Reservoir Overpressure Research Articles

The Influence of Viscoelastic Crustal Rheologies on Volcanic Ground Deformation: Insights From Models of Pressure and Volume Change

AbstractInelastic rheological behavior, such as viscoelasticity, is increasingly utilized in the modeling of volcanic ground deformation, as elevated thermal regimes induced by magmatic systems may necessitate the use of a mechanical model containing a component of time‐dependent viscous behavior. For the modeling of a given amplitude and footprint of ground deformation, incorporating a viscoelastic regime has been shown to reduce the magma reservoir overpressure requirements suggested by elastic models. This phenomenon, however, is restricted to pressure‐based analyses and the associated creep behavior. Viscoelastic materials exhibit additional constitutive time‐dependent behaviors, determined by the stress and strain states, that are yet to be analyzed in the context of volcanic ground deformation. By utilizing a mechanically homogeneous model space and distinct reservoir evolutions, we provide a comparison of three viscoelastic rheological models, including the commonly implemented Maxwell and Standard Linear Solid configurations, and their time‐dependent behaviors from a fundamental perspective. We also investigate the differences between deformation time series resulting from a pressurization or volume change, two contrasting approaches that are assumed to be equivalent through elastic modeling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress‐based pressurization models imparting enhanced deformation relative to the elastic models, thus reducing pressure requirements. Strain‐based volumetric models, however, exhibit reduced levels of deformation and may produce episodes of apparent ground subsidence induced by source inflation or vice versa, due to the relaxation of crustal stresses, dependent on whether the reservoir is modeled to be expanding or contracting, respectively.

Estimation of reduced pressure buildup due to brine seepage using a convolution technique

CO2 sequestration involves injection of large volumes of CO2 into a storage reservoir bounded above and below by low-permeability seals. Although capillary effects are usually sufficient to prevent CO2 leakage through the caprock, the native brine will slowly migrate through the over- and underlying units when subject to overpressure in the reservoir. At large scales and over long time periods, diffuse fluid migration may have an important impact on large-scale pressure development. Typically, simulation studies of CO2 injection often omit the possibility of brine migration through the top and bottom boundaries of the reservoir. One reason is that vertical fluid flow requires additional resolution outside of the storage reservoir that poses a large computational burden. Therefore, analytical methods are an attractive approach for capturing diffuse brine leakage. In low-permeability layers, the flow is predominantly vertical, and the local system can be reduced to a 1D (vertical) equation. This can be solved on a semi-infinite (vertical) domain for a thick seal (> 10 − 20m), with the reservoir overpressure applied as a boundary condition. Because the boundary condition is not constant in time, the resulting solution is a convolution integral that must be computed at regular time intervals. In this paper, we couple the analytical solution for vertical brine leakage with a vertical equilibrium simulator (VESA). The VESA simulator is a reduced-dimension (2D) numerical model for two-phase flow in gravity-segregated systems, which is an appropriate assumption for large-scale CO2 storage. Coupling analytical solution for brine migration into a numerical simulator gives greater flexibility modeling injection into heterogeneous reservoirs. We find that the additional computational burden of the convolution integral is minimal compared to solving the full 3D system at the correct resolution. A solution for pressure development in the adjacent strata is also obtained analytically, leading to a fully 3D representation of pressure in the system. The coupled code is benchmarked with a fully analytical solution, and then applied to large-scale CO2 injection into the Utsira formation. We study the impact of diffuse brine leakage on development of large-scale overpressure in the storage reservoir for scenarios of high-volume CO2 injection.

Damage and Strain Localization Around a Pressurized Shallow‐Level Magma Reservoir

AbstractStructures developing above long‐term growing shallow‐level magma reservoirs, such as resurgent domes, may contain information on the reservoir itself. To understand the formation of such tectonic features, we have investigated the deformation process around a shallow pressurized magma reservoir embedded in a damaging elastic volcanic edifice. Our model allows evidencing the effect of the progressive damage in producing the fault pattern associated to tectonic surface deformation. Damage is first isotropic around the cavity and constitutes a damaged zone. Then the free‐surface effect appears, and an anisotropic shear strain develops from the boundary of the damaged zone; it localizes on reverse faults that propagate upward to the surface. When the surface deformation is sufficient, normal faulting appears. Finally, the complete structure shows an undeformed wedge above the damaged zone. This structure is similar to those found by analog modeling and from field geologic observations. From this model, we found a relation to estimate the reservoir radius and depth from the graben and dome widths. From limit analysis, we deduced an analytical expression of the magma reservoir pressure which provides a better understanding of the magma pressure buildup during doming. The dip of reverse faults limiting the dome can be inferred from the minimal pressure required to rupture the crust around the reservoir. Finally, the magma reservoir overpressure, the dip of the faults, the reservoir depth, and the damaged zone radius are inferred from three parameters: the ratio ρR computed from the dome and graben widths, the cohesion, and the friction angle.

