Nader Dutta - Profile on Academia.edu (original) (raw)

Papers by Nader Dutta

Seismic Detection and Quantification of Gas Hydrates using Rock Physics and Inversion

Kluwer Academic Publishers eBooks, Feb 18, 2006

ABSTRACT In this paper, we present the results of our recent study of quantitative estimation of ... more ABSTRACT In this paper, we present the results of our recent study of quantitative estimation of gas hydrates in Alaminos Canyon block 818, Gulf of Mexico. The study was conducted as a part of the JIP Gulf of Mexico gas hydrates project. Sizable high concentration gas hydrates zones were detected as a result of the study, with hydrates saturation as high as 80% of the pore space. Comparison of the seismic prediction with estimation from one available shallow well shows high level of consistency, adding further to the reliability of the seismic prediction. Based on our findings, multiple wells are planned for drilling through the high concentration anomaly zones by JIP in the summer of 2008. The confirmation of our prediction through drilling will lead to the discovery of the first major gas hydrate accumulation in the Gulf of Mexico.

AGUSM, May 1, 2007

This study examines the accuracy of the predictions of gas hydrate saturations made based on five... more This study examines the accuracy of the predictions of gas hydrate saturations made based on five-step analysis of 3D seismic data prior to 2005 drilling, logging, conventional coring, and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern Gulf of Mexico. These predictions are detailed in Part I ( ). Here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and P-wave velocity log data and analyze the pre-drilling predictions, which were made almost exclusively on the basis of seismic data, with no local logging control. Well log measurements, core data analysis, and pressure core-degas experiments all indicated general agreement with the pre-cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments. We find that seismic predictions are generally consistent with log-based estimates after upscaling to seismic frequencies. We recalibrated the pre-drill model based on the new field data so that a refined version of the model could be used for future work.

Physical review, Dec 1, 1970

Gas Hydrate Estimation Using Rock Physics Modeling and Seismic Inversion

AGUSM, May 1, 2006

ABSTRACT ABSTRACT We conducted a theoretical study of the effects of gas hydrate saturation on th... more ABSTRACT ABSTRACT We conducted a theoretical study of the effects of gas hydrate saturation on the acoustic properties (P- and S- wave velocities, and bulk density) of host rocks, using wireline log data from the Mallik wells in the Mackenzie Delta in Northern Canada. We evaluated a number of gas hydrate rock physics models that correspond to different rock textures. Our study shows that, among the existing rock physics models, the one that treats gas hydrate as part of the solid matrix best fits the measured data. This model was also tested on gas hydrate hole 995B of ODP leg 164 drilling at Blake Ridge, which shows adequate match. Based on the understanding of rock models of gas hydrates and properties of shallow sediments, we define a procedure that quantifies gas hydrate using rock physics modeling and seismic inversion. The method allows us to estimate gas hydrate directly from seismic information only. This paper will show examples of gas hydrates quantification from both 1D profile and 3D volume in the deepwater of Gulf of Mexico.

A novel approach to reservoir characterization using seismic inversion, rock physics and Bayesian classification scheme

On the Inversion of Seismic Amplitudes for Lithology, Fluid and Pressure Analysis

