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This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 146998, โImproving Horizontal Completions in Heterogeneous Tight Shales,โ by Roberto Suarez-Rivera, SPE, Chaitanya Deenadayalu, Maxim Chertov, SPE, Ricardo Novalo Hartanto, SPE, and Patrick Gathogo, Schlumberger, and Rahul Kunjir, University of Utah, prepared for the 2011 Canadian Unconventional Resources Conference, Calgary, 15-17 November. The paper has not been peer reviewed. Production from nanodarcy-range-permeability shale formations requires extensive hydraulic fracturing, large volumes of water, and closely spaced wells. Comparing calculations of the possible fracture-surface area created during treatments to production results indicates that a large portion of that surface area is ineffective for production, resulting in ineffective use of resources. A fundamental understanding is required to improve the efficiency of horizontal completions in producing shales. The objective of this study was to improve completion design and horizontal-well-completionย efficiency. Introduction When considering tight-shale-formation characterization and completion design, one should evaluate the formation characteristics conducive to economic production: reservoir quality (RQ), representing the multiple properties defining reservoir potential, and completion quality (CQ), representing the multiple properties defining the potential for creating and sustaining a large surface area in contact with the reservoir. RQ and CQ properties vary in the near-wellbore and far-wellbore regions. For CQ, the far-wellbore region represents the region of contact between the created fracture and the reservoir. Well production depends on this surface area being in contact with good RQ, and depends on conditions of containment, fracturability, rock/fluid interactions, and loss of surface area and fracture conductivity during production. The near-wellbore region represents the choking point between the created surface area and the wellbore. The goal is to maximize connectivity between the fracture system and the wellbore. This goal is attainable by minimizing near-fracture tortuosity, maximizing fracture width, reducing breakdown pressures, and limiting the risk of solids production. The result is a nonsubjective and consistent method that provides a means for understanding variability in fracture performance along wellbores (e.g., inferred from microseismic monitoring, trace analysis, and stage-by-stage flow measurements) and for selecting perforation stages on the basis of measured or log-inferred rock properties. The method also provides a means for monitoring consistency between the predicted values and measured results.
- Asia > Middle East (0.28)
- North America > United States > Utah (0.24)
- North America > Canada > Alberta > Census Division No. 6 > Calgary Metropolitan Region > Calgary (0.24)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Passive Seismic Surveying > Microseismic Surveying (0.55)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- (4 more...)
Abstract With the development of deep-sea resource exploration, long steel-pipe piles of large diameter are widely used in offshore platform constructions. Some steel piles may have a diameter that exceeds 2m, and length that exceeds 100m. For such piles, it is almost impossible to accomplish continuous pile driving, as it may be affected by complicated environmental conditions of the sea, the welding of pile connections and the hammer replacement. After a long-term cessation of pile driving, it might become harder to resume and sometimes refusal can even happen. Analyses showed that the soil permeability, the crack development in the soil surrounding the pile, the duration of cessation and the soil-plug effect in the pile pipe are the main factors affecting the soil strength and skin friction. Based on the effective stress principle and the cavity expansion theory, a method has been proposed to evaluate the excess pore water pressure in the soil surrounding the pile during pile driving. In addition, the 1D wave equation has been introduced into the pile-driving analysis. The soil properties in the pile driving analysis are modified in terms of the measured data until the calculated results match the driving records. Therefore, the pile bearing capacity after refusal can be eventually determined. 1. Introduction Long steel-pipe piles of large diameter have been widely used in offshore engineering. Due to the complexity of working conditions offshore, factors such as weather conditions, ship arrangement and hammer replacement, may prevent piles (deep penetration pile) from being driven to the design elevation continuously, and driving interruptions can take place. In this paper, resuming driving after driving cessation is called re-driving. It can take hours, days or even a few weeks to restart the pile-driving process. Long-term cessation can lead to excess pore water dissipation and soil strength setup.
