Functional analysis of microRNA activity in Brugia malayi

The complement of the Brugia malayi microRNA-71 was inserted into the 3' untranslated region of a reporter plasmid, resulting in a decrease in reporter activity. Mutation of the seed sequence restored activity. Insertion of the 3' untranslated regions from two algorithm-predicted putative target genes into the reporter resulted in a similar decrease in activity; mutation of the predicted target sequences restored activity. These experiments demonstrate that B. malayi microRNA targets may be predicted using current algorithms and describe a functional assay to confirm predicted targets.

Geomechanical Factors Affecting Geological Storage of CO2 in Depleted Oil and Gas Reservoirs

Abstract

A key to the success of long-term storage of CO2 in depleted oil or gas reservoirs is the hydraulic integrity of both the geological formations that bound it, and the wellbores that penetrate it. This paper provides a review of the geomechanical factors affecting the hydraulic integrity of the bounding seals for a depleted oil or gas reservoir slated for use as a CO2 injection zone. Potential leakage mechanisms reviewed include fault reactivation, induced shear failure of the caprock, out-of-zone hydraulic fracturing, and poorly sealed casing cements in enlarged, unstable boreholes. Parameters controlling these mechanisms include the upper and lower bounds of pressure and temperature experienced by the reservoir, the orientation and mechanical properties of existing faults, rock mechanical properties, in situ stresses, and reservoir depth and shape. Approaches to mitigate the likelihood of geomechanics-related leakage include the identification of safe upper limits on injection pressures, preferred injection well locations, review of historical records for reservoir pressures, temperatures and stimulation treatments, drilling program design to mitigate rock yielding in new wells, and assessment of wellbore integrity indicators in existing wells.

Introduction

In order to achieve significant reductions in the atmospheric release of anthropogenic greenhouse gases, the implementation of technologies to capture carbon dioxide (CO2) and store it in geological formations will be necessary. Deep saline aquifers have the largest potential for CO2 sequestration in geological media in terms of volume, duration, and minimum or null environmental impact(1). The first commercial scheme for CO2 sequestration in an aquifer is already in place in the Norwegian sector of the North Sea, where 106 tonnes of CO2 are extracted annually from the Sleipner Gas Field and injected into the 250 m thick Utsira aquifer at a depth of 1,000 m below the sea bed(2).

In light of the economic benefits of enhanced oil recovery (EOR) derived from CO2 injection in oil reservoirs(3), these types of reservoirs will be attractive CO2 injection targets and, most likely, CO2 storage in depleted oil and gas reservoirs (or in conjunction with EOR) will be implemented before CO2 storage in aquifers. An advantage of CO2 storage in depleted oil or gas fields is the fact that much of the infrastructure for fluid injection (e.g., wellbores, compressors, pipelines) is already in place. The Weyburn CO2 Monitoring and Storage Project in Saskatchewan, Canada(4) is an example of a large-scale application of EOR operations using anthropogenic CO2, in which the oil reservoir is being evaluated for subsequent use as a long-term storage zone.

A key to the success of long-term storage in depleted oil and gas reservoirs is the hydraulic integrity of both the geological formations that bound it, and the wellbores that penetrate it. The initial integrity of this "bounding seal" system is governed by geological factors. A considerable amount of effort has been devoted to the development of procedures for assessing fault seal capacity in potential hydrocarbon reservoirs(5).

Sequestration of CO2 in Salt Caverns

Abstract

Permanent storage of CO2 in dissolved salt caverns is one of the geological options for reducing anthropogenic greenhouse gas emissions into the atmosphere. Alberta is singularly well endowed with suitable salt deposits. Of these, the Lotsberg Salt of east central Alberta is the best of the three major saltbearing zones, and is geographically close to present and future sources of CO2 associated with fossil fuel development projects in Alberta.

The characteristics of the Lotsberg Salt and overlying strata are presented in the context of the long-term future of stored CO2. There are a number of features that indicate a high level of security against leakage and migration of gas back to the biosphere.

A procedure for the creation, testing, and filling of a salt cavern is presented. A critical requirement was to achieve a reasonable long-term prediction of the behaviour of the cavern during slow closure, while taking into account the pressure and volume behaviour of the gas within the cavern. This was achieved with a semi-analytical model that predicts long-term pressures and volume changes.

