Quantifying Horizontal Well Logs in Naturally Fractured Reservoirs-I (original) (raw)
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SPE 22932 Quantifying Horizontal Well Logs in Naturally Fractured Reservoirs-II
Naturally fractured reservoirs are the most significant target for horizontal wells in the U. S. While most of the horizontal wells drilled to exploit naturally fractured reservoirs are not logged. substantial useful information can be obtained by logging such wells. A previous paper! contrasted various logging technologies including acoustic televiewers. sonic logs, and oriented microresistivity devices. Union Pacific Resources (UPRC) has logged 42 of the 120 horizontal wells drilled to date; 38 of these wells have been logged with Schlumberger's Formation MicroScanner (FMS), an oriented microresistivity device. Extensive analysis of these logs on UNIX-based workstations and correlation with horizontal well performance has resulted in a correlation between the horizontal well fracture index (RFI) and horizontal well fluid Productivity Index (PI). Attempts to correlate RFI with ultimate oil or oil and gas recoveries have been unsuccessful; however. a correlation with ultimate fluid (oil+water) recoveries has been developed. These correlations have been used to integrate FMS infonnation with artificial lift. stimulation, isolation, and repair decisions as well. Example cases are used to illustrate these decisions. Further. the quantified data have been used in making development. exploitation, and spacing decisions. Geostatistical techniques used in reservoir characterization efforts have also incorporated the spatial distribution and correlation of RFI density.
Integration of Horizontal Well Log Information in Fractured Reservoir Characterization
Representation of reservoir heterogeneity for simulation models is one of the most challenging aspects of reservoir engineering. Naturally fractured reservoirs present. an exceptionally difficult challenge in this respect. Vertical wells provide extremely limited information about the spatial distribution of fractures and fracture density as the hole size is small with respect to the characteristic spacing and distribution of natural fractures. Vertical wells fail to provide short scale (up to interwell distance) correlation information for geostatistical models in any type of reservoir. Outcrop representations of fracture distribution are generally inadequate and fail to correspond to in situ fracture characteristics. Formation evaluation in horizontal wells can provide both detailed information on fracture distribution and short-scale correlation information. This information can be integrated with geostatistical tools such as Sequential Indicator Simulation (SIS) models to provide much more realistic reservoir descriptions. These reservoir descriptions result ill dramatically improved simulation matches. Further, this reservoir characterization technique can explain behavior that is far more difficult to explain with conventional and dual-porosity models.
IDENTIFICATION AND CHARACTERIZATION OF NATURALLY FRACTURED RESERVOIRS USING CONVENTIONAL WELL LOGS
In petroleum exploration and production, fractures are one of the most common and important geological structures, for they have a significant effect on reservoir fluid flow. Despite their importance, detection and characterization of natural fractures remains a difficult problem for engineers, geologists and geophysicists. This paper presents a technique for the identification and characterization of naturally fractured reservoirs using conventional well logs. Logs are the most readily available source of information, however they are seldomly used in a systematic manner for quantitative analysis of naturally fractured reservoirs. Since all well logs are affected in one way or another by the presence of fractures, a Fuzzy Inference System is implemented in this study to obtain a fracture index using only data from conventional well logs. Additionally, a self-consistent model from O'Connell and Budiansky for the prediction of elastic properties of fractured porous rocks is inverted using genetic algorithms to obtain crack density and crack aspect ratio. The proposed algorithms are tested using data available from the Mills McGee # 1, an Austin Chalk formation well in Milam County, Texas. The results obtained are compared with core information available.
