--> Abstract: Global Basins Research Network: Advancing the Science of Fluid Flow Prediction in Sedimentary Basins, by J. A. Nunn and L. M. Cathles; #90933 (1998).

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Abstract: Global Basins Research Network: Advancing the Science of Fluid Flow Prediction in Sedimentary Basins

Nunn, Jeffrey A. - Louisiana State Univ.; Lawrence M. Cathles - Cornell Univ.

The Global Basins Research Network (GBRN) is in its 8th year and is an industry-supported research consortium of 5 universities and about 20 researchers which seeks an understanding of the coupled physical, chemical, and fluid flow processes in sedimentary basins that lead to hydrocarbon generation, migration, and entrapment. To date, we have concentrated on the Eugene Island (El) Block 330 area of the Gulf of Mexico, with about $4 million of funding (non-drilling) from the U.S. Department of Energy, National Science Foundation, the Gas Research Institute, and member companies. Hydrocarbons in shallow, hydropressured, Plio-Pleistocene reservoirs in El 330 appear to be derived from turbidite stacks within the salt withdrawal mini-basin buried deep within the geopressured zone. Volume processing and attribute analysis of 4D seismic data are used to identify seismic amplitude interconnectivity and changes over time that result from active fluid migration. Fluid Pressures and temperatures provide rate and timing constraints. Geochemical variability in reservoirs is attributed to mixing of oils and interaction of oil and gas.

In 1993, GBRN extended a Pennzoil-operated well through a bounding growth fault of the El 330 mini-basin (Fig. 1). Whole coring, extensive logging, and stress and production testing were made to determine in-situ conditions. Pore fluid pressures reach 93% of lithostatic pressure below 2000 m. The density of geopressured sediments is low, indicating undercompaction. Core plugs have a measured porosity of 30%. While a ductile rheology is indicated by low shear modulus (< 1 GPa) and high Poisson's ratio (> 0.4), the core plus a downhole FMI log revealed numerous micro-faults and fractures. Some of the microfaults and fractures contain oils. Formation waters from these Pleistocene strata have been isotopically dated as Oligocene or older. Drill stem tests around the fault showed that sediment permeability decreased from 100 mD to 0.1 mD as a function of drawdown pressure. Using hydrostratigraphic information constructed from seismic and well data, we have simulated episodic expulsion of fluids from the geopressured zone along faults into individual sand layers in the overlying hydropressured zone of El 330 (Fig. 2). Our finite element code realistically simulates fluid flow, heat and solute transport along and across faulted strata during basin evolution. Our finite element code also has been applied to 1) fluid flow on faults offshore Africa and 2) C02 gas generation in Southeast Asia.

Ongoing GBRN projects include: Prediction of compaction as a function of lithology, depth, and temperature gradients; Estimation of formation permeability and pore water salinity from wireline logs; Laboratory and field documentation of capillary seals in alternating fine-coarse layers which contain gas and water; A mixed equation of state model to predict the changes in hydrocarbon chemistry that occur during phase separation; Methane flux from the deeper parts of a basin transported by propagating fractures; Regional reconstructions of salt deformation; Organic geochemical evidence for episodic expulsion; 3D hydrocarbon geochemistry and vitrinite maturities; 3D evolution of El 330 fault array; Thermohaline convection in sands; measurements of permeability versus effective stress; and Geopressure generation by ductile shear deformation.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil