Meeting Information

"Log evaluation of gas shales: a 35-year perspective"

Bob Cluff
Discovery Group

Log evaluation of gas shales has taken two general paths over the past 35 years: recognition of a potentially gas saturated, prospective section; and quantification of the gas content in place, the latter of course being the far more difficult problem.

Early methods to recognize gas shales centered on the problem of estimating the total organic carbon (TOC) content of shales using some combination of gamma ray, density, sonic, and resistivity logs.  These began in the late 1970’s with work on eastern US Devonian gas shales, where it was recognized both the gamma ray and density logs exhibited reasonably linear correlations between TOC and log response.  This is because 1) organic matter is associated with uranium in reducing environments, leading to increased gamma radiation with increasing TOC; and 2) kerogen has low grain density and therefore leads to reduced bulk density as the TOC of a rock increases.  Later work showed there was also a relationship between formation resistivity and maturity of the source rock, so as maturity increased the resistivity also generally increased.  This is because the pore system of a mature source rock is flooded with hydrocarbons, so as everyone knows from Archie’s equation the resistivity must increase as water saturation decreases (all else being constant).  This led, in the early 1990’s, to F-overlay derived interpretation methods where TOC could be quantified from the logarithmic separation between formation resistivity and either the density or sonic log response so long as some independent measure of maturity was available (better known as the delta LogR method).

Although recognition of high TOC intervals and at least semi-quantitative measures of TOC content are very useful, it was quickly realized that gas shales also have porosity and much of the shale gas resides in pores.  Quantification (and distinction) of porosity and TOC, which yield similar responses with both sonic and density logs, is obviously critical in order to determine the gas in place.  Numerous methods have been proposed over the last 10 years to deal with this basic issue, including use of a TOC proxy (e.g. GR or NGT Uranium) and then iteratively solving for porosity (Discovery Group and others); full multimineral solutions via stochastic solvers that include TOC and porosity as components (in progress); use of elemental spectroscopy sondes to estimate the matrix mineralogy sans organic carbon and thereby determine the “kerogen free” grain density (Schlumberger approach); or simply regressing log properties against core determined properties and fitting a  set of non-linked equations on a well-by-well basis (Core Labs approach).  Once porosity and TOC have been determined within acceptable error bars by whatever method, the gas-in-place problem is then reduced to a gas saturation in porosity calculation (“free gas”) and a gas associated with kerogen computation using some form of an isotherm correlation (“adsorbed gas”).  The sum of these two storage volumes, which are assumed to be totally independent, is then considered total gas.   All approaches tend to take similar pathways towards these calculations, although there is little consensus as to what is the best saturation model to use, what specific parameters should be assumed to compute gas saturation in a shale, or even how to determine what those parameters should be.  To a great extent, the model used is the one that seems to give the “right” answers.

Current and future efforts include methods to estimate the mechanical properties of a gas shale and predict optimum placement of horizontal legs and fracture jobs within the section; better and more objective methods to determine gas-in-place; and figuring out how to do more with less, in particular how to evaluate shales without running expensive logging suites in deviated or horizontal sections.

From the President

Stefani Whittaker (The Discovery Group)

First of all I want to thank all who attended, the speakers, and the board members (especially Terri Olson) who helped make the spring workshop such a success. I learned a lot and I hope that all of you did as well. For those who attended, the modified electronic copy is now available for download. If you did not get an email from Dominic Holmes, but did attend the workshop please contact Dominic (HolmesD@DigitalFormation.com).  If you were unable to attend, but would like an electronic copy of the notes that we have permission to release, please contact Dominic as well.

