Ian D Stowe - Academia.edu (original) (raw)
Nationality: British
Born: 23 May 1951, Birmingham, England
Marital Status: M0
Degree: BA(Hons) Physics, Oxford, 1974, Honorary MSc
Joined Schlumberger: 1974
Field Expereince:
Field engineer Brunei, Egypt 1975-1977
Production logging, Formtion tester & cased hole specialist Egypt, Iraq, Iran, Saudi Arabia 1977 - 1979
Interpretation:
Log Anaylst Petrophysics, production logging and special projects Saudi Arabia 1979 - 1982
Interpretation Support & New Tools Evaluation & Interpretation, Paris 1982 -1985
Client Consultant/Petrophysicist, field studies, Hanover, 1985-1989
Senior Log Analyst for North Sea, London - 1989-1991
Petrophysics tutor for Schlumberger Log Analyst Training 1991
Tutor and world-wide Training Co-ordinator for Schlumberger Data Services, Paris 1992-1994
Future Product Marketing , Data Service Center Products, GeoQuest Houston, 1995-1997
Section Manager, Drilling Planning & Interpretation, Petrophysics software, Schlumberger Product Center, Sugar-Land, 1997-2000
Manager software outsourcing for Sugar Land Product Center, India, 2000-2001
Manager Petrophysics Beijing Geoscience Center, China, 2001-4
Manager Geomechanics Beijing Geoscience Center, China 2005
Manager Well Placement Construction and Stability, Beijing Geoscience Center, China 2005-6
Scientific consultant to Schlumberger on Geology, Petrophysics, software process & practice 2008-2011
Petrophysics Advisor on largest field study Schlumberger has undertaken. Confidential, Jan-July 2009
Member of SPWLA and SPE 1982-2007.
Co-chair leader of Schlumberger’s Eureka Reservoir Characterization community 1999-2003 (3 terms).
Schlumberger Scientific Advisor for Reservoir Characterization 2004-2007
Retired and acted as consultant to Schlumberger Beijing Geoscience Center December 2006-2011
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Papers by Ian D Stowe
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Annual Technical Conference and Exhibition, 1984
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Middle East Oil and Gas Show and Conference, 2007
A method, system and computer program product for invert- ing boundary conditions for rock mass f... more A method, system and computer program product for invert-
ing boundary conditions for rock mass field in-situ stress
computation for a geologic structure are disclosed. According
to an embodiment, the current invention includes a method
for inverting boundary conditions for rock mass field in-situ
stress computation for a geologic structure, the method com-
prising: considering physical constraint of the geological
structure; deriving and solving normal equations of penalized
weighted least squares, said normal equations of penalized
weighted least squares partially representing said physical
constraint of the geological structure; and outputting bound-
ary conditions and reproducing the rock mass field in-situ
stress based on the result of said solved normal equations of
penalized weighted least squares.
The present invention generally relates to the logging of earth formations, and more particularly... more The present invention generally relates to the logging of earth formations, and more particularly to methods and apparatus for formation characterization using logging tool responses corresponding to logging measurements.
Wireline tools have been employed to obtain formation measurement. In certain prior art apparatus, induction-logging instruments are susceptible to a variety of environmental effects due to considerable range of investigation. Therefore, to make useful logs, the effects of volume above and below the layer of the interest must be carefully removed. In practice, the Array Induction Imager (AIT) or AIT-family tools are popular in moderate conductive to oil-based-mud logging environment. The AIT tool consists of eight three-coil arrays, six of which are operated simultaneously at two frequencies (AIT-B) or one frequency (AIT-H/M family). The AIT tool can produce wellsite resistivity logs having high resolution and high rejection of borehole rugosity effects. For example, these tools can produce logs that are corrected for the most common environmental effects, e.g. borehole effect, shoulder effect, skin effect, et al.