- Asia > China (0.29)
- North America > United States (0.28)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.35)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.30)
ABSTRACT Rising gas occurs naturally and as a result of drilling, injection and construction activities, such as air jetting, fracturing, jet grouting and tunnelling. The effect of rising gas is difficult to quantify or model, but is known to reduce the bearing capacity of both shallow and deep foundations. Under gravity based structures (GBS) it can cause problems of flotation and subsequent base sliding and internal over pressure. Storm waves can liquefy shallow gaseous deposits. Gas venting facilities are essential but not always provided on offshore structures. The paper discusses rising gas in terms of sources, pathways, flow calculations, gas experiments trials, and calculations, settlement effects and precautions, as well as its effect on GBS, on bearing capacity (especially during storms) and on shallow and deep foundations. 1. Sources of Gases The most obvious sources of gases are hydrocarbons rising naturally or as a result of drilling operations. Additionally gases, such as nitrogen, are injected as liquid into strata to increase well production, while other gases are injected for storage or disposal. Compressed air is used in tunnels, caissons, jet grouting and jetting. There are also volcanic gases, hydrates and organic deposits releasing methane. 2. Flow Pathways Pathways for rising gas are mainly dependent on the lamination and dip of the strata and local anomalies such as faulting, joints or weaknesses. Layers of gas can be trapped below individual laminations or cyclotherms (due to seasonal depositional changes in particle size). Seismic surveys show numerous strong โghostโ reflections, which correspond to the pattern of lamination but cannot usually be distinguished in recovered core. A likely explanation is that trapped gas provides the ghost reflection. The air lifts the cuttings, but can also escape laterally and appear in adjacent boreholes. Shot hole blasts can show a similar behaviour.
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.70)
Estimating the Specific Productivity Index in Horizontal Wells From Distributed-Pressure Measurements Using an Adjoint-Based Minimization Algorithm
Farshbaf Zinati, F.. (Delft University of Technology, the Netherlands) | Jansen, J.D.. D. (Delft University of Technology, the Netherlands) | Luthi, S.M.. M. (Delft University of Technology, the Netherlands)
Summary Recent developments in the deployment of distributed-pressure-measurement devices in horizontal wells promise to lead to a new, low-cost, and reliable method of monitoring production and reservoir performance. Practical applicability of distributed-pressure sensing for quantitative-inflow detection will strongly depend on the specifications of the sensors, details of which were not publicly available at the time of publication. Therefore, we theoretically examined the possibility of identifying reservoir inflow from distributed-pressure measurements in the well. The wellbore and nearwellbore region were described by semianalytical steady-state models, and a gradient-based inversion method was applied to estimate the specific productivity index (SPI) as a function of along-well position. We employed the adjoint method to obtain the gradients, which resulted in a computationally efficient inversion scheme. With the aid of two numerical experiments (one of which was based on a real well and reservoir), we investigated the effects of well and reservoir parameters, sensor spacing, sensor resolution, and measurement noise on the quality of the inversion results. In both experiments, we generated synthetic measurements with the aid of a high-resolution reservoir-simulation model and used these to test the semianalytical inversion algorithm. In the first experiment, we considered a 2000-m horizontal well passing through two 300-m high-permeability streaks in a background with a permeability that was 10 times lower. The location of the streaks and the SPIs along the well were detected with fair accuracy using 20 unknown parameters (SPI values) and 20 pressure measurements. Decreasing the number of measurements resulted in a poorer detection of the streaks and their SPIs. The detection performance also decreased for increasing noise levels and deteriorated sensor resolution, though the negative effect of random measurement noise was cancelled out primarily by stacking multiple measurements. The detrimental effects of measurement noise and low sensor resolution were strongest in areas where the inflow was lowest (usually close to the toe). The second experiment concerned a high-rate near-horizontal well with slightly varying inclination that intersected a dipping package of formations with strongly variable permeabilities. Additionally, a satisfactory detection of SPIs was obtained even though the heterogeneities were no longer perpendicular to the well as in the first experiment. As a result of using the simple semianalytical forward model and the adjoint method, the inversions typically required less than 90 seconds on a standard laptop. This offered the opportunity to extend the algorithm to multiphase flow and dynamic applications (pressure-transient testing), while still maintaining sufficient computational speed to perform the inversion in real time.
- Europe (1.00)
- North America > United States (0.93)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (3 more...)
