Thin Sand Bodies Research Articles

A comparison of competing amplitude variation with offset techniques applied to tight gas sand exploration in the Cooper Basin of Australia

We have developed a tight gas amplitude variation with offset (AVO) case history from the Cooper Basin of Australia that addressed the exploration problem of mapping thin fluvial tight gas sand bodies. In the Cooper Basin, Permian Toolachee and Patchawarra sands are difficult to interpret on seismic data due to strong reflections from adjacent Permian coals. This is not the common AVO problem of distinguishing between coal and gas sand, but a more difficult class-I AVO problem of mapping fluvial sands beneath a sheet coal that varies in thickness. We have reviewed local rock properties and concluded that Poisson’s ratio is probably the most appropriate rock property to solve the above exploration problem. We have compared various seismic attributes made using the extended elastic impedance (EEI) technique and a rotation of near and far partial stacks. In a synthetic modeling study that included random noise and tuning, we compared the noise-discrimination abilities of three competing AVO crossplot techniques and “rotated” the attributes made from them. These three crossplots were as follows: intercept versus gradient (I-G), full-stack versus far-minus-near (Full-FmN), and near-stack versus far-stack (N-F). Previous papers on this subject have found that (I-G) crossplots had a spurious correlation in the presence of noise that did not occur with the (Full-FmN) and (N-F) crossplots. We found that for our class-I AVO case, (1) the advantage of the (Full-FmN) and (N-F) crossplots disappeared in the presence of tuning, (2) if tuning was present, the optimal rotation angle was determined by the “tuning angle,” not by the noise angle or some desired EEI angle, and (3) if the three different crossplots were rotated by their respective “tuning” angles, the results were identical.

ABOUT THE INFLUENCE OF GEOLOGICAL HETEROGENEITY OF MOUTH BAR ON THE HYDRODYNAMICS OF THE RESERVOIR ROCK OF RED FOREST FIELD (CHINA)

The article considers the geological structure of C 6 productive bed of Red forest oilfield (China). It is determined that reservoir rock belongs to mouth bar of delta front. The survey shows the laminated structure of the reservoir, consisting of several regressive sedimentation cyclical beds separated by impermeable clay layers. In the structure of the regression mouth bar are dedicated two subfacies: crest and slope. It is established that crest subfacie is characterized by high grain maturity and made more powerful and homogeneous sandy sediments with high permeability properties. Slope subfacie of mouth bar has a high stratification with frequent interlayering of discontinuous thin sand bodies composed of immature sediments with the deterioration of reservoir properties. The presence of macroheterogeneity in bar sediments determines the filtration reservoir structure and its dynamics that must be considered when selecting the system of the injection wells location, the design of horizontal wells and design of hydraulic fracturing. It is shown that the most significant effect on the fluid dynamics of the reservoir have a layered structure of the reservoir, the location of injection and production wells in relation to the bar body and, especially, differences in the azimuthal direction of seepage flow and the strike of mouth bar sand bodies. The simulation results showed that the reservoir with a large number of layers is watered with more effectively, and the amount of remaining oil in it more than in the reservoir with a small number of layers; quick the water-cut and the decline in oil production are established in models where the sand body strike coincides with the direction of fluid flow. Recommendations on the organization of the flooding system for optimal oil extraction of laminated heterogeneous bar reservoir.

The Structural Characteristics and Distribution of Sand Body of the Layer 7 of YanChang Formation in Ordos Basin

The tight sand in the layer 7 of YanChang Formation, Ordos Basin major develops braided river delta and gravity flow deposits. In this paper, based on previous studies on lake pelvic shape, provenance and hydrodynamic, the sand body in the research area has been systematically studied through core observation, logging data, and sedimentary theory. Various genetic types of sedimentary sand body are developed in this area, mainly as delta deposition, sandy debris flow deposits, turbidites (classic turbidites). We can identify 6 kinds of sand vertical combination type, they are the superimposed sand body (A-type), thick and uniform thickness sand body (B type), thin and uniform thickness sand body (C-type), up thinning sand body (D-type), thickening up sand body (E-type) , thick and thin interbed sand body (F-type). The 6 types mainly controlled by sedimentary facies. The A-type sand body mainly developed in the delta depositional environment, the B type sand body is visible both in the delta and slope belt, while the D-type, E-type, F-type sand body are mainly developed in the deep lake. The distribution of sand body in the plane is zonal pattern.

