Synthetic Sonic Logs Research Articles

The Application of Support Vector Machine to Estimate Synthetic Shear Sonic Log

Abstract – Rock physics modelling is commonly applied to characterize the subsurface. Sonic log provides the elastic properties in advanced petrophysics modelling or rock physics modelling. Although it is very important, to obtain shear sonic measurement results is very expensive. Therefore, empirical and artificial intelligence allow some solutions to estimate synthetic shear sonic log. This study applicate PCA as feature selection and SVM as the regressor with TAF as the target interval for well NEGF1P. The results of feature selection are GR, DTC, and MSF log as selected features. GS optimizes the SVM kernel parameter using selected features. The best parameters for each kernel (linear and rbf) and selected feature are the input to estimate synthetic shear sonic log. The estimation result using linear kernel has R2 0.845 and root mean square error (RMSE) 15.132 and using rbf kernel has R2 0.886 and RMSE 12.989. The estimation results construe that rbf kernel estimates the synthetic sonic log with more precision than the linear kernel and indicates the linear relation between the estimated and origin log. The three other wells apply SMV with rbf kernel best parameters and selected features to estimation the synthetic shear sonic in similar interval and younger interval (GUF).

Robust data smoothing algorithms and wavelet filter for denoising sonic log signals

Well logging is an essential approach to make geophysical surveys and petrophysical measurements. It plays a key role in interpreting downhole conditions. But, well logging signals usually contain noise that distort results and causes ambiguous interpretations. In this paper, the wavelet filter and robust data smoothing algorithms are tested for denoising synthetic sonic log and field sonic log data. Robust data smoothing algorithms include Gaussian, RLOESS (Robust locally estimating scatterplot smoothing), and RLOWESS (Robust locally weighted scatterplot smoothing) methods. Uniform and normal distribution noise applied to synthetic model. Results revealed that the wavelet filter performs better than data smoothing algorithms in denoising uniform distribution noise. However, the RLOESS removed uniform noise acceptably. But, for normal distribution noise, the wavelet filter disrupts and data smoothing algorithms, specifically RLOESS attenuated noise perfectly. Due to the noise nature of field sonic log data, wavelet filter completely disrupts, but data smoothing algorithms removed the noise of field data more efficiently, particularly RLOESS. So, it can be stated that the RLOESS is a perfect algorithm for denoising sonic log signals, regardless of noise nature.

Synthetic Sonic Log Generation With Machine Learning: A Contest Summary From Five Methods

Compressional and shear sonic traveltime logs (DTC and DTS, respectively) are crucial for subsurface characterization and seismic-well tie. However, these two logs are often missing or incomplete in many oil and gas wells. Therefore, many petrophysical and geophysical workflows include sonic log synthetization or pseudo-log generation based on multivariate regression or rock physics relations. Started on March 1, 2020, and concluded on May 7, 2020, the SPWLA PDDA SIG hosted a contest aiming to predict the DTC and DTS logs from seven “easy-to-acquire” conventional logs using machine-learning methods (GitHub, 2020). In the contest, a total number of 20,525 data points with half-foot resolution from three wells was collected to train regression models using machine-learning techniques. Each data point had seven features, consisting of the conventional “easy-to-acquire” logs: caliper, neutron porosity, gamma ray (GR), deep resistivity, medium resistivity, photoelectric factor, and bulk density, respectively, as well as two sonic logs (DTC and DTS) as the target. The separate data set of 11,089 samples from a fourth well was then used as the blind test data set. The prediction performance of the model was evaluated using root mean square error (RMSE) as the metric, shown in the equation below: RMSE=sqrt(1/2*1/m* [∑_(i=1)^m▒〖(〖DTC〗_pred^i-〖DTC〗_true^i)〗^2 + 〖(〖DTS〗_pred^i-〖DTS〗_true^i)〗^2 ] In the benchmark model, (Yu et al., 2020), we used a Random Forest regressor and conducted minimal preprocessing to the training data set; an RMSE score of 17.93 was achieved on the test data set. The top five models from the contest, on average, beat the performance of our benchmark model by 27% in the RMSE score. In the paper, we will review these five solutions, including preprocess techniques and different machine-learning models, including neural network, long short-term memory (LSTM), and ensemble trees. We found that data cleaning and clustering were critical for improving the performance in all models.

