Reservoir Shape Research Articles

Spatial and temporal diffusion-control of dynamic multi-domain self-assembled gels.

The dynamic assembly of a pH-responsive low-molecular-weight gelator (LMWG) within the pre-formed matrix of a second LMWG has been achieved via diffusion of an acid from a reservoir cut into the gel. Self-assembly of the acid-triggered LMWG as it converts from micellar aggregates at basic pH into gel nanofibers at lower pH values can be both spatially and temporally controlled. The pH-responsive LMWG has an impact on the stiffness of the pre-formed gel in the domains in which it assembles. When low acid concentrations are used, LMWG assembly is transient – after the initial proton diffusion phase, the pH rises and disassembly occurs as the system equilibrates. Re-application of additional acid as ‘fuel’ can then re-assemble the LMWG network. Using glucono-δ-lactone (which slowly hydrolyses to gluconic acid) instead of HCl gives slower, more spatially-restricted assembly, and creates longer-lasting pH gradients within the gel. The presence of an agarose polymer gel network improves the mechanical strength of the gels and appears to slightly enhance the rate of proton diffusion. More sophisticated reservoir shapes can be cut into these more mechanically robust gels, enabling the creation of diffusion waves with different geometries, and hence different patterns of LMWG activation. Multiple reservoirs can be used to create overlapping proton diffusion waves, hence achieving differentiated pH patterns in the gel. Using acid diffusion in this way within gels is an intriguing and powerful way of dynamic patterning. The ability to temporally-evolve spatially-resolved patterns using biocompatible weak acids, and the change in rheological performance of the triggered domains, suggest potential future applications of this strategy in tissue engineering.

Seismological and Geophysical Signatures of the Deep Crustal Magma Systems of the Cenozoic Volcanic Fields Beneath the Eifel, Germany

AbstractThe Quaternary volcanic fields of the Eifel (Rhineland‐Palatinate, Germany) had their last eruptions less than 13,000 years ago. Recently, deep low‐frequency (DLF) earthquakes were detected beneath one of the volcanic fields showing evidence of ongoing magmatic activity in the lower crust and upper mantle. In this work, seismic wide‐ and steep‐angle experiments from 1978/1979 and 1987/1988 are compiled, partially reprocessed and interpreted, together with other data to better determine the location, size, shape, and state of magmatic reservoirs in the Eifel region near the crust‐mantle boundary. We discuss seismic evidence for a low‐velocity gradient layer from 30–36 km depth, which has developed over a large region under all Quaternary volcanic fields of the Rhenish Massif and can be explained by the presence of partial melts. We show that the DLF earthquakes connect the postulated upper mantle reservoir with the upper crust at a depth of about 8 km, directly below one of the youngest phonolitic volcanic centers in the Eifel, where CO2 originating from the mantle is massively outgassing. A bright spot in the West Eifel between 6 and 10 km depth represents a Tertiary magma reservoir and is seen as a model for a differentiated reservoir beneath the young phonolitic center today. We find that the distribution of volcanic fields is controlled by the Variscan lithospheric structures and terrane boundaries as a whole, which is reflected by an offset of the Moho depth, a wedge‐shaped transparent zone in the lower crust and the system of thrusts over about 120 km length.

A simplified mathematical model for the dam-breach hydrograph for three reservoir geometries following a sudden full dam break

The prediction of dam-break water flow at dam site is essential to reduce the potential for loss of damage in the downstream floodplain. In this study, the influence of reservoir shapes (rectangular, trapezoidal and triangular wedge) on dam-break discharge hydrographs at a dam site was investigated to estimate the peak discharge and discharge hydrograph quickly. By assuming instantaneous and complete breaches to simplify the discharge process, a formula for the peak discharge and a simple analytical solution to the entire discharge hydrograph following a dam break at the dam site were generated. The discharge hydrograph at the dam site derived by the proposed mathematical model was validated through a comparison with the results calculated by the numerical simulation and other existing approaches. The outflow discharges calculated by both the mathematical and numerical model was very similar under the conditions of the three different reservoir shapes. The overall discharge hydrograph shape was mainly influenced by the length of the reservoir, while the magnitude of the outflow discharge was primarily affected by the initial water depth.