Application of Seismic Inversion Technique Base on Geostatistics in Prediction of Thin Sand Body Reservoir

Seismic inversion methods include constrained sparse pulse inversion and band limit inversion, etc. Although resolution of the seismic inversion results is higher than seismic data, it does not identify thin interbedding sand body and confirm the development of reservoirs. In this paper, in A block of Indonesia adopted geostatistical inversion in reservoir prediction, which is a method of seismic inversion combining geological statistics simulation and seismic inversion. This inversion method can establish various 3D geological model with the same probability of rock properties and lithology and it obey all seismic, logging and geological data. Using statistical regularity and seismic inversion technique we can obtain more fine reservoir model and finally reach the purpose of identification of single thin sand layer.

The Application of Peak Number Attribute in the Prediction of River Sand

Its a commonly used method to predict layer by using seismic attributes, especially for some of the less well control channel sand bodies whose role is more important. Putaohua reservoir in Gaotaizi oilfield mainly develop shallow water delta front subaqueous distributary channel sand bodies which has narrow rivers and thin sand bodies, meanwhile, the existing well density is difficult to control the trend and boundary of the channel. By using seismic forward modeling analysis techniques, this paper researched the differences of seismic reflection characteristics among different geological model of channel sand bodies, then , further pointed out the methods of channel sand prediction by using the peak number attribute and analyzed the predictive effect. The results show that this method can effectively improve the prediction accuracy of thin interbedded reservoir.

FRS<sup>TM</sup> Fracture-Based Pre-Stack Elastic Wave Impedance Inversion of Fuyang Oil Layer in Songliao Basin

The later-period structure of Fuyang oil layer is complex and its reservoir is mostly composed by the sand bodies of riverways. The oil and gas reservoir features obvious concealment, and also is difficult to identify. To accurately describe the reservoir, a pre-stack elastic wave impedance inversion was made for Fuyang oil layer in Songliao Basin using FRSTM fracture. The pre-stack inversion results statistical error was small if the thickness of sandstone was greater than 3m. The error was close to 100% according to the standard less than 20%, namely the pre-stack inversion prediction accuracy was higher. However, the statistical error was greater and the pre-stack inversion prediction accuracy decreased if the thickness of sandstone was less than 3m, so the prediction result could be only used as a reference value. Therefore, the pre-stack elastic wave impedance inversion can produce a significant effect for the anisotropic reservoirs of complex later-period structure, thin sand body, and complex changes, and can meet the needs of the oil field exploration and development.

Study on the Application of the EPSTM Image Based Post-Stack Spectrum Imaging to the Identification of the Riverway Sand Bodies in Fuyang Oil Layer of Songliao Basin

The later-period structure of Fuyang oil layer is complex and its reservoir is mostly composed by the sand bodies of riverways. The oil and gas reservoir features obvious concealment, and also is difficult to identify. To accurately describe the reservoir, a post-stack spectrum imaging was made for the identification of the riverway sand bodies in Fuyang oil layer using EPSTM image in the study area. The statistical error of the riverway sand body identification result using post-stack spectrum imaging was small if the sandstone thickness was greater than 3m. Seen from logging wells geological verification, the riverway identification fit rate was 81.6% on average, the microfacies type identification fit rate was 75%, and the microfacies types identification fit rate of the sandstone thicker than 3m was 80%. Using the nonlinear algorithm of the MDI software, the lithologic prediction was implemented based on the sand group as the unit, and the average prediction fit rate of the sandstone thicker than 3m reached 90% according to the standard relative error less than 20%. Therefore, the post-stack spectrum imaging can exert a significant effect for the anisotropic reservoirs of complex later-period structure, thin sand body, and complex changes, and can meet the needs of the oil field exploration and development to some extent.

Analysis on the FRS<sup>TM</sup> Fracture-Based Pre-Stack Seismic Azimuth Attributes of the Sand Bodies in Fuyang Oil Layer in Songliao Basin

The later-period structure of Fuyang oil layer is complex and its reservoir is mostly composed by the sand bodies of riverways. The oil and gas reservoir features obvious concealment, and also is difficult to identify. Therefore, in this study, the pre-stack seismic attributes of the sand bodies in riverways were identified using FRSTM fracture software in the study area, and the study results of the pre-stack detection on anisotropy showed that the relationship between the anisotropic development zone and the sedimentary microfacies is close and also they are affected by the fracture system. After a comprehensive analysis, it can be judged that the reliability of the anisotropic development features with fully-contained fluid or better physical properties after a pre-stack anisotropy analysis is very high, can objectively reflect the space distribution characteristics of the anisotropic strength at the targeted reservoir, and can plays an obvious effect on the areas of the complex later structure, and thin and complex sand bodies, so that the needs of oil fields exploration and development can be fulfilled.

