Fluid Migration Rates Research Articles

A Rapid Numerical Method to Constrain 2D Focused Fluid Flow Rates Along Convergent Margins Using Dense BSR‐Based Temperature Field Data

AbstractEstimates of the sub‐seabed fluid flow rates are important for understanding hydrological budgets, biogeochemical cycles, and physical properties of the sediments. Fluid flow rates and directions, however, are difficult to measure, particularly beneath the seafloor. We developed a rapid method to estimate regional fluid migration rates using an extensive database of seismic reflection profiles taken offshore SW Taiwan. We observe bottom‐simulating reflector (BSR) that deflects toward the seafloor near thrust faults that indicate localized heat flow variations. At these sites, advecting warm pore fluids transport heat to shallower depths and force the BSR shallower. Our 2D steady‐state numerical method quantifies the fluid flow rates required to cause such thermal anomalies. We found that fluid flow rates near the trench of the accretionary wedge range between 0.1 and 16 m3 yr−1 m−1, with slower and faster rates generally associated with slope basin discontinuities and faults, respectively. To evaluate the fluid pattern evolution from subduction to collision, we studied three transects: one along the Manila subduction zone in the south and two in Taiwan's initial collision zone in the north. We quantified the fluid budget and partitioning of fluid flow between focused discharge through faults and diffusive flow through the wedge. Faults in Taiwan's accretionary wedge capture on average 25% of the total dewatering flux in the younger subduction zone and 38.5% in the tectonically mature collision zone. Our method provides estimates of fluid migration rates along convergent plate boundaries, and contributes to our understanding of focused fluid flow processes in many other regions.

Effects of Nano Silica on oil well cement slurry charactreistics and control of gas channeling

In this work, different percentages of Nano silica additive have been added to the two basic drilling cement samples, with 90PCF and 118PCF densities. The results showed that not only has the rate of gas migration in cement decreased, but also other conventional properties of cement, including strength, have improved in some cases. Possible and testable percentages of Nano additive were 0.11, 0.22, 0.33 and 0.55 percent. Measurements by the SGSA device have shown a reduction in the transient time or critical time of cement hydration. In 90PCF slurry, the transient time from 120min to 55MIn has been reduced by adding 0.33% Nano silica. Compressive strength increased from 723psi to 1239psi. The FMA also showed a decrease in fluid migration from 38ml to 15ml. Triaxial experiments have shown an increase in Peak Stress from 22MPa to 25 MPa. In slurries with a density of 118PCF, adding 0.11% Nano silica, the transient time was reduced from 170min to 100min. The compressive strength has been increased from 2089psi to 3020psi. The rate of fluid migration in cement has decreased from 4ml to 0ml. Also, the peak stress rate has increased from 60MPa to 71MPa. In addition, the XRD experiment emphasized the improvement of the cement microstructure after the addition of Nano-silica

Spontaneous formation of fluid escape pipes from subsurface reservoirs

Ubiquitous observations of channelised fluid flow in the form of pipes or chimney-like features in sedimentary sequences provide strong evidence for significant transient permeability-generation in the subsurface. Understanding the mechanisms and dynamics for spontaneous flow localisation into fluid conductive chimneys is vital for natural fluid migration and anthropogenic fluid and gas operations, and in waste sequestration. Yet no model exists that can predict how, when, or where these conduits form. Here we propose a physical mechanism and show that pipes and chimneys can form spontaneously through hydro-mechanical coupling between fluid flow and solid deformation. By resolving both fluid flow and shear deformation of the matrix in three dimensions, we predict fluid flux and matrix stress distribution over time. The pipes constitute efficient fluid pathways with permeability enhancement exceeding three orders of magnitude. We find that in essentially impermeable shale (10−19 m2), vertical fluid migration rates in the high-permeability pipes or chimneys approach rates expected in permeable sandstones (10−15 m2). This previously unidentified fluid focusing mechanism bridges the gap between observations and established conceptual models for overcoming and destroying assumed impermeable barriers. This mechanism therefore has a profound impact on assessing the evolution of leakage pathways in natural gas emissions, for reliable risk assessment for long-term subsurface waste storage, or CO2 sequestration.

