Philip Ringrose

Satellite-based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide

Satellite-based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide D. W. Vasco 1 , Alessio Rucci 2 , Alessandro Ferretti 3 , Fabrizio Novali 3 , Rob Bissell 4 , Philip Ringrose 5 , Allan Mathieson 4 , and Iain Wright 4 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley; 2 Politecnico di Milano, Milano, Italy; 3 Tele-Rilevamento Europa-TRE, Milano, Italy; 4 BP Alternative Energy, Middlesex UK StatoilHydro Research Centre, Trondheim, Norway Interferometric Synthetic Aperture Radar (InSAR), gathered over the In Salah CO 2 storage project in Algeria, provides an early indication that satellite-based geodetic methods can be effective in monitoring the geological storage of carbon dioxide. An injected volume of 3 million tons of carbon dioxide, from one of the first large-scale carbon sequestration efforts, produces a measurable surface displacement of approximately 5 mm/year. Using geophysical inverse techniques we are able to infer flow within the reservoir layer and within a seismically detected fracture/ fault zone intersecting the reservoir. We find that, if we use the best available elastic Earth model, the fluid flow need only occur in the vicinity of the reservoir layer. However, flow associated with the injection of the carbon dioxide does appear to extend several kilometers laterally within the reservoir, following the fracture/fault zone. Introduction reflectors of suitable quality, InSAR can be used to detect surface motion with an accuracy of a few millimeters. In this fashion, InSAR has contributed significantly to the intermediate and long-term monitoring of ground motion associated with numerous phenomena, such as groundwater variations, geothermal production, earthquake-related strain, tunneling and mining, and oil and gas production [Massonnet and Feigl, 1998; Burgmann et al., 2000]. We should note that geodetic monitoring, as described here, can be extended to offshore fields through the use of precision seafloor gravity and pressureobservations [Zumberge et al., 2008; Alnes et al., 2008] or possibly through the use of interferometric synthetic aperture sonar [Chang et al., 2000; Hansen et al., 2006]. The In Salah CO 2 Storage Project The geological storage of carbon dioxide (CO 2 ) is likely to be an important tool for preventing greenhouse gases from entering the atmosphere [Baines and Worden, 2004; Schrag, 2007]. This approach involves injecting large quantities of carbon dioxide underground using one or more deep boreholes. However, in order for such storage to be safe and effective, the CO 2 must remain at depth. Past experience with the use of CO 2 for secondary oil recovery suggests that the migration of carbon dioxide within the Earth can be complicated, and can differ from the movement of injected water or the flow of hydrocarbons [Lazaratos and Marion, 1997; Hoversten et al., 2003; Arts et al., 2004; White et al., 2004]. Due to the complexity of the movement of carbon dioxide within the Earth, and the desire to keep this greenhouse gas from migrating towards the surface and eventually reaching the atmosphere, there is a need to monitor the fate of the injected CO 2 . In many important settings, satellite-based geodetic techniques can fulfill the twin goals of long-term, cost- effective monitoring [Massonnet and Feigl, 1998; Burgmann et al., 2000]. Satellite-based surveillance can be less expensive, more frequent, and less invasive than other geophysical monitoring techniques such as seismic or electromagnetic methods. On dry land, Interferometric Synthetic Aperture Radar (InSAR) can provide high spatial resolution (a few meters or tens of meters) and almost monthly measurements of surface deformation. Roughly speaking, InSAR utilizes the phase change of radar reflections off the Earth’s surface to measure minute changes in the position of the reflection points [Massonnet and Feigl, 1998; Burgmann et al., 2000]. Given the presence of radar We utilize InSAR observations gathered over a site of active CO 2 storage to image ground motion induced by the injected fluid volume. The injected carbon dioxide is associated with the In Salah CO 2 storage project located in Algeria [Vasco et al., 2008; Ringrose et al., 2009], one of only two existing large-scale sequestration efforts, the other being the Sleipner field under the North Sea [Arts et al., 2004]. In addition, there are projects in which carbon dioxide is injected into partially depleted oil reservoirs as a means of sequestration as well as enhancing oil recovery, as in the Weyburn project in Canada [White et al., 2004]. The In Salah project, which has been operational since 2004, gathers excess carbon dioxide that is present in natural gas extracted from three adjacent gas fields. The carbon dioxide is compressed, dehydrated, and transported to three horizontal wells, where it is injected into a 1800 to 1900 m deep saline formation, down-dip of the gas fields. The target formation for the storage of the CO 2 is twenty meters of Carboniferous sandstone with approximately 15% porosity and an estimated permeability of 10 mD [Ringrose et al., 2009]. The sandstone formation is part of a northwest trending anticline that defines the natural gas field. The reservoir is overlain by more than a kilometer of interbedded shales which act as a barrier to flow. From 2004 to 2008 over 3 million tons of CO 2 have been injected into the formation. The project has a planned life-span of more than 20 years. Satellite-Based Monitoring Following the initiation of injection at In Salah, Tele- Rilevamento Europa (TRE) and Lawrence Berkeley National Laboratory acquired, processed, and analyzed satellite radar images from the European Space Agency’s (ESA)

