Simple Reservoir Research Articles

Impacts of geological store uncertainties on the design and operation of flexible CCS offshore pipeline infrastructure

Planning for Carbon Capture and Storage (CCS) infrastructure needs to address the impact of store uncertainties and store flow variability on infrastructure costs and availability. Key geological storage properties (pressure, temperature, depth and permeability) can affect injectivity and lead to variations in CO2 flow, which feed back into the pipeline transportation system. In previous storage models, the interface between the reservoir performance and the transportation infrastructure is unclear and the models are unable to provide details for flow and pressure management within a transportation network in response to changes in the operation of storage sites. Variation in storage demand due to daily and seasonal variations of fossil fuels uses and by extension CO2 flow is also likely to influence transportation infrastructure availability and the capacity to deliver. This work evaluates, at the level of infrastructure planning, the impact of geological uncertainty on CCS pipeline transportation and injection infrastructure. The analysis presented shows how to consider uncertainty in store properties in combination with CO2 flow variability to estimate the likely impact on pipeline infrastructure design. The operational envelope of the storage site infrastructure is estimated by combining the Darcy flow analysis of simple reservoir models with rigorous process simulation of the storage site wells. The proximity of wellhead conditions to the CO2 equilibrium line and the maximum velocities inside the well constrain the operational envelope of the storage site and limit the ability of the storage site infrastructure to handle CO2 flow variation. These factors, which are significantly influenced by variations in subsurface conditions, have also an impact on the design of the offshore pipeline infrastructure, needing to accommodate changes in pressure delivery requirements. Based on the evaluation of examples developed for different offshore transportation scenarios relevant to the United Kingdom, detailed insight on the expected impacts of store properties on pipeline transportation infrastructure design and operation is provided. For instance, it is found that enabling storage site flexibility is simpler in stores with an initial pressure above 20MPa. Given reductions in reservoir permeability, the requirements for pressure delivery are strongly dependent on the store temperature. Although the analysis is performed for specific geological characteristics in the North Sea the evaluation methodology is transferable to other locations and can be used for site screening to identify sites which are more flexible in terms of uncertainty in store performance.

Predicting intra-seasonal fluctuations of NDVI phenology from daily rainfall in the East Sahel: a simple linear reservoir model

ABSTRACTShort-term predictive models are essential for understanding the temporal relationships between the variability of impulsive daily rainfall and the attendant dynamics of vegetation development in rangelands, particularly for the water-limited, semi-arid East Sahel. After identifying selected rain-dependent sites in southeast Sudan, this report applies a procedure to predict seasonal biomass development in response to impulse-like daily storm events using a simple linear reservoir model as an analogue for the coupled soil–plant–atmosphere ecosystem. Key parameters are the characteristic time () of the reservoir and the number (n) of elementary reservoirs in series. Surface vegetative biomass is represented by the normalized difference vegetation index (NDVI) provided by the MODIS satellite MOD13A2 16 day 1 × 1 km product. Our specific metric is the commonly used differential NDVI, or δNDVI, the difference between the actual NDVI value and its long-term fallow season baseline. We review the concept of the modelling method, with selected application to 15 years (2000−2014) of NDVI data from a 51 × 51 km study area in the East Sahel, centred on the standard WMO Gauge 62752 at Gedaref City in southeast Sudan. Results indicate that as few as four – even as few as two – model parameters might be used to describe intra-seasonal to multiple-year vegetation dynamics. Allowing for inter-annually variable parameters, the predicted results exhibit a coefficient of determination of 0.96. An alternative formulation using a single set of four, seasonally dependent model parameters, globally determined from 15 years of observed reference data, results in a coefficient of determination of 0.90; a version using only two, globally determined model parameters works almost as well for the type of phenology characteristic of this area. In addition to enabling a number of applications that would benefit from the availability of a synthetic phenological time series that is solely dependent on daily rainfall, one of the most important applications may be for infilling data gaps in the observed time series, which for this area of the Sahel are typically encountered during early-season green-up; a critical time for most NDVI studies. We found that the 1 year lagged autocorrelation coefficient, and some version of the conventional rain use efficiency (RUE) factor with its associated annual correlation coefficient, are essential adjunct screening parameters when identifying sites with the highest inter-annual variability in biomass production (typical of the most natural rain-fed sites in this area).

Direct simulation Monte Carlo modeling of relaxation processes in polyatomic gases

Relaxation processes of polyatomic molecules are modeled and implemented in an in-house Direct Simulation Monte Carlo code in order to enable the simulation of atmospheric entry maneuvers at Mars and Saturn’s Titan. The description of rotational and vibrational relaxation processes is derived from basic quantum-mechanics using a rigid rotator and a simple harmonic oscillator, respectively. Strategies regarding the vibrational relaxation process are investigated, where good agreement for the relaxation time according to the Landau-Teller expression is found for both methods, the established prohibiting double relaxation method and the new proposed multi-mode relaxation. Differences and applications areas of these two methods are discussed. Consequently, two numerical methods used for sampling of energy values from multi-dimensional distribution functions are compared. The proposed random-walk Metropolis algorithm enables the efficient treatment of multiple vibrational modes within a time step with reasonable computational effort. The implemented model is verified and validated by means of simple reservoir simulations and the comparison to experimental measurements of a hypersonic, carbon-dioxide flow around a flat-faced cylinder.

Magma chamber recharging and tectonic influence on reservoirs: The 1986 eruption of Izu-Oshima

Although analytical expressions for deformation due to simple reservoirs and planar dikes have been in use for decades, seldom are there sufficient data to provide well-constrained detailed models of volcanic activity. Deformation due to the eruption of Miharayama, Izu-Oshima, Japan, in November 1986 was captured by a wider array of monitoring than usual at that time. Here we show that the first eruptive stage requires a shallow non-spherical source, extended perpendicular to the axis of maximum tectonic tension, together with a deeper reservoir. The shallow reservoir was partially recharged, from a deeper reservoir, during the eruption, with a magma ascent rate of ~10km/day; this has important implications for estimation of reservoir gas content. Precursory changes starting 2h before the second phase require dike propagation from at least 10km depth. Surface elevation changes are indicative of a long sub-surface dike. A model incorporating dikes and a deep (10km) reservoir, extended in the same direction as the dikes, provides a very good match to the data. Such reservoir geometry may explain why the eruption was unexpected.

3-D numerical approach to simulate the overtopping volume caused by an impulse wave comparable to avalanche impact in a reservoir

Abstract. The impact of an avalanche in a reservoir induces impulse waves, which pose a threat to population and infrastructure. For a good approximation of the generated wave height and length as well as the resulting overtopping volume over structures and dams, formulas, which are based on different simplifying assumptions, can be used. Further project-specific investigations by means of a scale model test or numerical simulations are advisable for complex reservoirs as well as the inclusion of hydraulic structures such as spillways. This paper presents a new approach for a 3-D numerical simulation of the avalanche impact in a reservoir. In this model concept the energy and mass of the avalanche are represented by accelerated water on the actual hill slope. Instead of snow, only water and air are used to simulate the moving avalanche with the software FLOW-3D. A significant advantage of this assumption is the self-adaptation of the model avalanche onto the terrain. In order to reach good comparability of the results with existing research at ETH Zürich, a simplified reservoir geometry is investigated. Thus, a reference case has been analysed including a variation of three geometry parameters (still water depth in the reservoir, freeboard of the dam and reservoir width). There was a good agreement of the overtopping volume at the dam between the presented 3-D numerical approach and the literature equations. Nevertheless, an extended parameter variation as well as a comparison with natural data should be considered as further research topics.

Towards a hierarchical parametrization to address prior uncertainty in ensemble-based data assimilation

Ensemble-based methods are becoming popular assisted history matching techniques with a growing number of field applications. These methods use an ensemble of model realizations, typically constructed by means of geostatistics, to represent the prior uncertainty. The performance of the history matching is very dependent on the quality of the initial ensemble. However, there is a significant level of uncertainty in the parameters used to define the geostatistical model. From a Bayesian viewpoint, the uncertainty in the geostatistical modeling can be represented by a hyper-prior in a hierarchical formulation. This paper presents the first steps towards a general parametrization to address the problem of uncertainty in the prior modeling. The proposed parametrization is inspired in Gaussian mixtures, where the uncertainty in the prior mean and prior covariance is accounted by defining weights for combining multiple Gaussian ensembles, which are estimated during the data assimilation. The parametrization was successfully tested in a simple reservoir problem where the orientation of the major anisotropic direction of the permeability field was unknown.

Abstract 629: Label-free isolation of circulating tumor cells for cytomorphological analysis

Abstract INTRODUCTION: The isolation of circulating tumor cells (CTCs) from the bloodstream is a promising tool for improving cancer prognosis, targeted therapies, and to understand the biology of metastatic processes. CTC analysis could benefit from conventional cytology staining procedures and cytopathologist expertise in classifying malignant cells from body fluids, to monitor CTC levels in patients in a low-cost system. However, CTCs are very rare with usually only 1-10 CTCs per mL of blood, which limited their use by cytopathologists in the past. Many current approaches for CTC isolation lead to high backgrounds of non-malignant cells (low purity) and/or capture over large areas, which are difficult to analyze microscopically. METHODS: Vortex is a label-free approach for rare malignant cell enrichment from bodily fluids. This technology requires no prior sample preparation, is cost effective and able to deliver viable and pure cells in a small volume. 21 blood samples were processed through our Vortex device. Larger CTCs are trapped within an array of micro-scale fluid vortices that form in simple rectangular reservoirs, while smaller erythrocytes and leukocytes pass through. The tumor cells are released into a small volume of buffer (< 500uL) and collected directly on a chamber slide for fixation and cytological staining using cytopathology standard operating procedures. After Papanicolaou staining, the slides are examined by cytopathologists. RESULTS: Our CTC collection method was optimized to reduce the loss of rare atypical cells during the cytology procedure (>70% cell recovery), improve the cytological staining quality (defined as good by cytopathologists), with an overall fast workflow (<12H). The collection protocol was designed to be cost-effective, and compatible with commercially available reagents and consumables to facilitate the broad use of our platform by research and clinical labs. Atypical cell populations were isolated by Vortex and identified through conventional Papanicolaou staining in the blood of 15/16 patients with metastatic lung (N = 10) and breast cancer (N = 6). No atypical cells were identified in the blood of 5/5 healthy donors. For 2 lung cancer patients, similar morphological features were seen in the corresponding primary tumors. CONCLUSION: Vortex CTC enrichment is compatible with existing cytology staining and analysis procedures, with significant advantages in terms of processing time, low cost, simplicity, cell integrity and purity. The detection of atypical cells in 15/16 metastatic cancer patient blood samples demonstrates the utility of Vortex enrichment combined with cytological staining as a non-invasive and cost effective method to monitor disease progression and help guide clinical decision-making. Citation Format: Corinne Renier, Edward Pao, Derek E. Go, James Che, Jianyu Rao, Nagesh Rao, Edward Garon, Jonathan Goldman, Rajan P. Kulkarni, Stefanie S. Jeffrey, Elodie Sollier, Dino Di Carlo. Label-free isolation of circulating tumor cells for cytomorphological analysis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 629. doi:10.1158/1538-7445.AM2015-629

Abstract 1997: Label-free concentration of viable breast cancer CTCs for single cell Western blotting