Summary Water-soluble polymers have found extensive use in the oil and gas industry. For instance, high-molecular-weight polymers are very efficient drag-/friction-reducing agents and viscosifiers. Unfortunately, the adsorption of the polymer on the reservoir formation reduces the effectiveness of the recovery of oil and gas from low-permeability formations, such as shale. The availability of water-soluble polymers containing weak links in the backbone of the polymer that can be degraded upon experiencing a certain trigger, such as temperature, pH, or reducing agent, would be very advantageous. Because of the ability of weak links to degrade under certain conditions, such polymers can be used for their intended application and can afterward be degraded in a controlled and predetermined way. The resulting lower-molecular-weight fractions of that polymer lead to a reduced viscosity and quick partitioning into the water phase, and they are also less likely to adsorb onto formation surfaces. Additionally, no oxidizers need to be pumped to break or clean the deposited polymer, thus saving treatment time. It has been proved that using a bifunctional reducing agent containing degradable groups and oxidizing metal ions as a redox couple is an effective method to initiate free-radical polymerization and build degradable groups into the backbone of vinyl polymers. Temperature-degradable but hydrolytically stable azo groups showed the most-desirable results. The presence of azo groups in the backbone of the synthesized polyacrylamide (PAM) was confirmed by H-NMR spectra and differential scanning calorimetry (DSC). The degradation behavior of the PAM with temperature-sensitive azo groups was characterized using gel permeation chromatography (GPC) and proved that multiple labile links were built into the polymer backbone. It was also found that PAM with azo links in the polymer backbone is as good a drag-reducing agent as pure PAM. However, PAM with azo links in the backbone loses its drag-reduction properties once subjected to elevated temperatures, which for some applications is viewed as an advantage.
- North America > United States > Texas (0.28)
- North America > United States > West Virginia (0.28)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Modeling and Simulation of Nanoparticle Transport in Multiphase Flows in Porous Media: CO2 Sequestration
El-Amin, M. F. (King Abdullah University of Science and Technology) | Sun, Shuyu (King Abdullah University of Science and Technology) | Salama, Amgad (King Abdullah University of Science and Technology)
Abstract Geological storage of anthropogenic CO2 emissions in deep saline aquifers has recently received tremendous attention in the scientific literature. Injected CO2 plume buoyantly accumulates at the top part of the deep aquifer under a sealing cap rock, and some concern that the high-pressure CO2 could breach the seal rock. However, CO2 will diffuse into the brine underneath and generate a slightly denser fluid that may induce instability and convective mixing. Onset times of instability and convective mixing performance depend on the physical properties of the rock and fluids, such as permeability and density contrast. The novel idea is to adding nanoparticles to the injected CO2 to increase density contrast between the CO2-rich brine and the underlying resident brine and, consequently, decrease onset time of instability and increase convective mixing. As far as it goes, only few works address the issues related to mathematical and numerical modeling aspects of the nanoparticles transport phenomena in CO2 storages. In the current work, we will present mathematical models to describe the nanoparticles transport carried by injected CO2 in porous media. Buoyancy and capillary forces as well as Brownian diffusion are important to be considered in the model. IMplicit Pressure Explicit Saturation-Concentration (IMPESC) scheme is used and a numerical simulator is developed to simulate the nanoparticles transport in CO2 storages.
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (2 more...)
ABSTRACT We present a fluid-flow constrained inversion approach for integrating controlled-source electromagnetic data and production data. In this approach, we assumed that the reservoir model has been well defined from a priori knowledge obtained from other independent measurements such as seismic and/or well-logs. Our objective was to reconstruct the permeability distribution and the shape and location of the flooding front. A finite-difference reservoir simulator was used to model the water-flooding process to simulate the time-dependent production data as well as the temporal and spatial distributions of water saturation and salt concentration, which were then transformed into the reservoir resistivity distribution using a petrophysical relationship. A finite-difference frequency-domain electromagnetic forward-modeling code was then employed to simulate the controlled-source electromagnetic response. The permeability distribution was reconstructed using a multiplicative-regularized Gauss-Newton algorithm for jointly inverting controlled-source electromagnetic and production data. From the water saturation distribution, we can identify the shape and location of the fluid-front resulting from the recovery process.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- (3 more...)