A new fracture permeability model: Influence of surrounding rocks and matrix pressure

An appropriate fracture permeability model needs to include terms that characterize the effects of surrounding rocks and varying matrix pore pressure. This paper describes the use of Eshelby's inhomogeneity theory to derive equations that can be used to predict fracture permeability behavior for different shapes of reservoirs whose elastic properties differ from the surrounding rocks. In the equations, permeability is affected by two factors: reservoir volumetric strain and matrix volumetric strain. Reservoir volumetric strain is determined by properties of both the reservoir and surrounding rock. Matrix volumetric strain is controlled by fracture pressure as well as matrix pressure. When fracture permeability is significantly greater than matrix permeability, pressure drop first occurs in fractures and then matrix pressure decreases. In this case, fracture permeability first decreases and then increases. The increase of permeability is related to the matrix pressure drop and the bulk modulus ratio between the matrix and the grains. Results show that the smaller the initial fracture porosity, matrix modulus, shear modulus ratio between the reservoir and surrounding rocks, Poisson's ratio of the reservoir and shape factor of the reservoir, the stronger the stress-sensitivity of fracture permeability during hydrocarbon production. It is also found that when shear modulus of the reservoir is the same as that of surrounding rocks, fracture permeability is independent of reservoir shapes. The model is suitable for heterogeneous reservoirs and can be embedded into the reservoir numerical software to more accurately simulate the development of fractured reservoirs.

Water as an urban heat sink: Blue infrastructure alleviates urban heat island effect in mega-city agglomeration

Surface urban heat island (SUHI) shows higher surface thermal intensification in urban areas than suburban areas and countryside. Green spaces are widely recognized as the dominant nature-based strategy to mitigate thermal stress. In contrast, natural cooling processes of urban blue spaces are seldom addressed. In this study, we applied the Google Earth Engine (GEE) to map SUHI intensity and blue spaces in order to explore the cooling effect and efficiency of blue spaces in the Pearl River Delta Metropolitan Region (PRD). Significant in-situ cooling is observed, with a 10% increase in water-body coverage leading to a depression of SUHI intensity by 11.33%. The irregular shape of lakes and reservoirs may weaken the cooling effect, but the reshaping of rivers may not. Our results indicate ex-situ cooling spillover of water bodies that will benefit the surrounding areas within an envelope of 100-m effective cooling distance. Such findings underline the importance of urban blue infrastructure in alleviating the thermal discomfort and advocate blue spaces as an essential component of urban infrastructure to minimize the SUHI effect.

Diagnostic Tool Identifies Factors in Well-Productivity Decline

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 195331, “Identification of the Decline in Well-Productivity Index Caused by Wellbore Damage Through the Removal of Fluid and Formation Effects,” by Samiha Morsy, SPE, Yan Pan, and Usman Lari, Chevron, et al., prepared for the 2019 SPE Western Regional Meeting, San Jose, California, USA, 23–26 April. The paper has not been peer reviewed. Wells in deepwater reservoirs show significant rate decline with time as the result of various causes. A diagnostic tool for quantification of factors influencing well-productivity decline is presented in this paper. The diagnostic tool helps identify well-stimulation candidates and potentially can help increase production. The work flow presented provides a tool for monitoring well-productivity changes to identify the main causes of productivity decline and to quantify effects on the normalized productivity index (PI). Introduction Most current and future deepwater reservoirs are in structurally deep, high-pressure environments in which reservoir and rock mechanisms that affect long-term well productivity are poorly understood. PI trends derived from field production and pressure data reflect the composite effects of wellbore damage along with changes caused by multiphase-flow and pressure-depletion effects on fluid properties and permeability. However, only PI decline caused by wellbore damage should drive well-stimulation decisions because only stimulation can improve the permeability of the near-wellbore region. In addition, reservoir simulation input PI multipliers used to match well performance should be adjusted appropriately to ensure that the resulting simulated output PI trends are consistent and reliable and to avoid duplication of reservoir and fluid effects that are already captured in the simulation model. Effect of Reference Pressure on Well PI Calculations PI theoretically is estimated with the average reservoir pressure; however, average reservoir pressure may not be estimated accurately for fields where reservoir size and shape are highly uncertain. In cases where the average reservoir pressure is not available, initial reservoir pressure, or the buildup pressure at 1 hour after shut-in, have been used by different operators to estimate well PI. A need exists to understand how these different reference pressures can affect the reliability of the estimated well PI. Equations used to derive well PI, including under pseudosteady-state (PSS) flow conditions, are presented in the complete paper. Effect of Using Different Reference Pressures on PI Estimation: Synthetic Cases A numerical synthetic case is generated to investigate the effect of the reference pressure on well PI. The case represents a circular reservoir 50,000 ft in radius and 30 ft thick. The fluid viscosity is 3.6 cp, and the formation volume factor is 1.1 RB/STB. The reservoir porosity is 10%, and the permeability is 300 md. The skin is increasing with time. The flow rate is constant at 1,000 STB/D, and the well is shut in for 21 periods. PI is calculated at each buildup using a reference pressure from each recognized flow regime. PI using the initial reservoir pressure was also estimated. The first reference pressure is chosen from the wellbore storage flow regime period at 0.01 hours, while other reference pressures are chosen from the infinite acting radial flow (IARF) regime. The PI is calculated finally using the average reservoir pressure during transient and PSS conditions.

