Vibroseis or Dynamite: investigating source characteristics

Relevance of the work. The paper considers challenging problems related with outlining of intervals with oil and gas presence in the mature Khylly field by use of latest 3D seismic survey techniques in order to gain larger crude resources base. The purpose of this research is to discover the most promising intervals of target horizons with relatively high reservoir properties outlined by 3D seismic data. The subjects of research are 3D seismic survey data, downhole seismic survey – Vertical Seismic Profiling (VSP) and well logging diagrams. The object of research is the Khylly deposit. The paper describes in brief geological and geophysical characteristics, stratigraphic and lithological features of rocks making the section. It is noted that despite repeated surveys by use of various geological and geophysical techniques, the field setting is not thoroughly studied and it has been covered by 3D seismic survey in 2012. Research results. 3D seismic survey applied across Khylly area is resulted in drawing of 4 structural maps for III and I horizons of Productive Series (PS), Akchagyl and Lower Absheron suites. Taking into account the relevance of structural planes of various stratigraphic levels and III horizon of PS being one of the major reference horizons the paper gives description of structural map drawn for this horizon. The detailed velocity model is designed based on VSP data with wide use of velocity analysis data. It has been made clear that Khylly area has block structure and each block has been described in detail. Based on acquired data it has been recommended to drill exploratory well R-1. Conclusion. Processing and interpretation of seismic data are aimed at solving some geological problems; the main task was to obtain results that ensure the study of the geological structure in the seismic survey area, including tracing of seismic horizons, faults and outlining the areas and section intervals which may be of interest due to possible oil and gas presence. VSP data acquired in well 2012 and velocity analysis made it possible to design velocity model of the section under the study, with the use of which the temporary 3D cube was transformed into a depth cube. The quality of seismic data is good and made it possible to solve the tasks set for this research.

In some oilfield where 3D seismic survey has been done, the deeper structure cannot be discovered for poor deep seismic data. Layer stripping technique applied both seismic and gravity data is a solution, but it cannot get satisfied processing effect because the horizontal variation of formation density is ignored. To improve the gravity survey effect in 3D seismic survey area, this paper presents the formation separation technique. Based on 3D seismic depth data and the transformed density data from 3D seismic velocity data, the upper formation's gravity effects are calculated and removed from Bouguer gravity and then the formation‐separated gravity‐anomaly was obtained, which mainly reflects the deeper geological structure. In block XX, the seismic data of shallow formations are excellent but that of top of basement are poor. The formation‐separated gravity‐anomaly processed under the control of 3D seismic data fits well with the known seismic interpretation and wells. It makes the geological interpretation more reliable

Seismic data incorporation in reservoir simulation models history matching (HM) studies has been continuously growing. 4D seismic data, in contrast with well production data, can provide a very good scenario of fluids arrangement along reservoir. In this work we describe how 3D and 4D seismic data gathered in acquisitions performed in Campos Basin was incorporated in Marlim Sul deep water field geological model reconstruction and in assisted HM (AHM). It is taken advantage of both 3D and 4D seismic data in several stages of the study, for instance, in the construction of a new porosity – most influential in impedance – model by using a methodology based on the inversion of synthetic seismic (calculated by petro-elastic model) in porosity through an optimization process that aims to reduce the difference between observed and synthetic impedance, and when defining influential parameters based on fluids displacement registered by seismic signal, by using a technique based on the creation of transmissibility multipliers parameters regions that considers the fluids displacement shown in 4D signal. Another relevant point is the use of information from reservoir and 3D seismic data when weighting the 4D data in the objective function. Combining the above mentioned techniques with the knowledge of the field – supported by the 3D seismic data – which allowed, for instance, identification of faults – where fault transmissibility multipliers were used as parameters in the HM process – a fairly good agreement on the observed well and seismic production data was achieved. HM studies using AHM tools have been shown a much more time-efficient technique when compared to manual HM. The incorporation of 4D seismic data can considerably improve the HM quality by improving the reservoir description, once it increases the ability of describing fluids arrangement and pressure distribution. The techniques successfully applied in the Marlim Sul field HM support these conclusions.