As a result of our monthly meetings and short courses being so well attended this year, your 2009-2010 DWLS board made some decisions last month to donate funds to various organizations:

1. We decided to donate to the Denver Chapter SPWLA Foundation Scholarship again, with a lump sum of $20,000. Each SPWLA chapter contributions roll into the principal balance of the Foundation’s account. All the monies are invested together and there is one lump sum of interest returned. The interest is the only part of the monies that gets distributed for scholarships. The DWLS segment of the interest is based on a percentage of how much we contribute to the principal balance. Therefore, the more money we donate, the more scholarships get tagged as a DWLS contribution. If you are interested in knowing more about the SPWLA Foundation Scholarships, please visit the Foundation page on the SPWLA website (http://www.spwla.org/).
2. Next as a participating member of NGOGP(Next Generation Oil and Gas Professionals), your current board voted to support this organization financially in their networking social hours, lunch and learns, and charity events by giving a donation of $500. This will support any costs that are not already covered by corporate sponsors of the events. Again if you are a younger member of DWLS and would like to be more connected with all the events for younger members around the oil and gas industry, please contact me (StefaniWhittaker@discovety-group.com) to get on our mailing list!
3. Finally the DWLS would like to thank Norma Pickett (wife of Dick Pickett) for her donation of her late husband’s SPWLA “Petrophysics” publications. As a thank you we have asked Norma to pick a charitable organization so that we may make a $500 contribution in Dick Pickett’s name.

Finally, this year we have picked the Ship Rock Grille at Red Rocks Amphitheatre for our June 15^th meeting. We are going to do a happy hour from 4-7 again, and details will be announced as we get them organized! Get spring fever with the rest of us and mark it on your calendars now!

From the Past President

Bill Rodgers (Weatherford International)

This is the final request for nominations for the DWLS Officers and Board of Directors for the 2010-2011 term. After the April 19^th Meeting, we will send a link which will allow all members to vote for each position. To date, we have nominees for all positions, but I encourage additional nominees, especially for the Board Member positions. So, please email me at bill.rodgers@weatherford.com with your nominee(s). If you have any questions regarding any of the positions, please contact me via email, or at 720-635-6016.

Below is a description of the duties and responsibilities of each position.

President – Term of office is one year

• Be responsible for the operations and direction of the chapter;
• Preside at all meetings of the chapter;
• Plan and organize meetings of the Board of Directors;
• Organize the luncheon meetings with the venue;
• Appoint all temporary committees and chairpersons;
• Welcome members to each luncheon and chapter function, and ensure that the meeting remains on schedule;
• Introduce the event speaker when the VP-Technology is not available;
• Write a President’s Message each month for the newsletter;
• Call special elections;
• Communicate with the SPWLA by:
  • Contact with the SPWLA Regional Director, and with the SPWLA Board of Directors and office staff, as necessary;
  • Provide a formal report (on standard form) within 30 days of a chapter meeting;
  • Forward a list of officers elected to the next term before the Annual Business Meeting at the Symposium.
  • Entertain a proposal to host the SPWLA Symposium, and submit that proposal to the SPWLA Board of Directors in the fourth quarter of the calendar year.

Vice President-Technology – Term of office is one year

• Organize the schedule of speakers at the monthly technical luncheons;
• Chair the committee which organizes other technical workshops and meetings identified by the Past President and approved by the chapter;
  Preside at chapter meetings in the absence of the President.
• For all above events:
  • Obtain the abstract and biography of the speaker, and provide those to the Editor at a reasonable time before the event; usually a minimum of two months prior;
  • Arrange for local transportation and housing for out-of-town speakers;
  • Arrange for the projector and other audio-visual equipment for the presentation;
  • Arrange for and provide the digital welcome banner displayed prior to and, if appropriate, during the presentation;
    Introduce the speaker;
  • Make any announcements concerning upcoming technical events, including those of the local societies, and national societies, encouraging the submission of abstracts for presentations and papers.

Vice President-Membership – Term of office is one year

• Maintain the current membership roster.
• Handle the submission of membership forms, including the collection of dues payments. After updating the roster, checks should be sent to the Treasurer for deposit.
• Handle any delivery failures month-to-month by verifying email addresses.
• Provide the up-to-date membership roster to the Editor each month by the newsletter deadline.

Secretary. – Term of office is two years

• Organize the luncheon list with the person taking reservations.
• Provide statistics on luncheon attendance to the Editor each month by the newsletter deadline.

Treasurer - Term of office is two years.

Since this is an even numbered year. This position is not currently open.

Directors - Term of office is one year

• Help with organizing all special projects and events.
• Provide guidance and support to other board members as needed.

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