3D seismic data are widely used for many different purposes. Despite different objectives, a common goal in almost all 3D seismic programs is to attain better understanding of the subsurface features. In gas injection projects, which are mainly for Enhanced Oil Recovery (EOR) and recently for environmental purposes, seismic data have an important role in the gas monitoring phase. This thesis deals with a 3D seismic investigation at the CO2 injection site at Ketzin, Germany. I focus on two critical aspects of the project: the internal architecture of the heterogeneous Stuttgart reservoir and the detectability of the CO2 response from surface seismic data. Conventional seismic methods are not able to conclusively map the internal reservoir architecture due to their limited seismic resolution. In order to overcome this limitation, I use the Continuous Wavelet Transform (CWT) decomposition technique, which provides frequency spectra with high temporal resolution without the disadvantages of the windowing process associated with the other techniques. Results from applying this technique reveal more of the details of sand bodies within the Stuttgart Formation. The CWT technique also helps to detect and map remnant gas on the top of the structure. In addition to this method, I also show that the pre-stack spectral blueing method, which is presented for the first time in this research, has an ability to enhance seismic resolution with fewer artifacts in comparison with the post-stack spectral blueing method. The second objective of this research is to evaluate the CO2 response on surface seismic data as a feasibility study for CO2 monitoring. I build a rock physics model to estimate changes in elastic properties and seismic velocities caused by injected CO2. Based on this model, I study the seismic responses for different CO2 injection geometries and saturations using one dimensional (1D) elastic modeling and two dimensional (2D) acoustic finite-difference modeling. Results show that, in spite of random and coherent noises and reservoir heterogeneity, the CO2 seismic response should be strong enough to be detectable on surface seismic data. I use a similarity-based image registration method to isolate amplitude changes due to the reservoir from amplitude changes caused by time shifts below the reservoir. In support of seismic monitoring using surface seismic data, I also show that acoustic impedance versus Poisson’s ratio cross-plot is a suitable attribute for distinguishing gas-bearing sands from brine-bearing sands. / CO2SINK Project

The study area, Dhurnal oil field, is located 74 km southwest of Islamabad in the Potwar basin of Pakistan. Discovered in March 1984, the field was developed with four producing wells and three water injection wells. Three main limestone reservoirs of Eocene and Paleocene ages are present in this field. These limestone reservoirs are tectonically fractured and all the production is derived from these fractures. The overlying claystone formation of Miocene age provides vertical and lateral seal to the Paleocene and Permian carbonates. The field started production in May 1984, reaching a maximum rate of 19370 BOPD in November 1989. Currently Dhurnal‐1 (D-1) and Dhurnal‐6 (D-6) wells are producing 135 BOPD and 0.65 MMCF/D gas. The field has depleted after producing over 50 million Bbls of oil and 130 BCF of gas from naturally fractured low energy shelf carbonates of the Eocene, Paleocene and Permian reservoirs. Preliminary geological and geophysical data evaluation of Dhurnal field revealed the presence of an up-dip anticlinal structure between D-1 and D-6 wells, seen on new 2003 reprocessed data. However, this structural impression is not observed on old 1987 processed data. The aim of this research is to compare and evaluate old and new reprocessed data in order to identify possible factors affecting the structural configuration. For this purpose, a detailed interpretation of old and new reprocessed data is carried out and results clearly demonstrate that structural compartmentalization exists in Dhurnal field (based on 2003 data). Therefore, to further analyse the available data sets, processing sequences pertaining to both vintages have been examined. After great effort and detailed investigation, it is concluded that the major parameter giving rise to this data discrepancy is the velocity analysis done with different gridding intervals. The detailed and dense velocity analysis carried out on the data in 2003 was able to image the subtle anticlinal feature, which was missed on the 1987 processed seismic data due to sparse gridding. In addition to this, about 105 sq.km 3D seismic data recently (2009) acquired by Ocean Pakistan Limited (OPL) is also interpreted in this project to gain greater confidence on the results. The 3D geophysical interpretation confirmed the findings and aided in accurately mapping the remaining hydrocarbon potential of Dhurnal field.

