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Researchers at the Columbia University's Lamont-Doherty Earth Observatory were the first to think of applying the fourth dimension—that is, time—to oil production. As often occurs in scientific breakthroughs, an unsolved mystery drew Roger Anderson’s lab went in looking to see how an oil field charges itself, and in turn we found out how it was draining,” Anderson says.
We will develop a 4D seismic reservoir simulator (4D SeisRes) that couples a) our 4D Rapid Analysis technologies (patented) for analysis of repeated 3D seismic surveys of the subsurface, with b) our 4D Seismic Inversion (patent pending) and stochastic reservoir characterization techniques that describe the physical state of reservoirs at each observational time step. Output is in turn fed into c) a massively parallel reservoir fluid flow simulator to predict the history of fluid flow within reservoirs under study. This fluid flow history is then fed to d) a newly invented code for 3D Finite Element Modeling of wave propagation in anisotropic (transversely isotropic), elastic media (patent application in preparation). The fluid flow predictions are converted in the seismic simulator into expected acoustic responses, which are then tested against a) again to create a constantly updating loop that is the 4D SeisRes monitoring of reservoirs. The loop is constantly iterated so that the system learns the correct fluid flow behavior over time (Figure 1).
4D Security Imaging Technology Summary: 4D (volumetric differencing over time) is a natural extension of three 3D (length, width and depth) imaging that has been used in a wide variety of disciplines for detection of changes in medical conditions, weather, and even oil and gas reservoirs. 4D Security Imaging is the repeated scanning of the same volume at different time periods, thus adding the fourth dimension, time, to determinations of whether dangerous objects have been placed into the volume. 4D Security Imaging allows one to image a semi-trailer truck or shipping or airfreight container and then compare the differences over controlled time periods. Columbia has invented software for fast, accurate and reliable imaging of the 4D changes inside volumes. When integrated with other forms of time-depend information, such as the 3D image of the container body when it was first packed (Figure 1), or libraries of expected shapes or densities, our software can be used to improve security of closed shipping containers. Examples of 4D datasets with which our software is currently being used include acoustic, nuclear, magnetic, and gravity gradiometry scans. Technology Background: 4D imaging developed in the 1990's primarily from two industries, the medical and energy exploration businesses. In the medical profession, determining the growth, or hopefully, shrinkage of a cancer using repeated MRI volumetric images is an excellent example of 4D. In oil production, repeated 3D seismic surveys that detect pockets of bypassed oil and gas is representative of 4D. In contrast, the compaction technologies
The rate and volume of mid-ocean ridge magma supply and variations in the geometry of the melt delivery system control ridge axis structure, magma mixing and residence times, and hydrothermal fluid flow. Marine multichannel seismic reflection images of mid-ocean ridge crustal structure first revealed the presence of a narrow magma lens beneath the ridge axis. Two-dimensional (2-D) reflection profiles spanning hundreds of kilometers along-axis revealed variations in the continuity and depth of the melt lens which correlate with ridge segmentation. Further detailed analysis of seismic reflection waveforms have provided estimates of the thickness, width, and melt saturation of the melt lens. More recently, the first three-dimensional (3-D) multichannel seismic reflection study of a mid-ocean ridge revealed the complex geometry of the axial magma chamber lens near a ridge axis discontinuity. As the quality of seismic reflection data has improved, so has our understanding of the distribution of magma in the subsurface and magmatic processes at ridge crests. Now important questions are being posed based on results from continuous earthquake monitoring and frequent sampling of the ridge axis hydrosphere and biosphere which show that the mid-ocean ridge magmatic and associated thermal environment changes on short time scales on the order of years. In order to understand the dynamics of the mid-ocean ridge magmatic system, new time lapse seismic reflection imaging techniques are needed to observe changes in the geometry and physical properties of the magmatic system over time. Time lapse, or four-dimensional (4-D), seismic reflection monitoring involves repeated 3-D surveys to identify changes in seismic reflectivity due to fluid migration, faulting, or changes in pressure or melt saturation. 