CO2 sequestration monitoring and verification technologies applied at Krechba, Algeria

The In Salah project in Algeria is an industrial-scale CO2 storage project that has been in operation since 2004. CO2 from several gas fields, which have a CO2 content of 5–10%, is removed from the production stream to meet the sales gas-export specification of 0.3% CO2 . Rather than vent that separated CO2 to the atmosphere (as was normal industry practice for such gas plants), BP and its joint venture (JV) partner, Sonatrach, invested an incremental US

Deformation of Scottish Quaternary sediment sequences by strong earthquake motions

100 million in a project to compress, dehydrate, transport, and inject that CO2 into a deep saline formation downdip of the producing gas horizon. Statoil then joined the JV at production start-up in August 2004.

Petrophysical characterization of a heterolithic tidal reservoir interval using a process-based modelling tool

Summary Deformed Quaternary sand, silt, clay and peat sequences from four localities in Scotland are interpreted as seismites by the deformation history of liquefied, fluidized, slumped, and faulted units, and by comparison with seismites documented elsewhere. Two of the sequences consist of outwash sands and silts, deposited during the recession of the Devension ice cap in the region of Perth. Other deposits consist of glacial sands and interglacial peats in the Western Highlands, and glacio-lacustrine silts in the Glen Roy area; both probably deposited during the late stages of the Loch Lomond Readvance. Careful evaluation of internal geometries and deformation sequences reveals an intimate association of ball-and-illow, fluidization, dish, load, flame and ‘fault-grading’ structures which are most satisfactorily explained by prolonged ground shaking produced by shallow earthquakes. In some cases, potential fault sources for the inferred earthquakes have been identified.

Reservoir challenges of heterolithic tidal sandstone reservoirs in the Halten Terrace, mid-Norway

Heterolithic lithofacies in the Jurassic Tilje Formation, offshore mid-Norway, consist of three components – sand, silt and mud intercalated at the centimetre scale – and are generally difficult to characterize petrophysically with core and wireline data. A near-wellbore model of the lower part of the Tilje Formation in the Heidrun Field is constructed to illustrate the application of these results to formation evaluation studies. The sedimentological model is developed by detailed parameterization of a cored well interval and the petrophysical properties are based on core plug data, taking into account sampling bias and length scale. The variation in petrophysical properties as a function of sample volume is examined by calculating the representative elementary volume. The sensitivity of the representative permeability values to the contrast between the three components is studied and gives a better understanding of the flow behaviour of this system. These results are used to rescale the core plug data to a representative value and thereby quantify the uncertainty associated with the wireline-based estimates of porosity and horizontal permeability and to give an improved estimate of the kv/kh ratio.

Vertical permeability estimation in heterolithic tidal deltaic sandstones

Production from the Halten Terrace hydrocarbon province (Mid-Norwegian shelf) is mainly from heterolithic siliciclastic successions as well as diagenetically altered sandstones. Eight hydrocarbon fields are currently in production, which produce c. 840 000 BBL oil equivalent per day, with several new fields expected to come on stream in the next decade. This paper is an introduction to a thematic set on the characterization and modelling of heterolithic reservoirs and focuses on the three main types of heterogeneity: (1) heterolithic facies, (2) faulting and (3) diagenesis. Challenges vary according to field setting: shallow (1–3 km burial depth), deep (3–5 km) or very deep (currently up to 5.6 km). Water depths vary from 200 m to 500 m. Heterolithic sedimentary packages are composed of shale or siltstone layers intercalated with clean, but often thin, sandstone layers of varying lateral extent. These were deposited in Lower Jurassic tide-influenced or tide-dominated deltaic and estuarine environments along the margin of a shallow seaway. Hydrocarbon traps are formed by faulted and rotated fault blocks created during rifting. Faulting of these heterolithic facies is a critical parameter for fluid flow, with fault transmissibility and fault position often difficult to determine. Complex patterns of diagenetic cementation are an additional aspect of heterogeneity in the deeply buried reservoirs, such as the Smørbukk and Kristin fields. However, grain coatings of chlorite, illite/chlorite and illite have prevented or hindered the development of quartz overgrowths and allowed the preservation of anomalously high porosity and permeability. Modelling and assessing the impact of these reservoir uncertainties has included development of novel tools and methods, leading to a much-improved level of understanding, better prediction of recoverable reserves and significantly increased recovery factors.