Formation conditions and accumulation characteristics of Bozhong 19-6 large condensate gas field in offshore Bohai Bay Basin

Based on the study of natural gas resource, low buried hill trap formation mechanism, high quality reservoir control factors and natural gas preservation conditions, the formation conditions and reservoir accumulation characteristics of Bozhong 19-6 large condensate gas field were summarized. Large gas generation potential of multiple sets of thick humic-sapropelic source rocks in high maturity stage in Bozhong depression was the basis of large gas field formation. The multi-stage tectonic evolution since Indosinian period formed large-scale buried hill traps. The Tanlu fault activity formed multi-type reservoirs, and buried hill metamorphic rock of Archean and sand-conglomerate of Kongdian Formation were high-quality reservoirs. Thick overpressure lacustrine mudstone and weak neotectonic movement provided good preservation conditions. Bozhong 19-6 gas reservoir was a condensate gas reservoir with very high condensate oil content, and the gas origin was humic-sapropelic and kerogen-cracking gas, and the gas field had large gas thickness, high gas column characteristics and the accumulation process was first oil and then gas. The buried hill reservoir was a massive reservoir and the Kongdian reservoir was a stratified reservoir. The gas field had multi-channel hydrocarbon intense charge from overpressure source rocks, atmospheric-weak overpressure reservoir favorable for accumulation, thick overpressure mudstone caprock favorable for preservation, and natural gas ultra-late rapid accumulation model.

Including seismic risk mitigation measures into the Levelized Cost Of Electricity in enhanced geothermal systems for optimal siting

The seismic risk associated with deep fluid injection in Enhanced Geothermal Systems can be mitigated by stopping reservoir stimulation when the seismic risk becomes unacceptable or by reducing production flow rates when seismicity occurs during the operational phase. So far, none of these mitigation measures have been included in the Levelized Cost Of Electricity. A meta-model is introduced that estimates the optimal price of electricity, based on an analytical geothermal energy model, and updates this cost to include the outlay for mandatory seismic risk mitigation measures. The proposed energy model computes both electricity production and heat credit. The costs added during reservoir stimulation are based on the probability of abandoning an injection well, based on a traffic-light system, defined as the ratio of scenarios that exceed a given seismic safety threshold in the risk space. In the production phase, the net energy generated is reduced by clipping the production flow rate so that the reservoir's overpressure does not exceed the regional minimum effective stress. Based on a generic geothermal triplet, we investigate the trade-off between heat credit and seismic risk mitigation cost. The added cost, mostly due to financial risk aversion, shifts the optimal site for a plant from between a few kilometres to tens of kilometres away from populated areas, for increasingly vulnerable building stocks. Finally, using a simple yet realistic optimisation strategy, we study the role that a seismic safety standard plays for determining the number of EGS plants that can be sited in a given region.

Effect of formation overpressure on the reservoir diagenesis and its petroleum geological significance for the DF11 block of the Yinggehai Basin, the South China Sea

Abstract Overpressure is an essential factor that controls the accumulation and distribution of oil and gas. In this study, we systematically studied the effects of overpressured fluid activities on the diagenesis and diagenetic evolution of reservoirs in the DF11 Block of the Yinggehai Basin, the South China Sea. The employed methods included thin-section observation, scanning electron microscopy, geochemical analysis of formation water, and C-O isotopic study. The formation water in the DF11 Block was classified as NaHCO3-type continental sedimentary water, showing high HCO3− content and extremely low concentrations of Ca2+ and Mg2+. The formation overpressure drove the carbonate ion-bearing thermal fluid flowing into the top boundary of the overpressure. The carbonates ions were re-precipitated from the fluid due to decreasing pressure and temperature. As a result, a tightly plugged zone that consisted of high carbonate cement content was formed. On the other hand, the overpressure reduced the sources of carbonate cement and limited the secondary growth of quartz by inhibiting the transformation of clay minerals. Consequently, the primary pores in the reservoir were largely preserved. Furthermore, the overpressure increased the solubility of CO2 and generated a large amount of H+ ions in the CO2-rich reservoir, which promoted the dissolution of feldspar and cements in the reservoir. The formation overpressure restrained the mechanical compaction, enhanced the dissolution of minerals, and restricted the cement production, all of which facilitated the formation of high-porosity and mid-depth overpressure reservoirs in the DF11 Block.

