Subsurface temperature from seismic reflection data: application to the post break up sequence offshore Namibia

Accurate estimations of present-day subsurface temperatures are of critical importance to the energy industry, in particular with regards to geothermal energy and petroleum exploration. This paper uses seismic reflection observations of bottom-simulating reflections and subsurface velocities coupled with an empirical velocity to thermal conductivity transform to estimate subsurface temperature in a process dubbed reflection seismic thermometry. The case study is a frontier passive margin extending from the shelf edge to deep water in the central Lüderitz Basin, offshore Namibia. The bottom simulating reflector is used to derive surface heat flow. The thermal conductivity model was applied to seismic processing velocities to determine the subsurface thermal conductivity. Knowledge of surface heat flow and thermal conductivity structure allowed us to estimate subsurface temperatures across the study area. The results suggest the Lüderitz Basin has a working hydrocarbon system with the inferred Aptian Kudu source interval within the gas generation window.

Reflection Seismic Thermometry

An understanding of the subsurface thermal regime is beneficial to many disciplines, including petroleum and geothermal exploration, carbon capture and storage (CCS) and nuclear waste sequestration. This project developed and tested a new methodology for determining subsurface temperature using a non-invasive approach based on the velocity information derived from seismic reflection data. By solving a one-dimensional steady state approximation of Fourier’s Law, it is possible to determine a bulk thermal gradient as a function of depth, enabling the determination of temperatures across an entire volume using this methodology, termed reflection seismic thermometry. There are two principal components to this methodology, requiring 1) a bulk thermal conductivity structure and 2) heat flow and/or temperature data to condition the model. The first component uses an empirical velocity to thermal conductivity transform whilst the second uses sparse temperature data from boreholes or a bottom simulating reflector (BSR) to derive the shallow thermal regime and heat flow. The thermometry workflow has been applied to three case studies; in the Lüderitz Basin, offshore Namibia; the Blake Ridge, offshore USA; and the North Viking Graben (NVG) in the North Sea. In the frontier Lüderitz Basin, a BSR was identified and used to derive heat flow of 60-70 mW m-2. The Aptian source rock interval here was shown to presently be in the gas generative window. On Blake Ridge borehole velocities and a BSR were used to determine heat flow (43-56 mW m-2) and subsurface temperatures. Finally, methodology validation was conducted in the North Sea Basin using a high-resolution 3D full waveform inversion (FWI) velocity dataset calibrated with 141 wells. Forward models of subsurface temperatures were calibrated against the borehole temperatures, with inverse modelling used to derive heat flow at km scale lateral resolution. The availability of a fast track velocity volume for this area allowed comparison with the FWI derived thermal model results. It was found that stacking velocities were lower than well and FWI velocities, leading to overprediction of subsurface temperature. Modelling the temperature profile for CCS well 31/5-7 showed bottom hole temperature (BHT) within 6 °C of recorded BHT. With application and verification of the method in different basins, the versatility of the work conducted is demonstrated. It is envisioned that this technique opens avenues for the seismic characterisation of thermal regime in disparate settings and varied disciplines.

The interplay of Malm carbonate permeability, gravity-driven groundwater flow, and paleoclimate – implications for the geothermal field and potential in the Molasse Basin (Southern Germany), a foreland-basin play

The Molasse Basin in Southern Germany is part of the North Alpine Foreland Basin and hosts the largest accumulation of deep geothermal production fields in Central Europe. Despite the vast development of geothermal energy utilization projects especially in the Munich metropolitan region, the evolution of and control factors on the natural geothermal field are still debated. Especially seismic and deep well data from extensive oil and gas exploration in the Molasse Basin led to conceptual hydrogeological and thermal-hydraulic models. Corrected borehole-temperature data helped to constrain subsurface temperatures by geostatistical interpolation and facilitated the set-up of 3D temperature models. However, within the geothermally used Upper Jurassic (Malm) carbonate aquifer, temperature anomalies such as the Wasserburg Trough anomaly to the east of Munich and their underlying physical processes are yet poorly understood. From other foreland basins like the Alberta Basin in Western Canada, it is known that climate during the last ice age has a considerable effect even on subsurface temperatures up to two kilometres depth. Therefore, we study the impact of paleoclimatic changes on the Molasse Basin during the last 130 ka including the Würm glaciation. We consider the hydraulic and thermal effects of periglacial conditions like permafrost formation and the impact of the numerous glacial advances onto the Molasse Basin. The major difference between the thermal-hydraulic regime in the western and eastern parts of the Southern German Molasse Basin are delineated by calculating two contrasting permeability scenarios of the heterogeneously karstified Malm carbonate aquifer. Thermal-hydraulic modelling reveals the effect of recurrent glacial periods on the geothermally drillable subsurface, which is minor compared to the effect of permeability-related, continuous gravity-driven groundwater flow as a major heat transport mechanism. Practically, the results might help to reduce the exploration risk for geothermal energy projects in the Molasse Basin. More importantly, this study serves as a reference for the comparison and understanding of the interplay of high permeability aquifers, gravity-driven groundwater flow and paleoclimate in other orogenic foreland basins worldwide.