However, such tools typically need a wellsite post-processing to remove the environmental effects. Due to the high requirement of processing speed at well-sites, as well as the difficulty in quantifying the logging measurement error, the post-processing typically is based on Gaussian error assumption and least-squares inversion, thus the post-processed result is Gaussian mean value. In reality, however, the Gaussian error assumption is not always correct, thus the traditional post-processed result might not be ideal either. For example, if the Gaussian error assumption is violated, AIT 10, 20, 30 60 and 90-in curves can behave strangely, either formation inhomogeneity or vertical bedding being overlooked, or the separation of the five curves can not be explained from logging environment information. In such situation, the traditional AIT well-site post-processing result cannot provide accurate indication of formation characterization.
Wireline openhole formation evaluation has been the standard in petrophysics and quantitative res... more Wireline openhole formation evaluation has been the standard in petrophysics and quantitative reservoir evaluation for many years. During the last five years we have witnessed a migration of some of the basic, high-quality openhole services to cased hole logging applications. One major challenge remains: measuring the formation-bulk density in cased hole environments.
Several feasibility studies have indicated that under favorable casing-cement conditions density measurements are sufficiently sensitive to the formation bulk density in cased holes. Some experimental cased-hole-logging tools were developed to exploit this sensitivity; however, none of these experimental prototypes has been developed into a commercial service.
This study analyzes the response of a three-detector wireline density tool to formation density in cased wells. The tool response was experimentally measured in density blocks and in controlled test-tank conditions for a variety of formations, casing, and cement parameters. This new formation-density measurement has successfully been used in a number of cased wells. Under favorable casing-cement conditions the data agree with the openhole density logs within their accuracy. Several log examples illustrate this good agreement.
Logging operations and log-quality-control flags are adapted to the more difficult cased hole environment. The logging speed is reduced to compensate for the reduced count-rate statistics. The photoelectric-effect (Pe) log cannot be used for lithology identification, but serves to estimate the casing thickness. The thin-bed resolution is slightly impaired. Yet, the resulting formation-bulk-density log has proved to be a quantitative formation-evaluation measurement that is readily com-
bined with the other cased-hole formation-evaluation services to give a comprehensive formation description.
Sometimes the cement thickness behind the casing may exceed a cut-off threshold. In this case, complementary nuclear-porosity logs can be used to substitute the density measurement with a porosity-inferred density.
The success of Rotliegend gas exploration in North-Western Germany at depths between 4000 and 500... more The success of Rotliegend gas exploration in North-Western Germany at depths between 4000 and 5000 m is dependent on the depositional environment but more significantly on the degree of diagenetic alteration encountered in the Rotliegend sandstones. Some sandstones are not productive due to the lack of primary porosity caused by poor sorting and/or high clay content or the anhydrite cementation in sabkhas and erg deposits. Nevertheless, even originally porous aeolian sandstones or shoreline sands are often unproductive, due to the diagenetic cementation of the pore space by illite meshwork, kaolinite, carbonates (predominantly calcite) or quartz.
The core coverage in Rotliegend sequences is usally rather poor (on average about 10% of the total thickness) due to the enormous thickness of these sediments and the high cost of coring. Therefore, the obvious method to obtain facies information for uncored intervals and wells is the use of logs, since logs cover the entire Rotliegend interval. Furthermore, logs are acquired on a routine basis for petrophysical evaluation and contain much lithological information.
The value of openhole logs for facies analysis has been demonstrated in Zechstein carbonates of Northern Germany (Stowe and Hock 1988). The following discussion outlines an equivalent methodololy for Rotliegend sequences.
Recent technological progress requires a fundamental review of the approach to quantitative log i... more Recent technological progress requires a fundamental review of the approach to quantitative log interpretation. A modern and advanced interpretation must be able to combine both quantitative and qualitative information from different sources, of different natures and at different scales. It should no longer focus only on solution of n equations of m unknowns with purely petrophysical goals.