Reservoir description using seismic data has two major components: inversion of seismic data to e... more Reservoir description using seismic data has two major components: inversion of seismic data to extract attributes such as P- and S-wave velocities and bulk densities, and relate those parameters to reservoir properties, such as rock and fluid types, fluid saturation, porosity and pore pressure through fundamentals of rock physics. Implicit in the process are two key as-sumptions: the seismic data quality must be good enough for inversion, and the inversion algorithm must be robust and fast enough to yield reliable and consistent results economically with acceptable non-uniqueness. We have seen much progress in both areas. In seismic acquisition, we have seen considerable advancement that contributed to the quality of the seismic data, especially in the prestack domain. These are: single sensor recording (a large number of channels/offset), accurate and cali-brated source and receivers and their positions, digital group forming, and towing cables at shallow water depths to minimize swell noise. All of these enable us to access surface seismic data with high S/N and fidelity that often rivals the fidelity of the Vertical Seismic Profiles (VSP). Seismic inversion algorithms also reached new heights. The advent of high-speed digital data processors and cluster technology impacted significantly the performance of various inversion algorithms; we are now inverting routinely seismic data in the full offset domain and just not restricting ourselves to the stacked data. In this paper we discuss the advances in seismic inversion technology that utilizes the amplitude information along with data consistent velocity analyses. First, we briefly review the basic assumptions behind the AVO, EI and full waveform inversion techniques in the prestack domain. While the users of the AVO and EI technology have focused on carrying out inversions using “large angle” assumption- presumably for extracting bulk density information, we show that this may not be feasible due to the neglect of various physical effects, such as interbed multiples, mode conversions and reflection and transmission losses which are omnipresent. Full waveform prestack inversion (FWPI) is currently the highest level of inversion technology in the industry. Unlike prestack inversion methods such as AVO, the FWPI technique uses a finite-difference elastic model to compute the entire seismic waveform. This provides an advantage over AVO methods in capturing thin-bed effects in data and increasing the potential resolution of the process. The process is computationally intensive and discussed in detail by Mallick (1999). Rock physics-based constraints are applied to speed convergence as well as to reduce ambiguities. Nonetheless, results from this as well as any non-linear inversion process tend to be sensitive to the quality of the a-priori model. However, given a good rock physics model and a-priori information, the output resolution exceeds that produced by other inversion techniques. We have also found that the ambiguities associated with the inversion process can be further reduced if the prestack data has high S/N. The FWPI technique is computer intensive. Currently this is used in the 1D mode to create pseudo-logs of Vp, Vs and density at selected points in a 3D data volume. These pseudo-logs are then used in the hybrid inversion technique (Mallick (1999) to propagate the benefits of FWPI inversion over 3D volumes. In its current form, hybrid inversion involves computation of pseudologs from full-offset seismic data at selected pilot points in the 3D volume using the FWPI technique, as well as AVO p-intercept and pseudo-shear data over the entire volume. Shear-wave output from FWPI pilot points are used to calibrate the AVO pseudo-shear data. Then both p-wave and pseudo-shear data are independently inverted using a poststack algorithm. Poisson's ratio and other elastic attributes for lithology discrimination are computed from the poststack inversion results. The hybrid inversion process requires input of a 3D a-priori model and a geologically consistent rock physics model, calibration of 3D attribute volumes, and interactive 3D visualization. We illustrate the entire procedure with examples from several basins.

Seismic Characterization of Gas Hydrates in Northern Gulf of Mexico

Proceedings, 2013

Whether gas hydrates are considered as hazard or resource, we need to find it first. We developed... more Whether gas hydrates are considered as hazard or resource, we need to find it first. We developed an integrated, seismic-based, five-step workflow (Dutta et al 2010; Dutta and Dai, 2007) to delineate and quantify gas hydrates using an approach very similar to finding hydrocarbon. The approach is primarily based on seismic characterization, geologic analysis and seismic inversion that is constrained with rock physics principles. These are performed within the gas hydrate stability zone. The introduction of gas hydrates in the shallow unconsolidated sediments tends to enhance both the stiffness and rigidity of the hosting rocks. Gas hydrate drilling worldwide has indicated that the increases in the stiffness and rigidity are somewhat proportional to the concentration of gas hydrates in the porous space of the sediments. This provides basis for the gas hydrate characterization and quantification using seismic information. In this presentation, we will review the technology, and demonstrate its application, using multiple examples from the Gulf of Mexico (GOM). Based on our models for gas hydrate exploration, a set of wells were drilled by the Consortium of USA – DOE and several oil companies in the deep water GOM (e.g. Green Canyon, Walker Ridge, Atwater Valley) and the model

A New procedure to generate pseudo-shear wave log - Methodology and model verification

55th EAEG Meeting, 1993

Predrill estimation of rock and fluid types and subsequent calibration using Amplitude Versus Off... more Predrill estimation of rock and fluid types and subsequent calibration using Amplitude Versus Offset (AVO) technology require, among other things, availability of three logs: P-wave, density and shear wave. White the first two logs are commonly available, the shear wave log is not routinely available. This is either because rock formations are 'too soft' (e.g., offshore Tertiary Clasics of Gulf of Mexico) for shear refraction arrivals in conventional logging tools, or unavailability of dipole tools due to prohibitive cost or other logistics. Until the dipole logging industry matures and becomes competitive, we foresee the cost of acquiring borehole shear wave data to remain high. Thus, we need to pursue alternate avenues to 'estimate' shear wave speeds (foot-by-foot) from conventional borehole data. This is the premise of the work discussed here.

Using rock physics for pseudo well log construction

Quantitative analyses of seismic using well logs require two sets of data, none of which are usua... more Quantitative analyses of seismic using well logs require two sets of data, none of which are usually available: dipole sonic logs, due to cost and velocity and bulk density logs in the shallow part of the holes, due to large holes. In this abstract, we present a general rock physics based technique for constructing pseudo-logs. The pseudo-shear sonic log is based on the work by Dutta & Wendt’s (1993). The shallow pseudo-logs for P-velocity and density are based on mechanical compaction theory and rock physics based velocity-porosity relationships. We test the technique on well log data in the Gulf of Mexico.