Analytical Fractured Reservoir Characterization by using Geological and Petrophysical Logs
Current Research in Geoscience, 2022
Analytical Fractured Reservoir Characterization by using Geological and Petrophysical Logs Zohreh Movahed1 and Farzaneh Aghajari2 1 Faculty of Petroleum and Renewable Energy Engineering, Springer, Karun Energy and Teleperformance, University Teknologi Malaysia - UTM, Malaysia 2 Department of Geology, National Industrial Cluster Program, Iran Abstract Due to structural complexities in some wells, higher than the expected thickness of the Asmari formation is found. Fracture intensity and deep-rooted fractures broadly increase the risk of unpredictable water production. The well-test analysis is not sufficient in describing fracture properties. Unfortunately, the core condition is poor in the fractured zones and cannot be used to provide reliable information. So, the objectives of this study are developing an accurate structural model for the Asmari reservoir, and fracture characterization in the borehole by interpreting image logs and comparing the log's image results with core data. Dip classification based on a geological log has the value of providing a direct demonstration of structural origin and detecting Asmari fault and fracture systems and their impact on production and answering structural issues. So, in this study, the borehole imaging tools were interpreted to find solutions for fracture systems and fracture attributes. Interpreting accurate structural dip determined the structural problem, thus bringing the precise location of the well within the Asmari reservoir. Fracture properties (open or closed), occurrence, orientation, spacing, and porosity were interpreted using an Image log. The high density of fractures seen on FMS image logs in the study well has been confirmed by inspection of the cores and the distinction between major and minor fracture types from the FMS image logs has been established following core review. As a result, this exercise has been confirmed to be very valuable, not only for indicating the value of the log data, but it has also emphasized some significant limitations of the core data. The amount of information extracted from the FMS image logs goes beyond that achieved from the core. This exercise has validated why image logs are the main source of fracture information in the oil fields of Iran. Current Research in Geoscience Volume 12 No. 1, 2022, 11-28 DOI: https://doi.org/10.3844/ajgsp.2022.11.28 Submitted On: 18 July 2022 Published On: 3 December 2022 How to Cite: Movahed, Z. & Aghajari, F. (2022). Analytical Fractured Reservoir Characterization by using Geological and Petrophysical Logs. Current Research in Geoscience, 12(1), 11-28. https://doi.org/10.3844/ajgsp.2022.11.28 Open AccessCopyright: © 2022 Zohreh Movahed and Farzaneh Aghajari. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Characterizing natural fractures productivity in tight gas reservoirs
Journal of Petroleum Exploration and Production Technology, 2012
Tight formations normally have production problems mainly due to very low matrix permeability and various forms of formation damage that occur during drilling completion and production operation. In naturally fractured tight gas reservoirs, gas is mainly stored in the rock matrix with very low permeability, and the natural fractures have the main contribution on total gas production. Therefore, identifying natural fractures characteristics in the tight formations is essential for well productivity evaluations. Well testing and logging are the common tools employed to evaluate well productivity. Use of image log can provide fracture static parameters, and welltest analysis can provide data related to reservoir dynamic parameters. However, due to the low matrix permeability and complexity of the formation in naturally fractured tight gas reservoirs, welltest data are affected by long wellbore storage effect that masks the reservoir response to pressure change, and it may fail to provide dual-porosity dual-permeability models dynamic characteristics such as fracture permeability, fracture storativity ratio and interporosity flow coefficient. Therefore, application of welltest and image log data in naturally fractured tight gas reservoirs for meaningful results may not be well understood and the data may be difficult to interpret. This paper presents the estimation of fracture permeability in naturally fractured tight gas formations, by integration of welltest analysis results and image log data based on Kazemi's simplified model. Reservoir simulation of dual-porosity and dual-permeability systems and sensitivity analysis are performed for different matrix and fracture parameters to understand the relationship between natural fractures parameters with welltest permeability. The simulation results confirmed reliability of the proposed correlation for fracture permeability estimation. A field example is also shown to demonstrate application of welltest analysis and image log data processing results in estimating average permeability of natural fractures for the tight gas reservoir.
Geophysical Well Logging- a Contribution to the Fractures Characterization
2015
The need of a proper reconstruction of faults and fracture systems crossed during the well drilling is one of the most important feature for the deep exploration of a geothermal reservoir. The geophysical well logging have been always utilized for geological and stratigraphic determinations, for the measurement of the main physical characteristics in order to provide calibration parameters for the surface geophysical surveys and for a qualitative localization of fractured and potential productive layers. Recent and specialized techniques and sensors for the detection of geometrical-structural parameters are now widely used. One of them, the Circumferential Borehole Imaging Log (CBIL), when utilized for potential fractured layers already tagged by other techniques (as acoustic Wave Forms), has been proved as very effective and detailed. We applied a complete set of this techniques in a deep well of the Larderello-Travale geothermal field, and a detailed analysis and characterization ...