There appear to be no technical obstacles or undue risks identified that would militate against the use of salt caverns for permanent CO2 sequestration. It is an option that can be seriously considered in Alberta, or in other geographical locations where the geological conditions are suitable.

Introduction

Anthropogenic and naturally-generated greenhouse gases (CO2, CH4,...) are thought to be important factors in atmospheric warming, known as the greenhouse effect(1). Although the debate continues to be heated and a full consensus remains elusive, increasing political pressure is being placed on the fossil fuel energy industry (responsible for ~45% of anthropogenic CO2) to address atmospheric emissions. This requires assessing options such as energy conservation and switching to non-fossil fuels for energy production, emissions reduction, CO2 fixing in biomass, and direct CO2 capture and sequestration. A great deal of discussion on the economic impacts of these options, sociological changes, and the responsibility of individual countries has taken place in the public and the scientific media. These vital and contentious issues are set aside here so that the technological aspects of one of the geological sequestration options(2, 3) can be explored.

This article will address only the geological and technological factors in the potential use of salt solution caverns to permanently (>1,000 years) store CO2. More specifically, we will examine a particular salt deposit in Alberta, the Lotsberg Salt, which is near to present and future major stationary point sources of CO2 from heavy oil and oil sands development.

Overview

Sequestration Options(a)

There are a number of options for permanent sequestration of greenhouse gases in geological media(4), and the realistic ones will be briefly reviewed. Large point sources of CO2 may arise during energy generation (coal-, oil-, or gas-fired power plants), from natural gas processing facilities that remove CO2 from produced gas, from cement kilns, oil refineries and steam generation facilities, and from other manufacturing processes where large amounts of energy are consumed.

Evaluation of the CO2 Sequestration Capacity in Alberta's Oil and Gas Reservoirs at Depletion and the Effect of Underlying Aquifers

Abstract

Geological sequestration of CO2 is an immediately available means of reducing CO2 emissions into the atmosphere from major point sources, such as thermal power plants and the petrochemical industry, and is particularly suited to landlocked Alberta. Trapping CO2 in depleted hydrocarbon reservoirs and through enhanced oil recovery (EOR) will likely be implemented first because the geological conditions are already well known and the infrastructure is partially in place. Assuming that the volume occupied by the produced oil and gas can be backfilled with CO2, the ultimate theoretical CO2 sequestration capacity in Alberta's gas reservoirs not associated with oil pools is estimated to be 11.35 Gt. The sequestration capacity in the gas cap of oil reservoirs is 865 Mt of CO2, but this additional capacity will become available sometime in the more distant future after both the oil and gas have been produced from these reservoirs. The theoretical ultimate sequestration capacity at depletion in oil pools in single drive and primary production is only 615 Mt of CO2.

Depending on the strength of the underlying aquifer, water invasion has the effect of reducing the theoretical CO2 sequestration capacity of depleted reservoirs by 60% on average for oil pools and 28% on average for gas pools, if the reservoir is only allowed to be repressurized back to its initial pressure. Weak aquifers have no effect on reservoir CO2 sequestration capacity. If other factors are taken into account, such as reservoir heterogeneity and CO2 mobility and buoyancy, then the effective ultimate CO2 sequestration capacity at depletion in hydrocarbon reservoirs in Alberta is estimated to be 9,860 Mt for nonassociated gas pools and 242 Mt for oil reservoirs currently in single drive and primary production. However, most reservoirs have a relatively small CO2 sequestration capacity, rendering them largely uneconomic. In addition, shallow reservoirs are inefficient because of low CO2 density, while very deep reservoirs may be too costly because of the high cost of CO2 compression, and also inefficient in terms of the net CO2 sequestered. If only the largest reservoirs in the depth range of approximately 900 m to 3,500 m are considered, each with an ndividual capacity greater than 1 Mt CO2, then the number of reservoirs in Alberta suitable for CO2 sequestration in the shortto- medium term drops to 565 non-associated gas reservoirs and 22 oil reservoirs in single drive or primary production, with a practical CO2 sequestration capacity of 2,660 and 115 Mt of CO2, respectively. This practical capacity of Alberta's oil and gas reservoirs for CO2 sequestration may provide a sink for CO2 captured from major point sources that is estimated to last for a few decades.

