Abstract

Maximizing recovery in oil and gas fields relies on geological models that realistically portray the spatial complexity, composition, and properties of reservoir units.  Present day arid climate coastal systems, like the coastlines of Abu Dhabi and Qatar provide analogues for depositional and diagenetic processes that control reservoir quality in ancient reservoirs.  Many major reservoirs of the Middle East formed under conditions that are remarkably similar to those shaping the coastlines along the Arabian Gulf of today.

The studied coastal sabkha and salina environments of Abu Dhabi and Qatar represent a perfect training ground for teaching geologist, reservoir engineers, and geophysicists the importance of facies analysis (facies stacking patterns), diagenesis (dolomite and hardground formations), age-dating, and sequence stratigraphic correlation.  Furthermore, the analysis of modern analogs is one of the few means by which high-resolution spatial complexity of stratigraphic systems can be described.  If the horizontal dimensions of facies belts are less than the typical well spacing, modern analogs, together with seismic and production data help to construct realistic geologic and simulation models of subsurface reservoirs.

Significant amounts of dolomite were found within the studied peritidal carbonates of Abu Dhabi.  The dolomite is very fine-crystalline and displays spherical morphologies as well as subhedral to euhedral dolomite rhombohedra.  The formation of dolomite is interpreted to be related to dolomite-mediating microbial organisms which form the widespread microbial mats along the Abu Dhabi coastline.

Evaporites in the form of gypsum are the major diagenetic phase observed in coastal deposits.  During burial, gypsum dewaters to form anhydrite, a common mineral found in ancient arid climate sediments.  Abu Dhabi sabkha evaporites are often used as analogues for ancient carbonate-evaporite dominated formations.  However, thick bedded anhydrite deposits like those of the Permo-Triassic Khuff and the Upper Jurassic Arab formations mostly represent salina- or saltern-type rather than sabkha-type deposits.

As can be observed in cores from Permo-Triassic and Jurassic reservoirs, early diagenetic gypsum precipitation plays an important role in reservoir destruction.  Our studies along the coastlines of Qatar show that between about 20 and 60 percent of the initial pore space of the sabkha environment may be lost due to gypsum precipitation within 6,000 years; prior to any burial diagenesis.

Studying and documenting different types of microbial sedimentary structures preserved in gypsum is of particular interest, not only in the field of petroleum geology.  Whereas carbonate minerals quantitatively form the most important sediments for preserving morphological bio-signatures on Earth, the most relevant chemical sediments on Mars are likely formed by sulfate minerals, such as gypsum.  Gypsum has been widely detected on Mars and is interpreted to have formed under evaporitic conditions, broadly similar to those characterizing terrestrial sabkha and salina environments of the Middle East.

Biography

Dr. Christian J. Strohmenger retired from ExxonMobil in October 2022; after more than 32 years with the company.  He received a Diploma in Geology from the University of Giessen, Germany (1983) and a PhD in Sedimentology from the University of Heidelberg, Germany (1988).  From 1989 to 1990 he worked as Research Assistant in carbonate sedimentology and sequence stratigraphy at the University of Geneva, Switzerland.

He joined ExxonMobil Production Germany GmbH (EMPG) in 1990, working as Carbonate Sedimentologist and Seismic Interpreter on Upper Permian carbonate reservoirs of the Zechstein Formation until 1996.  From 1996 to 2002 he was with ExxonMobil Exploration Company in Houston, Texas where he worked on Paleozoic and Mesozoic carbonate and sandstone reservoirs of Kuwait and Saudi Arabia.  He was seconded to Abu Dhabi Company for Onshore Oil Operations (ADCO), United Arab Emirates in 2002, working as a Carbonate Stratigraphy Specialist on various Jurassic and Cretaceous carbonate reservoirs until 2009.  From 2009 to 2011 he worked for ExxonMobil Oil Indonesia, Jakarta as Carbonate Advisor on Tertiary carbonates and CBM projects of SE Asia for Exploration, Development, and Production.  From 2011 to 2015 he was with ExxonMobil Research Qatar (EMRQ), working as Team Lead and Geological Advisor at the Qatar Center for Coastal Research; studying modern coastal systems of Qatar as analogues for arid climate carbonate and siliciclastic reservoirs, and providing advice and technical support to ExxonMobil Joint Ventures.  From 2015 to 2016 he worked with Esso Australia Pty. Ltd. as Carbonate Specialist on Tertiary carbonates of Vietnam and Papua New Guinea.  From December 2016 until December 2018 he was with ExxonMobil Production Germany GmbH, working as Geological Advisor for the Houston based Vietnam Team on Tertiary carbonates of Vietnam.  He was with ExxonMobil Upstream Integrated Solutions, working as Geological Advisor for the Qatar Subsurface Team on Permo-Triassic carbonates from December 2018 until October 2022.

His main interests are carbonate sequence and seismic stratigraphy, sedimentology, reservoir quality prediction, and carbonate reservoir characterization.