ABSTRACT We examined the dependence of imaginary conductivity () on pore fluid conductivity () for an extensive database of 67 samples acquired from twelve independent studies. We compared fitting of functions describing the salinity dependence of for two models of the electrical double layer (EDL) polarization, both of which predict asymptotic behavior of at high . We define these models as the diffuse layer polarization (DLP) and Stern layer polarization (SLP) models based on the physical description of the salinity dependence of the surface polarization. We also examined the database for evidence of a high salinity decrease in not predicted by either model. The dependence of on prior to the polarization plateau predicted by both models approximates a simple empirical power law with an average exponent of 0.34. The salinity dependence predicted by the DLP model adequately describes most data sets. A fitting parameter representing the high salinity asymptote is strongly correlated () with pore normalized specific surface (). The SLP model describes well the observations when a recently proposed additive polarization term representing the contribution of the protons is included. In this case, the SLP model provides an excellent fit to the data sets, including a low salinity asymptote (in log-log conductivity space) seen in some samples. Predicted values of the fitting parameters of the SLP model generally are consistent with the values expected based on the theory; the fitting parameter describing the high salinity asymptote of the SLP model is also strongly correlated () with . The SLP and DLP models neglect a high salinity decrease in the polarization that is observed in numerous data sets from independent studies. New data acquired on a sandstone sample demonstrate that this high salinity decrease is likely not attributable to the limited phase accuracy of earlier measurements.
- Geology > Geological Subdiscipline (0.67)
- Geology > Rock Type > Sedimentary Rock (0.39)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.68)
Summary This paper examines the effects of matrix microfractures on the effective matrix permeability of a dual-porosity medium. An analytical model is presented, with composite matrix blocks consisting of a core in which unconnected microfractures do not contribute considerably to flow capacity and a surface layer where the microfractures connected to the matrix surface (resembling wormholes) cause a stimulation effect. The composite matrix flow is coupled with the flow in a network of macrofractures, as in the conventional dual-porosity idealizations of fractured media. This paper investigates the effect of matrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network because of matrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more-effective contribution of the matrix into flow rates. This contribution of the matrix because of microfractures cannot be simulated by enhanced matrix permeability because the microfractured surface layer of the matrix causes flow characteristics different from those of a homogeneous (unfractured) matrix. The effect of the microfractured surface layer of the matrix cannot be taken into account by a triple-porosity model used to incorporate two sets of connected natural fractures or connected fractures and vugs.
- North America > United States > Texas > Haynesville Shale Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > United States > Louisiana > Haynesville Shale Formation (0.99)
- (4 more...)
Summary The decline in conventional hydrocarbon resources coupled with the increase in energy demand has encouraged the development of unconventional gas resources. One specific type of unconventional gas is the natural-gas hydrate. It is expected that the substantial size of this hydrate resource will be a motivating factor in its development. In the early phases of development of hydrate reservoirs, data are limited and a large number of sensitivity studies are required. Efficient and accurate analytical models are suitable for such sensitivity studies. One such model is presented in this work. An analytical solution is developed to model the rate of gas generation and hydrate recovery when gas is produced from a tilted hydrate-capped gas reservoir in which the geothermal gradient is accounted for. As a result of the variation in temperature within the hydrate column, the size of the decomposing area increases with continued production. Development of the analytical model in this work is based on a material-balance equation that is combined with the solution for the temperature of the decomposed zone and the hydrate-equilibrium curve. The three equations are solved simultaneously for the gas-generation rate. To validate the assumptions made in the development of the analytical model, a numerical simulator was used that does not make the assumptions of the analytical model. A close agreement is shown between the two models, validating the assumptions made in the analytical solution. The effects of different reservoir parameters on the reservoir performance were investigated by performing sensitivity analyses. The sensitivity results show how a steeper reservoir that extends closer to the base of the permafrost leads to less recovery or how a thicker hydrate cap could maintain the reservoir pressure for a longer time. The model developed in this study can be used as an approximate engineering tool to evaluate the role of hydrates in improving the productivity and extending the life of tilted hydrate-capped gas reservoirs.
- North America > United States (1.00)
- North America > Canada > Alberta (0.28)
- North America > Canada > Ontario (0.28)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (3 more...)