Modeling Analysis of the Upper Limit Water Level Mechanism in the Upstream Reservoir of a Dam Embankment

The dam embankment (DE) is a highway structure used in the Loess Plateau to integrate the functions of a highway embankment and a dam. This paper studies the upper limit water level mechanism of the reservoir in the upstream of the DE to determine the criterion for setting upper culverts on the DE. A reservoir model is first established, and then the replenishment and loss of the reservoir water is simulated. The principle of water balance is employed to obtain water level formulas for the reservoir. Finally, an engineering example is used to verify the upper limit water level mechanism. The results show that the water level of the reservoir fluctuates near an ideal balance water level and an upper limit water level exists. Moreover, the upper limit water level has no relation to the water storage time, and is only related to the reservoir shape with big upper and small bottom, the small amount of water entering the reservoir each year, and the large water loss caused by evaporation and leakage. The upper culvert setting criterion is obtained through the upper limit water level mechanism, and it will provide important reference significance for the necessity of the DE culvert setting.

Flow description of gas well in basement granite reservoir from well test analysis

A sweet gas exploration well, penetrating 3286 feet thickness of Granite Basement with 200 feet thickness of extensive fracture was tested. Initial step was to study all geological and petrophysical aspects of reservoir and well. These data were used to obtain the sense of reservoir shape model and its fracture flow behaviour. Interpreting the log gives the presents of partial fracture and open fracture, which are shown in the early time region as a fracture dominated flow and very small wellbore storage effect. The bilinear flow before middle time region and followed by two porosity fracture model at middle time region are shown afterward. Constant pressure circle boundary is shown in the late time period. In summarized, the well flow model is in infinite acting conductivity with two porosity pseudo steady state reservoir model and constant pressure circle boundary. The permeability is 1.45 mD, with -0.52 skin and 1962 Psia reservoir pressure; meanwhile the fracture coefficient is 50 mD-ft, storativity is 0.51, and interporosity flow coefficient is 4.38x10-6 mD-ft. All well and reservoir data pertaining well test is very important for getting a reliable well test interpretation result; to get better understanding reservoir flow behaviour; in this case the reservoir is tight with expected better reservoir outside circle boundary.

3D geological modeling of the Upper Cretaceous reservoirs in GPT oil field, Abu Sennan area, Western Desert, Egypt

This study aims to construct 3D geological model using the integration of seismic data with well log data for reservoir characterization and development of the hydrocarbon potentialities of the Upper Cretaceous reservoirs of GPT oil field. 2D seismic data were used to construct the input interpreted horizon grids and fault polygons. The horizon which cut across the wells was used to perform a comprehensive petrophysical analysis. Structural and property modeling was distributed within the constructed 3D grid using different algorithms. The workflow of the 3D geological model comprises mainly the structural and property modeling. The structural model includes fault framework, pillar girding, skeleton girding, horizon modeling and zonation and layering modeling processes. It shows system of different oriented major and minor faults trending in NE–SW direction. The property modeling process was performed to populate the reservoir facies and petrophysical properties (volume of shale (Vsh), fluid saturations (Sw and Sh), total and effective porosities (Φt and Φe), net to gross thickness and permeability) as extracted from the available petrophysical analysis of wells inside the structural model. The model represents a detailed zonation and layering configuration for the Khoman, Abu Roash and Bahariya formations. The 3D geological model helps in the field development and evaluates the hydrocarbon potentialities and optimizes production of the study area. It can be also used to predict reservoir shape and size, lateral continuity and degree of interconnectivity of the reservoir, as well as its internal heterogeneity.

Combining sedimentary forward modeling with sequential Gauss simulation for fine prediction of tight sandstone reservoir

A considerable number of tight sandstone gas fields are observed in the Xihu Depression, East China Sea. The Y gas field is at the stage of development. It is necessary to describe the reservoir shape and permeability characteristics in detail to deploy development wells. The seismic prediction effects of tight sandstone are not good. Sedimentary forward modeling technology can effectively predict the macroscopic characteristics of sedimentary sand bodies, but this technique lacks micro-details. Geostatistical modeling can depict reservoir details, but this technique cannot easily reflect macro-laws. Therefore, taking H1 layer of the Oligocene Huagang Formation in the Y gas field as an example, the combination of sedimentary simulation and geostatistical modeling is proposed. Geostatistical modeling is combined to describe reservoir details by using the sequential Gauss simulation method under the control of sedimentary simulation results as macro-laws. First, based on the test data and the sensitivity test results of the adjacent study area, five parameters (transport capacity of the river, sand ratio, maximum initial water depth, lake level change, and tectonic subsidence) needed for the simulation are determined. A sedimentary forward simulation is carried out, and a sand ratio model reflecting macroscopic sedimentary law is obtained. Second, in the geostatistical modeling stage, the variogram which has a great influence on the results of geological modeling is discussed. The results show that the larger the length and width of the variogram, the larger the simulated reservoir scale. Then, considering the characteristics of fewer wells in the study area, a reliable variogram is obtained by using the sand ratio results of the sedimentary simulation (2538 m in length and 876 m in width) and the main input parameters of geological modeling (data probability distribution characteristics and variogram) are determined. Subsequently, under the trend of the sediment sand ratio simulation, geological modeling research was carried out by using the sequential Gauss simulation method, and a high-precision sand ratio prediction model was established. Finally, the sand ratio model is transformed into a sedimentary microfacies model and the permeability characteristics of different sedimentary microfacies are calculated. Under the control of sedimentary facies, the permeability model is established by the sequential Gauss simulation method. The model prediction results show that the simulation results can reflect the morphology, distribution and permeability of sedimentary microfacies in detail and the macroscopic characteristics of delta sedimentary law. The permeability of channels in the study area is 0.3 md, and the distribution area is much larger than that of other types of sedimentary microfacies. Compared with other types of deposits, the channel around well A area has better development potential in the front of the delta and is the most favorable oil and gas development area in the study area.

Magnetic and gravity signatures of the Kifl oil field in Iraq

Potential field methods are capable to provide satisfactory results on the tectonics and geology, especially when dealing with the hydrocarbon reservoirs and ore-bearing mineralization. In this study, magnetic and gravity survey were conducted at the west of Kifl area in central Iraq to image the subsurface geological structure and consequently the characteristics of the oil and gas reservoirs. Ground measurements were conducted on an area of 16 by 24 km with a regular grid spacing of 250 m. The results clarified the tectonic setting of the study area, where the fault system in the Kifl oil field was recognized by resembling both magnetic and gravity anomalies with distinct trends along NS and NW. A 3D inversion algorithm based on a weighted minimum length solution was used for reconstruction of the subsurface physical properties of magnetic susceptibility and density contrast. Weighting matrix is composed of multiplication of compactness and depth weighting functions, and truncated singular value decomposition (TSVD) was used for regularization. 3D inversion was first applied to a synthetic model to simulate the geological reality of the study area, while satisfactory results were obtained. Implementing the algorithm on the real potential field data, the physical properties of the hydrocarbon reservoir were determined. Four cross sections have been extracted from the inversion result to show geometric characteristics (depth and shape) of the main reservoir in the Kefl oil field. The results indicated the presence of a fault system in the middle area within a column of sedimentary sequences represented as a graben-horst structure. This phenomenon in the area could be attributed to the tectonic deformation and tension over the area and the Eurasian and Arabian plates collided back to the Permian - Paleocene periods.

Pseudo-Steady-State Parameters for a Well Penetrated by a Fracture with an Azimuth Angle in an Anisotropic Reservoir

Many oil wells in closed reservoirs continue to produce in the pseudo-steady-state flow regime for a long time. The principal objective of this work is to investigate the characteristics of two key pseudo-steady-state parameters—pseudo-steady-state constant (bDpss) and pseudo-skin factor (S)—for a well penetrated by a fracture with an azimuth angle (θ) in an anisotropic reservoir. Firstly, a general analytical pressure solution for a finite-conductivity fracture with or without an azimuth angle in an anisotropic rectangular reservoir was developed by using the point-source function and spatial integral method, and two typical cases were employed to verify this solution. Secondly, with the asymptotic analysis method, the expressions of pseudo-steady-state constant and pseudo-skin factor were obtained on the basis of their definitions, and the effects of permeability anisotropy, fracture azimuth angle, fracture conductivity and reservoir shape on them were discussed in detail. Results show that all the bDpss-θ and S-θ curves are symmetric around the vertical line, θ = 90° and form a hump or groove shape. The optimized fracture direction in an anisotropic reservoir is perpendicular to the principal permeability axis. Furthermore, a new formula to calculate pseudo-skin factor was successfully proposed based on these two parameters’ relationship. Finally, as an application of pseudo-steady-state constant, a set of Blasingame format rate decline curves for the proposed model were established.

Real-time hybrid dike breach model: simulating reservoirs of arbitrary shape and volume in laboratory tests

ABSTRACT Dikes and earthen embankments are common parts of modern infrastructure. Dike breaches resulting from extreme weather conditions and a lack of maintenance have caused significant damage to populated and agricultural areas in the past. Despite recent research findings, the effects of the parameters reservoir water volume and reservoir shape have not been properly assessed due to limitations in laboratory channel size and/or a lack of adequate test methodology. Furthermore, repeatability during the breach initiation phase has proved difficult to achieve when applying standard test methods. Therefore, a novel pump regulation method is introduced with the objective of simulating reservoirs of arbitrary size and shape during dike breach tests. This real-time, fully coupled hybrid modelling approach reduces test limitations due to limited laboratory space and considerably improves repeatability during the breach initiation phase. The pump regulation method, its limitations, test results and possible applications in the hydraulic laboratory are presented.

Application of Seismic Interpretation Technology in the Effective Utilization of Low Permeability Reservoir

With the gradual deepening of oilfield exploitation degree, the accurate description the distribution characteristics of faults and the distribution law of reservoir sand body has become the core problem of efficient exploitation and enhancement of recovery ratio. In allusion to the geological characteristics of complex structure, fault development and large lateral variation of sand body in the low permeability reservoir, this paper utilizes advantages of seismic interpretation technology, comprehensive apply geology, earthquake and well logging data to accurately describe the structural shape of reservoir, fault distribution and reservoir sand body development characteristics, select the favorable sand body parts, deploy horizontal well locations, guide drilling of horizontal well, and provide strong technological support for effective use of low permeability reservoirs in the end.

Assessment of the geometry and volumes of small surface water reservoirs by remote sensing in a semi-arid region with high reservoir density

ABSTRACTWater fluxes in highly impounded regions are heavily dependent on reservoir properties. However, for large and remote areas, this information is often unavailable. In this study, the geometry and volume of small surface reservoirs in the semi-arid region of Brazil were estimated using terrain and shape attributes extracted by remote sensing. Regression models and data classification were used to predict the volumes, at different water stages, of 312 reservoirs for which topographic information is available. The power function used to describe the reservoir shapes tends to overestimate the volumes; therefore, a modified shape equation was proposed. Among the methods tested, four were recommended based on performance and simplicity, for which the mean absolute percentage errors varied from 24 to 39%, in contrast to the 94% error achieved with the traditional method. Despite the challenge of precisely deriving the flooded areas of reservoirs, water management in highly reservoir-dense environments should benefit from volume prediction based on remote sensing.

Developing a mathematical framework in preliminary designing of detention rockfill dams for flood peak reduction

ABSTRACTHydraulic designing of rockfill detention dam is based on the treatment of nondarcian and non-linear turbulence flow in coarse porous media. Previous literature focused only on the regular outlet ponds, and there is a shortcoming in the design methodology for detention rockfill dams. So, this paper develops a simple novel design framework by combining the governing equation of non-linear and non-darcian flow through rockfill dams with the hydrologic flood routing in reservoirs and hydraulic rules of storage dams. An innovative mathematical framework developed for preliminary designing of detention rockfill dams. The effects of type and size of rock fill materials, the shape of reservoir, shape, and intensity of inflow hydrograph on the peak of outflow, the volume of a stored flood, coefficients of flood peak and storage are investigated by parametric study in 36000 simulations. A simple design equation for preliminary designing of detention rockfill dams is provided and its applications in two design examples are presented. Its results indicate that the developed design equation (with R2 = 0.996, MAE = 0.008, and RMSE = 0.0041) is superior to the previous equations and can be used in preliminary designing of detention rockfill dams for flood peak reduction.

Influence of reservoir shape upon the choice of Hydraulic vs. Hydrologic reservoir routing method

The objective of the paper is to compare the hydrologic and hydraulic reservoir routing methods in term of assumptions, equations, numerical computation procedures, necessary data and advantages-disadvantages of their use. To test the results provided by the two methods, a set of two reservoirs from Romania was chosen: one long and narrow and the other one roundly shaped. Corresponding inflow hydrographs were chosen, and similar conditions were imposed for the outflow dam control structures, namely the initial water level in the reservoir to be at the Spillway Crest Level (SCL) and no outflow control. For the hydrologic method the Puls procedure was used and a program was written in Scilab to solve the continuity equation in finite differences. For the hydraulic method HEC-RAS software was used to solve the 1D Saint-Venant equations. Outflow and stage hydrographs at the dam were compared together with the stage hydrograph at the reservoir tail for the hydraulic method. Results show that the hydraulic method should be used for the long and narrow reservoirs, as it considers the backwater effect, whereas the hydrologic method can be efficiently used for all other reservoirs where this effect is negligible.

Assessing the Potential of the Surface Water and Ocean Topography Mission for Reservoir Monitoring in the Mekong River Basin

AbstractThe planned Surface Water and Ocean Topography (SWOT) mission, scheduled to launch in 2021, is designed to significantly improve on current lake and reservoir remote monitoring capacity. These improvements are especially important for the Mekong River Basin (MRB), where rapid dam construction puts downstream food security at risk and upstream dam operations are largely unknown to downstream water managers due to lack of upstream hydrologic information. This study aims to answer: How accurately will SWOT estimate reservoir storage change in the MRB? A physically based simulation tool developed by NASA Jet Propulsion Laboratory to mimic SWOT‐like observations of water bodies was applied to 20 reservoirs in the MRB and for 17 of those reservoirs, synthetic SWOT‐based storage change estimates demonstrated high skill, with errors typically less than 8%. The remaining three reservoirs showed higher errors due to complex neighboring topography or long narrow reservoir shape. In comparison with current satellite observations of six reservoirs in the MRB, the synthetic SWOT observations showed between 4% and 10% lower storage change normalized root‐mean‐square error. Finally, the simulated elevation and surface area was successfully used to estimate the area‐elevation relationships for each reservoir, with a median percent difference of 6.9%. These relationships are a potential avenue for multisensor cooperation toward improved understanding of reservoir dynamics. Such cooperation, where observations from many difference remote sensors are synthesized to provide a more complete view of human interactions on the river system, is vital for the MRB as more dams as human influence over the system increases.

Anatomy of the Campi Flegrei caldera using Enhanced Seismic Tomography Models

Campi Flegrei caldera (Southern Italy) is a densely inhabited area and suffered several unrest episodes in the last centuries. The dynamic of the caldera is highly debated because of conflicting interpretations. Here we present a detailed reconstruction of the Campi Flegrei structure obtained using the microseismicity recorded during the 1984 unrest. Enhanced Seismic Tomography models obtained with these data allow us describing seismic velocities, attenuation, and scattering patterns. Results show: (1) a plumbing system with a diameter of 1 km located between 2.3 km and 4 km depth (2) a 0.5 km thick caprock located at 2 km depth interpreted as the main structure regulating the fluid interchange between deep and shallow sectors of the caldera, (3) the shape and volume of a shallow reservoir beneath the city of Pozzuoli; this reservoir played a key role during the 1982–1984 unrest, (4) several small reservoirs beneath the main craters of the caldera. All these features fit into the debated question on magmatic or hydrothermal mechanism driving the caldera deformation resulting of crucial importance to allow a better assessment of the hazard.

Buildup-Pressure Extrapolation of a Heterogeneous Reservoir: Application of the Crump and Hite Method to a Real Field Case

Summary Traditional methods of pressure-transient analysis rely on homogeneous reservoir models and require assumptions on reservoir shape and well-flow regimes. Unsteady flow rates offer further complexity because traditional methods are dependent on past production history. Crump and Hite (2008) proposed a new method for estimating average reservoir pressure that applies to heterogeneous reservoirs and only requires knowledge of the pressure-buildup data. The Crump and Hite (2008) method relies on obtaining the first few eigenvalues of a diffusion equation to predict average reservoir pressure. A large buildup time may be required for a successful application of the method, depending on the magnitude of the first eigenvalue. This work applied the Crump and Hite (2008) method to a real field case. A reservoir was produced by a single horizontal well for a period of a few years, which was followed by a shut-in period of approximately 200 days. The first four eigenvalues could be extracted, providing an estimate of average reservoir pressure. The pressure derivative was computed with a total-variation-regularization method, which showed lower noise levels compared with finite-difference methods. The extended version of the Crump and Hite (2008) method for shorter buildup times did not show a substantial reduction of the buildup-time requirement.