Proceedings, Jun 5, 1996

A good understanding of subsurface effective stress and fluid pressu re is essential at several s... more A good understanding of subsurface effective stress and fluid pressu re is essential at several stages of an exploration/development program . It can be used during explora tion to assess the effectiveness of a regional topseal section, to provide a map of hydrocarbon migration pathways, and to analyze 'trap' configuration and geometry of a prospective basin . In the exploration and appraisal dri lling and development phase, pressure prediction is a pre-requisite for safe and economic drilling. An optimized cas ing and mud-program design can avoid well control problems. We have developed an integrated geological and geophysical technique for p ressure prediction where pressure is derived from seismic velocity data . This technique is being increasingly applied in the deep water acreage in BP 's community, where seismic data may provide the only measure of subsurface pore pressure. This technique has two major components : a rock p roperty model that links effec tive stress, temperature and lithology to velocity and a subsurface image based on high resolution veloci ty analysis of reflection seismic data.

Correlation energy contribution to the ammonia inversion barrier

Chemical Physics Letters, Mar 1, 1975

Abstract Diagrammatic many-body double-perturbation theory is used to study the correlation contr... more Abstract Diagrammatic many-body double-perturbation theory is used to study the correlation contribution to the inversion barrier in ammonia. With a one-center solution as the zero-order function, the perturbation energy diagrams are shown to be of three types: Hartree-Fock diagrams (geometry dependent), atom-like correlation diagrams (geometry independent) and non-atom-like correlation diagrams (geometry dependent). Only the third class of diagrams enter into the correlation correction to the barrier. These diagrams, which appear first in third order, contribute a small fraction (1%) of the total correlation energy. We estimate from them that the correlation energy contribution to the barrier is small (less than 10% of the total barrier), although the bond length dependence of the correlation correction is such that it is difficult to obtain an exact value for it.

Advances in Depth Imaging Technology: Rock Physics Guided Migration of Seismic Data In 3D

Proc. Indon Petrol. Assoc., 36th Ann. Conv., Mar 5, 2018

Marine and Petroleum Geology, Nov 1, 2008

Geohazard Detection in Deepwater Clastics Basins Using a Seismic Technique Guided by Geology and Rock Physics Model: Methodology and Examples

Detection of hazardous zones, associated with high-pressured fluids in unconsolidated sands and s... more Detection of hazardous zones, associated with high-pressured fluids in unconsolidated sands and shales, prior to drilling, is essential for environmental as well as health and safety. Drilling for deepwater targets is associated with high cost and risk, while margins of commercial operations are small. Therefore, it is imperative to control cost through accurate well planning and reliable anticipation of geohazards. This paper deals with a novel seismic approach that uses the full bandwidth and the entire offset range of the conventional 3D seismic data to detect the presence of hazardous zones. Both in shallow and deeper zones, P- and S-velocities are determined using seismic full waveform prestack inversion. Shallow water flow (SWF) layers in the deepwater are identified through the associated high ratios of P- to Svelocities. A new, rock model-based approach especially suited for deepwater pore pressure imaging was applied to predict the presence of both shallow and deeper over-pressured zones. This paper covers the essential elements of the workflow - a "five-step process" for hazard identification that integrates a special data processing flow with prestack and full waveform inversion of 3D seismic data with geology and rock models appropriate for shallow water flow, gas hydrates and deeper geohazards. Real data examples from deepwater elucidate the approach. Introduction During the last two decades, the oil and gas industry has reported major discoveries in deepwater basins worldwide: Gulf of Mexico, Angola, Brazil, Nigeria and Mediterranean, for example. Along with these discoveries, the industry also encountered many risks. These risks are generally of two types: prospect risk associated with 'seal' integrity of potential reservoirs and various drilling hazards, such as those associated with Shallow Water Flow (SWF) sands, Gas Hydrates (GH) and geopressure. The former is due to geopressure build up in the sediments, especially in the shales surrounding the reservoir rocks, causing weakening of seals. The later is also associated with high pressure build up in sediments in the shallow portion of the stratigraphy and in an environment conducive of gas hydrate formation (appropriate thermal and pressure regimes). Pre-drill detection of these hazards and careful well planning are keys to managing these risks. Below we outline briefly the use of seismic data to help in this process. Shallow Water Flow Sands Shallow water flow (SWF) layers are frequently encountered in deepwater areas when drilling into poorly consolidated geopressured sands (Figure 1). These sands, when flowing, can cause extensive damage to a borehole. Shallow water flow sands are known to occur in water depths of 450 m or more, and typically between 300 m and 600 m below the mud line. They are known to be present in almost all deepwater ocean basins where the rate of sedimentation is high. Loose and unconsolidated sediments with high rates of sedimentation characterize the overburden. Compacted shales or mudstones for which the rate of sedimentation is low create a low permeability seal.