Fluid origin and migration of the Huangshaping W–Mo polymetallic deposit, South China: Geochemistry and 40Ar/39Ar geochronology of hydrothermal K-feldspars

The Huangshaping deposit is a world-class W–Mo–Pb–Zn–Cu polymetallic deposit that formed during the Jurassic magmatic event in the central Nanling region, South China. In order to reveal the three-dimensional development of mineralization and alteration in this complicated fluid-rock system, four typical hydrothermal K-feldspar samples were collected from potassic alteration zones at different elevation levels around main W–Mo ore bodies, followed by precise trace element analysis and 40Ar/39Ar dating. The results show that these K-feldspars have a pronounced lanthanide tetrad effect with high contents of Ga, Ta, Nb, U, Y and HREE but low concentrations of Ba, Sr, Eu and Zr, suggesting a hydrothermal origin. Additionally, correlation between the Ca/Cl/K ratios and the apparent ages suggest that metasomatic fluids played an important role in the formation of the hydrothermal K-feldspars. The plateau 40Ar/39Ar ages which represent the timing of potassic alteration vary from 152.9±0.5 to 154.3±0.6Ma, spatially showing younger trends from north to south and from shallow to deep. These dates correspond to the previous published molybdenite Re–Os data variations in different elevation levels, which record the mineralization event with relatively older ages ranging from 153.8 to 159.4Ma. Combined with the spatial relation analysis among samples, the fluid migration rates associated with the mineralization and alteration are calculated at 10–100mMa−1. Thus, we propose a fluid downward migration model for the Huangshaping polymetallic deposit.

Geologic model and fluid flow simulation of Woodbine aquifer CO2 sequestration

Most simulation studies have focused on small-scale CO2 injection in deep saline aquifers. Recently, a significant amount of simulation studies on large-scale CO2 storage have been conducted. This study investigates what an actual CO2 storage project might entail using field data for the Woodbine aquifer in East Texas.A geological model of the Woodbine aquifer was created based on existing structural, petrophysical, and aquifer data found in the Bureau of Economic Geology (BEG) website. A key feature in the model is the Mexia-Talco fault system that serves as a likely boundary between the saline aquifer region suitable for CO2 storage and an updip fresh water region. Three CO2 injection scenarios were considered: CO2 bulk injection and two aquifer management strategies (AMS). The AMS were CO2 injection with brine extraction; and CO2 injection with brine extraction, and concentrated brine reinjection (from desalination).Simulation results indicate that aquifer pressurization limits bulk injection of the CO2 from surrounding power plants to 20 years, but the AMS would store CO2 injected at the same rate for up to 240 years. The simulation also enabled investigation of fluid migration across the Mexia-Talco fault system by using a fault transmissibility multiplier to adjust fault transmissibilities. For bulk CO2 injection small leakage through or around the fault system permits a volume of brine equal to the injected CO2 volume eventually to leak into the fresh water aquifer. For the two AMS, fresh water is drawn into the saline aquifer during brine extraction, and brine and/or CO2 ultimately will migrate into the fresh water aquifer. The rate of fluid migration across the fault system depends on its transmissibility, and CO2 would leak into the fresh water aquifer after 905 and 1080 years for cases with fault transmissibility multiplier of 0.1 and 1, respectively.Because fault displacements are typically more than 200m (700ft), and because there is a sharp contrast in salinity across the Mexia-Talco fault system, the likelihood of nonzero fault transmissibility may be low and may remain low provided that neither increased nor decreased pressure across the fault system from CO2 and concentrated brine injection or brine production alter the fault transmissibility over time.

Effects of episodic fluid flow on hydrocarbon migration in the Newport‐Inglewood Fault Zone, Southern California

