Image Log Data Research Articles

Generating porosity spectrum of carbonate reservoirs using ultrasonic imaging log

Imaging logging tools can provide us the borehole wall image. The micro-resistivity imaging logging has been used to obtain borehole porosity spectrum. However, the resistivity imaging logging cannot cover the whole borehole wall. In this paper, we propose a method to calculate the porosity spectrum using ultrasonic imaging logging data. Based on the amplitude attenuation equation, we analyze the factors affecting the propagation of wave in drilling fluid and formation and based on the bulk-volume rock model, Wyllie equation and Raymer equation, we establish various conversion models between the reflection coefficient β and porosity ϕ. Then we use the ultrasonic imaging logging and conventional wireline logging data to calculate the near-borehole formation porosity distribution spectrum. The porosity spectrum result obtained from ultrasonic imaging data is compared with the one from the micro-resistivity imaging data, and they turn out to be similar, but with discrepancy, which is caused by the borehole coverage and data input difference. We separate the porosity types by performing threshold value segmentation and generate porosity–depth distribution curves by counting with equal depth spacing on the porosity image. The practice result is good and reveals the efficiency of our method.

Microseismic monitoring in unconventional reservoirs: are natural fractures hiding in plain sight?

As the shale revolution is adjusting to the realities of the new market and lower oil prices, the operators’ focus is shifting towards unconventional reservoirs and increasing hydrocarbon production efficiencies. The oil and gas operators’ demands are transforming our paradigm of reservoir characterization, forecasting, and monitoring. As such, heterogeneity of an unconventional reservoir is one of the main factors impacting well productivity. Well performance is driven by the size and efficiency of the interconnected fracture ‘plumbing system’ which is influenced by the presence of natural fractures and the process of multistage hydraulic fracturing. A complex, interconnected natural fracture network can significantly increase the size of the stimulated reservoir volume, provide additional surface area contact and enhance permeability. However, the interaction of the natural fracture networks and the completions-induced fractures is complex and can be affected by multiple factors, such as present-day maximum horizontal stress orientation, character of pre-existing natural fractures, presence of faults, lithology types that the horizontal well is being drilled through, as well as the well completions design itself. With a trend of unconventional resource plays’ development, the Niobrara Formation has become a focus of interest for operators. Recent advances in horizontal drilling and hydraulic reservoir stimulation have allowed for economic development of tight resource plays. In the presence of heterogeneity optimal well placement, orientation, and spacing are especially important. Natural fractures are expected to significantly influence the completions’ efficiency and have the potential to contribute to SRV (stimulated reservoir volume) and drainage volume. Hydraulic fracturing with evenly-spaced frac stages may not be the most successful stimulation method or yield the greatest production. In the given circumstances the process of reservoir monitoring is essential for accurate assessment of the produced reservoir volume (PRV) and for our understanding of how effectively the target formation is being stimulated. Microseismic data is being called upon with ever increasing frequency to satisfy the industry’s reservoir monitoring needs. In this study we take a look at one of the major unconventional resource plays in the US. The research was designed to conduct dynamic reservoir characterization and to test the strengths and limitations of microseismic monitoring. The study integrated 3D seismic data, microseismic data, geophysical well log and formation image log data, and core and outcrop data within the focal area. One of the goals of the study is to analyse factors capable of affecting the distribution of microseismic events. An important question to be answered: ‘Will microseismic data, taken alone, prove to be a sufficiently representative source of information when evaluating the reservoir response and estimating success of completion strategies?’