The recent introduction of imaging techniques has created a breakthrough in reservoir characterization. Because the reservoir can now be seen, it is possible to describe it in great detail as a three-dimensional organization of geological objects which are themselves classified as volumes, with their corresponding facies, bounded by surfaces with their own transmissivity properties.
Petrophysical properties control the volume flow properties. The latter depend on the depositional facies attributes and the diagenetic effects undergone by the sediment since its deposition. They can be determined partly from standard logs, but more fully from borehole images that provide fundamental information about the reservoir anisotropy and the nature and distribution of reservoir heterogeneities.
Surface attributes are defined through the shape, planarity, rugosity, extent, angular relationship, resistivity contrast, etc., of the surface. Practically all surfaces crossing a wellbore may be classified as they are detected by electrical imaging techniques from which their nature and origin can be precisely determined. Based on their origin and resistive characteristics transmissivity properties can be assigned to them. In addition, the influence of apparent dip can be taken into account in the response function of other tools.
A modem and complete interpretation must, as far as possible, take into account all the accessible attributes at different scales, and from them determine the dynamic attributes associated with the reservoir.
In addition, one can say that a succession of facies and surfaces defines a genetic sequence, itself limited by breaks of hierarchy and extent, and characterized by a set of attributes. A sequence and succession of sequences allow the recognition of the depositional environment that, consequently, has itself a set of attributes of higher rank, including seismic attributes. Finally, the reservoir geometry may be inferred from the determination of the depositional environment and the tectonic structure.
The solution of this new truly global and integrated approach can be achieved through a generalization of the electrofacies concept. This is illustrated by examples.
Sedimentary facies and their diagenetic equivalents in Zechstein carbonates and adjacent evaporit... more Sedimentary facies and their diagenetic equivalents in Zechstein carbonates and adjacent evaporites are determined from wireline logs using a petrophysical database calibrated in 14 key wells. The selected key wells have between 8 and 10007o core cover with 49070 on average, and a logging suite consisting of density, neutron, photo-electric factor (Pe), sonic, gamma ray, deep, shallow and micro-resisitivity logs. The database was constructed in three major steps: (A) A volumetric analysis including mineralogic composition, porosity and saturations was computed using an iterative minimisation program and checked against petrophysical core data, petrographic data provided by core description, and mineralogical data based on micorscopy and x-ray analysis. Principal minerals were calcite, dolomite, anhydrite, and halite, with occasionally significant amounts of potassium salts, pyrite, clay, sulfur and bitumen. Gas corrections based on the calculated saturations were used to normalize the logs for each key well. (B) T h e gas-corrected log data were then grouped using a cluster analysis of their principal components to obtain electrofacies for each single well. These electrofacies were matched with geological facies defined from the petrographic core descriptions. (C) L o g data values of similar electrofacies from the individual key wells were plotted in 10 two-dimensional multiwell-crossplots. To avoid ambiguities produced by the cluster analyses an independant five-dimensional ellipsoid was created from the multiwell-crossplots for each geological facies. The defined ellip-soids were combined to form a petrophysical database. In general the following carbonate facies with significant differences in log responses are distinguished based on different mineralogy and porosity types: — replacement dolomites such as mudstones, mouldic mudstones, wacke-, grain-and packstones, which show a curved density/neutron response; — replacement and recrystallized dolomites as above, but evaporite cemented with anhydrite and/or halite; — dedolomites including layered, nodular (concretionary), vuggy types and calcite-cemented grainstones;-limestones divided into micrites, sparitic mudstones, wacke-and grainstones. Petrophysically significant traces of minerals such as pyrite and evaporite mixes also require separate ellip-soids, resulting in 48 carbonate and 24 evaporite lithofacies. The correctness of the database was verified on three cored test wells. Evalutation using old logging suites consisting of density, sidewall or gamma-ray neutron, gamma ray, sonic and laterolog seven is now also performed. Routine application of the database provides complete facies descriptions in uncored sections and wells for use in geological profiles and facies maps.