AbstractFault permeability may vary through time due to tectonic deformations, transients in pore pressure and effective stress, and mineralization associated with water‐rock reactions. Time‐varying permeability will affect subsurface fluid migration rates and patterns of petroleum accumulation in densely faulted sedimentary basins such as those associated with the borderland basins of Southern California. This study explores the petroleum fluid dynamics of this migration. As a multiphase flow and petroleum migration case study on the role of faults, computational models for both episodic and continuous hydrocarbon migration are constructed to investigate large‐scale fluid flow and petroleum accumulation along a northern section of the Newport‐Inglewood fault zone in the Los Angeles basin, Southern California. The numerical code solves the governing equations for oil, water, and heat transport in heterogeneous and anisotropic geologic cross sections but neglects flow in the third dimension for practical applications. Our numerical results suggest that fault permeability and fluid pressure fluctuations are crucial factors for distributing hydrocarbon accumulations associated with fault zones, and they also play important roles in controlling the geologic timing for reservoir filling. Episodic flow appears to enhance hydrocarbon accumulation more strongly by enabling stepwise build‐up in oil saturation in adjacent sedimentary formations due to temporally high pore pressure and high permeability caused by periodic fault rupture. Under assumptions that fault permeability fluctuate within the range of 1–1000 millidarcys (10−15–10−12 m2) and fault pressures fluctuate within 10–80% of overpressure ratio, the estimated oil volume in the Inglewood oil field (approximately 450 million barrels oil equivalent) can be accumulated in about 24 000 years, assuming a seismically induced fluid flow event occurs every 2000 years. This episodic petroleum migration model could be more geologically important than a continuous‐flow model, when considering the observed patterns of hydrocarbons and seismically active tectonic setting of the Los Angeles basin.

Deriving regional vertical fluid migration rates offshore southwestern Taiwan using bottom-simulating reflectors

Fluid migration rates are important parameters for understanding the structural characteristics and evolu- tion of the crustal tectonics and hydrocarbon exploration. However, they are difficult to measure on the seafloor. Densely sampled temperature measurements might shed light on our study of the fluid migration rates. In this study, we first use reflection seismic data to derive geothermal gradient patterns at different sub-seafloor depths, then calculated 1D vertical fluid flow models by analyzing the Peclet numbers in the offshore regions of SW Taiwan. We found Peclet numbers ranging from 2 to 5, implying that vertical fluid flow velocities are between 6 and 44 cm/year. Assumed a homogenous permeable layer and no lateral variation of the temperature fields, we analyzed possible errors caused by depth-dependent thermal conductivity and velocity-depth function. They probably cause less than 2 cm/year of errors in the estimated vertical fluid flow rate. In terms of regional fluid flow patterns, we found higher fluid flow rates near the toe of the trench, and a dramatic increase in fluid flow rate when the continental slope of the Chinese passive margin enters into the trench, and reduced fluid flow rates in the hinterland. We propose that this is a new and potentially useful method to derive regional fluid flow rate models for studying geochemical and biological processes in shallow seafloor sediments and the regional hydrological budget.

Determination of crustal fluid residence times using nucleogenic [formula omitted

Argon-39 is a radioactive isotope of Ar with a half-life of 269years. There are two natural sources of 39Ar on Earth; cosmogenic production in the upper atmosphere and nucleogenic production in rocks. Cosmogenic 39Ar has been recognized as an ideal tracer for groundwater residence times and oceanic circulation. Nucleogenic 39Ar has generally been considered problematic for groundwater studies. In this work, we developed simple models for the evolution of 39Ar/40Ar∗ ratios (where 40Ar∗ denotes radiogenic 40Ar produced in the model system) in rocks and fluids. In rocks, both 39Ar and 40Ar∗ are produced, and a fraction of the 39Ar and 40Ar∗ is released into the mobile fluid phase. In both reservoirs, 39Ar reaches production- or supply-decay equilibrium, whereas 40Ar∗ accumulates with time. Thereby, the 39Ar/40Ar∗ ratio in rocks and fluids generally decreases with time. Our models suggest that the co-evolution of these two isotopes in rocks and fluids provides a new chronometer of fluid migration and reaction in the crust. This chronometer is relevant to a much wider time range than that limited by radioactive decay of cosmogenic 39Ar (i.e., ∼1400years at the current detection limit of 3% modern atmospheric value). The 39Ar/40Ar∗ chronometer is applicable to estimating residence times of very old groundwater as well as for studying fluid–rock interactions and fluid migration rates, such as those occurring during CO2 sequestration and the formation of hydrocarbon reservoirs.