DETERMINATION OF PORE TYPES AND POROSITY TRENDS USING OF VELOCITY-DEVIATION LOG FOR THE CARBONATE MISHRIF RESERVOIR IN HALFAYA OIL FIELD, SOUTHEAST IRAQ

Halfaya field is located south of Iraq towards southeast Amara city in Missan. Mishrif Formation is a major reservoir in Halfaya Oilfield and is one of the principal carbonate reservoirs in central and southeastern Iraq. The aim of this study is to predict pore types using well logs data at missing core intervals. This study includes calculating the velocity deviation log for the Mishrif carbonate reservoir in two wells in Halfaya oil fields (HF-1 and HF-2) by converting porosity-log data into a synthetic velocity log by means of a time-average equation. A velocity-deviation log, which is calculated by integrating a sonic log with a neutron-porosity or density log, provides a means of obtaining downhole details in carbonates about the major pore forms. These data can be used to track the downhole distribution of diagenetic processes and their effects on secondary porosity trends. The differences are plotted as a velocity-deviation log between the actual sonic log and the synthetic sonic log. These velocity-deviation logs reflect the different physical rock markings of different types of pores: (1) Positive velocity deviations mark areas in which pore types form frames dominate; (2) zero deviations indicate periods in which the rock lacks a rigid frame and exhibits dissolution porosity or microporosity; and (3) Negative deviations mark areas in which sonic velocities are remarkably low due to cavernous borehole walls, fractures or possibly high free-gas content. &nbsp

Machine learning regressors and their metrics to predict synthetic sonic and mechanical properties

Planning and optimizing completion design for hydraulic fracturing require a quantifiable understanding of the spatial distribution of the brittleness of the rock and other geomechanical properties. Eventually, the goal is to maximize the stimulated reservoir volume with minimal cost overhead. The compressional and shear velocities ([Formula: see text] and [Formula: see text], respectively) can also be used to calculate Young’s modulus, Poisson’s ratio, and other mechanical properties. In the field, sonic logs are not commonly acquired and operators often resort to regression to predict synthetic sonic logs. We have compared several machine learning regression techniques for their predictive ability to generate synthetic sonic ([Formula: see text] and [Formula: see text]) and a brittleness indicator, namely hardness, using the laboratory core data. We used techniques such as multilinear regression (MLR), least absolute shrinkage and selection operator regression, support vector regression, random forest (RF), gradient boosting (GB), and alternating conditional expectation. We found that the commonly used MLR is suboptimal with less-than-satisfactory predictive accuracies. Other techniques, particularly RF and GB, have greater predictive capabilities. We also used Gaussian process simulation for uncertainty quantification because it provides uncertainty estimates on the predicted values for a wide range of inputs. Random forest and extreme GB techniques also show low uncertainties in prediction.

Hydrocarbon type detection using the synthetic logs: A case study, Baba member, Gulf of Suez, Egypt