Abstract The isolation of circulating tumor cells (CTCs) in blood can aid in cancer prognosis, characterize genetic mutations for targeted therapies, and elucidate the biological mechanisms of metastasis. While CTCs provide clinical utility, there are still several technical difficulties with CTC isolation and analysis. CTCs are very rare (1-10 cells/mL of blood) and current isolation methods rely on immunocapture, require long sample preparation, and fail to deliver viable cells. Further, recent advances in single cell analysis of CTCs have been limited to genomic studies, in which DNA/mRNA does not provide a complete picture of CTCs at the functional level, as mRNA expression may only account for a portion of protein expression. The ability to study and measure the protein expression of CTCs could provide insight into the mechanisms driving cancer progression and signaling dysregulation. Unfortunately, conventional proteomic tools (e.g. immunocytochemistry and Western blot) either do not provide sufficient specificity or sensitivity toward single cell levels. Thus, there is a lack of tools that can provide quantitative protein analysis for rare CTCs. To address this gap, we enable rare cell Western blotting by combining isolation and proteomic technologies in a unique workflow: (i) Label-free Vortex enrichment of rare larger cells from blood samples. Larger cancer cells are trapped within an array of microscale fluid vortices that form in simple rectangular reservoirs, while smaller blood cells pass through. The cancer cells are stably maintained in the vortices, allowing for solution exchange, followed by release upon lowering the flow rate. With this device, we were able to release a small volume (∼500 μL) of concentrated, viable cancer cells (MCF7) from healthy blood, at high throughput, capture efficiency (35%), purity (>80%), and ∼10,000 fold enrichment. CTCs were also successfully extracted and enumerated from the blood of patients with breast cancer (N = 18, from 0.75 to 23.25 CTCs/mL). (ii) High-specificity and multiplexed protein analysis of rare cancer cells with single cell Western blotting (scWB). Enriched CTCs are placed into microwells patterned into a polyacrylamide gel for the scWB assay (in-situ chemical lysis in the microwells, electrophoresis into bulk gel layer, photo-immobilization, and subsequent antibody-probing of immobilized proteins). Here, we demonstrate scWB compatibility with rare cells by spiking MCF7s into normal blood and performing protein separations. The scWB is multiplex and can assay several target proteins simultaneously. Cells stained for surface markers (anti-EpCAM) are also compatible, and the scWB can resolve complete immunocomplexes without disrupting the location of the intracellular targets (GAPDH, ERK). With the integration of these technologies, we push the limits of quantitative protein analysis of CTCs, an essential step to better understand these rare populations. Citation Format: Elly Sinkala, Elodie Sollier, Corinne Renier, James Che, Stefanie S. Jeffrey, Amy E. Herr. Label-free concentration of viable breast cancer CTCs for single cell Western blotting. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1997. doi:10.1158/1538-7445.AM2015-1997

The Sleipner CO2 storage site: using a basin model to understand reservoir simulations of plume dynamics

When simulating CO2 storage, an accurate match to the observed CO2 plume distribution is a prerequisite to establishing the dominant flow physics, and forecasting the storage site behaviour beyond the observed and expected injection period. The scale of industrial CO2 storage pilots such as Sleipner, offshore Norway, is similar to that of small hydrocarbon fields, and lends itself to reservoir simulation. However, the reservoir conditions and dynamics are significantly different: oil and gas production are dominated by imbibition, which is suited to multi-phase Darcy flow simulation; whereas CO2 storage represents the injection of a non-wetting fluid that displaces the in situ brine. The latter process is often termed ‘drainage’, and with respect to simulation, is more typical of regional basin modelling and percolating oil and gas migration. The challenge of modelling CO2 storage is to accurately represent this drainage displacement at the reservoir scale on short decadal timescales. The advantage is the detailed observational dataset with which such models are constrained. Using a Darcy flow model, the first decade of reservoir simulations for Sleipner has been characterized by poor matches to the known plume distribution, and forecasted plume dynamics that persisted for decades-to-centuries beyond the injection period. To overcome this problem of poor simulated replication, and to test the veracity of long term plume dynamics, we applied a basin model to Sleipner, which simulated the gravity-dominated migration of a buoyant fluid using a capillary percolation method. The basin model achieved an accurate match to the observed CO2 plume distribution. This suggests that simple Darcy-based reservoir simulation forecasts are misleading. The basin modelling insights allowed us to revisit the reservoir simulations, and, focusing on benchmark models of the uppermost layers, approximate the gravity-dominated regime of percolating flow. A pressure-compensated black oil reservoir simulation accurately matches the distribution and dynamics of the uppermost layers. The reservoir simulations also indicate that dissolution of CO2 will contribute significantly to storage within decades. While both approaches have their limitations, a combination of basin modelling and reservoir simulation provide perspectives that illuminate the dominant flow physics processes within the storage site, implying that the plume is in a state of dynamic equilibrium and likely to stabilize within years of the injection ending. Two challenges remain for the benchmark reservoir simulations: (A) how to represent the trapping and breaching behaviour of thin shale barriers for percolating CO2 within a storage formation; and (B) how to address pressure field artifacts in larger regional Darcy flow models of CO2 storage.