An improved algorithm based on CLAHE for ultrasonic well logging image enhancement

This study presents a novel image enhancement method in consideration of low contrast and blurred details of ultrasonic well logging images by combining the contrast limited adaptive histogram equalization (CLAHE) with power-law transformation. The red, green, and blue (RGB) color image is first transformed into hue, saturation, and intensity (HSI) space and the CLAHE is applied only to the intensity (or luminance) component (I) of the image. This enhances local details and prevents excess brightness in flat areas and uniform regions while maintaining the chromaticity values of the degraded image. Limitation of the CLAHE technique is that it limits the amplification of contrast by clipping the histogram of every sub-region at a predefined clip-limit. The power-law transformation is then applied to the processed image following the CLAHE processing. This maps a wide range of dark input values into a narrower range of output values, whereas a narrow range of bright input values into a wider range of output values, which further improve the contrast and highlight the local details. Finally, the result is presented as an RGB image. The performance of the proposed technique is compared with histogram equalization and CLAHE methods based on image quality objective measurement tools such as the mean square error (MSE) involving peak signal-to-noise ratio (PSNR), information entropy (IE), and luminance contrast (LC). Experimental results show that the proposed algorithm produces better ultrasonic well logging images than the existing enhancement schemes. The underlying improvement is of great significance for further upgrading the accuracy of sonic imaging logging data interpretation.

Monte Carlo CLEAN Spectral Analysis Method for Detecting the Stratigraphic Cycles Based on High-resolution Electrical Image Log Data

This paper performs a Monte Carlo CLEAN (MC-CLEAN) spectral analysis with high-resolution electrical image log data and interpret the high-resolution formation sequence by investigating the cycles in the sediments. Firstly, in order to perform a spectral analysis with high-resolution electrical image log data, the background conductivity log curve was extracted from the borehole image. Secondly, the MC-CLEAN spectrum analysis method was used to isolate all the peaks of the logging signal. Then the 95% significance level of the CLEAN spectrum was calculated to identify the true period of the formation by Monte Carlo simulation. Finally, the MC-CLEAN spectral analysis method was applied in the two shale intervals from Lower Pannonian interval of Vienna basin to identify the stratigraphic cycles. The analysis results showed that the identified cycles in the sedimentary record good matched the Milankovitch cycles. This paper provided a new approach of identifying stratigraphic cycles and interpreting high-resolution sequence stratigraphy.

Fault detection using principal component analysis of seismic attributes in the Bakken Formation, Williston Basin, North Dakota, USA

Seismic fault detection using principal component analysis (PCA) is an effective method for interpreting fault distribution and orientations in the Bakken Formation. The PCA fault attribute indicates significantly different, and geologically more plausible, 3D fault distributions than conventional seismic attributes, such as curvature. The PCA fault attribute has identified different fault patterns in the Upper, Middle, and Lower Bakken members and the Three Forks Formation. Two distinct fault trends in approximately 40°–50° northeast–southwest and 50°–60° northwest–southeast directions are observed in the Bakken Formation in the study area, and they are apparent on the strike and dip attributes derived from the PCA fault attribute. Fault cuts interpreted from missing well-log sections correlate well with the PCA fault attribute. Seismically derived fault orientations correlate with borehole image log data in the horizontal wells. Crossing conjugate faults observed on the fault dip attribute may result in the widening of the faulted area and localized thinning of the rock sequence where the faults intersect, and this could potentially enhance permeability along the fault strike.

Experiments on acoustic measurement of fractured rocks and application of acoustic logging data to evaluation of fractures

Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoir core samples to investigate true underground conditions. Due to the diversity of the fracture parameters, the simulation and evaluation of fractured rock in the laboratory setting is also difficult. Previous researchers have typically used a single material, such as resin, to simulate fractures. There has been a great deal of simplifying of the materials and conditions, which has led to disappointing results in application. In the present study, sandstone core samples were selected and sectioned to simulate fractures, and the changes of the compressional and shear waves were measured with the gradual increasing of the fracture width. The effects of the simulated fracture width on the acoustic wave velocity and amplitude were analyzed. Two variables were defined: H represents the amplitude attenuation ratio of the compressional and shear wave, and x represents the transit time difference value of the shear wave and compressional wave divided by the transit time of the compressional wave. The effect of fracture width on these two physical quantities was then analyzed. Finally, the methods of quantitative evaluation for fracture width with H and x were obtained. The experimental results showed that the rock fractures linearly reduced the velocity of the shear and compressional waves. The effect of twin fractures on the compressional velocity was almost equal to that of a single fracture which had the same fracture width as the sum of the twin fractures. At the same time, the existence of fractures led to acoustic wave amplitude attenuations, and the compressional wave attenuation was two times greater than that of the shear wave. In this paper, a method was proposed to calculate the fracture width with x and H, then this was applied to the array acoustic imaging logging data. The application examples showed that the calculated fracture width could be compared with fractures on the electric imaging logs. These rules were applied in the well logs to effectively evaluate the fractures, under the case of no image logs, which had significance to prospecting and development of oil and gas in fractured reservoirs.