Lack of pressure data and/or one curve of the essential well logs such as density, neutron, sonic, resistivity and gamma ray curves in some reservoirs, is not preferred situation for the petrophysict, which will affect the petrophysical evaluation process and the reservoir characterization study.Four wells (A, B, C and D), in the area of interest, penetrated Baba sandstone zone in Badri field. The main challenge in the studied zone is the absence of pressure gradients and the density-neutron separation is not clear enough to judge the hydrocarbon type in all wells at the level of baba sandstone reservoir, where they are needed for the estimation of the hydrocarbon type (oil or gas). So it is preferred to use the three porosity logs to investigate the hydrocarbon type. The second challenge is constructing synthetic logs in the absence of the three main porosity logs.In this paper, all available data were used to estimate the hyocarbon type in two studied wells at the level of Baba sandstone zone, firstly by using well logging relationships between density and sonic in the wells which have sonic logs at the zone of interest, secondly by applying special petrophysical studies to help for estimation of hydrocarbon type.Crossplot technique was used to estimate the hydrocarbon type in the zone of interest using the synthetic sonic curve, original density curve, original neutron curve plus their derived porosity and variables values in the used well logging crossplots including some petrophysical crossplots, which can help in this situation.The results of this study revealed that, 1) the synthetic logs play a great role in solving of petrophysical and geological problems, 2) there is a good relationship between the density and sonic logs in the analogues (A and D) wells, and 3) the obtained synthetic sonic log makes a sense with lithology and other logs (neutron and gamma). Therefore, the synthetic sonic log, in corporation with the density and the neutron logs as well as the crossplots can detect the fluid type in the studied wells. The final result that the most likely hydrocarbon type in well (B) is oil while it has gas signature in well (C).

Inversion-based method to mitigate noise in borehole sonic logs

A major challenge in the interpretation of seismic measurements and sonic logs is the presence of deleterious noise that impacts the quality and reliability of the estimated seismic wavelets and seismic inversion products. Spatial averaging effects and borehole drilling damage can also bias the estimation of in situ stress and elastic properties from sonic logs. We have developed an inversion-based method to mitigate processing errors, spatial averaging effects, and borehole environmental noise on sonic logs, which does not require arbitrary numerical filters, effective-medium theory models, or time-consuming waveform reprocessing. The inversion-based method estimates layer-by-layer slownesses via joint inversion of shear and compressional logs measured in a vertical well, and it uses the estimated slownesses of the assumed horizontal layers to model noise-mitigated sonic logs. By making use of geometric and physical constraints for noise reduction implicit in the inversion-based method, we obtain sonic logs that more accurately reflect the physical properties of rock formations penetrated by wells. Sonic logs are efficiently modeled by invoking axial sensitivity functions. First, we test the inversion-based method with synthetic sonic logs contaminated with noise. Estimated layer-by-layer slownesses agree with those of the original model within a standard deviation of [Formula: see text], while effectively reducing the numerical noise included in the input measurements. When bed-boundary locations are unknown, we perform the inversion-based method by assuming bed boundaries uniformly spaced at the same sampling interval of sonic logs; in this case, although the accuracy of the estimated layer slownesses decreases, the noise on sonic logs decreases. Then, we apply the method to sonic logs acquired in the North Sea and estimate angle reflectivity from the noise-mitigated logs. Results verify the reliability of the inversion-based method to reduce biases in the calculated angle reflectivity within a few minutes of central processing unit time.

Methodology to design of synthetic sonic log (SSL), using artificial neural networks. Colorado field application

A method that allows the creation of the Synthetic Sonic Log (SSL) was developed from the Spontaneous Potential (SP) logs, the resistivity logs of the flushed zone (SN), and the resistivity zone of the uninvaded zone (ILD), using Artificial Neural Networks (ANN). The SSL was obtained with the created tool calledGeneration of Synthetic Sonic Logs (GSSL).
 The results obtained are presented hereinafter: in the Colorado 70 well, 90% of the generated SSL data present errors of less than 10%; in the Colorado 72 well; 53% of the SSL data obtained with the tool are below 5% error, in the Colorado 75 well, 80% of the SSL data present errors of less than 10%, and finally, the SSL generated for the Colorado 38 well follows the behavior of the original Sonic Logs of the well in an accurate manner. From the foregoing we conclude that the quality of the created tool is good and that the deviations are minimal in the times of transit of synthetic sonic profile.