Determination of hydraulic conductivity and fines content in soils near an unlined irrigation canal in Guasave, Sinaloa, Mexico

The determination of hydraulic conductivity is essential for the assessment of fluid migration rates in the subsurface. Geoelectric methods are often used in hydrogeological studies as quick and inexpensive tools. The relation between saturated soil hydraulic conductivity (K), clay content and soil resistivity allows an estimation of clay content and K from electrical measurements made in the field or laboratory. In this work, a methodology for estimating fines (silt + clay) content and K from electrical measurements in silt-loam soils is presented. A textural analysis was performed in 73 soil samples collected from 21 boreholes located in the municipality of Guasave, Sinaloa, Mexico, to determine the sections with a greater infiltration of water from the Valle del Fuerte irrigation canal to the local aquifer. The calculated values of texture and K were used to develop a new empirical equation, K = 0.101176 * FINES -1.62 , which achieved a new relation to properly estimate the K values from the percentage of fines content. Electrical measurements were performed in the laboratory for each soil sample to determine the fines content. The K values, which were determined by a new empirical equation, showed an acceptable correlation with the values obtained by traditional techniques for silt and silt loam soils with a clay content < 35%. Water resistivity measurements were performed for samples collected from wells and flumes, showing that the water salinity of the canal is significantly lower than the groundwater. Due to the location of the Valle del Fuerte canal and soil K values, the water infiltrated from the flume into the subsoil creates a barrier preventing or slowing down the advance of the saltwater intrusion from the Sea of Cortez. Short Electrical Resistivity Tomography (ERT) profiles were carried out to determine the surface stratigraphy. The results achieved by the application of ERT and the groundwater salinity values allowed the recalculation of the geoelectrical sections in the fines content and K sections, resulting in a new, faster and less expensive procedure for the determination of hydraulic and petrophysical parameters.

Reaction-assisted hierarchical fracturing during serpentinization

Hierarchical fracture patterns are the result of a fracturing process that successively divides rocks into smaller domains. In a 2D (outcrop) section such fracture patterns are characterized by four sided domains, and T-junctions where new fractures stop growing at right angles to pre-existing fractures. Here, we describe fracturing of mm to dm thick serpentinized orthopyroxenite dykes in a dunite matrix from the Leka Ophiolite Complex in Nord-Trøndelag, Norway. The fracturing process is driven by volume changes associated with the serpentinization of the dunites. During this process the orthopyroxenite dykes are extended by the expanding dunite and undergo considerable fracturing. The resulting fracture patterns are hierarchical. The cumulative distributions of fracture lengths show a scaling behavior that lies between a log–normal and power law (fractal) distribution. This is consistent with a simple fragmentation model in which domains are divided according to a ‘top hat’ distribution of new fracture positions within unfractured domains. Reaction-assisted hierarchical fracturing is also likely to be responsible for other structures commonly observed in serpentinized ultramafic rocks, including the mesh-textures observed in individual olivine grains, and the high abundance of rectangular domains at a wide range of scales. This mechanism may provide first-order controls on fluid migration rates in a wide variety of geological settings.

Formation of ice lenses and frost heave

I examine the morphology of ice growth in porous media. Intermolecular forces cause premelted fluid to migrate and supply segregated ice growth (e.g., lenses) and frost heave. I account for the net effect of these microscopic interactions in a homogenized model formulated in terms of fundamental physical properties and characteristics of the porous medium that can be measured; no ad hoc parameterizations are required. Force equilibrium constraints yield the rate of fluid migration toward the ice lens boundary and predict the conditions under which new lenses are initiated. By combining this analysis with considerations of the heat flow problem in a step‐freezing (Stefan) configuration, I elucidate the boundaries between different regimes of freezing behavior. At higher overburden pressures and relatively warm surface temperatures, ice lenses cannot form, and freezing of the available liquid occurs within the pore space, with no accompanying deformation. When conditions allow a lens to form, water is drawn toward it. If the fluid supply is sufficiently rapid, the lens grows faster than the latent heat of fusion can be carried away, and its boundary temperature warms until it reaches a stable steady state configuration. At lower fluid supply rates, the lens boundary temperature cools until a new lens can form at a warmer temperature beneath. With subsequent freezing this lens grows until yet another lens forms and the process repeats. An approximate treatment leads to estimates of the evolving lens thickness and spacing, as well as the accumulated total heave.