Quantifying opening-mode fracture spatial organization in horizontal wellbore image logs, core and outcrop: Application to Upper Cretaceous Frontier Formation tight gas sandstones, USA

The Upper Cretaceous Frontier Formation is a naturally fractured gas-producing sandstone in Wyoming. Regionally, random and statistically more clustered than random patterns exist in the same upper to lower shoreface depositional facies. East-west- and north-south-striking regional fractures sampled using image logs and cores from three horizontal wells exhibit clustered patterns, whereas data collected from east-west-striking fractures in outcrop have patterns that are indistinguishable from random. Image log data analyzed with the correlation count method shows clusters ∼35 m wide and spaced ∼50 to 90 m apart as well as clusters up to 12 m wide with periodic inter-cluster spacings. A hierarchy of cluster sizes exists; organization within clusters is likely fractal. These rocks have markedly different structural and burial histories, so regional differences in degree of clustering are unsurprising. Clustered patterns correspond to fractures having core quartz deposition contemporaneous with fracture opening, circumstances that some models suggest might affect spacing patterns by interfering with fracture growth. Our results show that quantifying and identifying patterns as statistically more or less clustered than random delineates differences in fracture patterns that are not otherwise apparent but that may influence gas and water production, and therefore may be economically important.

Evaluation on the effectiveness of natural fractures in Changxing Fm reef-flat facies reservoirs, Yuanba area, Sichuan Basin

Study on the effectiveness of fractures is of great significance for understanding reservoir types and properties, identifying reservoir seepage mechanisms and delineating the reasonable development technologies and policies. In this paper, the Changxing reef-flat facies reservoirs in the Yuanba area, Sichuan Basin, was taken as an example. After the characteristics of natural fractures were evaluated, the effectiveness of different types of fractures was investigated by using core, thin section, imaging logging and production performance data. Then, the main geological factors that influence fracture effectiveness were analyzed, and the development significance of effective fractures was illustrated. The following results are obtained. (1) Structural fractures and diagenetic fractures are mainly developed in Changxing Fm carbonate reservoirs in Yuanba area. Structural fractures include shear fractures and extensional fractures, and diagenetic fractures include dissolution fractures, structural-dissolution fractures and pressure-solution fractures. (2) High-angle structural fractures are the most effective, followed by horizontal fractures and then oblique fractures, and pressure-solution fractures are the least effective. (3) Among structural fractures, those of NW–SE and nearly E–W oriented are more effective than those of the NE–SW oriented. (4) The earlier the fractures are formed, the more likely they are to be filled with calcite or dolomite and become invalid. (5) The fractures which are formed before or during the oil and gas charging tend to be filled with organic matters and become invalid. The late fractures which are formed after oil and gas charging are mostly effective and their contribution to the reservoir is the greatest. (6) The fractures nearly parallel to the maximum principal stress direction of current ground stress present good effectiveness with large opening. It is concluded that the opening and filling features of natural fractures help determine if fractures are effective or not, and the development degree, distribution and combination features of effective fractures and the matching relationship between fractures and pores further dominate the development significance of effective fractures; that when the effective fractures are more developed and are connected with each other to form a large-scale fracture network, separated and isolated pores and dissolved fractures and cavities can be connected, as a result, the physical properties of reservoirs are improved and high production rates of gas wells are realized.