Sedimentary facies and their diaeenetic equivalents in Zechstein carbonates and adjacent evaporit... more Sedimentary facies and their diaeenetic equivalents in Zechstein carbonates and adjacent evaporites are determined from wireline logs using a petrophysical database calibrated in 14 key wells. The selected key wells have between 8 and 100% core cover with 49% on average, and a logging suite consisting of density, neutron, photo-electric factor (Pe), sonic, gamma ray, deep, shallow and micro-resistivity logs. The database was constructed in three major steps: (A) A volumetric analysis including mineralogical composition, porosity and saturations was computed using an iterative minimisation program and checked against petrophysical core data, petrogt-aphic data provided by core description, and mineralogical data based on microscopy and X-ray analysis. Principal minerals were calcite, dolomite, anhydrite and halite, with occasionally significant amounts of potassium salts, pyrite,clay, sulfur and bitumen. Gas corrections based on the calculated saturations were used to normalize the logs for each key well. (B) The gas-corrected log data were then grouped using a cluster analysis of their principal components to obtain electrofacies for each single well. These electrofacies were matched with geological fades defined from the petrographic core descriptions. (C) Log data values of similar electrofacies from the individual key wells were plotted in 10 two-dimensional multiwell-crossplots. To avoid ambiguities produced by the cluster analyses an independant five-dimensional ellipsoid was created from the muldwell-crossplots for each geological facies. The defined ellipsoids were combined to form a petrophysical database. In general the following carbonate fades with significant differences in log responses are distinguished based on different mineralogy and porosity types:-replacement dolomites such as mudstones, mouldic mudstones, wacke-, grain-and pacicstones, which show a curved density/neutron response;-recrystallized dolomites derived from successive microsolution, accretive crystallization and subsequent compaction, which show a straight line response in the density/neutron crossplot;-replacement and recrystallized dolomites as above, but evaporite cemented with anhydrite and/or halite;-dedolomites including layered, nodular (concretionary), vuggy types and calcite-cemented grainstones;-limestones divided into micrites, sparitic mudstones, wacke-and grainstones. Petrophysically significant traces of minerals such as pyrite and evaporite mixes also require separate ellipsoids, resulting in 48 carbonate and 24 evaporite lithofacies. The correctness of the database was verified on three cored test wells. Evaluation using old logging suites consisting of density, sidewall or gamma-ray neutron, gamma ray, sonic and laterlog seven is now also performed. Routine application of the database provides complete facies descriptions in uncored sections and wells for use in geological profiles and facies maps.-1
To complement the now traditional Cement Bond Log (CBL/VDL)l, a device called CET* (Cement Evalua... more To complement the now traditional Cement Bond Log (CBL/VDL)l, a device called CET* (Cement Evaluation Tool)2 was commercially introduced in 1982. It features an array of eight ultrasonic transducers allowing a radial inspection of the casing and its annulus. Its response can be interpreted in terms of cementation quality. In particular, distinction between acceptable cement, unset slurry or liquid, gaseous cement and free gas can be made. Analysis of the radial and vertical distribution of the materials located by the device provides the basis for the identification of possible causes of poor cementation. With these indications primary cementing procedures can be controlled and improved.
Also, cementing methods can be more rigorously adapted to individual situations.
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Middle East Oil and Gas Show and Conference, 2005
Copyright 2005, Society of Petroleum Engineers Inc. This paper was prepared for presentation at t... more Copyright 2005, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 14th SPE Middle East Oil & Gas Show and Conference held in Bahrain International Exhibition Centre, Bahrain, 1215 March 2005. This paper was selected for presentation by an SPE ...