Two methods of carbonate collector properties forecasting by using 2D and 3D seismic data are considered. Both methods show good results despite on some troubles related with data analysis and interpretations. Data processing with using multipletrace method allows to find correlation of rift anomalies at 3D and 2D seismic data. The rift bodies are found by using the acoustic inversion of seismic data, attributive analysis and neuron network simulation. This analysis allows forecasting the collector properties for territory of 2D seismic survey using local 3D cubes. Thus if velocities and anomalies related with rift bodies are found correctly, the waives picture can be determined without artificial structures and results of rift bodies search and their properties within 3D cubes can be extended on the whole 2D seismic survey domain

Ram Powell is a stratigraphically trapped sequence of turbidite reservoirs in 2,500-4,000 ft of water in the Eastern Gulf of Mexico. The discovery was made in 1985 and the field has been the subject of extensive geoscience and engineering studies. In spite of this work there is still significant uncertainty in Ram Powell reserves. The Ram Powell development plan is underway, with fabrication of a tension-leg platform and 60,000 b/d plus 200 MMcf/d facility. Drilling will include 7 high rate horizontal wells and 3 water injection wells. Reserves accessed in this development scheme are approximately 250 million barrels equivalent. Model-based seismic inversion (constrained by 12 appraisal penetrations, rock property data and seismic interpretation) was employed over the main reservoir interval (J, L and N sands) to create models that are consistent with 3D seismic data. These models were used in several simulation studies including element models to determine optimal well placement, and full-field models to predict overall reservoir performance. The results of the study both reduced and enabled management of reservoir volume uncertainty; they were critical for determining the number, horizontal length and placement of wells (vertically and areally). The results also provided the basis for a proposal to increase the facility capacity limits to 70,000 b/d plus 260 MMcf/d. Some significant learnings are (1) model-based inversion is now in a production mode that can be rapidly applied to reservoir problems, (2) many reservoir complexities are simply below seismic resolution and inversion is unable to add with certainty significantly more resolution and, (3) detailed reservoir models that reflect reservoir conditions and are easily manipulated are required for reservoir optimization. Introduction Purpose. The Ram Powell Field is currently under development with fabrication of a tension-leg platform and 60,000 b/d and 200 MMcf/d production facility. Development will include 7 high rate horizontal wells and 3 water injection wells with a single subsea well drilled much later. Production is scheduled to begin in August, 1997 and the expected reserves are 250 million barrels equivalent. The purposes of this paper are (1) to describe the process used to integrate 3D seismic, geological, and rock property data into a static model that was used for reservoir simulation, (2) to illustrate how the modeling was used to manage uncertainty, and (3) to illustrate the impact of this work on development planning and facility design. Setting. Ram Powell is a stratigraphically trapped sequence of turbidite oil and gas reservoirs in 2,500-4,000 feet of water in the eastern Gulf of Mexico. The discovery was made in 1985 and has had extensive geoscience studies performed since then by each of the Ram Powell joint venture partners. A fairly extensive set of data is available including three 3D seismic surveys, twelve wells (drilled from five surface locations), 420 feet of conventional core, one production test, in addition to the normal set of petrophysical logs, RFT's, and sidewall samples (Figures 1, 2 and 3). In spite of the extensive data set, uncertainty remains with respect to Ram Powell reserves. Uncertainty in reservoir limits, net thickness, effective permeability (vertical and horizontal), fluid properties, well placement, and well design all have an impact on reservoir performance prediction (rate and cumulatives). There are three reservoirs in the initial development phase (J, L, and N sands). P. 477

Three-dimensional seismic has had a major impact on the performance of Amoco's E&P operations. In the last 4 years, 3D seismic has helped improve reserves replacement, improved exploration finding rates and volumes, and had a positive effect on field-reserves revisions. This paper discusses the performance improvements that 3D seismic has brought to the company and suggests ways to measure the impact of emerging technologies. These measures gauge the benefits as well as the easily measured costs when managing technology investments.

Mesozoic reactivated transpressional structures and multi-stage tectonic deformation along the Hong-Che fault zone in the northwestern Junggar Basin, NW China

Interpretation of three-dimensional (3D) seismic data from the northern part of central Saudi Arabia allowed mapping of the Permo-Carboniferous Unayzah Formation's aeolian sand deposits and fluvial channels. These types of depositional environments have been associated frequently with better reservoir-quality sandstones within Saudi Arabia. The depositional setting of the Unayzah reservoirs can be highly variable and range from glacial, to lacustrine, to meandering fluvial, to aeolian, to braided stream. Seismic amplitude data were instrumental in mapping a truncation of the upper Unayzah reservoir against the overlying Pre-Khuff Unconformity. The use of seismic attributes, such as coherence and curvature, indicated the existence of faulting and a fluvial channel network at the top of the Unayzah Formation. The integration of well and seismic amplitude data, via acoustic impedance inversion, revealed the direction of potentially higher porosity fairways within the channel system. The structural and depositional architecture depicted in this study is being appraised through drilling of an exploration well.