This research investigates the character and significance of shelf-edge deltas within the sedimentary source-to-sink system, and how variability at the shelf edge leads to different styles of deep-water deposition. Because the shelf-edge represents one of the key entry points for terrigenous sediment to be delivered into the deep water, understanding of the sedimentary processes in operation at these locations, and the character of sediment transported through these deltas is critical to understanding of deep-water sedimentary systems. The research was carried out using three datasets: an outcrop dataset of 6000 m of measured sections from the Permian-Triassic Karoo Basin, South Africa, a 3D seismic data volume from the Eocene Northern Santos Basin, offshore Brazil and a dataset of 29 previously published descriptions of shelf-edge deltas from a variety of locations and data types. The data presented highlight the importance of sediment instability in the progradation of basin margins, and deep-water transport of sediment. The strata of the Karoo Basin shelf margin represent river-dominated delta deposits that become more deformed as the shelf-edge position is approached. At the shelf edge, basinward dipping, offlapping packages of soft-sediment-deformed and undeformed strata record repetitive collapse and re-establishment of shelf-edge mouth bar packages. The offlapping strata of the Karoo outcrops record progradation of the shelf margin through accretion of the shelf-edge delta, for over 1 km before subsequent transgression. The Eocene Northern Santos Basin shelf margin, in contrast, exhibits instability features which remove kilometers-wide wedges of the outer shelf that are transported to the basin floor to be deposited as mass-transport packages. In this example, shelf-edge progradation is achieved through „stable. accretion of mixed turbidites and contourites. The data also emphasize the importance of the role of shelf-edge delta processes in the delivery of sediment to the basin floor. A global dataset of 29 examples of shelf-edge systems strongly indicates that river domination of the shelf-edge system (as read from cores, well logs or isopach maps) serves as a more reliable predictor of deep-water sediment delivery and deposition than relative sea level fall as traditionally read in shelf-edge trajectories or sequence boundaries. / text

This study integrates sequence stratigraphy of the Late Permian Toolachee Formation in the non-marine intracratonic Permian-Triassic Cooper Basin, Australia with 3-D seismic attribute analysis to predict the extent of depositional environments identified on wireline and well core data. The low resolution seismic data (tuning thickness 23 - 31 m) comprised of six seismic horizons allowed the successful testing of sequence stratigraphic interpretations of the productive Toolachee Formation that were based on wireline data. The analysis of 29 well logs and three 20 m core intervals resulted in the identification of eleven parasequences that comprise the building blocks of an overall transitional systems tract, characterised by a gradual increase in accommodation. The parasequences reflect cyclic transitions between braided and meandering fluvial systems as a result of fluctuations in sediment flux, possibly driven by Milankovitch climatic-forcing. The seismic horizon attribute maps image mostly the meandering fluvial bodies within the upper parts of the parasequences, but some maps image the lower amalgamated sand sheets and show no channel structures. Categorisation of the fluvial bodies in the overbank successions reflects a gradual decrease in sinuosity, channel width, and channel belt width up-section, supporting the overall increase in accommodation up-section. Similar acoustic impedance values for shales and sands do not suggest successful seismic forward modelling between the two lithologies. Geological interpretations suggest most imaged channel fill to be made up predominantly of fine sediments, as channel avulsion and abandonment is common and increases with time. Seismic forward modelling resulted in the interpretation of carbonaceous shale as a possible channel fill, supporting the geological interpretations. The three major identified fluvial styles; braided, meanders, and distributaries are potential targets for future exploration. Extensive sand sheets deposited from braided fluvial systems require structural traps for closure. Meandering and anastomosing channel systems represent excellent stratigraphic traps, such as the basal sands/gravels of laterally accreted point bars.

Our knowledge of elastic wave propagation in general heterogeneous media with complex geological structures comes principally from numerical simulations. In this dissertation, I demonstrate through rigorous theoretical analyses and comprehensive numerical experiments that the Fourier method is a suitable method of choice for large scale 3D seismic modeling and imaging problems, due to its high accuracy and computational efficiency. The most attractive feature of the Fourier method is its ability to produce highly accurate solutions on relatively coarser grids, compared with other numerical methods for solving wave equations. To further advance the Fourier method, I identify two aspects of the method to focus on in this work, i.e., its implementation on modern clusters of computers and efficient high-order time stepping schemes. I propose two new parallel algorithms to improve the efficiency of the Fourier method on distributed memory systems using MPI. The first algorithm employs non-blocking all-to-all communications to optimize the conventional parallel Fourier modeling workflows by overlapping communication with computation. With a carefully designed communication-computation overlapping mechanism, a large amount of communication overhead can be concealed when implementing different kinds of wave equations. The second algorithm combines the advantages of both the Fourier method and the finite difference method by using convolutional high-order finite difference operators to evaluate the spatial derivatives in the decomposed direction. The high-order convolutional finite difference method guarantees a satisfactory accuracy and provides the flexibility of using non-blocking point-to-point communications for efficient interprocessor data exchange and the possibility of overlapping communication and computation. As a result, this hybrid method achieves an optimized balance between numerical accuracy and computational efficiency. To improve the overall accuracy of time domain Fourier simulations, I propose a family of new high-order time stepping schemes, based on a novel algorithm for designing time integration operators, to reduce temporal derivative discretization errors in a cost-effective fashion. I explore the pseudo-analytical method and propose high-order formulations to further improve its accuracy and ability to deal with spatial heterogeneities. I also extend the pseudo-analytical method to solve the variable-density acoustic and elastic wave equations. I thoroughly examine the finite difference method by conducting complete numerical dispersion and stability analyses. I comprehensively compare the finite difference method with the Fourier method and provide a series of detailed benchmarking tests of these two methods under a number of different simulation configurations. The Fourier method outperforms the finite difference method, in terms of both accuracy and efficiency, for both the theoretical studies and the numerical experiments, which provides solid evidence that the Fourier method is a superior scheme for large scale seismic modeling and imaging problems. / text