Geological Investigations of Late and Post Glacial Earthquake Activity in Scotland

A method for estimation of vertical permeability in heterolithic tidal deltaic sandstones is proposed. Three-dimensional, stochastic, process-based models of sedimentary bedding are used to give estimates for the effective permeability of heterolithic tidal sandstone units where heterogeneities in the sandstone and mudstone components are evaluated explicitly. Subsurface core (probe permeameter) data from two contrasting reservoir intervals in the Tilje Formation, offshore mid-Norway, have been used to derive representative petrophysical properties for the models. These data illustrate the nature of petrophysical variability in heterolithic sandstones and provide estimates of the mean and standard deviation of sandstone permeability at the lamina scale. The coefficient of variation, Cv, for permeability within sandstone beds is found to be around 0.5 while the Cv for heterolithic units is in the range of 1.0 to 4.0 (i.e. very heterogeneous). Measurement of mudstone permeability is a challenge; however, a limited set of mudstone (pulse-decay) measurements gives values in the range of 10−6 mD to 10−2 mD. Effective vertical permeability is mainly a function of mudstone fraction with different characteristics above and below the percolation threshold. Vertical permeability functions have been integrated with conventional well logs and compared with available subsurface estimates for vertical permeability.

Flow through fault systems in high-porosity sandstones

Evidence for palaeoseismicity in Scotland is presented and includes evidence of: (1) Surface fault movement during late and post glacial time; (2) Soft-sediment deformation in lacustrine sediment attributable to seismic ground shaking; (3) Large landslides triggered by earthquakes. These features are located in areas asssociated with rapid post glacial uplift. Events estimated to be as large as Magnitude 6.5–7.0 occurred around 10,000 years ago and Magnitude 5.0–6.0 events as recently as 2–3000 years ago. Shallow active stress measurements indicate the presence of the dominant horizontal compressive stress in directions around 130° (NW-SE). Stress and palaeoseismic field evidence form the basis to our hypothesis for post glacial fault activity, that: (1) Long-term stress controls fault ruptures associated with glacial rebound; (2) Fracture directions are orientated close to the direction of maximum horizontal compressive stress; (3) Displacements are predominantly strike-slip and are coseismic; (4) Glacially reactivated fracture zones continue to be the sources of present-day low level seismicity; (5) Surficial displacements result from the interaction of tectonic, lithostatic and hydrostatic stresses within a “partially detached” thin upper-crustal layer associated with glacial rebound.

High coverage sequencing of DNA from microorganisms living in an oil reservoir 2.5 kilometres subsurface

Abstract Small-scale faults in high-porosity sandstones form highly connected systems over a range of length scales. The effective permeability and oil recovery in such systems are strongly controlled by their geometrical architecture. This paper describes partially sealing faults in terms of: (a) characterization of their spatial distribution; (b) their effects on reservoir compartmentalization; and (c) their significance for fluid flow. Four suites of numerical flow simulations in highly compartmentalized fault systems are used to assess the influence of geometrical variability on single- and two-phase flow. The single-phase suites demonstrate that effective permeability is approximately linearly related to the number of fault-enclosed compartments present in a fault system. Use of a fault heterogeneity measure allows effective permeability for a geometrical case to be estimated from fault density and fault and matrix permeability. The two-phase simulations model water-floods, and show the relationships between length scale, fault system geometry and oil recovery. In a self-similar fault system, oil recovery is preferentially inhibited at the smaller length scales. Oil recovery is influenced by compartment volume distribution and is therefore sensitive to fault clustering. The fault density necessary to severely affect either single- or two-phase flow is likely to occur only close to structures which are large relative to the scale under consideration. This improved understanding of the relative influences of fault system geometry, density and petrophysics should lead to significantly improved hydrocarbon recovery from faulted high-porosity sandstones.

Ranking of stochastic realizations of complex tidal reservoirs using streamline simulation criteria

Microorganisms colonize a variety of extreme environments, and based on cultivation studies and analyses of PCR-amplified 16S rDNA sequences, microbial life appears to extend deep into the earth crust. However, none of these studies involved comprehensive characterizations of total DNA. Here we report results of a high-coverage DNA pyrosequencing of an apparently representative and uncontaminated sample from a deep sea oil reservoir located 2.5 km subsurface, attributing a pressure and temperature of 250 bars and 85°C respectively. Bioinformatic analyses of the DNA sequences indicate that the reservoir harbours a rich microbial community dominated by a smaller number of taxa. Comparison of the metagenome with sequences in databases indicated that there may have been contact between the oil reservoir and surface communities late in the sequence of geological events leading to oil reservoir formation. One specific gene, encoding a putative enolase, was synthesized and expressed in Escherichia coli. Enolase activity was confirmed and was found to be much more thermotolerant than for a corresponding E. coli enzyme, consistent with the conditions in the oil reservoir.