Abstracts – Houston SPWLA Topical Conference May 21, 2008

                                 May 2008 Topical Conference
                                 Determining Residual Oil Saturation

  Abstracts and Biographies

KEYNOTE PRESENTATION

The Origin and Significance of Residual Oil Zones as Applied to
CO2 EOR and Sequestration

L. Stephen Melzer

Melzer Consulting

The presence of oil transition zones just beneath the base of geological oil traps is a long observed condition of many oil reservoirs.  Investigations to develop a complete understanding of the origins of these zones has been hampered by two limitations: 1) a general lack of interest in the intervals due to their uneconomic nature during primary or secondary production phases of production and 2) a tendency for companies to avoid drilling into the zone to avoid the production of water.

The relatively recent advent of tertiary oil production methods has amply demonstrated that previously waterflooded zones with dramatically reduced oil concentrations are made economic by injectants such as carbon dioxide.  This is just now beginning to change the interest in the transition zones because of the similar properties of post-waterflood intervals and these zones beneath main pay zones (hereinafter deemed “residual oil zones”).  This presentation examines these potential resources by:

Summarizing two on-going CO2 EOR projects that illustrate not only the technical merits of CO2 flooding of the residual oil zones but also the commercial nature of such floods,
Presenting three explanations of the origins of residual oil zones that account for observed abnormal thicknesses over that which would be forecast for simple oil-water transition zones, and
Suggesting further investigations that are needed to allow a first order estimation of this sizable oil resource within the United States.

All of the parameters needed for defining a U.S.-wide volumetric target for CO2 flooding the ROZ intervals are challenging.  However, it does not alter the need for establishing first order estimates for the size of the resource target.  Future definition of the exact targets will need to occur first on a regional basis then, ultimately, a field-by-field basis.  The latter effort will likely be on-going for many years as the field operators acquire the additional data needed.  These regional and field specific studies are clearly outside the scope of the recommendations herein; however, some initial specific target areas should be addressed early and on a priority basis. 

Mr. Melzer works with a variety of clients through his consulting company, Melzer Consulting wherein he assists with CO2 enhanced oil recovery business planning and conducts private studies forecasting CO2 flood performance.  He has performed recent research related to the origin, characteristics, and commerciality of residual oil zones beneath main pay intervals at a variety of locales including the Central Basin Platform of the Permian Basin. He is a practicing geological engineer (Texas Reg. No. #46859) and is the managing partner in Melzer Exploration Company, a family owned oil and gas investment company.  He is a past Director of the University of Texas of the Permian Basin’s Center for Energy and Economic Diversification where he led research projects and served (and continues to this day to serve) as the conference director of the annual CO2 Flood Conference held each year in December in Midland, Texas.

Residual Oil and Gas Determination with NMR

Ron Balliet

Halliburton

Early work with NMR in the 1960’s and 1970’s revealed the potential of NMR in formation evaluation. It was not until advances in downhole sensor instrumentation during the early 1990’s, that widespread utilization of commercial NMR measurements began.

As NMR measurements are acquired within inches of the wellbore, it is normally considered to be a flushed zone measurement and as a fluids only measurement, lends itself to residual hydrocarbon estimation.  The industry’s various measurement volumes and geometries will be discussed and also a description of T1 and T2 relating to NMR physics.

The industry’s current generation of sensors offer unique NMR based applications for determining residual oil and gas volumes.  An overview of NMR based applications and methodologies for Wireline and LWD will be discussed with value added case histories.

Ron Balliet is currently the Global NMR Product Champion for Halliburton.   Ron joined NUMAR in 1991 and worked with oilfield NMR in several locations worldwide. Since 1997, he has held various positions with Halliburton in West Africa and the USA.  Ron has BS (’84) in Geology and BS (‘84) in Geophysics from the University of Minnesota.  He is a member of the Society of Professional Well Log Analysts and the Society of Petroleum Engineers.

Sponge Coring for Improved Reservoir Oil Saturation Data

John Dacy

Core Laboratories

Sponge coring technology is in its third decade and market forces have once more brought it forward as a useful validation method for determining reservoir remaining oil saturation.  Improved core-based methods, unavailable or limited in the early 1980’s, can be routinely merged with sponge coring.  An overall review of the technology is merited as many current industry decision-makers may have little to no experience with sponge coring.

Reservoir and core saturations can be different due to a variety of factors related to core acquisition and recovery.  Sponge coring places controls on many of these factors.  A review of sponge coring concepts is followed by fundamentals of wellsite and laboratory processing.  The analysis of sponge cores is examined with respect to core quality assessment, sample preparation, core analyses, sponge analyses, and tracer analyses.  Key equations and example results are assessed.

John Dacy is Technical Director for the Petroleum Services division of Core Laboratories and is based in their Houston, Texas office.  He graduated from the University of Texas at Arlington with a BS degree in geology in 1972 and began his career with Core Lab the same year working in their Dallas Advanced Rock Properties lab.  He has held a variety of technical and administrative positions with Core.  As technical director he provides training and other support to Core Lab's worldwide network of rock properties laboratories on issues of technology transfer, testing protocols, data applications, and quality assurance.  He is a member of SPWLA, SPE, AAPG, SEG, and the Society of Core Analysts.

Hydrocarbon Saturation Determination for Primary Formation Evaluation and Production Monitoring using Through Casing Measurements

Jeff Grant

Schlumberger

With the price of oil over $100 a barrel, it is very important to be able to accurately evaluate the hydrocarbon production potential through casing.  This evaluation could be for determination of by-passed pay intervals prior to well abandonment, or for determination of flood break through in mature fields.