Quantifying Porosity and Estimating Permeability from Well Logs in Fractured Basement Reservoirs
All Days, 1995
Low porosity fractured reservoirs have been successfully described using a combination of high resolution geometrical information from borehole images together with deeper penetrating log evaluation methods. Borehole images from acoustic or electrical scanning tools provide statistics of fracture distribution, first order estimates of fracture opening and porosity, and a basis for geological inference. Their drawback is that, in this environment, the events on the images bear a strong overprint of the drilling process. Deeper penetrating but lower resolution techniques such as Stoneley wave reflectance and deep resistivity log inversion are used to distinguish the deep and permeable fractures that may contribute to flow. By making some assumptions about the nature of the porosity in basement reservoirs we develop a new method to estimate the porosity and the fraction of this porosity due to fractures. This method makes use of the Kuster-Toksoz acoustic scattering model and requires ...
Sensitivity of fractured horizontal well productivity to reservoir properties in shale-gas plays
2013
This research presents an investigation of the sensitivity of fractured horizontal well performances to reservoir properties in ultra-tight, naturally fractured shale-gas reservoirs under depletion. The method of the research is analytical. Following a general review of the existing literature on well performances in unconventional tight reservoirs, the analytical trilinear flow model developed by Ozkan et al. (2011) is introduced. The original dimensionless trilinear flow solution in Laplace domain is converted to dimensional form to be used in productivity index calculations. The productivity of fractured horizontal wells in shale-gas plays is discussed in terms of transient productivity index defined by Araya and Ozkan (2002). For the purposes of this research, the stimulated reservoir volume (hydraulically fracturing the horizontal well in order to create pathways from the induced fractures towards the existing naturally fractured reservoir, creating either a complex network of fractures through hydraulic fracturing, or rejuvenating the existing healed fractures to create an effective stimulation zone around the well) assumption is implemented. This assumption, commonly used for shale-gas wells, limits the drainage of the well to the stimulated volume around the well and strongly influences the average pressure to be used in productivity computations. Derivation of the average pressure relationship for the dual-porosity (naturally fractured) stimulated reservoir volume is presented and the expression for the average pressure is combined with the transient trilinear flow solution to obtain a relation for the transient productivity index. As a means of investigating the iv sensitivity of productivity to a selected set of reservoir properties, the derivatives of the productivity index with respect to these properties are derived. The results of the research are presented in three forms: (i) productivity index versus time for the low, base, and high values of the selected property and the productivity index versus the change in property value at selected times, (ii) tornado charts indicating the sensitivity of the productivity index to the selected properties at different times, and (iii) change in productivity index (derivative of productivity index) with the variation of the selected properties. The results indicate that, unlike the common expectation, the productivity of the fractured horizontal wells in shale-gas plays is not very sensitive to the permeability of the natural fractures in the stimulated reservoir volume and/or the distance between hydraulic fractures. The permeability of the shale matrix and the density of the natural fractures in the stimulated reservoir volume, on the other hand, influence productivity by 600% and 300% respectively. The hydraulic fracture permeability and half-length appear to moderately influence productivity on a 5% to 20% range. These results should be useful to guide well completion in shale-gas plays, and the sensitivity analysis provided in this thesis should be useful for engineering analysis of projects. v
SPE Drilling & Completion, 1999
Summary In this article we discuss drilling mud losses in naturally fractured reservoirs with fracture permeability larger than 50 odd md and much larger than the matrix permeability. Type curves are provided that describe mud loss volume vs. time and allow the determination of the hydraulic width of natural fractures through the usual type curve matching technique of log/log plots. Real time logging while drilling of natural fracture width permits the proper selection of loss-circulation material (LCM) with respect to particle size distribution. Efficient (rapid) mud loss control is made possible, increasing the chances of minimizing fracture damage by the drilling mud, the cuttings and the LCMs themselves. The total mud losses experienced when drilling a long horizontal section are shown to agree with reservoir properties (derived by well testing) in particularly well-documented examples of the central North Sea. The equations provided can therefore be utilized as well by reservoi...
Analytical Fractured reservoir characterization by using geological and petrophysical log
Background and Objectives: Due to structural complexities in some wells, higher than the expected thickness of Asmari formation is found. Fracture intensity and deep-rooted fractures broadly increase the risk of unpredictable water production. The well test analysis is not sufficient in describing fracture properties. Unfortunately, the core condition is poor in the fractured zones and cannot be used to provide reliable information. So, the objectives of this study are developing an accurate structural model for Asmari reservoir,fracture characterization in the borehole by interpreting image logs ,and comparing the log's image results with core data.Materials and Methods: Dip classification based on a geological log has the value of providing a direct demonstration of structural origin and detect Asmari fault and fracture systems and its impact on production and answer structural issue. So, in this study, the borehole imaging tools were interpreted to find solutions for fracture...