On the Effect of Supplied Flow Rate to the Performance of a Tilting-Pad Journal Bearing—Static Load and Dynamic Force Measurements

Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, safe pad temperatures, and ensuring a rotor-dynamic stable rotor operation. End users focus on reducing the supplied oil flow rate into a bearing to both lower operational costs and to increase drive power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB whilst focusing on the influence of supplied oil flow rate, below and above a nominal condition (50% and 150%). The test bearing has five pads, slenderness ratio L/D = 0.4, spherical pivots with pad offset = 50%, and a preload –0.40, with a clearance to radius ratio (Cr/R) ≈ 0.001 at room temperature. The bearing is installed under a load-between-pads (LBP) orientation and has a flooded housing with end seals. The test conditions include operation at various shaft surface speeds (32 m/s–85 m/s) and specific static loads from 0.17 MPa to 2.1 MPa. A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant supply temperature. Measurements obtained at a steady thermal equilibrium include the journal static eccentricity and attitude angle, the oil exit temperature rise, and the pads' subsurface temperatures at various locations, circumferential and axial. The rig includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. As expected, the drag power and the lubricant temperature rise depend mainly on shaft speed rather than on applied load. A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise (6 °C) in pads' subsurface temperatures, a slight increase (up to 6%) in the direct stiffnesses, and a decrease (up to 7%) in direct damping coefficients. Conversely, a 1.5 times increase in oil flow rate causes a slight increase (up to 9%) in drag power loss, a moderate reduction of pads' temperatures (up to 3 °C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping. The paper also presents comparisons of the test results against predictions from a thermo-elastohydrodynamic (TEHD) lubrication model. In conclusion, a 50% reduced oil flow rate only causes a slight degradation in the test bearing static and dynamic force performance and does not make the bearing operation unsafe for tests with surface speed up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant-specific heat, and the oil exit temperature rise.

Ultrasonic monitoring of pipe wall interior surface temperature

Accurate temperature measurement is a crucial aspect of structural health monitoring and prognosis. Conventional temperature measurement devices are either incapable of measuring subsurface temperatures in solids or need to be invasively installed. This study investigates the use of an ultrasonic technique for non-invasive measurement of subsurface temperatures in steel components; the temperature of a point on an inaccessible surface is inferred using a time-of-flight measurement from a transducer placed on an opposing accessible surface. Two different inversion approaches are presented, one named the assumed distribution method and the other named the inverse thermal modelling method. The robustness and accuracy of the two ultrasonic temperature inversion methods are quantitatively assessed via simulations and controlled experiments. It was found that both the assumed distribution and inverse thermal modelling methods demonstrate short thermal response times and are able to track the temperature evolution of inaccessible surfaces. A series of experimental studies show that in the presence of a 15°C difference between the accessible and inaccessible surfaces, the inaccessible surface temperature is typically measured to within better than 2°C with respect to a resistance temperature detector reference measurement. Additionally, the article compares the measurement performance achieved using a deployable electromagnetic acoustic transducer and a permanently installed piezo-electric PZT transducer. The time-of-flight measurements taken using the electromagnetic acoustic transducer system had higher random noise than the PZT system (standard deviations of 0.42 and 0.016 ns, respectively), subsequently leading to higher random noise in the temperature estimates.

On the Effect of Supplied Flow Rate to the Performance of a Tilting-Pad Journal Bearing: Static Load and Dynamic Force Measurements

Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, safe pad temperatures, and ensuring a rotordynamic stable rotor operation. End users focus on reducing the supplied oil flow rate into a bearing to both lower operational costs and to increase drive power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB whilst focusing on the influence of supplied oil flow rate, below and above a nominal condition (50% and 150%). The test bearing has five pads, slenderness ratio L/D = 0.4, spherical pivots with pad offset = 50% and a preload ∼ 0.40, with a clearance to radius ratio (Cr/R) ≈ 0.001 at room temperature. The bearing is installed under a load-between-pads (LBP) orientation and has a flooded housing with end seals. The test conditions include operation at various shaft surface speeds (32 m/s-85 m/s) and specific static loads from 0.17 MPa to 2.1 MPa. A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant supply temperature. Measurements obtained at a steady thermal equilibrium include the journal static eccentricity and attitude angle, the oil exit temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial. The rig includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. As expected, the drag power and the lubricant temperature rise depend mainly on shaft speed rather than on applied load. A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise (6°C) in pads’ subsurface temperatures, a slight increase (up to 6%) in the direct stiffnesses, and a decrease (up to 7%) in direct damping coefficients. Conversely, a 1.5 times increase in oil flow rate causes a slight increase (up to 9 %) in drag power loss, a moderate reduction of pads’ temperatures (up to 3°C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping. The paper also presents comparisons of the test results against predictions from a thermo-elasto-hydrodynamic lubrication model. In conclusion, a 50% reduced oil flow rate only causes a slight degradation in the test bearing static and dynamic force performance and does not make the bearing operation unsafe for tests with surface speed up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant specific heat and the oil exit temperature rise.