Multi-threshold de-noising of electrical imaging logging data based on the wavelet packet transform

A key problem of effectiveness evaluation for fractured-vuggy carbonatite reservoir is how to accurately extract fracture and vug information from electrical imaging logging data. Drill bits quaked during drilling and resulted in rugged surfaces of borehole walls and thus conductivity fluctuations in electrical imaging logging data. The occurrence of the conductivity fluctuations (formation background noise) directly affects the fracture/vug information extraction and reservoir effectiveness evaluation. We present a multi-threshold de-noising method based on wavelet packet transform to eliminate the influence of rugged borehole walls. The noise is present as fluctuations in button-electrode conductivity curves and as pockmarked responses in electrical imaging logging static images. The noise has responses in various scales and frequency ranges and has low conductivity compared with fractures or vugs. Our de-noising method is to decompose the data into coefficients with wavelet packet transform on a quadratic spline basis, then shrink high-frequency wavelet packet coefficients in different resolutions with minimax threshold and hard-threshold function, and finally reconstruct the thresholded coefficients. We use electrical imaging logging data collected from fractured-vuggy Ordovician carbonatite reservoir in Tarim Basin to verify the validity of the multi-threshold de-noising method. Segmentation results and extracted parameters are shown as well to prove the effectiveness of the de-noising procedure.

The use of microresistivity image logs for facies interpretations: An example in point-bar deposits of the McMurray Formation, Alberta, Canada

Well logs such as spontaneous potential and gamma ray historically have been the only tools available for facies evaluation of noncored wells in the McMurray Formation. The addition of microresistivity image logs has greatly improved facies identifications and interpretations, particularly when integrated with core data sets. In the case of McMurray channel complexes, core descriptions provide detail about bedding contacts, sedimentary texture, stratification, bioturbation intensity, and trace fossil diversity. Image logs provide texture, fabric, bedding contact style, dip directions and angles, and bedding architecture information, yielding paleoflow and lateral accretion directions. This study characterizes facies by integrating interpretations from 414 image logs with core-based descriptions from 138 of these wells. The reservoir targets, and most prolific depositional facies in this study, are associated with channel systems and their associated point-bar deposits. Facies identifications are based on several image log criteria. Mud clast breccias display variable dip angles and dip directions. Cross-stratified sands comprise vertical successions of stacked, internally consistent bedsets with high dip angles (>15°) that indicate paleoflow direction. Lateral accretion beds show consistent dip directions with a progressive change from shallow-to-steep-to-shallow dip angles (e.g., <4 to 15° to <4°) from the base to the top of the succession, as well as beds that dip toward the thalweg of the paleochannel. Flat-lying (<4°) mud records vertical accretion associated with point-bar tops or channel abandonment. Although this facies classification is specific to the McMurray Formation in the study area, the principles provided here are applicable to other subsurface studies and demonstrate the enhanced reliability of integrated core–image log data sets.

Geology and in situ stress of the MH-2 borehole, Idaho, USA: Insights into western Snake River Plain structure from geothermal exploration drilling