Study on the PNN Neural Network Inversion Based on the Integration of Seismic Multi-Attribute with Frequency Division RGB - Fuyu Oil Layer in Gaotaizi Area, Songliao Basin is Taken for an Example

Fuyu oil layer in Changyuan of Daqing is a strategic area for Daqing oil field to increase and stabilize production at present, but its reservoir is structured mostly by riverway sand bodies. The sand bodies are thin and change with complexity, so they are difficult to identify. Through PNN probability neural network, and combined with the seismic multi-attribute and earthquake frequency division data, wave impedance inversions are implemented, and the maximum correlation coefficient is 0.517 if a single attribute is described and it is raised to 0.773 by linear weighting, and also 9 independent attributes are used for PNN network training so that a more complex nonlinear relationship is obtained. Then, the correlation coefficient continues to increase until 0.869, so that the spatial distribution characteristics of the sandstones in the study area are accurately described. This indicates that the PNN neural network inversion based on the integration of seismic multi-attribute with frequency division RGB can play an obvious effect in the areas of thin and changing sand bodies, and can meet the needs of the oil field exploration and development.

Dynamic Updating of Reservoir Models

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 123671, ’Dynamic Updating of Reservoir Models,’ by Harun Ates and Asnul Bahar, SPE, Kelkar and Associates, and Vitaly Krasnov, SPE, Rosneft, and Mohan Kelkar, SPE, University of Tulsa, prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October. The paper has not been peer reviewed. In sandstone reservoirs, an important challenge is scaling up a fine-scale model effectively. Conventional methods are not adequate when significant shale distribution exists in the reservoir. In the fine-scale model, some sand bodies are connected to the wells and some are not. As the fine-scale model is scaled up, some discontinuous sand bodies become combined with connected sands. A new procedure was developed to overcome this problem. Introduction Traditional reservoir modeling involves developing a fine-scale geocellular model that incorporates the small-scale static uncertainties. Once such a description is created, it is scaled up to an appropriate scale such that it can be flow simulated to understand the dynamic performance of the reservoir. It is difficult to flow simulate a fine-scale model because it is computationally demanding. Some sandstone reservoirs tend to be highly discontinuous, with sand and shale dispersed within the reservoir. The continuity of the sand bodies may not be known precisely and reflects an uncertainty in static models. The problem becomes even more complex if the reservoir is thick and contains multiple thin sand bodies. When a fine-scale model is constructed, it may contain many vertical layers to account for all the thin sands present in the reservoir. Scaling up of such models is very difficult because of the following. If the model is coarsened (scaled up) significantly, many of the discontinuous sands will connect to other sands, and this will increase the pore volume (PV) “connected” to the wellbore, changing the transmissibility (connectivity) distribution between wells. In the scaled-up model, because of artificially connected sands, infill wells would not indicate true potential of additional recovery because some of the virgin sands that would have been connected to the newly drilled wells would show to have been drained already by existing wells in the model. If the model is maintained at relatively fine scale, the simulation can be computationally demanding. The dynamic modeling (e.g., history matching) would be more time consuming. Therefore, many uncertainties may not be investigated correctly.

Application of the continuous wavelet transform on seismic data for mapping of channel deposits and gas detection at the CO2SINK site, Ketzin, Germany

ABSTRACTConventional seismic data are band limited and therefore, provide limited geological information. Every method that can push the limits is desirable for seismic data analysis. Recently, time‐frequency decomposition methods are being used to quickly extract geological information from seismic data and, especially, for revealing frequency‐dependent amplitude anomalies. Higher frequency resolution at lower frequencies and higher temporal resolution at higher frequencies are the objectives for different time‐frequency decomposition methods. Continuous wavelet transform techniques, which are the same as narrow‐band spectral analysis methods, provide frequency spectra with high temporal resolution without the windowing process associated with other techniques. Therefore, this technique can be used for analysing geological information associated with low and high frequencies that normally cannot be observed in conventional seismic data. In particular, the continuous wavelet transform is being used to detect thin sand bodies and also as a direct hydrocarbon indicator. This paper presents an application of the continuous wavelet transform method for the mapping of potential channel deposits, as well as remnant natural gas detection by mapping low‐frequency anomalies associated with the gas. The study was carried out at the experimental CO2 storage site at Ketzin, Germany (CO2SINK). Given that reservoir heterogeneity and faulting will have significant impact on the movement and storage of the injected CO2, our results are encouraging for monitoring the migration of CO2 at the site. Our study confirms the efficiency of the continuous wavelet transform decomposition method for the detection of frequency‐dependent anomalies that may be due to gas migration during and after the injection phase and in this way, it can be used for real‐time monitoring of the injected CO2 from both surface and borehole seismics.