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Annual Technical Conference and Exhibition, 1984
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Middle East Oil and Gas Show and Conference, 2007
A method, system and computer program product for invert- ing boundary conditions for rock mass f... more A method, system and computer program product for invert-
ing boundary conditions for rock mass field in-situ stress
computation for a geologic structure are disclosed. According
to an embodiment, the current invention includes a method
for inverting boundary conditions for rock mass field in-situ
stress computation for a geologic structure, the method com-
prising: considering physical constraint of the geological
structure; deriving and solving normal equations of penalized
weighted least squares, said normal equations of penalized
weighted least squares partially representing said physical
constraint of the geological structure; and outputting bound-
ary conditions and reproducing the rock mass field in-situ
stress based on the result of said solved normal equations of
penalized weighted least squares.
The present invention generally relates to the logging of earth formations, and more particularly... more The present invention generally relates to the logging of earth formations, and more particularly to methods and apparatus for formation characterization using logging tool responses corresponding to logging measurements.
Wireline tools have been employed to obtain formation measurement. In certain prior art apparatus, induction-logging instruments are susceptible to a variety of environmental effects due to considerable range of investigation. Therefore, to make useful logs, the effects of volume above and below the layer of the interest must be carefully removed. In practice, the Array Induction Imager (AIT) or AIT-family tools are popular in moderate conductive to oil-based-mud logging environment. The AIT tool consists of eight three-coil arrays, six of which are operated simultaneously at two frequencies (AIT-B) or one frequency (AIT-H/M family). The AIT tool can produce wellsite resistivity logs having high resolution and high rejection of borehole rugosity effects. For example, these tools can produce logs that are corrected for the most common environmental effects, e.g. borehole effect, shoulder effect, skin effect, et al.
However, such tools typically need a wellsite post-processing to remove the environmental effects. Due to the high requirement of processing speed at well-sites, as well as the difficulty in quantifying the logging measurement error, the post-processing typically is based on Gaussian error assumption and least-squares inversion, thus the post-processed result is Gaussian mean value. In reality, however, the Gaussian error assumption is not always correct, thus the traditional post-processed result might not be ideal either. For example, if the Gaussian error assumption is violated, AIT 10, 20, 30 60 and 90-in curves can behave strangely, either formation inhomogeneity or vertical bedding being overlooked, or the separation of the five curves can not be explained from logging environment information. In such situation, the traditional AIT well-site post-processing result cannot provide accurate indication of formation characterization.
Wireline openhole formation evaluation has been the standard in petrophysics and quantitative res... more Wireline openhole formation evaluation has been the standard in petrophysics and quantitative reservoir evaluation for many years. During the last five years we have witnessed a migration of some of the basic, high-quality openhole services to cased hole logging applications. One major challenge remains: measuring the formation-bulk density in cased hole environments.
Several feasibility studies have indicated that under favorable casing-cement conditions density measurements are sufficiently sensitive to the formation bulk density in cased holes. Some experimental cased-hole-logging tools were developed to exploit this sensitivity; however, none of these experimental prototypes has been developed into a commercial service.
This study analyzes the response of a three-detector wireline density tool to formation density in cased wells. The tool response was experimentally measured in density blocks and in controlled test-tank conditions for a variety of formations, casing, and cement parameters. This new formation-density measurement has successfully been used in a number of cased wells. Under favorable casing-cement conditions the data agree with the openhole density logs within their accuracy. Several log examples illustrate this good agreement.
Logging operations and log-quality-control flags are adapted to the more difficult cased hole environment. The logging speed is reduced to compensate for the reduced count-rate statistics. The photoelectric-effect (Pe) log cannot be used for lithology identification, but serves to estimate the casing thickness. The thin-bed resolution is slightly impaired. Yet, the resulting formation-bulk-density log has proved to be a quantitative formation-evaluation measurement that is readily com-
bined with the other cased-hole formation-evaluation services to give a comprehensive formation description.
Sometimes the cement thickness behind the casing may exceed a cut-off threshold. In this case, complementary nuclear-porosity logs can be used to substitute the density measurement with a porosity-inferred density.