Geopressure Detection Using Reflection Seismic Data and Rock Physics Principles: Methodology and Case Histories From Deepwater Tertiary Clastics Basins

All Days, Oct 8, 2002

Subsurface formations with pore fluid pressure in excess of the hydrostatic pressure (geopressure... more Subsurface formations with pore fluid pressure in excess of the hydrostatic pressure (geopressure) are encountered worldwide. Although there are a multitude of causes that can result in geopressure, under compaction due to rapid burial of sediments is the predominant cause of geopressure. Typically, if the loading process is rapid, fluid expulsion through compaction is severely retarded, especially in fine-grained sediments with low permeability such as silts or clays. This results in stress redistribution within the column -a greater proportion of the overlying weight of the sediments is borne by the fluids than when the sediments compact normally, causing a decrease in the stress acting on the rock framework. Dehydrating bound water from clays within shales further complicates this phenomenon as compaction proceeds with the depth of burial with increase in temperature. Geopressured formations pose significant threats to drilling safety, and the cost of mitigation, especially, in deepwater settings, is high…to the tune of $1.08 billion per year world-wide. Proper planning before drilling is key to lowering costs and increasing safety. In this regard, the role of seismic is of paramount importance. Seismic wave attributes (amplitude, velocity, coherency, etc.) are affected when stresses acting on the sedimentary column (effective or differential stress) are low. These attributes can be analyzed to obtain signatures, or lack of fluid transport over the geologic time- both qualitatively and quantitatively. Using the seismic, zones of trapped fluids and pressured compartments can also be mapped prior to drilling. With either an analogue or a reliable low-frequency velocity model, it is also possible to map fluid transport effects in the reservoir scale using seismic inversion techniques. In this paper, we illustrate how this process works using seismic data at various scales, from the low frequency reflection seismic at exploration frequency scales to those employed at well-logging scales. A rock-model-based approach especially suited for deepwater pore pressure imaging is introduced. It includes the effect of shale burial diagenesis, and uses the velocities derived from inversion of prestack seismic data. The procedure yields details of pre-drill pore pressure images with significant clarity as well as pressure versus depth profiles appropriate for drilling applications. In particular, prestack full waveform inversion yields Poisson's ratios that are useful not only for pressure and fracture gradient estimations but also for lithology and fluid identification. This technique is also applicable to identification of shallow water flow formations that pose drilling hazards in deep water. The procedure is illustrated with examples from several deepwater basins.

Detection of hazardous, fluid-filled, unconsolidated, porous sediments in the deepwater tertiary elastics basins: a seismic approach

Pseudo-Shear Wave Log Construction - Methods, Results and the Road Ahead

Geopressure prediction using seismic data: Current status and the road ahead

Geophysics, Nov 1, 2002

The subject of seismic detection of abnormally high‐pressured formations has received a great dea... more The subject of seismic detection of abnormally high‐pressured formations has received a great deal of attention in exploration and production geophysics because of increasing exploration and production activities in frontier areas (such as the deepwater) and a need to lower cost without compromising safety and environment, and manage risk and uncertainty associated with very expensive drilling. The purpose of this review is to capture the “best practice” in this highly specialized discipline and document it. Pressure prediction from seismic data is based on fundamentals of science, especially those of rock physics and seismic attribute analysis. Nonetheless, since the first seismic application in the 1960s, practitioners of the technology have relied increasingly on empiricism, and the fundamental limitations of the tools applied to detect such hazardous formations were lost. The most successful approach to seismic pressure prediction is one that combines a good understanding of rock properties of subsurface formations with the best practice for seismic velocity analysis appropriate for rock physics applications, not for stacking purposes. With the step change that the industry has seen in the application of the modern digital computing technology to solving large‐scale exploration and production problems using seismic data, the detection of pressured formations can now be made with more confidence and better resolution. The challenge of the future is to break the communication and the “language barrier” that still exists between the seismologists, the rock physicists, and the drilling community.