Two-phase flow visualization under reservoir conditions for highly heterogeneous conglomerate rock: A core-scale study for geologic carbon storage

Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; however, understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. This study presents, for the first time, a two-phase (CO2 and brine) flow visualization under reservoir conditions (10 MPa, 50 °C) for a highly heterogeneous conglomerate core obtained from a real CO2 storage site. Rock heterogeneity and the porosity variation characteristics were evaluated using X-ray computed tomography (CT). Multiphase flow tests with an in-situ imaging technology revealed three distinct CO2 saturation distributions (from homogeneous to non-uniform) dependent on compositional complexity. Dense discontinuity networks within clasts provided well-connected pathways for CO2 flow, potentially helping to reduce overpressure. Two flow tests, one under capillary-dominated conditions and the other in a transition regime between the capillary and viscous limits, indicated that greater injection rates (potential causes of reservoir overpressure) could be significantly reduced without substantially altering the total stored CO2 mass. Finally, the capillary storage capacity of the reservoir was calculated. Capacity ranged between 0.5 and 4.5%, depending on the initial CO2 saturation.

An analytical plane-strain solution for surface uplift due to pressurized reservoirs

In this paper, we present an analytical plane strain solution for surface uplift above pressurized reservoirs. The solution is based on a Fourier representation of the reservoir pressure. The plane strain model is developed in two stages: First, an exact solution is derived for the displacement field for the reservoir alone subjected to a periodic overpressure distribution of one wavelength. This one-layer model forms the basis for the analytical plane strain solution for a two-layer model — a pressurized reservoir with an overburden. We give an example where numerically computed uplift is quite accurately estimated by a simple 1D estimate, except for in the near well area. The plane-strain solution is well suited to study conditions for when the simple 1D approximation of the uplift is accurate. A condition for the accuracy of the simple 1D approximation is first derived for just the reservoir expanded by a periodic overpressure distribution of one wavelength, which corresponds to one term in a Fourier series. The 1D estimate is accurate for wavelengths larger than 2π times the reservoir thickness. Then, a condition is derived for when the 1D estimate is accurate for the two-layer model. We show that the wavelength of the overpressure distribution must be larger than 2π times the maximum of the reservoir thickness and the overburden thickness for the 1D approximation to be accurate. We demonstrate how uplift is computed from a Fourier decomposition of the reservoir overpressure. The resulting uplift is analysed in terms of Fourier coefficients, using the knowledge of how a single wavelength behaves. The analytical results for the displacement field and the uplift are tested by comparison with finite element simulations, and the match is excellent.

Integrated CO2 Storage and Brine Extraction

Carbon dioxide (CO2) capture, utilization, and storage (CCUS) can reduce CO2 emissions from fossil fuel power plants by injecting CO2 into deep saline aquifers for storage. CCUS typically increases reservoir pressure which increases costs, because less CO2 can be injected, and risks such as induced seismicity. Extracting brine with enhanced water recovery (EWR) from the CO2 storage reservoir can manage and reduce pressure in the formation, decrease the risks linked to reservoir overpressure (e.g., induced seismicity), increase CO2 storage capacity, and enable CO2 plume management. We modeled scenarios of CO2 injection with EWR into the Rock Springs Uplift (RSU) formation in southwest Wyoming. The Finite Element Heat and Mass Transfer Code (FEHM) was used to model CO2 injection with brine extraction and the corresponding increase in pressure within the RSU. The model was analyzed for pressure management, CO2 storage, CO2 saturation, and brine extraction due to the quantity and location of brine extraction wells. The model limited CO2 injection to a constant pressure increase of two MPa at the injection well with and without extracting brine at hydrostatic pressure. We found that brine extraction can be used as a technical and cost-effective pressure management strategy to limit reservoir pressure buildup and increase CO2 storage associated with a single injection well.