An Extended Model Evaluation Method under Uncertainty in Hydrologic Modeling

This paper proposes an extended model evaluation method that considers not only the model performance but also the model structure and parameter uncertainties in hydrologic modeling. A simple reservoir model (SFM) and distributed kinematic wave models (KWMSS1 and KWMSS2 using topography from 250-m, 500-m, and 1-km digital elevation models) were developed and assessed by three evaluative criteria for model performance, model structural stability, and parameter identifiability. All the models provided acceptable performance in terms of a global response, but the simpler SFM and KWMSS1 could not accurately represent the local behaviors of hydrographs. Moreover, SFM and KWMSS1 were structurally unstable; their performance was sensitive to the applied objective functions. On the other hand, the most sophisticated model, KWMSS2, performed well, satisfying both global and local behaviors. KMSS2 also showed good structural stability, reproducing hydrographs regardless of the applied objective functions; however, superior parameter identifiability was not guaranteed. A number of parameter sets could result in indistinguishable hydrographs. This result indicates that while making hydrologic models complex increases its performance accuracy and reduces its structural uncertainty, the model is likely to suffer from parameter uncertainty.

High-performance photonic reservoir computer based on a coherently driven passive cavity

Reservoir computing is a recent bio-inspired approach for processing time-dependent signals. It has enabled a breakthrough in analog information processing, with several experiments, both electronic and optical, demonstrating state-of-the-art performances for hard tasks such as speech recognition, time series prediction and nonlinear channel equalization. A proof-of-principle experiment using a linear optical circuit on a photonic chip to process digital signals was recently reported. Here we present a photonic implementation of a reservoir computer based on a coherently driven passive fiber cavity processing analog signals. Our experiment has error rate as low or lower than previous experiments on a wide variety of tasks, and also has lower power consumption. Furthermore, the analytical model describing our experiment is also of interest, as it constitutes a very simple high performance reservoir computer algorithm. The present experiment, given its good performances, low energy consumption and conceptual simplicity, confirms the great potential of photonic reservoir computing for information processing applications ranging from artificial intelligence to telecommunications

Modulation of Skeletal Muscle Fatigue Kinetics by Extracellular Glucose and Glycogen Content

Increasing activity and the demand on skeletal muscle invariably leads to a depletion of energy reserves and a reduction in the ability of the muscle to produce force, known as muscle fatigue. Studies have shown glycogen to be of integral importance to this process and to play a role that is more complex than as a simple glucose reservoir. Here, using mouse FDB muscle bundles, we investigated the respective influence of glycogen and extracellular glucose on muscle fatigue. During a first bout of fatigue (FAT1) glycogen usage and force production was similar between control and insulin-exposed muscles. Glycogen replenishment 60 min after FAT1 was such that glycogen content prior to a second fatigue bout (FAT2) and the amount used during FAT2 was greater than for FAT1. This corresponded to an increase in time to fatigue. For a low glycogen model, FAT1 was followed by a 60 min recovery period in 0 glucose, resulting in a decline in pre-FAT2 glycogen content. When FAT2 was elicited also in 0 glucose, a marked decrease in time to fatigue was observed, which was partially recovered when if glucose was reintroduced 10 min before FAT2, to spite very low glycogen content and usage. A correlation was revealed when pre-FAT glycogen content and time to fatigue were compared for FAT2 bouts. From these results, we support that glycogen is a consistently critical factor in muscle fatigue, and suggest that extracellular glucose cannot fully compensate for force loss after excessive glycogen depletion.