Project HOTSPOT, the Snake River Scientific Drilling Project (International Continental Scientific Drilling Program), tested for deep geothermal resources and examined the petrology of volcanic rocks with three drillholes in the central and western Snake River Plain (western USA). The MH-2 drillhole targeted fractured crystalline and hydrothermally altered basalt in the area of the Mountain Home Air Force Base (Idaho) to a total depth of 1821 m. At 1745 m depth the drillhole encountered flowing artesian hydrothermal fluids of at least 150 °C. We integrate geological analyses of core, image log, and borehole geophysical data, and in situ stress analyses to describe the structural environment that produces permeability for artesian flow. The rocks in the lower 540 m of the drillhole consist of basalt flows as much as 30 m thick, altered basalt, and thin sedimentary horizons. The mechanical stratigraphy is defined by nine mechanical horizons that are in three ranges of rock strength on the basis of experimentally determined strength data, core logging, and geophysical log signatures. Hydrothermal alteration products and mineralization in the core are associated with three highly faulted sections; the lowermost section is associated with the zone of flowing thermal water. Shear slip indicators on faults observed in core indicate slip ranging from pure strike slip to normal failure mechanisms in the stronger horizons. The borehole breakouts indicate that the maximum horizontal stress, SH, is oriented 047° ± 7°, and drilling-induced tensile fractures indicate that SH is oriented at 67° ± 21°. The in situ stress orientations exhibit little variation over the depth of the measured interval, but the SH magnitude varies with depth, and is best explained by an oblique normal fault stress regime. The geomechanical model indicates that if pore pressures at depth are elevated above the normal hydrostatic gradient, as observed here, the system has the potential to deform by mixed normal and strike-slip failure. Our observations and interpretations suggest that the MH-2 borehole was drilled into oblique normal faults that intersect a buried 300°-trending fault block masked by the basaltic volcanic complex. These data indicate that the transition from the central to western Snake River Plain is characterized by complex structures developed in response to a transitional stress state related to Snake River Plain and western Basin and Range stress regimes. The western Basin and Range stress and tectonic regime may extend from northern Nevada into western Idaho and may enhance the potential for geothermal resources by creating interconnected fracture and fault-related permeability at depth.

In situ stress distribution and mechanical stratigraphy in the Bowen and Surat basins, Queensland, Australia

Abstract We present regional in situ stress analyses based on publicly available log and pressure data from coal seam gas developments in the Permian Bowen basin, Australia. Together with earlier data from the eastern part of the Jurassic Surat basin, our results show a broad, but systematic, rotation of S Hmax azimuths in this part of eastern Australia as well as systematic changes in stress state with depth. Overall, the geomechanical state of the region appears to reflect the interplay between basin-controlling structures and a complex far-field stress regime. At the reservoir level, within and between Permian coal seams, this stress complexity is reflected in highly variable stress states both vertically and laterally. Stress data, including direct pressure measurements and observations of borehole failure in image logs, have been used to calibrate sonic-derived one-dimensional wellbore stress models that consistently exhibit a change in tectonic stress regime with depth. Shallow depths (&lt;600 m) are characterized by a reverse-thrust stress regime and deeper levels are characterized by a strike-slip regime. Changes in the stress state with depth influence the mechanical stratigraphy of rocks with widely contrasting mechanical attributes (coals and clastic sediments). Our results highlight the interdependency between regional tectonic, local structural and detailed rheological influences on the well scale geomechanical conditions that have to be taken into consideration in drilling and completion designs. Supplementary material: Database of additional wells with image log data are available at https://doi.org/10.6084/m9.figshare.c.3785849

Natural fracture distribution and a new method predicting effective fractures in tight oil reservoirs in Ordos Basin, NW China

Abstract Based on core, imaging logging, and thin section data, the distribution features of natural fractures in the tight oil reservoirs of the Ordos Basin are examined. The tight reservoirs in the Ordos Basin are rich in natural fractures, the fractures are mainly high-angle structural shear fractures in continuous step arrangement. Affected by rock mechanical anisotropy and present stress field, the NE trending fractures are the dominating seepage flow direction. These fractures feature high angle, small cutting depth, small aperture and short extension, controlled by rock lithology and single layer thickness in development degree, natural fractures are most developed in fine siltstone, most undeveloped in mudstone. The thinner the single layer, the more developed the natural fractures will be. Based on distribution features of natural fractures and quantitative evaluation of natural fracture characteristic parameters, by using reservoir matrix and natural fracture geologic modeling, a comprehensive reservoir geologic model considering natural fractures was built, by using reservoir numerical simulation modeling inversion, the plane distribution of effective natural fractures was found out, and the contribution of natural fractures to single well production was quantitatively evaluated at around 30.0%−50.0%. The research results are of great significance for well-pattern deployment and optimization of development technical policies of similar reservoirs.