Side lobes of wavelets impact identification of thin sand bodies

Recently, we found that side lobes of wavelets have a large impact on the identification of thin sand reservoirs when studying some gas fields in a basin in Northwest China. Reflections from the top of the H Formation, in which there are gas-bearing thin sand bodies, have the main wavelet lobe between two weak peak side lobes. The lower one always mixes with another peak reflected from the top of a thin sand reservoir. That makes it difficult to identify the sand reservoir. In order to solve this, many forward models were set up using typical well logs. 2D synthetic profiles were produced using Ricker wavelets to study the relationships between the effects of wavelet side lobes and thin sand position and frequency and between amplitude and the thin sand body. We developed the following conclusions: First, it is easier to identify thin sands in a shallower position. Second, a good way to tell sand body reflections from side lobes is by comparing profiles with different frequency windows. Third, it is helpful and effective to describe sand extent using amplitude attributes.

Middle Miocene Stratigraphic Traps, Southeast Manila Village Field, Louisiana

ABSTRACT Southeast Manila Village Field, Louisiana, produces from two middle Fleming Group sandstones at depths ranging from 11,400 to 12,000 ft. Hydrocarbon production occurs mainly by a pressure deplion mechanism; a waterflood has been initiated to stabilize reservoir pressure. Fourteen wells have been drilled to date, and ultimate recovery from the field is estimated to be 4,609 MBO and 3,267 MMCFG. Thin sand bodies, designated as the 28 and 29 Sands, occur in a shale interval, which ranges in thickness from 500 to 600 ft. The reservoir rocks are thinly laminated, moderately to well-sorted, and very fine-grained sands. Thin sand laminations have sharp lower contacts with the interbedded shales, indicating episodic deposition. Foraminiferal assemblages indicate that the sands have been deposited in 100 to 400+ ft of water. The sands are probably the result of turbidity flow deposition in a distal-delta environment. Diagenetic reactions are, in part, responsible for the hydrocarbon accumulation in the sands. Dissolution of primary calcite cement and detrital K-feldspar grains has generated secondary porosity in the sands. Precipitation of authigenic minerals, such as chlorite, pyrite, siderite, kaolinite, illite, and mixed-layer clays has, however, influenced primary and secondary oil recovery. Migration and accumulation of hydrocarbons apparently halted secondary cementation by inhibiting the precipitation of authigenic clays.

Subsurface Study of Lower Tuscaloosa Formation at Olive Field, Pike and Amite Counties, Mississippi: ABSTRACT

ABSTRACT Olive Field is located on the Amite-Pike County line in southwestern Mississippi. The field was discovered by Shell Western Exploration and Production Inc., and produces from a sandstone within the Lower Tuscaloosa Stringer Member; the trap is stratigraphic. The Stringer Member consists of alternating sandstones, siltstones, and shales, which have an average thickness of 230 ft (76 m) at Olive Field. The Stringer Member is a transgressive sequence deposited on eroded Washita-Fredericksburg sediments and is overlain by Middle Tuscaloosa marine shales. The coarse-to fine-grained sandstones are quartz-rich with a high percentage of sedimentary rock fragments. The majority of sandstones are shale arenites. However, a large number of rock fragments were badly altered; these fragments could not be identified with confidence; many may be of volcanic origin. The sandstones are cemented by quartz overgrowths, Fe-rich carbonate cement, and chlorite. Sandstones commonly have a high preserved interparticle porosity that is characteristic of Lower Tuscaloosa sandstones. This interparticle porosity is attributed to chlorite, which occurs as an isopachous cement that coats grains and reduced nucleation sites for quartz overgrowths. The Stringer Member was subdivided into five zones in this study based on lithology and electric log responses. The lower three zones were deposited in a fluvial environment. The sandstones were deposited as point bars and channel sands in a meandering system. Siltstones and shales represent overbank, flood basin, and channel fill deposits. The upper two zones consist of sediments deposited at or near sea level. Finely laminated shales and siltstones represent marsh and bay deposits. The topmost zone is a thin continuous sand body that represents a remnant beach deposited before major marine transgression.