Objective hydrograph baseflow recession analysis

Summary A streamflow hydrograph recession curve expresses the theoretical relationship between aquifer structure and groundwater outflow to a stream channel. That theoretical relationship is often portrayed empirically using a recession plot defined as a plot of ln(− dQ / dt ) versus ln( Q ), where Q is streamflow discharge. Such hydrograph recession plots are commonly used to estimate recession parameters, aquifer properties and for evaluating alternative hydrologic hypotheses. We introduce a comprehensive and objective approach to analyze baseflow recessions with innovations including the use of quantile regression, efficient and objective numerical estimation of dQ / dt , inclusion of groundwater withdrawals, and incorporation of seasonal effects. We document that these innovations when all combined, lead to significant improvements, over previous studies, in our ability to discern the theoretical behavior of stream aquifer systems. A case study reveals that our methodology enables us to reject the simple linear reservoir hypothesis of stream aquifer interactions for watersheds in New Jersey and results in improved correlations between low flow statistics and aquifer properties for those same watersheds.

A methodology to evaluate and reduce reservoir uncertainties using multivariate distribution

History matching is a challenging and time-consuming task related to reservoir simulation. Probabilistic approaches using dynamic data are often used to reduce reservoir uncertainties and improve matching. This work presents a new process to evaluate and reduce reservoir uncertainties using multivariate analysis incorporating the interaction between reservoir properties. The proposed uncertainty reduction workflow provides a multivariate approach without the use of proxy models, allowing understanding of the reservoir response through the R2 matrix as well as more reliable reservoir predictions. The methodology offers a quantitative analysis and a new tool to evaluate and reduce uncertainties. The process uses a Latin Hypercube (LHC) to sample the reservoir attribute range and a smoothed mismatch data set from the LHC selected objective functions. The attribute interval, which minimizes the mismatch, is identified through polynomial fitting. The main objective is to reduce uncertainties considering the reservoir attributes range and a multivariate sensitivity matrix. The methodology was firstly applied to a simple synthetic reservoir simulation model with 20 uncertainty attributes and we drew the following conclusions: (1) R2 sensitivity matrix clearly showed the key physical features of the reservoir model; (2) all reservoir attributes ranges were reduced, providing a set of simulation models with improved history matching. We successfully applied to the UNISIM-I-H reservoir model based on Namorado field, Campos basin, Brazil.

Something for Nothing: Solid-Oxide Fuel Cells

S omething for N othing : S olid -O xide F uel C ells B S J Karthik Gururangan Fuel cells have been a popular contender for the usage. Recently, scientists have proposed using solid-state gateway to the hydrogen economy for some time. Indeed, diffusion of hydrogen and oxygen ions through an oxide today we can see zero-emission buses and cars powered by electrolyte to make the hydration reaction (Park, 2000). These a hydrogen fuel cell. Generally speaking, a fuel cell is an fuel cells are called solid-oxide fuel cells, or SOFCs. At high electrochemical system that drives the transferred electron enough temperatures, SOFC diffusion can quickly outpace occurring in redox reactions through an external circuit to regular chemical kinetics, give us greater fuel choice flexibility, power something. It is really and eliminate harmful carbon the most straightforward way monoxide by-products of At high enough temperatures, to convert chemical energy into common liquid fuel cells (Park, electrical energy, and provided SOFC diffusion can quickly outpace 2000). that the reactants remain in a regular chemical kinetics, give us Diffusion is a temperature- steady supply, a fuel cell can controlled exponential law based greater fuel choice flexibility, and on two things: the diffusivity of indefinitely supply a steady eliminate harmful carbon monoxide by- a particular electrolyte and the current. By referring to Figure activation energy of diffusion products of common liquid fuel cells. 1 we can understand the setup for that particular solute. of a hydrogen fuel cell. At the The activation energy can be blue side (anode), hydrogen loses decomposed into the energy electrons and the resultant protons migrate into a reaction needed to move around through the solid and the energy chamber. The green side (cathode) is very often an opening associated with moving around through holes called vacancies or simple air reservoir. The electrons flow through the circuit in the solid. Figure 2 gives an intuitive idea of what this and reach the oxygen, completing the chemical reaction to means. produce water. Using the hydration electrochemical reaction is the basis of our intended hydrogen economy. In reality, one cell of this type hardly produces 1 volt so we combine single cells in series into what is called a fuel cell stack for applications. The main drawback of classical gas or liquid hydrogen fuel cells is that they require a platinum catalyst to speed up the reaction process to usable values (Minh, 2004). In Figure 1, the middle plate is the platinum – this is an expensive metal and is one of the main obstacles of widespread hydrogen fuel cell Figure 1. : Simple schematic of a single hydrogen fuel cell An atom can either push its way past two others to move to another position or it can move through the existing gap defects. By choosing a solid oxide electrolyte, the much larger oxygen ions have an easier time migrating through the lattice, making the overall diffusion rate much faster than it 12 • B erkeley S cientific J ournal • W aste • S pring 2015 • V olume 19 • I ssue 2