An analysis of the nonlinear magma‐edifice coupling at Grimsvötn volcano (Iceland)

AbstractContinuous monitoring of seismicity and surface displacement of active volcanoes can reveal important features of the eruptive cycle. Here high‐quality GPS and earthquake data recorded at Grimsvötn volcano by the Icelandic Meteorological Office during the 2004–2011 intereruptive period are analyzed. These showed a characteristic pattern, with an initial ∼2 year long exponential decay followed by ∼3 year long constant surface displacement inflation rate. We model it by using a one magma reservoir model in an elastic damaging edifice, with incompressible magma and constant pressure at the base of the magma conduit. Seismicity rate and damage were first modeled, and simple analytical expressions were derived for the magma reservoir overpressure and surface displacement as functions of time. Very good fits of the seismicity and surface displacement data were obtained by fitting only three phenomenological parameters. Characteristic time and power strain show maxima from which reference times were inferred that split the intereruptive period into five periods. After the pressurization periods, damage occurring in the third period induced weakly nonlinear variations in magma overpressure and flow, and surface displacement. During the fourth period, the damage dominated and variations became more strongly nonlinear, the reservoir overpressure decreased, and magma flow increased. This process lasted until the power strain reached its second maximum, where instability was generalized. This maximum is a physical limit, the occurrence of which shortly precedes rupture and, eventually, eruption. This analysis allows characterization of the state of the volcanic edifice during the intereruptive period and supports medium‐term prediction of rupture and eruption.

A two‐step model for dynamical dike propagation in two dimensions: Application to the July 2001 Etna eruption

AbstractWe developed a hybrid numerical model of dike propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure, the magma physical properties (density and viscosity), and the crustal density and stress field. This model is used to characterize the influence of surface load changes on magma migration toward the surface. We confirm that surface loading induced by volcanic edifice construction tends both to attract the magma and to reduce its velocity. In contrast, surface unloading, for instance, due to caldera formation, tends to divert the magma to the periphery‐retarding eruption. In both cases the deflected magma may remain trapped at depth. Amplitudes of dike deflection and magma velocity variation depend on the ratio between the magma driving pressure (source overpressure as well as buoyancy) and the stress field perturbation. Our model is then applied to the July 2001 eruption of Etna, where the final dike deflection had been previously interpreted as due to the topographic load. We show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field. We use the dike propagation duration to estimate the magma overpressure at the dike bottom to be less than 4 MPa. This approach can be potentially used to forecast if, where, and when propagating magma might reach the surface when having knowledge on the local stress field, magma physical properties, and reservoir overpressure.

Fault-valve behaviour and episodic gas flow in overpressured aquifers - evidence from the 2010 Ms5.1 isolated shallow earthquake in Sichuan Basin, China

We investigated the 2010 Ms5.1 Suining earthquake (a temporally and spatially isolated event) centred in Moxi gas field in the tectonically stable central region of Sichuan Basin, China. The focal depth is estimated to be approximately 2.8 km and thus the earthquake is nucleated in Triassic marine sediment, coincident with the depths of the top boundary of an overpressured gas reservoir. The strike/dip/rake of the estimated source fault is 223/48/122, showing a rupture area of a dimension of ∼2.4 km along a blind reverse fault in agree with the geological structures and regional stress regime of this area. Through an integrated analysis, we propose that the associated fault slip of this earthquake was most probably initiated and driven by gas injection from the underlying overpressured reservoir into the shallower gas reservoirs. No aftershocks following the Suining earthquake indicates that the gas injection from the deeper reservoir is somewhat episodic and a fault-valve behaviour.

Fault activation and induced seismicity in geological carbon storage – Lessons learned from recent modeling studies

In the light of current concerns related to induced seismicity associated with geological carbon sequestration (GCS), this paper summarizes lessons learned from recent modeling studies on fault activation, induced seismicity, and potential for leakage associated with deep underground carbon dioxide (CO2) injection. Model simulations demonstrate that seismic events large enough to be felt by humans require brittle fault properties and continuous fault permeability allowing pressure to be distributed over a large fault patch to be ruptured at once. Heterogeneous fault properties, which are commonly encountered in faults intersecting multilayered shale/sandstone sequences, effectively reduce the likelihood of inducing felt seismicity and also effectively impede upward CO2 leakage. A number of simulations show that even a sizable seismic event that could be felt may not be capable of opening a new flow path across the entire thickness of an overlying caprock and it is very unlikely to cross a system of multiple overlying caprock units. Site-specific model simulations of the In Salah CO2 storage demonstration site showed that deep fractured zone responses and associated microseismicity occurred in the brittle fractured sandstone reservoir, but at a very substantial reservoir overpressure close to the magnitude of the least principal stress. We conclude by emphasizing the importance of site investigation to characterize rock properties and if at all possible to avoid brittle rock such as proximity of crystalline basement or sites in hard and brittle sedimentary sequences that are more prone to injection-induced seismicity and permanent damage.