Local regularity analysis of strata heterogeneities from sonic logs

Abstract. Borehole logs provide geological information about the rocks crossed by the wells. Several properties of rocks can be interpreted in terms of lithology, type and quantity of the fluid filling the pores and fractures. Here, the logs are assumed to be nonhomogeneous Brownian motions (nhBms) which are generalized fractional Brownian motions (fBms) indexed by depth-dependent Hurst parameters H(z). Three techniques, the local wavelet approach (LWA), the average-local wavelet approach (ALWA), and Peltier Algorithm (PA), are suggested to estimate the Hurst functions (or the regularity profiles) from the logs. First, two synthetic sonic logs with different parameters, shaped by the successive random additions (SRA) algorithm, are used to demonstrate the potential of the proposed methods. The obtained Hurst functions are close to the theoretical Hurst functions. Besides, the transitions between the modeled layers are marked by Hurst values discontinuities. It is also shown that PA leads to the best Hurst value estimations. Second, we investigate the multifractional property of sonic logs data recorded at two scientific deep boreholes: the pilot hole VB and the ultra deep main hole HB, drilled for the German Continental Deep Drilling Program (KTB). All the regularity profiles independently obtained for the logs provide a clear correlation with lithology, and from each regularity profile, we derive a similar segmentation in terms of lithological units. The lithological discontinuities (strata' bounds and faults contacts) are located at the local extrema of the Hurst functions. Moreover, the regularity profiles are compared with the KTB estimated porosity logs, showing a significant relation between the local extrema of the Hurst functions and the fluid-filled fractures. The Hurst function may then constitute a tool to characterize underground heterogeneities.

Heterogeneities characterization from velocity logs using multifractional Brownian motion

Well logs provide additional information from the borehole that cannot be derived from other subsurface investigations. Their analysis may bring supplementary features about the earth’s heterogeneities. In previous researches, the logs were modeled using fractional Brownian motions indexed by Hurst (or Holder) exponents quantifying their global regularity degrees. Indeed, these monofractal models, characterized by the same Hurst exponent, do not allow to study the depth-evolution of the local Hurst parameter. In order to overcome this problem, we propose to model the logs using multifractional Brownian motions and suggest an algorithm, developed previously for financial time series, to estimate the local Hurst exponent function. First, the potential of this algorithm is assessed through its application on synthetic sonic log data simulated by the successive random additions method. We note that the estimated Hurst functions (or regularity profiles) are very close to the theoretical Hurst functions. Second, this analysis is extended to sonic logs data from the KTB pilot borehole (Germany). Using the resulted regularity profiles, we carry out a lithological segmentation and fault identification on the geological layers crossed by the well. We derived also a correlation between the Hurst value variation and the lithological changes.

The Velocity-Deviation Log: A Tool to Predict Pore Type and Permeability Trends in Carbonate Drill Holes from Sonic and Porosity or Density Logs

The velocity-deviation log, which is calculated by combining the sonic log with the neutron-porosity or density log, provides a tool to obtain downhole information on the predominant pore type in carbonates. The log can be used to trace the downhole distribution of diagenetic processes and to estimate trends in permeability. Laboratory measurements on over 300 discrete carbonate samples reveal that sonic velocity is a function not only of total porosity, but also of the predominant pore type. In general, there is an inverse porosity-velocity correlation, but significant deviations occur from this relationship for certain pore types. Frame-forming pore types, such as moldic or intrafossil porosity, result in significantly higher velocity values at equal total porosities than do pore types that are not embedded in a rigid rock frame, such as interparticle porosity or microporosity. The results of the laboratory measurements can be applied to expand interpretations of standard wireline-log data, as shown in this study on two drill holes through Neogene carbonates from the Great Bahama Bank. The velocity-deviation log is calculated by first converting porosity-log data to a synthetic velocity log using a time-average equation. The difference between the real sonic log and the synthetic sonic log can then be plotted as a velocity-deviation log. Because deviations are the result of the variability of velocity at a certain porosity, the deviation log reflects the different rock-physical signatures of the different pore types. Positive velocity deviations mark zones where velocity is higher than expected from the porosity values, such as zones where frame-forming pore types dominate. Zero deviations show intervals where the rock lacks a rigid frame, such as in carbonates with high interparticle porosity or microporosity. Negative deviations mark zones in which sonic log velocities are unusually low, caused, for instance, by a cavernous bore-hole wall, fracturing, or possibly by a high content of free gas. By tracing the velocity deviations continuously downhole, one can identify diagenetic zones that are characterized by these different pore types. In addition, this method can be used to observe permeability trends because pore types influence the permeability of the rock.