4-D seismic reflection studies have been in use in the oil exploration industry for more than ten years and have proven their value by a threefold increase in hydrocarbon recovery over 2-D seismic methods. Quantitative 4-D seismic analysis techniques developed by the Lamont 4-D Technologies Group are currently being applied to commercial 3-D seismic reflection data sets at Lamont-Doherty Earth Observatory. 4-D seismic analysis steps include cross-equalization, seismic attribute analysis, and differencing of 3-D data volumes followed by inversion for acoustic impedance, fluid flow simulation, and forward seismic modeling of the melt reservoir model to match predicted reflectivity changes with observations from seismic reflection and other monitoring methods. The results can be used to guide additional ridge axis studies and may even be used as a predictive tool to identify the potential location of future eruptions from sites of subsurface melt accumulation. Seismically imaging the geometry and volume of magma flow will be useful for constraining geochemical models of magma mixing and for constraining the thermal regime which controls hydrothermal circulation at the ridge axis. Fast spreading ridges or slower spreading ridge segments with locally elevated magma supply are most likely to produce seismically observable changes on short time scales. Seismic detection and resolvability issues will need to be carefully examined from existing data, and various ridge axis monitoring methods will be needed to determine the appropriate place and time to perform repeated 3-D surveys. High resolution mapping of seafloor bathymetry and magnetics will provide critical information on near-surface processes including volcanic activity and caldera collapse or graben formation. Passive seismic studies of ridge axis seismicity will be particularly helpful; however, the most magmatically active areas where the brittle crust is thin will produce the smallest earthquakes. Studies of hydrological and biological systems or other geophysical indicators of magmatism at the ridge axis which can be performed frequently will help us to track multiple stages of the magmatic accretionary cycle. 4-D seismic technology enhances the value of other time series measurements because patterns of seismicity, hydrothermal fluid flow and biological productivity can be correlated with measurable changes in the axial magmatic plumbing system. Overall, 4-D seismic studies of the axial magma chamber offer great promise for improving our understanding of the processes of rifting, magmatism, and accretion of oceanic crust at mid-ocean ridges in both space and time.
3D Emersive Environment at the Univ of Houston used to Visualize Oil Drainage in a Gulf of Mexico 4D Seismic Analysis
The tracking of fluid drainage over time is a required condition for efficient reservoir monitoring. 4D time-lapse seismic differencing holds great promise as the keystone to an integrated reservoir management strategy that is able to image acoustic changes over time not only within a reservoir but within the stack of reservoirs that make up most of the oil and gas fields of the world.
4D seismic has become a widely accepted technique to interpret changes between successive 3D seismic surveys in terms of fluid substitution and pressure depletion in a producing reservoir. However, most time-lapse studies have been mostly qualitative and based on simplified reservoir representation in order to adjust to the time constraints of today's oil market. In this paper, we present how reservoir simulation constrained by stochastic characterization and non-linear optimization can be used in an integrated series of tools to refine 4D interpretation. Because of its direct relationship with pore fluid content and properties, we use seismic impedance rather than seismic amplitude as the primary data between the various steps of our 4D interpretation loop. Non-linear inversion of the 3D seismic data sets allows a preliminary interpretation. Stochastic simulation of the lithology and porosity, constrained by these "observed" impedance volumes and by well logs, provide the static reservoir characterization for the reservoir simulator. Once simulated production matches the recorded production history, empirical or Biot/Gassmann-type petrophysical models are used to calculate the "simulated" impedance volume from the fluid saturation and pressure distribution calculated by the reservoir simulator. Non-linear optimization is used iteratively to improve first the production history match and next the agreement between "simulated" and "observed" impedance volumes over time. This optimization is performed over a limited set of poorly constrained parameters in the permeability calculation and petrophysical models. In the case study presented here, the analysis of a turbidite reservoir in the South Timbalier 295 field, our results show how stochastic characterization helps reproducing the complexity of reservoir fluid dynamics while the results of the optimization underlines the robustness of the 4D interpretation despite the large amount of unknowns.
