New Publication - Aaron Meltzner & Tom Rockwell

Bulletin of the Seismological Society of America, December 2006, Vol. 96, Issue 6, pp. 2304-2328

Recent and long-term behavior of the Brawley fault zone, Imperial Valley, California; an escalation in slip rate?
Meltzner, Aron J. (San Diego State University, Department of Geological Sciences, San Diego, CA, United States); Rockwell, Thomas K.; Owen, Lewis A.

ABSTRACT

The Brawley fault zone (BFZ) and the Brawley Seismic Zone constitute the principal transfer zone accommodating strain between the San Andreas and Imperial faults in southernmost California. The BFZ ruptured along with the Imperial fault in the 1940 M (sub w) 6.9 and the 1979 M (sub w) 6.4 earthquakes, although in each case only minor slip apparently occurred on the BFZ; several other episodes of slip and creep have been documented on the BFZ historically. Until this study, it has been unclear whether the past few decades reflect average behavior of the fault. Two trenches were opened and a series of auger holes were bored across three strands of the BFZ at Harris Road to compare the amount of slip observed historically with the displacements observed in the paleoseismic record. Evidence is presented, across the westernmost strand of the BFZ and across the entire BFZ at Harris Road, to show that both the average vertical slip rate observed in modern times (since 1970) and the vertical creep rate (excluding coseismic slip) observed during the 1970s are significantly higher than the long-term average. Across the westernmost strand, the long- term vertical rate is 1.2 (+1.5/-0.5) mm/yr, and the average rate since about A.D. 1710 is determined to be no greater than 2.0 mm/yr; in contrast, the average vertical rate between 1970 and 2004 across that strand was at least 4.3 mm/yr, and the 1970s vertical aseismic creep rate was 10 mm/yr. Likewise, across the entire BFZ, the long-term vertical rate is 2.8 (+4.1/-1.4) mm/yr, whereas the rate between 1970 and 2004 was at least 7.2 mm/yr, and the 1970s aseismic creep rate was 10 mm/yr. The long-term strike-slip rate cannot be determined across any strands of the BFZ but may be significant. In contrast to the commonly accepted higher sedimentation rates inferred for the entire Imperial Valley, we find that the average sedimentation rate on the downthrown side of the BFZ adjacent to Mesquite Basin, in the millennium preceding the onset of agricultural influences, was at most 3.5 mm/yr. Finally, a creep event occurred on the BFZ during our study in 2002 and is documented herein.

Southern Salton Trough deltaic system, based on DEM imagery. Color contours indicate elevation; each color band represents a 5- to 10-m change in elevation. Sections of some contours are highlighted with thin black lines for improved visibility. The band labeled “12m” is the contour at an elevation of 12 m above mean sea level, which represents the highstand shoreline of Lake Cahuilla. Note the location of the modern delta, which is interpreted to have formed initially in response to the 1905– 1907 filling of the Salton Sea; slow retreat of the lake combined with regular flow of the New and Alamo Rivers has built this modern delta that is prograding into the Salton Sea. In addition to the modern delta, four prehistoric delta lobes have been interpreted on this DEM: deltas N1 and N2 on the New River, and deltas A1 and A2 on the Alamo River. Main faults are mapped in black. SMF, Superstition Mountain fault; SHF, Superstition Hills fault. Modified from Ragona (2003). ( E A color version of this figure is available in the electronic edition of BSSA.)

Full Text (pdf)

Tidal Bore on the Dordogne River

Alumni Banquet presentation by honoree Dr. Clive Dorman

Video from Clive's trip to France

SEMINAR - Lee T. Billingsley

Lee Billingsley received a B.S. in Geology from Texas A&M in 1975, an M.S. in Geology from the Colorado School of Mines in 1977, and a Ph.D. in Geology from Texas A&M in 1983. He began his oil and gas career in 1976 with Tenneco Oil Company in Denver, and later worked with American Quasar Petroleum (Denver) and Monterrey Petroleum Corporation (San Antonio). From 1983-1998, he was President and Founder of Sandia Oil & Gas Corporation, until joining Abraxas Petroleum Corporation in 1998. He is currently Vice-President of Exploration. Dr. Billingsley is a member of many regional and national professional societies, and he has received numerous awards including the AAPG Distinguished Service Award (1997) and Certificate of Merit (1999), as well as the GCAGS Distinguished Service Award (1998). He served as President of the South Texas Geological Society (1985-86) and as General Chairman of the 2004 GCAGS Convention in San Antonio. Within AAPG, he has held several positions including Treasurer, member of House of Delegates, Associate Editor of the Bulletin, and Division of Professional Affairs Secretary. Currently, he is AAPG President (2006-2007).

Lee's seminar title: "Exploiting the Devonian Reservoir in Oates SW Area, Western Delaware Basin, Texas"; Wednesday the 28th of February 2007

Abstract
The Oates SW field area is located in southwestern Pecos County, Texas, and it is in the southwestern portion of the Delaware basin. The dominant producing reservoir in the area is simply called Devonian, but it is probably Devonian-aged chert in the Thirtyone Formation. Regional structure is NE dip into the basin with some NW-SE trending faults. The Oates SW area is flanked by large structural closures that have produced gas from the Devonian and adjacent reservoirs. These fields include: Perry Bass, 26 BCF from nine wells; Oates NE 266 BCF from 25 wells, and Pikes Peak, 48 BCF from eight wells.
In contrast to surrounding fields, Oates SW consists of four small structural closures that vary in size from about 320 to 1280 acres. Abraxas acquired 3-D seismic data to refine the structural interpretation and guide potential horizontal well bores. Each closure has from one to three vertical wells, and the wells produced from 0.2 to 2.4 BCFG each from the Devonian chert. Production from each vertical well near the top of closures roughly correlates to Devonian reservoir quality determined from log analysis. However, a comparison between calculated original gas-in-place and actual production for each closure indicates a relatively low recovery factor. All the vertical wells exhibited high rates of water production late in their productive history.
Abraxas has drilled three horizontal well bores within the Devonian chert on separate closures. Results span the spectrum of potential outcomes. The best well has produced at a constant rate of 8 MMCFD and the worst well only makes 150 MCFD. The third well is a re-entry of a vertical well, which had produced 1.8 BCFG. Abraxas drilled horizontally within the Devonian chert. Initially, the well produced 100% water, but gas rates eventually increased. Currently, the well produces at relatively constant rates of 700 MCFD and 4000 BWPD. The source of the water production is unknown. It could be from: 1) near well bore, but not from the Devonian interval, 2) micro-fractures within the Devonian, which are connected to deeper water sources like the Ellenburger, or 3) near well bore water coned upward during production form the vertical well bore.
Detailed correlation of logs indicates an unconformity at the top of the Devonian chert. Consequently, the porous Devonian chert interval is thinner in structurally high wells. This interpretation may explain the variable reservoir quality of the three wells, based on the projected trajectory of the horizontal well bores.
As with other horizontal Devonian chert fields, results are highly variable from well-to-well. Overall the economics of the play in Oates SW have been favorable, but much still needs to be learned in order to repeat the success.