Wavelet power spectrum analysis of heterogeneities from sonic velocity logs

The continuous wavelet transform (CWT) is used to evaluate local variations in the power‐law exponents of sonic log data. The resulting wavelet spectrum can be compared with the corresponding global estimates obtained by conventional Fourier transform methods. In Fourier analysis, the fundamental tool used to characterize a fluctuating velocity distribution is the power spectrum. It represents the energy contained in each wavenumber and thus provides information regarding the importance of each scale of heterogeneity. However, important spatial information regarding the location of events becomes implicit in the phase angle of the Fourier transform. In this paper, it is shown how the square of the amplitude of the wavelet transform is related to the Fourier spectrum and how spatial information can be expressed in an explicit manner. Using the conservation of energy, it is shown that the average wavelet power spectrum over the total depth range is equal to the global power spectrum. A Gaussian wavelet is chosen to realize the wavelet transform. Two synthetic sonic logs with exponential and von Karman correlation functions are used to demonstrate the potential of the suggested analysis. Furthermore, the wavelet transform is applied to the KTB (Continental Deep Drilling Program) sonic log data. The wide range of applications of the CWT shows that this transform is a natural tool for characterizing the structural properties of underground heterogeneities. It offers the possibility of separating the multiscale components of heterogeneities.

Modeling studies of interference reflections in thin‐layered media bounded by coal seams

High‐resolution seismic data collected over a major U.S. coal basin indicated potential complex problems associated with interference reflections. These problems differed from those normally encountered in the exploration of oil and gas because of differences in the geologic boundary conditions. Modeling studies were conducted to investigate the effects of overlapping primary reflections and the composite reflection that result from stacking individual wavelets. A modified empirical formula of Lindseth’s linear relationship between acoustic impedance and velocity is used to extrapolate velocity information from density logs to provide appropriate geophysical properties for modeling. The synthetic seismograms generated from density and synthetic sonic logs correlated well with the processed seismic data. A 150-Hz Ricker wavelet is used to convolve with the computer models, and the models showed that certain anomalous composite reflections result from the superposition of overlapping primary reflections. Depending on the traveltime delay of latter primary reflections, constructive or destructive interference could significantly alter the signature of the initial reflection associated with the bed of interest, which may lead to misinterpretations if not properly identified. The stratigraphic modeling technique further enhances the interpretation process and shows a close correlation with the seismic data, suggesting that more precise analytical methods need to be used to interpret, sometimes complex, high‐resolution seismic data.

Frontier seismic geologic techniques and the exploration of the Miocene reefs in offshore Palawan, Philippines

An 88 km grid of Seislog sections (synthetic sonic log traces) was used to supplement the conventional seismic interpretation to assess the hydrocarbon potential of Lower Miocene reefs of offshore Palawan, Philippines. The porosity distribution in the zone of interest as well as the oil-water contact in and around the Tara and Libro patch reefs were mapped. The structural mapping was also fine tuned, including mapping of faults with small displacements. The paradox of pooling of hydrocarbons is evident in the maximum fill in the front line of traps near the shelf-slope break that are in the lowest structural position. Progressively dwindling amounts of fill in the structurally higher updip basin positions are interpreted to be due to the migration of hydrocarbons from the hydrocarbon kitchen in the Palawan Trough. The front line of traps had the benefit of maximum fill, the traps at the rear only of residual fill that spilled past the frontal traps. Three play types corresponding to the front line of traps, the rear line of traps and the most remote line of traps have been identified. Frontal reefs are considered to have the highest hydrocarbon potential. Diminishing hydrocarbon potential is inferred for closures in the updip direction. A thorough screening of all available seismic control for mapping all the patch reefs that might compensate for their dimensions by their numbers as well as for detecting possible pinnacle reefs in the downdip basin position has been suggested.