Reconciling Log-Derived Water-Saturation and Saturation-Height Function Results

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 175053, “Reconciling Log-Derived-Water-Saturation and Saturation- Height-Function Results Through Resistivity Modeling, Core-Log Integration, and Image-Log Data: A Case Study From Deepwater Gulf of Mexico,” by Javier Miranda, Michael Rabinovich, Jeffry Hamman, and Maryam Mousavi, SPE, BP, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. Saturation-height functions (SHFs) play a key role in reservoir description and in quantifying oil in place. The functions must compare well with other sources of water saturation (Sw), such as core measurements and well-log interpretations, when they are available. The authors have reconciled different Sw sources through a reliable SHF function based on the Brooks-Corey model with parameters optimized for the Gulf of Mexico (GOM) Thunder Horse (TH) Field. The function is used to populate oil volumes in the 3D static and dynamic models. General Description of the Hydrocarbon Field TH is located in a six-block “lease unit” of the Mississippi Canyon (MC) area of the deepwater GOM. The field is approximately 69 miles from the Louisiana coastline in water depths ranging from 6,000 to 6,500 ft. The TH facility consists of a taut-wire-moored semisubmersible system with production, drilling, and quarters (PDQ). The PDQ is located near the southern boundary of MC 778. The PDQ is designed to handle 250,000 BOPD, 200 MMscf/D, and 140,000 B/D of produced water. The facility was also designed to handle 300,000 B/D of mixed seawater/produced water for injection. The TH wells are located in subsea drill centers, with additional satellite subsea-production wells located where the reservoir structure dictates. Sixteen producers have been brought on line since first oil on 14 June 2008. The total volume produced as of the end of 2014 is estimated at 300 million BOE. Oil and water rates (December 2014) are 100,000 BOPD and 26.500 BWPD, respectively. The TH discovery contains hydrocarbon resources in two structural closures commonly referred to as the TH South (THS) and TH North (THN). TH Reservoir Distribution and Architecture. The current depositional model for TH is that all three reservoir intervals are part of a stacked sequence of Miocene lower slope aprons. In a general architectural model for a single slope apron, the proximal region is dominated by amalgamated channels, bypass lags (acting as baffles and barriers), and lateral complexity. Net/gross ratio (NTG) can vary significantly in the proximal region, depending on the distance to sediment sources. The medial portion of the apron is dominated by more-sheet-like sands interspersed with the occasional silt- or mud-rich unit, and the distal portion of the apron is dominated by interlayered sand, silt, and mud units. In a vertical sequence, the apron model leads to an increase in system energy and channelization from bottom to top. After the apron healed the terrain, sediments began bypassing down the slope and were able to erode into the apron itself. This led to the formation of canyons and canyon-fill successions that segmented the original reservoirs and yielded isolated compartments and major production barriers.

Fractured zones detection using conventional petrophysical logs by differentiation method and its correlation with image logs

Abstract Evaluation of reservoir structure and fracture zones is necessary in oil production optimization and field development. The purpose of this study is to find a quick method for identification of fractured zones using petrophysical logs, which are available in all wells, and then use the Velocity Deviation Log (VDL) to identify fracture aperture opening and their effects on porosity and permeability. The result shows that some parameters, such as lithology and reservoir fluids, affected on petrophysical logs, but fracture zones can be determined using conventional logs with logs corrections by mathematical methods, such as differentiation, which has great correlation with image logs. Results show that zones with high fracture density can be easily recognized by first stage of differentiation on petrophysical logs. Also among fracture parameters, fracture aperture has the most effect on logs. To check the results, other data, such as mud loss data, thin section and VDL log, were used to support our interpretation. Based on VDL log, the production in the Asmari reservoir in this field is a combination of fractures and rock matrix. In addition, fractures and porous zones have had a great impact on the reservoir rock properties. RHOB, NPHI, GR, DT, PEF, and CAL logs used in this study, and they are the best types of logs that can be used in the identification of fracture zones and will be used for old wells without image log and core data. Based on their responds in fractured zones and correction on responds, they can be used to detect fractures. In this method, understanding of structure and stratigraphy of the studied field is important as well as mathematical and software knowledge in fractured zones identification. Finally, the knowledge of geology of the field is necessary for all petrophysical analyses as well as interpreting the fracture zones.