We present results of the 4D seismic monitoring of the Ekofisk field waterflood. The thick, high porosity chalk reservoir compacts strongly in response to water injection1,4,6. This compaction has a clear effect on the 4D seismic data, which has a baseline 3D survey acquired at the beginning of the waterflood in 1989, and a monitoring survey acquired in 1999. Ekofisk 4D seismic data has been a valuable qualitative tool for describing the spatial distribution of reservoir compaction and subsidence. The 4D data shows that some faults are significant barriers to water flow, and some reservoir compartments have been substantially compacted, from which we infer an increase in water saturation. These observations guide improvements to the reservoir simulation history match. The 4D seismic also helps explain recent drilling results and helps plan optimal well paths for future development drilling. Recent work to incorporate the 4D seismic into a compaction model gives quantitative reservoir compaction results that agree well with geomechanical and log-based compaction models. The seismic data can be used to monitor reservoir compaction over long time periods and serves as calibration data for detailed compaction modeling. Introduction The Ekofisk Field in the Norwegian Sector of the North Sea was discovered in 1969 and began production in 1971. In 1984, Phillips recognized that the seafloor over Ekofisk field was subsiding and determined that the cause was reservoir compaction. Since then, the seafloor subsidence has been monitored by repeated bathymetry surveys, and the reservoir compaction is monitored by measuring the movement of radioactive bullets implanted in wellbores in and above the reservoir1. The cumulative maximum subsidence today is more than 8m above the crest of the field, corresponding to a maximum reservoir compaction of 10m. The reservoir compacts by two mechanisms-pressure reduction associated with the initial production phase from 1971-1989, and waterweakening associated with the waterflood from 1989-present. A 3D seismic survey covering Ekofisk field coincided with the start of the field-wide water injection program. Phillips acquired a repeat 3D seismic survey in 1999 to monitor the waterflood-induced compaction by 4D seismic analysis. The Ekofisk field seismic data is not mappable at the crest of the field, due to overburden velocity anomalies associated with gas and overpressure. This appears as a blank area in the middle of all the seismic maps presented in this paper. Ekofisk 4D Seismic Observations In 1997, Phillips completed a time-lapse seismic feasibility Study2 that indicated chalk compaction from water weakening could be observed with 4D seismic. The new seismic survey, completed in 1999, indeed shows compaction-related differences when compared to the baseline 1989 seismic survey. Three main horizons are mappable on Ekofisk 3D seismic data. These are the top chalk reservoir, a tight zone separating the upper reservoir (Ekofisk formation) from the lower reservoir (Tor formation) and the base reservoir. The main 4D observation is a time shift of these main chalk horizons.

Seismic data offer valuable spatial information that contributes to the development strategy, such as drilling decisions and well planning. Inverting 3D seismic reflectivity data to impedance unlocks the potential of using seismic data to estimate the lateral variability and to predict reservoir geomechanical behaviour. The geomechanical model contributes for the evaluation of wellbore stability, frackability and drilling direction. The objective of this work is to illustrate the use of seismic derived models for reservoir and geomechanical properties, such as total porosity, total organic carbon (TOC) and rock rigidity. These properties are instrumental to characterize tight reservoirs and useful tools for defining a horizontal well trajectory.The study area has an exploration potential of unconventional reservoirs, targeting tight carbonates from Upper Jurassic. To date, only one well has been drilled in the area of the interest and high quality 3D seismic data is available. The process consists of conducting seismic inversion, using the well and the 3D PSTM seismic data, and resulting in the generation of 3D subsurface impedance model. The well-log relationships between impedance and reservoir quality (effective porosity, source richness) and completion quality (brittleness) were determined and showed high correlation. Hence, 3D rock quality and geomechanical volumes were derived to characterize the behaviour of the reservoir target.Seismic derived properties models yield a better description of the reservoir heterogeneity than using seismic reflectivity data only. The horizontal well trajectory was planned taking into account the observed and significant lateral variability revealed by the 3D models estimated based on seismic inverted data.The results obtained using this methodology demonstrate the importance of integrating geophysical characterisation as a relevant supporting factor in the drilling decision making process. In particular, it validates the use of seismic derived reservoir and completion quality models as an additional tool in the definition of a horizontal well trajectory in a tight/unconventional deep gas target.