The success of Rotliegend gas exploration in North-Western Germany at depths between 4000 and 500... more The success of Rotliegend gas exploration in North-Western Germany at depths between 4000 and 5000 m is dependent on the depositional environment but more significantly on the degree of diagenetic alteration encountered in the Rotliegend sandstones. Some sandstones are not productive due to the lack of primary porosity caused by poor sorting and/or high clay content or the anhydrite cementation in sabkhas and erg deposits. Nevertheless, even originally porous aeolian sandstones or shoreline sands are often unproductive, due to the diagenetic cementation of the pore space by illite meshwork, kaolinite, carbonates (predominantly calcite) or quartz.
The core coverage in Rotliegend sequences is usally rather poor (on average about 10% of the total thickness) due to the enormous thickness of these sediments and the high cost of coring. Therefore, the obvious method to obtain facies information for uncored intervals and wells is the use of logs, since logs cover the entire Rotliegend interval. Furthermore, logs are acquired on a routine basis for petrophysical evaluation and contain much lithological information.
The value of openhole logs for facies analysis has been demonstrated in Zechstein carbonates of Northern Germany (Stowe and Hock 1988). The following discussion outlines an equivalent methodololy for Rotliegend sequences.
Recent technological progress requires a fundamental review of the approach to quantitative log i... more Recent technological progress requires a fundamental review of the approach to quantitative log interpretation. A modern and advanced interpretation must be able to combine both quantitative and qualitative information from different sources, of different natures and at different scales. It should no longer focus only on solution of n equations of m unknowns with purely petrophysical goals.
The recent introduction of imaging techniques has created a breakthrough in reservoir characterization. Because the reservoir can now be seen, it is possible to describe it in great detail as a three-dimensional organization of geological objects which are themselves classified as volumes, with their corresponding facies, bounded by surfaces with their own transmissivity properties.
Petrophysical properties control the volume flow properties. The latter depend on the depositional facies attributes and the diagenetic effects undergone by the sediment since its deposition. They can be determined partly from standard logs, but more fully from borehole images that provide fundamental information about the reservoir anisotropy and the nature and distribution of reservoir heterogeneities.
Surface attributes are defined through the shape, planarity, rugosity, extent, angular relationship, resistivity contrast, etc., of the surface. Practically all surfaces crossing a wellbore may be classified as they are detected by electrical imaging techniques from which their nature and origin can be precisely determined. Based on their origin and resistive characteristics transmissivity properties can be assigned to them. In addition, the influence of apparent dip can be taken into account in the response function of other tools.
A modem and complete interpretation must, as far as possible, take into account all the accessible attributes at different scales, and from them determine the dynamic attributes associated with the reservoir.
In addition, one can say that a succession of facies and surfaces defines a genetic sequence, itself limited by breaks of hierarchy and extent, and characterized by a set of attributes. A sequence and succession of sequences allow the recognition of the depositional environment that, consequently, has itself a set of attributes of higher rank, including seismic attributes. Finally, the reservoir geometry may be inferred from the determination of the depositional environment and the tectonic structure.
The solution of this new truly global and integrated approach can be achieved through a generalization of the electrofacies concept. This is illustrated by examples.
