Coast Geological Society

Ventura, California


The 2018 19th Annual Woolley Golf Tournament has been cancelled 

The Woolley Golf Tournment is an incredibly important yearly event that helps fund scholarships the Coast Geological Society provides for local geology students.

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Please Join CGS on Tuesday May 15th, 2018

Joseph M. Saenz, Engineering Lead for the Heavy Construction IPT, Naval Facilities and Expeditionary Warfare Center , will give his talk titled:

23 Years of Historic Hydrocarbon Seep Studies in Santa Maria Basin, Offshore California Using Seismic and Stratigraphic Data (1995 through 2018)

The monthly CGS meeting is held at the Poinsettia Pavilion in Ventura!

Meeting Schedule:

6:00 - 7:00 PM: Social Hour - Snacks and Beverages 

7:00 - 7:30 PM: Dinner Service

7:30 - 8:00 PM: Announcements & Raffle

8:00 - 9:00 PM:  Main Presentation

May 2018 Sponsor
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CGS would like to thank Marta and YCE Inc. for sponsoring the May 2018 meeting!

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Talk Abstract:

23 Years of Historic Hydrocarbon Seep Studies in Santa Maria Basin, Offshore California Using Seismic and Stratigraphic Data (1995 through 2018)

Joseph M. Saenz

Ventura County Community College District

Oxnard College


Thomas J. O’Neil, Director

Ventura County Community College District

Oxnard College Marine Center and Aquarium at Channel Islands Harbor

Oxnard College


Frank Denison

Frank Denison Consultant

Westlake California


In Honor of Peter J. Fischer, PhD

Department of Geological Sciences,

California State University, Northridge


In Honor of James W. Vernon, PhD


Camarillo, California


Historical seismic and stratigraphic records were used to understand the relative effects of active tectonics on hydrocarbon seeps in the Santa Maria Basin (SMB), offshore California.  The study confirms that hydrocarbon seeps are associated with the Hosgri-Purisima-Lompoc fault zones tapping into a single major reservoir, the Monterey Formation.  In the northern and central areas, these Monterey reservoirs occur in growing anticlinal folds that are faulted and fractured by these faults zones acting as a major conduit for gas and oil seeps.


The stratigraphy of the offshore SMB is known from seismic surveys, cores, electric logs, drill stem test records, and 73 well logs within the basin.  Over 60 multi-sensor, shallow drilling hazard and deep seismic reports provided data sets of seeps, seafloor features, and geologic structure. 


We find an abundance of evidence to suggest continuous or episodic upward movement of fluids as migrating gas plumes from deeper sediments into surface sediments.  The analysis shows that bright spots on the seismic reflection profiles are gas-plumes, linked to the highest geothermal gradients and controlled by active tectonics.  Gas, deeply sourced in the Monterey Formation migrates upward along faults, anticlinal folds, and steeply dipping beds into shallow sediment from depth.  Gas chromatograph analysis from mud logs samples in wells near gas plumes also show the highest concentrations of continuous total gas, methane, ethane, propane, and butane.


We believe that temperature changes induced by geothermal heating during burial caused in-reservoir thermal cracking of the oil to lighter-end hydrocarbon gases that migrate as gas plumes into shallow burial depths.  Drill stem test records indicate that Monterey Formation API oil gravities range from 3° to 35°.  Oil gravities are related to zones of shallow gas-charged sediments, and variable geothermal gradients ranging from 1.7°F/100 ft to 3°F/100 ft, and downhole temperatures ranging from 118°F to 248°F in the Monterey Formation. 


Within close proximity to the Hosgri Fault zone, lithologic analysis also revealed three areas where siliceous Monterey rocks have been diagenetically altered to glassy cherts linked to well logs with high temperatures, and reservoir pressures that range from 2,115 to 3,385 pounds per square inch gage.  Active tectonics has subsequently fractured these brittle rocks throughout the study area.  In the northern and central areas, the fracturing is significant, as it allows migration pathways to the reservoirs and to faults that serve as conduits for hydrocarbon seeps emanating from the seafloor.


The Hosgri-Lompoc-Purisima fault zone is transpressional, exhibiting both right lateral slip and reverse offsets.  Over 87-km-long (54 miles) in the study area, the three major faults zones are terminated by the North Channel Fault zone in the northwestern Santa Barbara Channel.  The compressional tectonics of the North Channel Fault zone, brings the Monterey Formation to the surface resulting in a loss of volatiles and biodegradation of the oil to tar at the surface in the southern area.  The occurrence of these features is generally limited to the Arguello Slope.  The heavy oil-tar seeps form tar sheets and growing tar mounds found near the seep vent structures, and in one case associated with Beggiatoa, a chemosynthetic bacterium that metabolizes petroleum was found near a seep in area S-II.

Joseph M. Saenz
Speaker's Bio:

Mr. Joseph M. Saenz "Manny" has over 30 years of combined experience.  He is employed as the “Engineering Lead” for the Heavy Construction IPT, Naval Facilities Engineering and Expeditionary Warfare Center, and as an Adjunct Faculty Geology Professor at Oxnard College.  He received degrees at California State University, Northridge, earning a B.S. in 1991 and a M.S. in 2002.  Saenz's practical experience in numerous heavy construction projects has allowed him to work on engineering geologic and water resource efforts, globally.  Saenz was the 2006 recipient of the prestigious Certificate of Commendation from the Combined Joint Task Force - Horn of Africa.

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