Origin of abnormal high pressure and its relationship with hydrocarbon accumulation in the Dina 2 Gas Field, Kuqa Depression

AbstractBased on distribution of formation pressure by indirect estimation and formation testing, this study investigates origin of abnormal high pressure in the Dina 2 Gas Field in the Kuqa Depression in combination with the latest research findings. Contribution of major overpressure mechanisms to this gas field is estimated, and generation of the abnormal high pressure as well as its relationship with natural gas accumulation is explored. Disequilibrium compaction, tectonic stress, and overpressure transfer are the major overpressure mechanisms. Overpressure transfer resulted from vertical opening of faults and folding is the most important cause for the overpressure. Gas accumulation and abnormal high pressure generation in the reservoirs of the Dina 2 Gas Field show synchroneity. During the early oil-gas charge in the Kangcun stage, the reservoirs were generally normal pressure systems. In the Kuqa deposition stage, rapid deposition caused disequilibrium compaction and led to generation of excess pressure (approximately 5–10MPa) in the reservoirs. During the Kuqa Formation denudation stage to the Quaternary, reservoir overpressure was greatly increased to approximately 40–50MPa as a result of vertical pressure transfer by episodic fault activation, lateral overpressure transfer by folding and horizontal tectonic stress due to intense tectonic compression. The last stage was the major period of ultra-high pressure generation and gas accumulation in the Dina 2 Gas Field.

Formation and destruction mechanism as well as major controlling factors of the Silurian shale gas overpressure in the Sichuan Basin, China

Taking the Well JY1 and Well PY1 in the Eastern Sichuan Basin as examples, the formation mechanism of shale gas overpressure was studied by using the cross plot of acoustic versus density logging data. During the processes of hydrocarbon generation and the uplifting, the pressure evolution of fluids in shale gas layers was reconstructed by fluid inclusions and PVTSIM software. The major factors controlling the evolution of shale gas overpressure were established according to the study of fracture, the timing of the uplifting, and episodes of tectonic deformation. Our results showed that the main mechanism of overpressure in the Silurian shale gas reservoirs in the Sichuan Basin was the fluid expansion, which was caused by hydrocarbon generation. Since the Yanshanian, the strata were uplifted and fluid pressure generally showed a decreasing trend. However, due to the low compression rebound ratio of shale gas reservoir rocks, poor connectivity of reservoir rocks, and low content of formation water and so on, such factors made fluid pressure decrease, but these would not be enough to make up the effects of strata erosion resulting in a further increase in fluid pressure in shale gas reservoirs during the whole uplifting processes. Since the Yanshanian, the Well PY1 zone had been reconstructed by at least three episodes of tectonic movement. The initial timing of the uplifting is 130 Ma. Compared to the former, the Well JY1 zone was firstly uplifted at 90 Ma, which was weakly reconstructed. As a result, low-angle fractures and few high resistance fractures developed in the Well JY1, while high-angle fractures and many high resistance fractures developed in the Well PY1. In totality, the factors controlling the overpressure preservation in shale gas reservoirs during the late periods include timing of late uplifting, superposition and reconstruction of stress fields, and development of high-angle fractures.

Static arrangement of a capillary porous system (CPS): Modelling

The static arrangement is studied of a thin CPS wafer which is filled from below with a liquid metal. The CPS is modelled as a thin cylindrical disk that is resting on a flat wall. It is in contact with a reservoir that provides liquid lithium. Isothermal conditions are considered and a liquid metal layer is assumed to have been established on top of the CPS and reached an axisymmetric static arrangement. A numerical solution is obtained via the finite element methodology that solves the Young-Laplace equation which incorporates surface tension, gravitational, pressure and electrostatic forces. The layer thickness is predicted at static equilibrium as a function of the imposed pressure drop across the wafer, i.e. between the reservoir and the surrounding medium, and the wetting and dielectric properties of the liquid metal. It is seen that at large reservoir overpressure surface tension balances pressure forces and the liquid metal assumes the form of an almost hemispherical drop of small radius. Gravity is not important in this limit. As the pressure drop decreases the drop assumes an oblate shape and a thin film is gradually formed that entirely covers the CPS and extends onto the wetted rigid substrate. In this range, gravity balances pressure drop and surface tension and the film thickness is on the millimeter range, which is relatively large and has negative implications on the stability of the liquid metal layer as the electric field strength increases. Below a certain pressure drop the film in conjectured to become very thin, on the order of μm, and the disjoining pressure is expected to balance the imposed pressure drop across it. Such static arrangements have been reported in the literature and are favored in terms of stability of the CPS against j→×B→ effects.