Experimental investigation of microbially induced carbonate precipitation in sandstone cores under in-situ North Sea temperature and pressure conditions

<p>Bio-grouting using ureolytic microorganisms has been developed over the past decade for civil engineering applications including: (i) sealing fractures in rock, (ii) sealing cracks in cement, (iii) reducing the permeability of porous media  and (iv) soil stabilisation and (v) repair of concrete and stone. This study investigates the potential application of microbially induced carbonate precipitation (MICP) within the oil and gas industry. To deploy MICP in a well abandonment context a more in-depth knowledge of the influence and performance under elevated subsurface pressures and temperatures is required.</p><p>Batch experiments investigated the ureolytic activity at subsurface temperatures ranging from 20-90°C and fluid pressures from 1-13MPa for up to 2hrs exposure time. Strong evidence of increased ureolytic activity was observed in specimens at temperatures of 60°C and above, but with increasing exposure time ureolytic activity ceased. In comparison increased fluid pressures had little influence on ureolytic activity. Our results imply that the bacterial cell protects the enzyme from denaturation at elevated temperature conditions.</p><p>A second set of experiments consisted of multiple injections of the treatment fluids in a fine-grained sandstone sampled from the Brent sandstone formation of the Dunlin oilfield in the North Sea. With a focus on simulating the in-situ environmental conditions, we set-up a high pressure high temperature system consisting of a HPLC pump, water bath, Hassler core-holder with pressure capabilities of up to 2400psi and a temperature rating of 90°C with high sensitivity pressure transducers and a backpressure regulator. The cores were exposed to realistic North Sea subsurface temperatures of 20, 50, 60°C and fluid pressures of 442, 1326, 1621psi according to their corresponding depths: at 1000ft, 3000ft and 3667ft.</p><p>The study investigated the influence of the pressure and temperature conditions on (i) permeability reduction, (ii) distribution of CaCO<sub>3</sub> precipitates via X-CT imaging and (iii) mineralogy via FE-EPMA coupled with EDX/WDX spectroscopy.</p><p>Permeability reductions in the coarse-grained sandstones of 5 orders of magnitude were achieved in all the subsurface temperature-pressure combinations tests. Micro xCT scans indicate that CaCO<sub>3</sub> precipitation occurred closer to the inlet as the temperature and pressure increased, due in part to the higher ureolytic activity at higher temperatures and the lower solubility of CaCO<sub>3</sub> at higher temperatures. At elevated pressure and temperature conditions the energy barrier to transform from a calcite dominated system could be overcome and formed predominantly aragonite.</p><p>This study has demonstrated the potential for deploying MICP at subsurface conditions in oil and gas applications. The biotechnology itself could be used to seal off reservoir formations in mature oil and gas assets, repair fluid migration pathways or act as an environmental wellbore barrier element and therefore could ultimately reduce the number of well barriers required to be installed during plugging and abandonment.</p>

Beyond Sea Surface Temperatures: a Holistic Approach to Addressing Pliocene Tropical Conditions

<p>The tropical Pacific thermocline structure is critical to tropical sea surface temperatures (SSTs) and variability. During the mid-Pliocene warm period (~3 Ma), the zonal SST gradient was reduced due to relatively warm SST in the Eastern Equatorial Pacific; we call this mean state “El Padre.” How did the equatorial thermocline contribute to this reduced zonal SST gradient? Here we summarize published Mg/Ca (surface and subsurface dwelling foraminifera) and alkenone records and generate new SST estimates from Mg/Ca and alkenones. The subsurface dwelling <em>Globorotalia tumida</em> Mg/Ca-based temperature records from the eastern and western equatorial Pacific show mid-Pliocene warm period subsurface temperatures warmer than today; El Padre included a basin-wide thermocline that was relatively warm, deep, and weakly tilted. We compare the published and newly generated SST and subsurface temperature records to the Pliocene Modeling Intercomparison Project (PlioMIP1) and show that few models capture the magnitude and spatial pattern suggested by the temperature records. Those models that do corroborate the temperature records have warm subsurface temperatures in the Eastern Equatorial Pacific that dynamically link to warm SSTs in the cold tongue. This highlights the need to accurately model thermocline dynamics and mid-latitude conditions, where equatorial thermocline waters originate, in order to gain an understanding of the underlying processes that explain the mid-Pliocene warm period.</p>