Cenozoic marine sediments were drilled and cored by the Deep Sea Drilling Project at Site 613 in the Baltimore Canyon Trough, and four channel sonic waveforms were recorded downhole from 125.4 to 581.7 meters below sea floor. Compressional wave velocities and spectra were calculated from the sonic waveforms. Compressional velocity increased as porosity decreased with depth. However, the energy loss between near and far receivers increased and the peak crosspower frequency decreased with depth, suggesting that attenuation increases over the same interval. The observed changes in energy and frequency cannot be explained solely by changes in the elastic properties of the sediments. We calculate the compressional wave Q at 10-m depth intervals using the spectral ratio technique. Mean compres-sional wave Q decreases from about 69 above to 28 below a diagenetic boundary at 442.0 m. Attenuation estimates at the peak frequency are lower than the spectral ratio values, but clearly increase below the diagenetic boundary. SonicA wave attenuation can be explained by a surface stress relaxation mechanism in thin fluid-filled pores. A decrease in pore aspect ratio and an increase in pore surface area due to diagenetic effects may explain the observed increase in attenuation with depth at Site 613. These diagenetic effects are not unique to conditions at this site. .#-1-SPWLA TWENTY-SIXTH ANNUAL LOGGING SYMPOSIUM, JUNE 17-20, 1985
Constructing reservoir models using time-lapse 3D seismic data and well data is time-dependent reservoir characterization, it is a challenging problem that requires integration of multidisciplinary knowledge of hydrocarbon reservoir. We developed a time-dependent reservoir characterization method and applied it to a complex turbidite sand reservoir, K8, of the South Timbalier 295 Field in the northern Gulf of Mexico basin. The method is implemented in a hierarchical order according to the dependence of reservoir properties of the K8 reservoir. In addition to the quantitative delineation of static and dynamic properties of the K8 reservoir, we further analyzed the characterized reservoir model to explain the observed 4D seismic amplitude differences of the K8 reservoir between the year 1988 and 1994. From constructed reservoir model and production, we found that although seismically compartmentalized, the turbidite channel sands of the K8 reservoir is in good communication overall, and permeability pathways are in excellent agreement with high sand content. Furthermore, the observed amplitude increase in the downdip portion of the reservoir is probably caused by gas-dissolution from liquid oil due to the pore pressure decrease associated with oil production in the middle of the reservoir. However, the amplitude decrease observed in the updip of the reservoir is difficult to explain. Fluid simulation using the newly constructed reservoir model is highly recommended.
4D processes 3D seismic differences observed over time to identify drainage and bypassed oil within each reservoir --New oil from old fields. 4D is in the early stages of market penetration. 4D is expected to extract 30% added value (oil and gas) over 3D exploitation (Aylor, Amoco, 1996)
4-D reservoir monitoring is a cost-effective way to expand revenues throughout the development history of reservoirs through tracking and monitoring of oil, gas and water drainage patterns over time. Bypassed pay can then be targeted and remediation programs planned, increasing recovery efficiency of oil-in-place to previously unheard-of-levels that are expected to approach 70% by early next century. This added efficiency comes from a fundamental paradigm shift in the way that oil fields are produced--spacetime monitoring of oil fields.
This first part of a six-part series explains how 4-D was developed, and how any company can take advantage of this new technology. Actual seismic response at various times in the life of a producing field are used to illustrate how 4-D technology is applied. Bypassed production is identified, and improved reservoir management is the end result.
The oil industry is still staggering from the recent price collapse, with management energy focused on cutting costs and improving return on capital employed (ROCE). The major fiscal problem of the energy business is that it is not competitive as an investment vehicle when compared to other growth industries such as computing, the internet, and biomedicine, because our ROCE is so poor. While new exploration hotspots like offshore west Africa and the ultra deepwater Gulf of Mexico offer the promise to return >30% ROCE, refining and marketing is a drag at <5%. The industry's hope to return from its current "contrarian" financial position to become a sound fiscal industry rests in the delivery on promise from the high return offshore areas around the globe. It is not enough to discover and prove out large reserve numbers anymore in these giant and super giant oil fields. As often as not, survival of the oil company owners rests on delivering to market at a 60% or higher recovery rate. When the economics of 4D Reservoir Management are considered in a stochastic portfolio model of future cash flow, various price scenarios can be considered quantitatively in terms of the relative contributions of each large field to the company's overall success. It becomes clear that high recovery rates are required to balance risk and reward sufficiently. However, if cost cutting models are used that exclude 4D Reservoir Management from future development scenarios for these fields, cash flow shortfalls result in all but the most optimistic future price scenarios. Thus, reservoir development plans that deliver cash when it is needed for a company are required, and in all-important fields, 4D Reservoir Management becomes essential. The costs of repeated acquisition of 3D seismic surveys and continuous downhole instrumentation and monitoring become cost effective near term investments when considered in this long-term cash flow framework. There are several examples from key fields in prime offshore areas where it has already been demonstrated that 4D Reservoir Management is a key to economic success of the basin. We will review a Gulf of Mexico field where 4D seismic monitoring produced significantly different drainage patterns from those expected, and early on in the life of the field, as well. Extraction of as much of the discovered oil and gas in known reservoirs is a critical capability that will be required to balance supply/demand in the 21 st century. 4D Reservoir Management returns substantial capital versus that invested, and therefore is an essential component of responsible Business Unit management in the modern age. Introduction to Portfolio Management (PM) Oil and gas production companies make money based upon on their skills in identifying a portfolio of properties and utilizing technologies to discover, produce, and sell oil and gas produced from those properties in an optimal manner. The key ingredient to improved business performance is portfolio management, which allows a company to present the performance of all its producing properties and exploration targets in a normalized way.