Use of SEISLOG for basin evaluation and field development

Seismic traces can be converted into a series of synthetic sonic logs of SEISLOGS. SEISLOGS, with a vertical axis in depth can be used in exploration to delineate productive units in the subsurface, as well as lithology and facies distributions in basins. In delineation and production, this method can predict reservoir continuity, and optimize platform locations thus avoiding dry holes. Six examples of its use are given—three in carbonates and three in elastics, the latter from the South China Sea.

Predicting Interval Transit Time for Synthetic Seismograms from Nuclear Well Logs: ABSTRACT

Sonic logs commonly were not included as part of the logging program on older wells. In certain areas, wells are drilled with air. The absence of drilling fluid in the borehole eliminates the possibility of recording a sonic log. In other areas, sonic logs are either of poor quality or, for one reason or another, omitted from the logging program. A method has been developed to predict interval transit times using nuclear well logs. It involves combining neutron, density, and gamma-ray log measurements into a log of predicted interval transit times referred to as a synthetic sonic log. The method involves a combination of commonly used and accepted well-log interpretation techniques. It effectively accounts for lithology, shale, porosity and hydrocarbon effects. The method requires only 3 parameters, which may be selected based on the well-log data. The synthetic sonic log agrees well with actual sonic-log measurements over a wide variety of geographic areas and borehole depths. The method is effective for formations commonly encountered in geophysical well logging including salt, shale, sandstone, and carbonate. The synthetic sonic log is an excellent substitute for use in generating synthetic seismograms and establishing time-depth relationships. End_of_Article - Last_Page 246------------

Williston Basin Seislog Study: ABSTRACT

This paper describes the results of Seislog® (trade name) processing and interpretation of an east-west line in the North Dakota region of the Williston basin. Seislog processing involves inversion of the seismic trace data to produce a set of synthetic sonic logs. These resulting traces, which incorporate low-frequency velocity information, are displayed in terms of depth and isotransit times. These values are contoured and colored, based on a standard stratigraphic color scheme. The section studied is located just north of a dual producing oil pool from zones in the Ordovician Red River and Devonian Duperow Formations. A sonic log from the Long Creek 1 discovery well was digitized and filtered to match the frequency content of the original seismic data. This allows direct comparison between units in the well and the pseudosonic log (Seislog) trace nearest the well. Porosity development and lithologic units within the lower Paleozoic stratigraphic section can be correlated readily between the well and Seislog traces. Anomalous velocity zones within the Duperow and Red River Formations can be observed and correlated to producing intervals in the nearby wells. These results emphasize the importance of displaying inversion products that incorporate low-frequency data in the search for hydrocarbons in the Williston basin. The accumulations in this region are local in extent and are difficult to pinpoint by using conventional seismic data or displays. Seislog processing and displays provide a tested method for identification and delineation of interval velocity anomalies in the Red River and Duperow stratigraphic sections. These techniques can significantly reduce risks in both exploration and delineation drilling of these types of targets. End_of_Article - Last_Page 290------------