Physics of unconventional shale gas reservoirs for a long-term production perspective

A simple unconventional reservoir model is developed that accounts for complex physics affecting production from hydraulically-fractured wells in shale resources. Integrating these physics and evaluating their order of importance on future production of an unconventional reservoir is very essential. The proposed model divides the formation into three zones, rock matrix (I), induced-fracture (II) and hydraulic fracture (III) that hold varying characteristics. Also, a history matching process with Marcellus shale field production data is performed in order to obtain the most uncertain parameters defined in the model. Results showed that combined effect of permeability losses of hydraulic and induced-fracture zones results in 15% gas production drop in 30 years. It is also concluded that the minimum ingredients required for long-term production forecast of unconventional shale gas reservoirs are considering two physics; shale surface methane desorption along with pressure-dependent permeability for fracture network and other physical phenomena are inconsequential. [Received: August 12, 2014; Accepted: December 13, 2014]

Evaluating LSM-Based Water Budgets over a West African Basin Assisted with a River Routing Scheme

AbstractWithin the framework of the African Monsoon Multidisciplinary Analysis (AMMA) Land Surface Model Intercomparison Project phase 2 (ALMIP-2), this study evaluates the water balance simulated by the Interactions between Soil, Biosphere, and Atmosphere (ISBA) over the upper Ouémé River basin, in Benin, using a mesoscale river routing scheme (RRS). The RRS is based on the nonlinear Muskingum–Cunge method coupled with two linear reservoirs that simulate the time delay of both surface runoff and base flow that are produced by land surface models. On the basis of the evidence of a deep water-table recharge in that region, a reservoir representing the deep-water infiltration (DWI) is introduced. The hydrological processes of the basin are simulated for the 2005–08 AMMA field campaign period during which rainfall and streamflow data were intensively collected over the study area. Optimal RRS parameter sets were determined for three optimization experiments that were performed using daily streamflow at five gauges within the basin. Results demonstrate that the RRS simulates streamflow at all gauges with relative errors varying from −20% to 3% and Nash–Sutcliffe coefficients varying from 0.62 to 0.90. DWI varies from 24% to 67% of the base flow as a function of the subbasin. The relatively simple reservoir DWI approach is quite robust, and further improvements would likely necessitate more complex solutions (e.g., considering seasonality and soil type in ISBA); thus, such modifications are recommended for future studies. Although the evaluation shows that the simulated streamflows are generally satisfactory, further field investigations are necessary to confirm some of the model assumptions.

Apatite Loss in Pothwar Loess Plain (Pakistan) Fits a Simple Linear Reservoir Model

Apatite is the dominant phosphorus (P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents (Rajar), Typic Calciustepts (Missa), Udic Calciustepts (Basal), and Udic Haplustalfs (Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron (oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x) = M0[1 – exp(–wx)] with r2 = 0.996, where M(x) is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg−1 at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.

