masked by wellbore storage effects Therefore, afterflow should be minimized by using downhole shut-in The storage effects can be estimated with empirical equations These relationships also mark the beginning of the first interpretable flow regime It is shown that for very thin formations or in situations where the well is drilled close to the top or bottom boundaries the early radial flow regime may not be seen at all The length of an almost fully laterally penetrating horizontal well may also distort the late-time radial flow In both of these instances, calculation of the controlling permeabilities becomes difficult to impossible It may thus be desirable to test smaller segments of the well Placing an observation gauge in an isolated segment during the flow testing of another segment can provide further information It is shown that the derivative of the pressure response in the observation gauge exhibits a characteristic hump When the hump appears, the permeability along the well axis can be calculated Testing of isolated segments would also deliver a detailed picture of the skin distribution along an extended horizontal well From such a test valuable information for enhanced stimulation and selective well completion design can be drawn

Michael J. Economides

Papers

Matrix treatment process for oil extraction applications

Real-time evaluation of matrix acidizing treatments

Application of Pressure-Transient and Production-Data Analysis for Hydraulic-Fracture-Treatment Evaluation

Horizontal Well Testing of Isolated Segments

Adjustment of Hydraulic Fracture Design in Gas-Condensate Wells