Use of Seislog for Basin Evaluation and Field Development: ABSTRACT

Generation of synthetic sonic logs (Seislogs) from seismic data can provide lithologic, porosity, and fluid-content identifications in a variety of End_Page 290------------------------------ geologic settings. Case studies illustrate the type of information that can be extracted from seismic data on carbonate rocks, including North Sea chalk, fractured limestones in Venezuela, and porosity development in regional limestones of western Canada. In the North Sea, 2 adjacent structures that appear similar on conventional seismic sections display porosity development and fluid content changes within the chalk reservoir on the Seislog section. In a South American example, the Seislog display demonstrates the ability of seismic data to locate vertical fracture zones. In western Canada, secondary porosity development within Devonian carbonates was identified on Seislog displays, which led to the extension of a gas field. Examples from southeast Asia display a variety of depositio al environments in Miocene sediments. Shallow-marine and shoreline sands can be identified in a Malaysian example. An example from the Natuna Sea displays a lower delta-plain setting, with regional shale markers and thick clastic packages. An upper delta-plain example (Gulf of Thailand) displays more faulting, expansion of clastic packages, and discontinuous channel sands. End_of_Article - Last_Page 291------------

Use of Synthetic Sonic Logs Derived from Seismic Data in Interpretation of Stratigraphic Variation in Cretaceous Carbonates of North Field Area, Qatar: ABSTRACT

This study uses synthetic sonic sections to evaluate the hydrocarbon potential of the carbonate reservoirs of the Lower and middle Cretaceous Thamama Group, namely the Mishrif, Nahr Umr, Shuaiba, and Kharaib formations of the North field, Qatar. The North field area was a regional high throughout Early and middle Cretaceous time. Oil and gas accumulations are found on the crestal portions of this paleohigh in structural/stratigraphic traps. The synthetic sonic program produces a series of synthetic sonic logs from real seismic traces. It is a powerful addition to conventional seismic section because it monitors the additional parameters of seismic continuity and rock properties in what otherwise is a relatively structureless subsurface carbonate terrain. Detailed studies of seven regional synthetic sonic lines across the North field area indicate that significant decreases in interval velocities occur in all of the studied carbonate reservoir formations. Three factors effect the interval velocities on both a regional and local basis. These are (1) variation of carbonate facies - higher energy wackestone/packstone and possible grainstones flanked by predominantly mudstones, (2) secondary porosity developed near the top of unconformity surfaces, and (3) the existence of hydrocarbons in the reservoir. Many local lateral and vertical variations in interval velocities were noted. Areas of tight or porous reservoir development, permeability barriers, and subtle faulting were observed on the synthetic sonic sections that would have otherwise been undetected using more conventional processing. In these formations, there are many examples of low interval velocity zones that are known to contain hydrocarbons whereas equivalent higher interval velocity on the seismic sections at other well locations do not contain hydrocarbons. In many cases, these lateral variations are of sufficient magnitude to be mapped as intraformational permeability barriers. These variations were useful in explaining the occurrence of different oil-water and gas-water contacts within the same formation that could n t be explained solely on structural criteria. It can be concluded from this study of North field, Qatar, that the synthetic sonic technique is a particularly useful exploration tool in carbonate reservoir environments because it is able to delineate areas of higher exploration potential. The geologist can use this tool in areas of known well control to project carbonate reservoir variation in between or away from bore holes where log or petrographic information is unavailable. The SEISON-II modeling was found to be a well-suited modern seismic technique in this offshore marine environment, where it was used to investigate relatively shallow reservoir depths (2,500 to 3,700 ft [762 to 1,128 m]), and relatively thick formation subzones (40 to 90 ft [12 to 27 m]) having a fairly consistent regional development.

A Late Cretaceous Submarine Canyon in Brazil: Seismic Stratigraphy: ABSTRACT

A continuous sequence of gently dipping clastics covers a deep submarine canyon which was cut into Upper Cretaceous sediments and subsequently filled with Tertiary clastics. Conventional seismic work provides some indication of the complex sequence which filled the channel, but the full detail of the depositional history is revealed in detail by inverting the seismic data to produce synthetic sonic logs. The results reveal classic patterns of sedimentation, illustrate several changes which occurred in the source and distribution of sediments which filled the canyon, and map the individual members in close detail. End_of_Article - Last_Page 594------------