Sedimentary facies and their diagenetic equivalents in Zechstein carbonates and adjacent evaporit... more Sedimentary facies and their diagenetic equivalents in Zechstein carbonates and adjacent evaporites are determined from wireline logs using a petrophysical database calibrated in 14 key wells. The selected key wells have between 8 and 10007o core cover with 49070 on average, and a logging suite consisting of density, neutron, photo-electric factor (Pe), sonic, gamma ray, deep, shallow and micro-resisitivity logs. The database was constructed in three major steps: (A) A volumetric analysis including mineralogic composition, porosity and saturations was computed using an iterative minimisation program and checked against petrophysical core data, petrographic data provided by core description, and mineralogical data based on micorscopy and x-ray analysis. Principal minerals were calcite, dolomite, anhydrite, and halite, with occasionally significant amounts of potassium salts, pyrite, clay, sulfur and bitumen. Gas corrections based on the calculated saturations were used to normalize the logs for each key well. (B) T h e gas-corrected log data were then grouped using a cluster analysis of their principal components to obtain electrofacies for each single well. These electrofacies were matched with geological facies defined from the petrographic core descriptions. (C) L o g data values of similar electrofacies from the individual key wells were plotted in 10 two-dimensional multiwell-crossplots. To avoid ambiguities produced by the cluster analyses an independant five-dimensional ellipsoid was created from the multiwell-crossplots for each geological facies. The defined ellip-soids were combined to form a petrophysical database. In general the following carbonate facies with significant differences in log responses are distinguished based on different mineralogy and porosity types: — replacement dolomites such as mudstones, mouldic mudstones, wacke-, grain-and packstones, which show a curved density/neutron response; — replacement and recrystallized dolomites as above, but evaporite cemented with anhydrite and/or halite; — dedolomites including layered, nodular (concretionary), vuggy types and calcite-cemented grainstones;-limestones divided into micrites, sparitic mudstones, wacke-and grainstones. Petrophysically significant traces of minerals such as pyrite and evaporite mixes also require separate ellip-soids, resulting in 48 carbonate and 24 evaporite lithofacies. The correctness of the database was verified on three cored test wells. Evalutation using old logging suites consisting of density, sidewall or gamma-ray neutron, gamma ray, sonic and laterolog seven is now also performed. Routine application of the database provides complete facies descriptions in uncored sections and wells for use in geological profiles and facies maps.
Sedimentary facies and their diaeenetic equivalents in Zechstein carbonates and adjacent evaporit... more Sedimentary facies and their diaeenetic equivalents in Zechstein carbonates and adjacent evaporites are determined from wireline logs using a petrophysical database calibrated in 14 key wells. The selected key wells have between 8 and 100% core cover with 49% on average, and a logging suite consisting of density, neutron, photo-electric factor (Pe), sonic, gamma ray, deep, shallow and micro-resistivity logs. The database was constructed in three major steps: (A) A volumetric analysis including mineralogical composition, porosity and saturations was computed using an iterative minimisation program and checked against petrophysical core data, petrogt-aphic data provided by core description, and mineralogical data based on microscopy and X-ray analysis. Principal minerals were calcite, dolomite, anhydrite and halite, with occasionally significant amounts of potassium salts, pyrite,clay, sulfur and bitumen. Gas corrections based on the calculated saturations were used to normalize the logs for each key well. (B) The gas-corrected log data were then grouped using a cluster analysis of their principal components to obtain electrofacies for each single well. These electrofacies were matched with geological fades defined from the petrographic core descriptions. (C) Log data values of similar electrofacies from the individual key wells were plotted in 10 two-dimensional multiwell-crossplots. To avoid ambiguities produced by the cluster analyses an independant five-dimensional ellipsoid was created from the muldwell-crossplots for each geological facies. The defined ellipsoids were combined to form a petrophysical database. In general the following carbonate fades with significant differences in log responses are distinguished based on different mineralogy and porosity types:-replacement dolomites such as mudstones, mouldic mudstones, wacke-, grain-and pacicstones, which show a curved density/neutron response;-recrystallized dolomites derived from successive microsolution, accretive crystallization and subsequent compaction, which show a straight line response in the density/neutron crossplot;-replacement and recrystallized dolomites as above, but evaporite cemented with anhydrite and/or halite;-dedolomites including layered, nodular (concretionary), vuggy types and calcite-cemented grainstones;-limestones divided into micrites, sparitic mudstones, wacke-and grainstones. Petrophysically significant traces of minerals such as pyrite and evaporite mixes also require separate ellipsoids, resulting in 48 carbonate and 24 evaporite lithofacies. The correctness of the database was verified on three cored test wells. Evaluation using old logging suites consisting of density, sidewall or gamma-ray neutron, gamma ray, sonic and laterlog seven is now also performed. Routine application of the database provides complete facies descriptions in uncored sections and wells for use in geological profiles and facies maps.-1
To complement the now traditional Cement Bond Log (CBL/VDL)l, a device called CET* (Cement Evalua... more To complement the now traditional Cement Bond Log (CBL/VDL)l, a device called CET* (Cement Evaluation Tool)2 was commercially introduced in 1982. It features an array of eight ultrasonic transducers allowing a radial inspection of the casing and its annulus. Its response can be interpreted in terms of cementation quality. In particular, distinction between acceptable cement, unset slurry or liquid, gaseous cement and free gas can be made. Analysis of the radial and vertical distribution of the materials located by the device provides the basis for the identification of possible causes of poor cementation. With these indications primary cementing procedures can be controlled and improved.