Sedimentary microfacies and palaeogeomorphology as well as their controls on gas accumulation within the deep-buried Cretaceous in Kuqa Depression, Tarim Basin, China

The gas and oil exploration in Kuqa Depression has entered the deep-buried and ultra-deep areas below 5000 m. This paper represents the systematic research accomplished which included microfacies observation and sandstone modeling in the outcrop, the lithofacies interpretation with imaging logging data, and the recovery of nappe tectonics as well as the folding analysis based on the single sedimentary factors in order to define the characteristics of lithofacies and microfacies, the background of paleography and their effects on gas accumulation. This study illustrated that the climate was mainly hot and dry during the sedimentary period of Bashijiqike within the deep-buried Cretaceous, and the deposited water was characterized by low to medium salinity. The deep-buried areas were controlled by three provenances, namely, the Kapushaliang River, the Kelasuhe River, and the Kuqa River. The Dabei-Bozi area was mainly the proximal deposit, the silty-fine sandstone with subrounded and well-sorting features developed in the main channel areas of underwater distributary channel which was constructed in the braided (or fan) delta front. The Keshen area, on the other hand was the distal deposit, the medium-fine sandstone with subangular-subrounded and medium-well sorting features developed in the main channel areas of underwater distributary channel which was constructed also in the braided (or fan) delta front. In the latter stage of the Yanshanian Period, the silty-fine sandstone of the underwater distributary channel had developed with the background of residual palaeohigh and drought climate in Dabei-Bozi area-meanwhile the medium-fine sandstone of the underwater distributary channel had developed with the background of residual palaeohigh slopes and humid climate in Keshen area. In addition, the gas accumulation within the deep zone was evidently controlled by the lithofacies paleography. The gas in the medium-fine sandstone lithofacies of paleoslope was significantly richer than the silty-fine sandstone lithofacies of the paleohigh; the silty lithofacies in the paleohigh was relatively poor. It was supposed that systematic studies would accelerate the oil and gas exploration and development in the deep zones, not to mention provide guidance for the trillion cubic prospects of gas reserves in the deep zones.

A logging identification method of tight oil reservoir lithology and lithofacies: A case from Chang7 Member of Triassic Yanchang Formation in Heshui area, Ordos Basin, NW China

Abstract Based on the observation results of cores, structural analysis, sedimentary microfacies analysis, lithologic analysis and other analytical tests and logging data, the characteristics of lithology and lithofacies of the Member Chang7 tight oil reservoir of the Triassic Yanchang Formation in Heshui area are described and summarized and the criteria for identification of lithology and lithofacies by logging are established. The lithofacies in the Chang7 tight oil reservoir were classified into five types: fine sandstone deposited by sandy debris flow, turbidite fine siltstone, fine sandstone deposited by slump, semi-deep to deep lacustrine mudstone, and oil shale. The lithology and lithofacies in the Chang7 tight oil reservoir were characterized, both qualitatively and quantitatively, with electric logging and imaging logging and several means and methods, the response characteristics of different lithology and lithofacies were summarized through analyzing the image log and conventional log data, and the parameters characterizing sandstone's structures were used to quantitatively characterize the lithology and lithofacies, the criteria for identification of different lithology and lithofacies by logging were established. The vertical and horizontal identification and classification of lithology and lithofacies in a single well was then accomplished by processing the log data from each well, the results of lithology and lithofacies identification tally well with the results of formation testing. In-depth lithology and lithofacies analysis proves to be an important method of tight oil reservoir evaluation and “sweet spot” prediction.

