April, 1999 HGS Meetings Calendar

April, 1999HGS Meetings

HGS Dinner Meeting
"Balanced Filled Lakes Worldwide: Insights for Optimum Source Character and Distribution In Brazilian Continental Margin Basins"

Authors: BOHACS, KEVIN M. & NEAL, JACK E., Exxon Production Research Company, Houston, Texas, USA
Date: Monday Apr. 5, 1999
Place: Westchase Hilton, 9999 Westheimer
Time: 5:30 Social 6:30 Dinner

Abstract:
Exxon has developed the concept of lake-basin type, which is useful for sorting out the complexities of lacustrine deposition to derive a predictive framework. Balanced-filled lakes are one of three lake-basin types recognized from recurring lithofacies associations and stratal stacking patterns. Balanced-Filled lake systems contain the most prolific lacustrine source rocks and beneficent facies juxtapositions for hydrocarbon accumulation, based on observations of lacustrine strata of many different ages and basins (e.g.: East Africa Quaternary, USA Tertiary, China & Africa Cretaceous).
Balanced-Filled lakes can be shallow or deep with thick or thin sequences but they share similar geochemical and sequence-stratigraphic attributes. Parasequences and sequences are meters to tens of meters thick, distinctly expressed in seismic, logs, and geochemistry, and formed by a combination of progradation and desiccation. Lake-water chemistry varies systematically from fresh to saline/alkaline. Most organic-rich rocks are deposited in the profundal zone, with subordinate amounts in the lake plain behind mixed biogenic-clastic shorelines. Organic matter is dominantly algal Type I, typically with TOC £ 30% and HI £ 650 mgHC/g C. Organic facies are relatively constant laterally, changing only relatively close to shore. Sequence boundaries are formed by a mix of erosion and desiccation— erosion may be best developed during transgression.
Comparison of geochemical, geological, and geophysical data from Balanced-Filled lakes worldwide with Brazilian basins provides a greater understanding of source rocks in the lacustrine systems responsible for most of the giant oil accumulations in offshore Brazil and suggests strategies for successful exploration and exploitation.
Speaker Biography:
Kevin M. Bohacs is a sedimentologist and stratigrapher with the Petroleum Geochemistry section of Exxon Production Research Company. He received his B.Sc.(Honors) in geology from the University of Connecticut in 1976 and his Sc.D. in experimental sedimentology from M.I.T. in 1981. At EPR, he leads the application of sequence stratigraphy and sedimentology to organic-rich rocks from deep sea to swamps and lakes, in basins around the world. As a Research Associate, his primary focus is to keep the geo- in geochemistry. He has written numerous papers on the stratigraphy and sedimentology of hydrocarbon source rocks. He was co-recipient of the AAPG Jules Braunstein Memorial Award for best poster session paper in 1995 for work on coal sequence stratigraphy and of the AAPG Best International Paper in 1998 for work on lakes.

HGS Environmental / Engineering Section Dinner Meeting
Title of talk

Author: Date: Apr. 14, 1999 Place: Jalapeno''s - 2702 Kirby (at Westheimer) Time: 6:00 - 7:00 PM - Dinner; 7:00 - 8:30 PM Lecture, Career Opportunities, and NetworkingCost: $16.00 per person for a full dinner including tip. Dinner is optional.

Abstract:

International Dinner Meeting
The paleo-Volga delta and lacustrine sequence stratigraphy of the South Caspian basin

Author: Dag NummedalDate: Monday Apr. 19, 1999 Place: Westchase Hilton, 9999 Westheimer Time: 5:30 Social 6:30 Dinner Poster Session: Click here

Abstract:
The Productive Series of the South Caspian basin consists primarily of Pliocene delta deposits of the Volga River. GCA reservoirs at the Apsheron Sill and numerous old fields in the transition and onshore areas of Azerbaijan contain Productive Series beds. Outcrops on the Apsheron Peninsula north of Baku, extensive seismic data, and cores in the GCA field provide the data base to determine age, depositional systems, stratigraphic architecture, and reservoir properties of the Productive Series.
SOCAR (State Oil Company of Azerbaijan) invited five companies (Agip, BP Amoco, Conoco, Tpao, Unocal) to undertake a joint study of the sedimentology and stratigraphy of much of the Productive Series. The 13 investigators involved in the study (see Project Team) emphasized the highly productive Pereriva and Balakhany suites and outcrops of the Kirmaku, Nkp, and Nkg suites. Related projects by other Unocal personnel added valuable insights into the sedimentology, with some being presented as posters in conjunction with this talk.
Age of the Productive Series was determined by a combination of Ar39/Ar40 dates of ash deposits bracketing the Productive Series, graphic correlation of micropaleontological data and event beds, and adjustments based on the global oxygen isotope curve for the Pliocene and latest Miocene. The Miocene-Pliocene boundary (5.3 Ma) lies at or near the base of the Pereriva Sandstone, and the top of the Productive Series (top Surakhany) is about 3.0 Ma.
Lake levels in the Caspian repeatedly rose and fell during deposition of the Productive Series. Climatic cycles responsible for the changes in lake level dramatically affected the sediment yield from the Volga drainage basin. At lowstands of lake level, the climate was hot, evaporation from the lake was high, and there was little to no flow of water or sediment into the lake. Extensive lake-margin exposure surfaces characterize the lowstands.
As cooler and wetter climate replaced the hot and dry periods, lake levels rose. During early, slow rises in lake level, major sandstone packages of braided fluvial deposits grading lakeward into thin mid-channel bars and braid-delta fronts accumulated.
During late transgressions and highstands, the deltas were well north of the Apsheron region and only distal prodelta mudstones accumulated in the study area. With no sandstones deposited between the transgressive and highstand muds and the next overlying exposure surface, the Volga delta apparently did not prograde back south during the subsequent fall in lake level. Return to a hot, dry climate probably left the river dried out as lake level fell. This is very different from marine systems where major delta complexes generally prograde as sea level falls.
Changes in lake level occurred on time scales ranging from about 106 to 104 years, with some or all perhaps driven by Milankovitch cycles. Longer cycles may include a tectonic component unrelated to cmatic variations. Because of the strong climatic influence on lake level change and stratigraphic architecture, there is more "order" (predictive cyclicity) in the paleo-Volga deposits than in any documented marine deltaic succession.
Understanding how climate/lake level cycles control the timing of sand delivery into the Caspian basin has clear exploration significance. At the development scale, the systematic vertical change in depositional systems within nested sequences of different thicknesses exerts the dominant control on heterogeneity and connectivity of reservoirs and seals.
Project Team
1 Project team: V. Abreu (Unocal), Z. Bati (Tpao), H. E. Clifton (Conoco), ), T. D. Demchuk (Conoco), M. Fornaciari (Agip), A. A. Narimanov (Socar), D. Nummedal (Unocal), G. W. Riley (BP Amoco), A. Sayilli (Tpao), J. A. Stei