There is technology available to accurately determine porosity, lithology, water saturation and hydrocarbon type, through casing.  This presentation will briefly overview some of the technology and techniques available for evaluating a reservoir, through casing. Whether it is for primary formation evaluation, in lieu of open hole log data, or for continuing monitoring of a water or CO2 flood.

This presentation demonstrates the measurement response of the most common through casing reservoir evaluation tools, such as  pulsed neutron tools, dipole sourced array sonic tools and the cased hole resistivity to various production scenarios.

The measurement responses will be demonstrated using actual case examples, as well as modeled log responses.

Jeffrey Grant joined Schlumberger in 1980 as a wireline field engineer in Fairmont West Virginia.  He spent the next 11 years working in field before serving in Tyler, Texas as a specialist engineer for the Phasor Induction and Digital Array Sonic.  Jeff has also been a field service manager for Schlumberger’s LogNet service in Sedalia Colorado, a petrophysicist for Schlumberger’s Data and Consulting Services in Houston, Texas and a DCS center manager in Lafayette, Louisiana.  Since 2004, Jeff has been  the Schlumberger North American Data and Consulting Services technical manager, based in Houston, Texas.

Single Well Chemical Tracer Testing for Sor

Charlie Carlisle

Chemical Tracers, Inc

The Single Well Chemical Tracer (SWCT) test is a method for measuring fluid saturations in oil producing reservoirs.  The method has been used to measure residual oil saturation (Sor) for more than 30 years.  More than 500 reservoirs worldwide have been tested during that period.

The test is normally performed on watered out wells.  If the target well produces a substantial oil cut, water can be injected to water out the zone.  After water injection, the well will produce 100% water, and will be ready for Sor testing.  SWCT testing is non-destructive; after testing for Sor, the well can be returned to oil production status. 

The SWCT test for Sor is carried out by injecting a volume of water containing about 1% by volume of a partitioning ester into the target zone of the test well.  A larger volume of water that does not contain ester pushes the ester bank until it reaches a position ten to fifteen feet into the reservoir.  The total volume injected is typically labeled with a suitable non-reactive, non-partitioning (material balance) tracer. 

During a shut-in period of one to ten days, a portion of the ester reacts with the reservoir water and forms the secondary or product tracer in-situ.  The product, an alcohol, is virtually insoluble in the residual oil.  The shut in period is designed to allow a measurable amount of the alcohol to form.  Typical ester to alcohol conversion is from 10% to 50%.  At the end of the shut-in step, the unreacted ester and the product alcohol tracers are superimposed and located about 10 to 15 feet from the test well bore.

After the shut-in period, the well is produced.  The produced fluid is periodically sampled at the wellhead and immediately analyzed for content of the un-reacted ester, the product alcohol, and the material balance tracer.  SWCT test results from high Sor cases show a large separation between the product alcohol and ester.  Test results from low Sor cases show a small separation between the product alcohol tracer and ester.  This separation, combined with the laboratory measurement of the ester oil/water partition coefficient, is the basis of the Sor measurement.

In ideal cases, the Sor results can be calculated directly from field measured tracer concentration vs. produced volume profiles by measuring the degree of separation between the secondary tracer and ester.  A more rigorous interpretation is made through mathematical modeling.  Simulated SWCT production profiles are compared to field SWCT production profiles and Sor is obtained from the best-fit simulation model. 

Charlie Carlisle is the President and founder of Chemical Tracers, Inc.  Charlie has been deploying tracers to measure reservoir fluid saturations since 1979, has performed well over 450 chemical tracer tests and is a globally recognized expert in reservoir testing and analysis.   Charlie holds a MS in Chemistry from the University of Louisiana, Monroe, LA.

Residual Oil Saturation in a Large Middle Eastern Sandstone Reservoir: Comparisons of Time-Lapse PNC Logging, Openhole Calculations, and Core Flood Tests

Clarke Bean

Chevron

Because of its large size, residual oil saturation (Sorw) had a large impact in the reservoir modeling of this sandstone reservoir.  This study was designed to use a low-cost approach using mostly existing data.  Preliminary scoping showed the field had an active drilling/coring program with budget for SCAL analysis, 50 or so wells with modern openhole log suites, and a wealth of PNC logs spanning 35 years (allowing use of the Time-Lapse technique).  Open and cased hole techniques measure in-situ remaining oil saturation (ROS), and with sufficient time, this value approximates the true Sorw.

Through the study, several adjustments had to be made in the laboratory core flooding procedures and the PNC analyses to account for unforeseen problems that occurred.  In the end, final ROS results from the three methods show remarkable consistency. 

Among the lessons learned:

1. PNC analyses showed that ROS changes through time.  Measurements taken in zones which were exposed to water for less than 22 years had about a 50/50 chance of being incompletely swept. 

1. Sand quality (high perm vs low perm) did not affect the final ROS value, which is counter-intuitive to conventional wisdom.  Both core data and PNC logs showed similar ROS values in clean and shaly sandstones.

1. Areally, all three major sub-areas of the field showed similar ROS values, from both open hole and PNC logging.

Clarke Bean is a Senior Staff Petrophysicist with Chevron and is currently assigned to the Deepwater Gulf of Mexico Appraisal group.  He received his B.A. from Albion College in 1978, and M.A. from Indiana University in 1981, both in geology.  He spent his first 10 years with Chevron as a geologist before discovering the infinite learning curve of petrophysics.  Since then, Clarke has had a series of assignments in the Gulf of Mexico and the Middle East.  Among his interests are Pulsed Neutron Logging, image log creation/interpretation, and sonic logging.