Wind-blown sands and how to recognize them in modern dunes, outcrops and subsurface.
In and around the 4-corners, we are blessed with an abundance of well preserved and exposed ancient dune deposits. Most of the spectacular outcrops in the Utah National Parks are ancient dune deposits. At Zion it’s the Navajo, at Arches it’s the Entrada, at Canyon De Chelle it’s the De Chelle Sandstone. The Canyon Lands area of Utah has the Page, Cedar Mesa, Wingate and White Rim sandstones. All the sandstones mentioned above are formed by the same process, they are wind deposited.
The wind can only move a very narrow distribution of grain sizes. Too small and the particles get carried off as ‘dust’ to be deposited a long distance away as loess. Too big and the particles are left behind as a lag deposit. What ends up in a dune field are sand grains ranging from .1mm to 1mm. The dune sand mineral composition is the result of the source or provenance for the sand and transportation time. For the most part, dune sands are pure quartz because quartz has the combination of mineral properties necessary to ‘weather’ the eolian depositional process. Quartz is mechanically very stable. It is hard and does not have a cleavage, which allows quarts to withstand being windblown. Quarts is also chemically very stable. Most naturally occurring solvents (water and acid rain) have no effect on quartz. There are rare examples of other minerals making up dune sands such as garnet, found in dunes along the SW Australian coast but that is another story.
All dunes have the same facies making up the deposit. They are: wind ripples, grain fall or grain flow. These three facies make up all dunes regardless of the dune type. To understand the dune type, or classification, we need more information. Dunes can be classified by morphology based on the shape of the dune (crescentic, linear or star) or classified morphodynamically based on the dune crest line relative to the wind transport direction (Longitudinal, Oblique or Transverse). The dune classification is very important when chasing dune sand bodies in the subsurface for oil and gas exploration.
In the subsurface, the borehole image is king when trying to understand the classification of dune sands and their distribution. The subsurface example used in this talk will be a Permian Unayzah eolian reservoir in Saudi Arabia. The Unayzah had great coverage for both Borehole image logs and conventional core, together I was able to put together a sand distribution map guiding exploration drilling and reservoir development efforts.
Five distinct facies can be recognized in core and on image log: dune, sand-sheet, paleosol, playa and ephemeral-fluvial deposits. Although the eolian reservoir is not present in outcrop in Saudi Arabia, the Permian Cedar Mesa Formation of Southern Utah serves as an excellent outcrop analog for the Permian ‘wet’ eolian Unayzah reservoir and will be used to illustrate the nature of the wet eolian system. Barren of consistent datable organic material, the Unayzah eolian reservoir is sandwiched between the Lower Permian glacial deposits of the Unayzah and the Middle Permian tropical deposits of the Khuff carbonates, both of which have very good palynological control for the age of the units. A dominant west-to-east wind direction is identified on image logs for the Unayzah transverse dune system which would place the eolian reservoir in a mid-latitude, southern hemisphere desert setting at the time of deposition around 45 degrees south latitude in the location of the prevailing westerlies (~285Ma).
About the Speaker:
Christian J. Heine FTF (First Things First) Geosciences
Chris is a retired Senior Geological advisor with over 40 years industry experience. He began his career with Mobil Oil in Dallas Texas in 1982, and after several U.S. postings including Lafayette, Houston and New Orleans, Chris was seconded to Saudi Aramco in 1991 and in 1996, he joined Saudi Aramco permanently. While in New Orleans with Mobil, Chris was an Associate Professor at Tulane (1990 and 1991) in the Petroleum Engineering Department where he taught Gulf Coast Geology.
Chris made an immediate impact at Saudi Aramco where through core and image log studies he redefined the (Permo-Carboniferous) Unayzah reservoir as eolian rather than the accepted marine interpretation. This discovery changed both the way Aramco explored for the Unayzah as well as the geological modeling and development drilling of the reservoir. He was a strong proponent of using analogs, both outcrop and modern, to guide the geological thinking behind, and ultimately the modeling of, this stratigraphically complex and compartmentalized reservoir.
Chris was very active in the Aramco training program where he taught several courses for both the geology and petroleum engineering programs. He has lead or participated as an instructor for over thirty geological field trips and is a firm believer in the benefits of fieldwork and the use of outcrops in reservoir mapping, modeling and reservoir characterization. While at Aramco, Chris served as the Professional Development Advisor (PDA) for the Exploration Organization, as well as the Subject Matter Expert (SME) for clastic reservoirs and reservoir characterization.
Chris joined QRI in October 2010 and worked in Mexico on the off-shore Jurassic sandstones and Cretaceous carbonate fields of the Cantarell complex. Here he took more of a project management roll coordinating the geological input to the geocellular models. January 2014 to September 2015 Chris worked the Upper & Lower Burgan reservoir development project for QRI/KOC in Kuwait city. The Burgan sandstones are the most prolific producers in Kuwait.
Chris was an active member of the Dhahran Geoscience Society where he held several offices and was an active member of the AAPG where he has served as a delegate representing the Middle East for over 10 years. Chris also served on several AAPG committees including the international regions committee, AAPG Research Committee, Visiting Geologist Program, and Reservoir Geology Committee. He was a session chair in Perth, Cape Town and San Antonio and Cancun, and in Cape Town he was the oral sessions co-chair for the Technical program. Chris served as the AAPG Middle East Region Vice President from June 2005 – 2009.
Education
1978 Bachelor’s degree, Penn-State University
1983 Masters Geology, University of Tennessee
1991 Masters Petroleum Engineering, Tulane University
2004 Successfully defended his PhD. in Geology University of Aberdeen
Awards:
- Best poster Geology in Geo 2002.
- Best oral paper in Geology Geo 2004.
- Best oral paper in Geology Geo 2006.
- AAPG International Distinguished lecturer 2009 & 2010.