Integration of Pressure-Transient Data in Modeling Tengiz Field, Kazakhstan—A New Way To Characterize Fractured Reservoirs

Summary A systematic work-flow to integrate pressure-transient data collected from single-well buildup tests in numerical reservoir-simulation models for a fracture/matrix system is presented. The results of its application in a sector model in the southeast region of Tengiz field in Kazakhstan are also discussed. The procedure starts with a selected numerical-simulation model, either a discrete fracture/matrix (DFM) model or a dual-porosity dual-permeability (DPDK) model, and follows with the analysis of a numerically generated buildup test to calculate the fracture spacing and shape factor of the model. Then, following the correlations between pressure-transient-analysis results and the average or representative values of the model-input parameters near the well, which contain the previously obtained fracture spacing and shape factor, the numerical-model parameters are adjusted in each iteration to match the pressure-transient behavior observed in the buildup test including the interporosity flow between matrix and fracture and the radial flow in the total system. Before field application, the numerical-simulation results from both DFM and DPDK models were validated against analytical pressure-transient solutions for a dual-porosity system. The gridding and time-steps were calibrated to reproduce the analytical transient behavior. Finally, the new work-flow was applied to a sector model of Tengiz field in the southeast region focusing on two wells. Following the developed work-flow, a DFM model was constructed, and its fracture and matrix properties were adjusted to honor buildup-test data at both wells and the transient data collected during a pulse test conducted between them. The study results show that the key factors of a DFM model on buildup transient response are the fracture permeability, fracture aperture, and matrix permeability in the well-drainage area, and the dominant parameters on pulse-test response are the fracture permeability and matrix porosity in the influence area between the two wells. Using the correlations quantitatively for each simulation step could reduce the total number of iterations needed to converge to the numerical solution. The modified model also generated flow distribution along the wellbore, consistent with production-logging data at one well. The resulting sector map of pressure change during buildup test indicates the area with well-connected fracture network. Dynamic transient data contain rich information about reservoirs, and the effective integration of dynamic and static data would have a big impact on reservoir management by potentially minimizing the number of wells to be drilled, maximizing the production, and optimizing recovery. The novelty of this study is the quantitative use of the correlations between pressure-transient-analysis results and the representative values of the input parameters in a numerical model to reduce the number of simulation iterations. Its application in Tengiz is also one of the rare examples in which single-well and multiple-well transient data, production logging, and image-log data are all available.

Discussing the internal structural characteristics of coal seams using electrical microresistivity image logging data

This paper summarises the response characteristics of electrical microresistivity image logging on different coal seam structures through systemic pectination from Qinshui Basin in Central China. We use these characteristics to describe the internal structure characteristics of coal seams. The results show that image logging is a good way to provide reliable information for many aspects, such as the division of coal seams, deformed soft coal, the internal structure of coal seams, and so on. Coal seams with a layered structure are commonly shown to be relatively homogeneous orange-yellow (2,700-3,900 &omega;·m) and to have clear lamination characteristics of dark and tan strips (800-1,500 &omega;·m) inside. The layered-block structure is mainly shown in bright yellow (3,300-3,600 &omega;·m) and has few dark stripes (800-1,200 &omega;·m). The block structure is shown as bright yellow-white (3,300-4,800 &omega;·m). The partings show up as clear and complete dark stripes (800-1,200 &omega;·m) in images. The layers in which deformed soft coal develops normally have irregular fractures and present dark stripes of dark grey strata (1,000-1,500 &omega;·m) in image logs [Received: June 17, 2014; Accepted: April 7, 2015].

FRACTURE MODELING IN OIL AND GAS RESERVOIRS USING IMAGE LOGS DATA AND PETREL SOFTWARE

The purpose of modelling the fractures is to create simulation properties with the power to predict the reservoir behaviour. Petrel software is one of the best softwares in the market that can do this task very well, but there is no available educational paper for every researcher. Therefore, in this work, a fracture modelling job was done in one of the most important Iranian fields using Petrel software and image log data. The purpose of this work was to determine the new information of the fractures in Gachsaran field and also to prepare a valuable educational paper for other researchers who are interested to learn about the fracture modelling. This work revealed that in this field, the longitudinal fractures had been parallel to minimum stress (Zagros trend), fracture intensity was the nearest to the major fault and northern flank, fracture porosity was 0-7%, fracture permeability was 0-6000 MD, and more valuable information is provided in this paper.