Innovative use of rate-transient analysis methods to obtain hydraulic-fracture properties for low-permeability reservoirs exhibiting multiphase flow

Multifractured horizontal wells, while enabling commercial production from unconventional gas and light-oil reservoirs, are challenging to analyze quantitatively to obtain reservoir and hydraulic-fracture properties. Production rates and flowing pressures gathered immediately after hydraulic-fracture stimulation (flowback) and over a longer time period (on-line production) can be interpreted for hydraulic-fracture properties such as fracture surface area or half-length and fracture conductivity, but dynamic fracture properties and multiphase flow during both stages of production can complicate the analysis. Recent studies have suggested that flowback data can provide early insight into these fracture properties if high-resolution fluid rates/pressures are gathered, but the physics of the process are complex, and analytic methods for interpretation are at an early stage of development. Analytic methods for longer-term production data analysis, although better established, are still limited primarily to single-phase flow and simple fracture and reservoir behavior. Rate-transient methods can be applied to both flowback and long-term production data to quantify hydraulic-fracture properties and changes in effective hydraulic-fracture length during production. For the flowback period, simplified analytic methods have been developed for before-breakthrough production of hydraulic-fracturing fluids and after-breakthrough production of hydraulic-fracture and reservoir fluids. These methods are still under development, and early applications can be illustrated. For long-term production analysis, classic rate-transient analysis techniques, such as the square-root-of-time plot, have been modified to account for multiphase flow and stress-sensitive permeability exhibited by low-permeability gas condensate and black-oil reservoirs producing below saturation pressure. A field example consisting of a multifractured horizontal well completed in a tight-oil reservoir isused to to compare hydraulic-fracture properties derived from flowback and long-term production data. Although flowback analysis yields hydraulic-fracture half-lengths consistent with hydraulic-fracture modeling results, long-term production analysis yields much smaller fracture half-lengths, possibly because of breakthrough of gas once bubble-point pressure is reached. Additional mechanisms for effective producing fracture half-length reduction can be proposed. Another important observation is that estimation of fracture properties from long-term production analysis of a reservoir producing below saturation pressure can be in significant error if the estimates are derived from techniques assuming single-phase flow. Corrections to the analytic methods for multiphase flow yield fracture half-lengths consistent with those obtained from history matching using rigorous numerical simulation. In a preliminary analysis, the techniques under development are intended to aid hydraulic-fracture evaluation and design in tight reservoirs that exhibit complex flow characteristics. Furthermore, implications of the findings will be important to assist in designing well operations to maximize well performance.

Investigation on coal seam gas formation of multi-coalbed reservoir in Bide-Santang Basin Southwest China

This paper presents a comprehensive study on the geological characteristics of a multi-coalbed reservoir using coal cores collected from well drilling tests in Bide-Santang Basin, China. The study focuses on the investigation of the coalbed methane (CBM)-bearing property, porosity and permeability, sealability of capping rocks, and groundwater characteristics in coal seams, providing the experimental information on the control function of sequence strata for the coalbed methane. This reservoir is comprised of a large number of coalbeds and exhibits many distinctive geological characteristics of a CBM reservoir, such as high CBM content, complex vertical volatility of CBM content, vertical discontinuous distribution of porosity and permeability, strong sealing capping property and many vertical water-bearing systems, etc. The investigation shows that the unattached multiple superposed CBM-bearing system (UMSCS), which formed the unique multi-coalbed CBM reservoir, can be identified in the study area. Depending on the development scale of vertically unattached CBM-bearing coal seams, the CBM reservoir in the study area can be classified as simple UMSCS and complex UMSCS. The former, typically appearing in Zhuzang syncline and Agong syncline, exhibits the continuity of geological reservoir-forming characteristics in terms of less coal seams, much weaker sealability of capping rocks, higher CBM content, and many vertical water-bearing systems. The latter, typically represented by Shuigonghe syncline and Santang syncline, shows the continuity of geological reservoir-forming characteristics with a large number of coal seams, strong sealing capping property, and reasonably high CBM content. For simple UMSCS reservoirs, a sublevel exploitation method should be adopted for CBM exploitation in order to minimize the effect caused by larger variation of the reservoir energy in different systems. For complex UMSCS reservoirs, one effective way for CBM exploitation is to fracture virtual reservoir (mainly key sandstone member) to depressurize it uniformly and thus achieve large-scale discharging and mining in several adjacent CBM-bearing subsystems.