Introduction

As a result of anthropogenic CO2 emissions, atmospheric concentrations of CO2, a greenhouse gas, have risen from pre-industrial levels of 280 ppm to the current level of more than 360 ppm, primarily as a consequence of fossil-fuel combustion for energy production. This has led to climate warming and weather changes.

Screening, Evaluation, and Ranking of Oil Reservoirs Suitable for CO2-Flood EOR and Carbon Dioxide Sequestration

Abstract

Geological sequestration of CO2 in EOR operations has been recognized as one of the more viable means of reducing emissions of anthropogenic CO2 into the atmosphere in response to global climate change. This option, which lowers the cost of CO2 sequestration by recovering incremental oil, is particularly attractive in mature sedimentary basins, such as the Western Canada Sedimentary Basin where many oil pools are near depletion, and where most of the needed infrastructure is already in place. A method was developed for the rapid screening and ranking of oil reservoirs suited for CO2-flood EOR, which is particularly fit for a very large number of reservoirs as listed in eserves databases, and which does not require detailed reservoir engineering analysis. Oil reservoirs are screened on the basis of oil gravity, reservoir temperature and pressure, minimum miscibility pressure and remaining oil saturation, to determine their suitability for CO2 flooding, and an analytical method is used to calculate the incremental oil recovery at breakthrough and for any hydrocarbon pore volume (HCPV) fraction of injected CO2. In addition, the reservoir capacity for CO2 sequestration is calculated. eservoirs are ranked according to a set of criteria with corresponding assigned weights to identify and select the best-suited reservoirs for CO2 flooding and sequestration.

The method was applied to 8,637 oil reservoirs listed in the 2000 Alberta reserves database. Of these, 4,470 passed the screening criteria and were ranked based on technical and performance characteristics. Preliminary calculations predict that 150 × 106, 422 × 106, or 558 × 106 m3, of additional oil could be produced from Alberta's reservoirs at breakthrough, and at 50% and 100% HCPVof injected CO2, respectively; meanwhile sequestering 127, 591 and 1,118 Mt CO2, respectively. Thus, geological sequestration of CO2 in Alberta oil reservoirs suitable for CO2 flooding could provide a means for significantly reducing anthropogenic CO2 emissions from major point sources while, at the same time, realizing an economic benefit.

Introduction

As a result of anthropogenic CO2 emissions, atmospheric concentrations of CO2 have risen significantly from pre-industrial levels, primarily as a consequence of fossil-fuel combustion for energy production. Circumstantial evidence suggests that the increase in greenhouse-gas concentrations in the atmosphere leads to climate warming and weather changes(1). In response to the need to avoid irreversible climate changes and the associated risks resulting from greenhouse effects, most of the developed world, including Canada, has committed to reduce by 2012 the release into the atmosphere of anthropogenic CO2 to levels below those of 1990. However, although the intensity of CO2 emissions has markedly decreased, Canada's emissions have increased steadily since 1990 as a result of economic development.

Given the inherent advantages, such as large resources, availability, ease of transport and storage, and competitive cost, fossil fuels, which currently provide about 75% of the world's energy, will likely remain as a major component of the world's energy supply for at least this century(1, 2). In light of this, producing regions, such as Western Canada, need to find ways to both increase oil production and reduce CO2 emissions.

Geological Sequestration of Anthropogenic Carbon Dioxide in the Western Canada Sedimentary Basin: Suitability Analysis

Abstract

Geological sequestration of anthropogenic carbon dioxide is a potential solution to the release into the atmosphere of CO2, a greenhouse gas thought of as significantly contributing to the global warming trend observed since the beginning of the industrial revolution. Basically, CO2 can be sequestered in geological media:through enhanced oil recovery (EOR),by storage in depleted oil and gas reservoirs,through replacement by CO2 of methane in deep coal beds (ECBMR),by injection into deep saline aquifers, and

by storage in salt caverns. Criteria in assessing the suitability of a sedimentary basin for CO2 sequestration are:tectonism and geology,the flow of formation waters and geothermal regime, andthe existence of storage media (hydrocarbon reservoirs, coal seams, deep aquifers and salt structures).