Quantitative analysis of slip-induced dilation with application to fault seal

A new quantitative model for calculating the volumes and rates of fault-zone fluid migration during dynamic slip events is developed. This model is based on observations from laboratory rock mechanics experiments of porosity evolution during frictional sliding and geophysical data that demonstrate the existence of propagating slip pulses that experience transient dilation during earthquakes. The nature of dilation during slip is dependent on the frictional behavior; that is, whether the fault experiences seismic or aseismic slip. The transient dilation that occurs during seismic slip is more efficient in transporting fluids along the fault than the relatively reduced dilation that occurs during aseismic slip. For aseismic faults, fluid-migration rates are primarily dependent on the intrinsic permeability structure of the fault rock during periods of no slip (static permeability). In contrast, both the static and dynamic permeabilities are important along faults that slip seismically. We infer that aseismic slip does not enhance migration significantly other than providing a transient, spatially restricted permeability increase that may act to initiate migration. The proposed models are applied to estimate the maximum amounts of hydrocarbon leakage from seismically active faults that trap hydrocarbons in the Cusiana field, Colombia, and aseismic faults at Eugene Island Block 330 field, Gulf of Mexico. Model results are grossly consistent with observed hydrocarbon volumes and inferred along-fault migration rates from the two areas. The proposed models have broad implications for understanding the effects of faults on fluid migration during both exploration (geologic) and production time scales.

The time and frequency response of tracer experiments

Two distinctly different approaches to the interpretation of advective and dispersive transport characteristics of an intermediate scale (0–6 m) tracer experiment are examined and compared. The first, or time domain method, is based on a direct analysis of the tracer breakthrough via the widely used moment method. The second, or frequency domain method, is based on a comparison of the Fourier transform of the tracer breakthrough and its theoretical counterpart the frequency response function. Both methods provide satisfactory estimates of the mean advective transport component of the experiment for both conservative and nonconservative tracers. For the sampling ports closest to the source (0–2 m), the moment method produces much larger estimates of the dispersivity than the frequency response method. This difference is attributed to a buildup of errors in the estimation of higher moments, resulting from local variations in the tracer and fluid migration rates within this zone. In the lower part of the caisson (> 2m), the tracer breakthrough is smoother, and both methods provide similar and smaller dispersivity estimates. Overall the frequency domain approach is less sensitive to random variations in the breakthrough response. This idea is illustrated with an example from optimal filtering theory.

Use of Hydraulic Head and Hydraulic Gradient to Characterize Geopressured Sediments and Direction of Fluid Migration in Louisiana Gulf Coast: ABSTRACT

ABSTRACT The characterization of geopressured sediments in the Gulf Coast is commonly made on the basis of increases in pressure gradient or geostatic ratio, that is, in situ fluid pressure divided by total depth. Fluids and sediments having geostatic ratios in excess of 0.47 psi/ft are usually considered 'geopressured', those with geostatic ratios greater than 0.70 psi/ft, 'hard-geopressured'. An alternative and more informative way of characterizing geopressured sediments is by use of the parameter hydraulic head. Hydraulic head can be used not only to distinguish between hydropressured and geopressured sediments, but also to provide potentially quantitative information on the direction and rate of subsurface fluid flow. Hydraulic head, h (feet), is defined as h = Z + Pg/, where z is depth below a reference datum, P is measured or calculated fluid pressure, g is acceleration due to gravity, and is fluid density. In the absence of osmotic effects, the hydraulic gradient, dh/dl (dimensionless), where l is path length, can be used in conjunction with hydraulic conductivity in Darcy's Law to predict the direction and rate of fluid migration. Variations in calculated hydraulic head have been correlated along several regional cross-sections through the Tertiary sedimentary sequence of South Louisiana. Four distinct hydrodynamic zones can be distinguished with depth in the region studied: Near surface to 7000 feet in depth. Hydropressured fresh to saline waters having hydraulic heads near zero and vertical hydraulic gradients of 0.01 or less. 7000 feet to 10,000-14,000 feet in depth. A transition zone of weakly geopressured sediments with hydraulic heads ranging from 0 to 3000 feet above sea level. Hydraulic gradients range from 0.1 to 4 and show many reversals with depth. Many commerically important hydrocarbon plays occur within this zone: 10,000-14,000 feet to 12,000-18,000+ feet. The hard geopressured zone in which hydraulic head progressively increases with depth from values of 3000 to 16,000+ feet of head above sea level. Gradients of 4 to 5 are typical but locally can exceed 25. There are few reversals in gradient with depth. Depths below Zone 3. Suggestion, based on sparse data, that hydraulic gradients begin to decrease with depth. In contrast to the hard geopressured zone, where hydraulic flow appears to consist of a broad, generally upward-moving front, hydraulic flow in the transition zone appears to be more strongly focused through preferred channel-ways.