Also, cementing methods can be more rigorously adapted to individual situations.
SPE Middle East Oil and Gas Show and Conference, 2007
SPE Middle East Oil and Gas Show and Conference, 2005
Copyright 2005, Society of Petroleum Engineers Inc. This paper was prepared for presentation at t... more Copyright 2005, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 14th SPE Middle East Oil & Gas Show and Conference held in Bahrain International Exhibition Centre, Bahrain, 1215 March 2005. This paper was selected for presentation by an SPE ...
The importance and challenges of obtaining reliable estimations of lithology and total porosity i... more The importance and challenges of obtaining reliable estimations of lithology and total porosity in carbonates in general are often ignored. Hence, following definitions of terms to be used for carbonate geometry, pore size, and more importantly pore throat size and classification; a brief review of both classical and more modern lithological and porosity log responses in carbonates is made. Recommendations are put forward for logging acquisition and processing to ensure the basic fundamental properties are correctly evaluated before attempting evaluation of porosity partitioning, permeability and producibility. These include appropriate but routine use of photoelectric factor (Pef) logs, Natural Gamma-Ray Spectroscopy and Elemental Spectroscopy. The issue of partitioning the porosity in vuggy and fractured carbonates is then addressed firstly with as review of main tools that respond to vug porosity and the advantages and drawbacks of each technique, followed by suggestions for extending the latest methods and integrating various measurements to quantify the vug porosity and most importantly its effect, connected or isolated, on the permeability and producibility of the reservoir. Some examples of one of the many response equations that treat pore shape and vug effects on sonic are used to illustrate the challenges of interpreting such data in the presence of multiple interacting influences based on models that are still too simple to evaluate the complex acoustic behavior of carbonates in a universal manner. Nuclear Magnetic Resonance and evaluation of connected and isolated vugs from electrical images is then reviewed in a similar fashion, concluding with some suggestions for service companies for new tool and interpretation developments to further extend the advances in integration of the current tools and processing that has recently been published. Fracture detection and evaluation for porosity and permeability is treated next, again with a short review of the various tools and suggestions for optimal techniques, and recommendations for combinations of measurements, acquisition techniques and processing to obtain the best results. Electrical resistivity image processing for fracture evaluation is well established, but often needs careful tuning, and the detection of fractures can still not be done reliably in an automatic manner. Sonic evaluation from independent techniques is still subject to error, but new methods integrating dispersive processing of dipole shear integrated with Stoneley and resistivity information shows promise of reliable evaluation of position, number, porosity and permeability of fractures. However, caution is advised as it is now clear that some of the effects evaluated as being caused by either fractures or local stress fields that are separable, are in fact changes (including in stress) due to water replacing hydrocarbons. A final reference is made to pressure and fluid sampling as although closer to the reservoir-engineering domain, they do measure some form of permeability by moving fluid and are " logs ". In order to provoke discussion the author has also deliberately selected examples of many of the log responses and evaluation techniques that clearly do NOT work or have severe limitations. For the extension of the information to evaluation of 'm;' and 'n' to cope with both vugs and fractures, and their use in some appropriate saturation equation with resistivity measurements, the reader is directed back to the Aguilera and Aguilera paper cited in the references.