Three-dimensional (3D) seismic data visualization is a critical technique in 3D seismic data interpretation. In the paper, the characteristics of seismic data, the technology of 3D data sets visualization and the technology of 3D graphics construction and display using interactive data language (IDL) were discussed. The author proposed new solutions for 3D seismic data visualization, moreover expounded how to reorganize 3D seismic data and how to realize direct volume rendering and surface rendering using IDL. Using the interface provided by IDL based on COM standard, the author applied the new solutions to practice and built a 3D Seismic Data Visualization Platform..

Integration of 3D and time-lapse 4D seismic data into reservoir modelling and history matching processes poses a significant challenge due to the frequent mismatch between the initial reservoir model, the true reservoir geology, and the pre-production (baseline) seismic data. A fundamental step of a reservoir characterisation and performance study is the preconditioning of the initial reservoir model to equally honour both the geological knowledge and seismic data. In this paper we analyse the issues that have a significant impact on the (mis)match of the initial reservoir model with well logs and inverted 3D seismic data. These issues include the constraining methods for reservoir lithofacies modelling, the sensitivity of the results to the presence of realistic resolution and noise in the seismic data, the geostatistical modelling parameters, and the uncertainties associated with quantitative incorporation of inverted seismic data in reservoir lithofacies modelling. We demonstrate that in a geostatistical lithofacies simulation process, seismic constraining methods based on seismic litho-probability curves and seismic litho-probability cubes yield the best match to the reference model, even when realistic resolution and noise is included in the dataset. In addition, our analyses show that quantitative incorporation of inverted 3D seismic data in static reservoir modelling carries a range of uncertainties and should be cautiously applied in order to minimise the risk of misinterpretation. These uncertainties are due to the limited vertical resolution of the seismic data compared to the scale of the geological heterogeneities, the fundamental instability of the inverse problem, and the non-unique elastic properties of different lithofacies types.

3D seismic analysis of gravity-driven and basement influenced normal fault growth in the deepwater Otway Basin, Australia

In the previous chapters, we have seen that time domain methods are good for denoising the seismic data with moderate noisy record. In order to separate true reflection amplitudes from the noisy seismic data, in this chapter, we discuss time slice singular spectrum analysis (TSSSA), a data adaptive signal decomposition based on SSA to alleviate such coloured and complex noise. This method is the time domain version of Cadzow filter but did not gain full attention until 2012. This method is applicable to pre-stack and post-stack data for denoising. By virtue of using seismic amplitudes corresponds to particular time (time slice) to benefit their strong correlation, the method was named as Time Slice SSA. It is a time domain method. In view of the above, in this chapter, Time Slice SSA (TSSSA) denoising algorithm was presented for denoising of 2D seismic reflection data. The first part of this chapter is devoted to provide the testing of the method on synthetic seismic data in comparison with f-x deconvolution (Canales 1984) and f-x SSA (Sacchi 2009) methods. In the second part, the method was applied to high-resolution seismic pre-stack and post data field data.

Editor's note: This paper won the Best Poster Paper Award from the 2001 Annual Meeting in San Antonio. The study area consists of 180 miles2 within the Val Verde Basin. A new interpretation is proposed and is based primarily on 3D seismic data. Emphasis is placed on the Lower Permian to Pennsylvanian Section in which hydrocarbons have been found from tight reservoirs. The general stratigraphy is summarized, the focus being on hydrocarbon source, reservoirs, and seal. Seismic lines, spread across the area, illustrate structure. The producing fields sit atop the Foreland Thrust, which was transported as a decollement zone on Mississippian shales. A series of backthrusts is invoked to accommodate the movement of competent rocks up the ramped Foreland Thrust, creating the main structures in the fields. The Foreland Thrust is thought to be the primary migration pathway while the back-thrusts appear to be secondary migration pathways. The new interpretation incorporates 3D seismic, well, and reservoir performance data. The 3D seismic data, in particular, demonstrate the overall sequence stratigraphy of the basin and lead to a new structural interpretation. This interpretation is based mainly on 3D seismic data. Emphasis is placed on the Lower Permian to Pennsylvanian geologic section where hydrocarbons have been found in tight reservoirs. Currently, these reservoirs are being developed by Conoco Inc. in partnership with Tom Brown Inc. Geographically, the study area is located about 120 miles south of Midland in Texas. It encompasses Conoco's 3D seismic coverage in the Val Verde Basin and occupies an area roughly 30 × 6 miles. Geologically, the Val Verde Basin comprises the southern portion of the greater Permian Basin of mid-continent United States. It lies between the Central Basin Platform to the north and the Marathon Uplift to the south (Figure 1). Figure 1. Location map. Based on 2D seismic …