Generally, the Western Canada Sedimentary Basin is suitable for CO2 sequestration by all means because it is tectonically stable, it has regional-scale aquifers confined by aquitards or aquicludes, and it has oil and gas reservoirs in various stages of depletion, uneconomic coal seams, and extensive salt beds. However, various regions in the basin have different degrees of suitability, ranging from not suitable along the eastern edge of the basin, to extremely suitable in southwestern and central Alberta. Most major CO2 producers, such as power plants and refineries around Edmonton, are found in regions that are unsuitable for CO2 sequestration in geological media; however, some, such as the oil sands plants in the Athabasca area, are in regions that are not suitable. This analysis of the suitability of the Western Canada Sedimentary Basin for CO2 sequestration in geological media should provide industry and governments with essential information needed for developing plans and policies in response to climate change effects of anthropogenic greenhouse gas emissions into the atmosphere.

Introduction

Human activity since the industrial revolution had the effect of increasing atmospheric concentrations of gases with a greenhouse effect, such as carbon dioxide (CO2) and methane (CH4), leading to climate warming and weather changes(1, 2). Because of its relative abundance compared with the other greenhouse gases, CO2 is by far the most important, being responsible for about 64% of the enhanced "greenhouse effect"(1). On a sectoral basis, the energy sector contributes globally the most (45%) to anthropogenic (produced by human activity) effects on climate change(3). The high use of fossil fuels (85% of the world's energy needs), foreseen to continue well into the future(2, 4), is the major contributor to increased emissions of CO2 into the atmosphere. Thus, a major challenge in mitigating anthropogenic (man-made) effects on climate change is the reduction of these emissions.

Figure 1 shows Canada's profile in CO2 emissions by sector and by province. The profile of CO2 emissions in the Western Canada Sedimentary Basin is different from the national and other regions' profile because the basin is a major North American producer of fossil fuels.

A Multidisciplinary Approach To Reservoir Characterization: The Provost Upper Mannville B Pool

Abstract

The Provost Upper Mannville B Pool of the heavy oil belt in east central Alberta is contained in McLaren Formation sands of Upper Mannville (Lower Cretaceous) age. The reservoir is up to 35 m thick and contains local areas of underlying water, a water-in-oil transition zone and patches of overlying gas.

The reservoir sands were deposited in fluvial environments filling the McLaren valley as it was aggraded during a sea level rise. The sands are mineralogically mature and composed predominantly of quartz. The reservoir pore systems are being characterized using petrographic image analysis techniques. Actual pore images obtained from thin sections are used to provide petrophysical data and to correlate the pore systems with geological facies. An important feature of the reservoir is the presence of zones of shale clasts in a sand matrix. These zones vary in thickness from several centimetres to several metres. Shale clasts constitute as much as 85% by volume in some zones and thus represent a significant barrier to vertical fluid flow. In order to numerically simulate the impact of the shale clast zones on recovery processes, parameters such as kh and kv have to be estimated. To arrive at realistic parameters, small-scale numerical models, based on actual clast distributions from core, have been constructed and equivalent alues for kh and kv have been obtained at the core and grid block scale.

Introduction

The oil sands and heavy oil deposits of western Canada with their impressive (471.6 × 109 m3(1–3)) resources represent Canada's "ace-in- the-hole" for future energy resources. Of these resources only a small portion is recoverable by mining methods. The greatest percentage must be recovered by in situ techniques. The oil sands and heavy oil reservoirs are complex and heterogeneous, and an integrated team of geologists, petrophysicists, reservoir engineers and numerical modellers is needed to develop processes specific to particular reservoirs for the recovery of these resources. These recovery processes need to be based on a detailed characterization of the reservoir. It was with this in mind that the Alberta Geological Survey, in its Joint Oil Sands Geology Program with the Alberta Oil Sands Technology and Research Authority (AOSTRA) and the Alberta Department of Energy, initiated a project to characterize oil sands/heavy oil reservoirs. The objective is to develop and evaluate techniques for the detailed characterization of oil sands and heavy oil reservoirs for use in numerical process simulations.

This paper reports on studies carried out in the Provost Upper Mannville B Pool In this project a detailed geological characterization of the reservoir has served as a basis on which specific aspects of the reservoir description (or characterization) are focussed on, using novel techniques. The pore systems of the more "uniform" portions of the reservoir have been characterized at the pore scale using petrographic image analysis techniques and relating geology to permeability.