The formation mechanism of overpressure reservoir and target screening index of the marine shale in the South China.

The formation mechanism of overpressure reservoir and target screening index of the marine shale in the South China.

Distribution and formation of tight oil in Qijia area, Songliao Basin, NE China

Abstract By using geologic, geochemical, well test, well drilling and well logging data, the formation conditions and distribution pattern of tight oil in Gao 3 and Gao 4 oil layers of Gaotaizi layer, Upper Cretaceous Qingshankou Formation, Qijia area, Songliao Basin were examined systematically. There are four favorable conditions for the formation of tight oil: high quality source rocks and reservoirs, good source and reservoir combination, and formation pressure. There are three series of source rocks in this area, K2qn1, K2qn2+3 and K2n1, which provided material basis for the tight oil reservoirs; reservoirs including a variety of sands like distributaries channel, mouth bar and sheet sand are large in total thickness, wide in lateral distribution and good in continuity, providing accumulation space for tight oil; reservoir rocks of delta front in direct contact with the hydrocarbon source rock or pinching out in hydrocarbon source rock like fingers or interbedded with hydrocarbon source rock, constituted good source-reservoir combinations; abnormal overpressure in tight oil reservoirs with the pressure factor of 1.2-1.5, provided drive force for tight oil migration and charging. The study shows tight oil of Gao 3 and Gao 4 oil layers in Qijia area is mainly distributed in the center of, and slope and terrace around the sag.

Influence of faulting on reservoir overpressure distribution in the Northern Carnarvon Basin

The Northern Carnarvon Basin has a complicated geological history, with numerous sub-basins containing varying formation thicknesses, lithology types, and structural histories. These settings make pre-drill pore pressure prediction problematic; the high number of kicks taken in wells shows this. Kicks suggest unexpected pore pressure was encountered and mudweights used were below formation pressure. The horst block penetrated by the Parker–1 well is focused on in this peer-reviewed paper. This horst is one of many lying along Rankin Trend’s strike. In this well, kicks up to 17.2 ppg (pounds per gallon) were taken in the Mungaroo reservoir. The authors investigate whether the kicks represent shale pressure—or rather, represent pressure transferred into foot-wall sandstones—by using well data from Forrest 1/1A/1AST1 and Withnell–1, and wells located in the Dampier Sub-basin and the hanging-wall to the horst. This anomalous pressure could result from either cross-fault flow from juxtaposed overpressured Dingo Claystone or transfer up faults from a deeper source. Using a well data derived Vp versus VES trend, the authors establish that the kicks taken in Parker–1 are more likely to result from pressure transfer using faults as conduits. These data lie off a loading trend and appear unloaded but likely represent elevated sand pressures and not in situ shale pressure. Pressure charging up faults in the Northern Carnarvon Basin has been recognised in Venture 1/1ST1, however, this paper presents a focused case study. Pressure transfer is noted in other basins, notably Brunei. From unpublished data, the authors believe that buried horst blocks, up-fault charging and adjacent overpressured shale may explain high reservoir pressures in other basins, including Nam Con Son in Vietnam.

Insulin Micropump with Embedded Pressure Sensors for Failure Detection and Delivery of Accurate Monitoring

Improved glycemic control with insulin pump therapy in patients with type 1 diabetes mellitus has shown gradual reductions in nephropathy and retinopathy. More recently, the emerging concept of the artificial pancreas, comprising an insulin pump coupled to a continuous glucose meter and a control algorithm, would become the next major breakthrough in diabetes care. The patient safety and the efficiency of the therapy are directly derived from the delivery accuracy of rapid-acting insulin. For this purpose, a specific precision-oriented design of micropump has been built. The device, made of a stack of three silicon wafers, comprises two check valves and a pumping membrane that is actuated against stop limiters by a piezo actuator. Two membranes comprising piezoresistive strain gauges have been implemented to measure the pressure in the pumping chamber and at the outlet of the pump. Their high sensitivity makes possible the monitoring of the pumping accuracy with a tolerance of ±5% for each individual stroke of 200 nL. The capability of these sensors to monitor priming, reservoir overpressure, reservoir emptying, outlet occlusion and valve leakage has also been studied.