|Characterization of Turbiditic Oil Reservoirs Based on Geophysical Models of Their Formation
To develop, test, and validate a new method for the characterization of turbiditic reservoirs based on the fundamental physics of the formation of the reservoirs.
The University of Texas at Austin
Departments of Chemical and Petroleum Engineering
The project developed a new, deterministic tool for characterizing turbiditic oil reservoirs to complement geostatistics.
The need for improved characterization of turbiditic oil reservoirs is timely. The valuable reservoirs currently being explored and developed in the deepwater Gulf of Mexico are turbidites. Such deposits, constituting the most active hydrocarbon play in the U.S., are light oil or natural gas reservoirs found at great depths and in relatively unexplored regions. Economic viability of these reservoirs depends strongly on their production rates; therefore, the ability to estimate and characterize prime locations in the reservoir is vital. Further, valuable turbiditic oil reservoirs are located off western Africa, another location of importance for U.S. oil interests.
Turbidites are formed by the deposition of sand and clay particles from a turbidity current, which is a subsurface, suspension-laden flow driven by the density difference between the current and ambient fluid. The fluid mechanics of this buoyancy-driven, multiphase flow are fairly well-understood. Researchers developed a computational simulation of the process of deposition as function of the initial volume of the suspension or its flow rate, its initial sediment load, and the local topography (all can be inferred from cores, logs, and seismic data). From the predicted pattern of deposition and the distribution of particle sizes in the deposit, it is possible to determine the spatial distribution of porosity and permeability at a centimeter length-scale. This information is invaluable for running other simulations of oil recovery to determine optimal methods for extraction of oil from the reservoir. The project's proposed method is an excellent complement to geostatistical methods for spatial characterization of a reservoir because it includes additional information based on the physics of the formation of the reservoir.
From the simulation comes a detailed distribution of the particle concentration for each deposit or layer, from which one can produce porosity or permeability distributions. The sum of all the events produces a layered porous medium, as is often seen in depositional systems. The information on the porosity and permeability can be used in flow simulators.
- Developed first-principle model equations for highly concentrated turbidity flows.
- Developed numerical methods to solve equations for the highly concentrated flows.
- Developed simulation of flow and deposition from turbidity flows over arbitrary and dynamically changing topography for multiple particle sizes and multiple events.
- Identified efficient methods to determine simulation inputs (initial sediment load, particle-size distribution, event location, etc.) to match or honor available data.
- Developed a method to convert depositional data into petrophysical data (e.g., porosity, permeability).
In practice, the resulting depositional profiles can be matched to seismic, core, and well logs by adjusting process inputs, such as sediment load and particle size. For example, if one has only seismic information and hence the shape and volume of the deposit, one could run simulations adjusting the particle size to produce the best fit to known data. With this particle size, it is possible to produce an estimate of permeability that often is critical in effective bidding for expensive deepwater leases. This tool provides a quantitative, physics-based means to estimate and infer valuable parameters from subsurface/subsea turbidites.
Current Status (June 2006)
The project is completed. The final report is in progress.
Project Start: September 1, 2001
Project End: January 15, 2006
Anticipated DOE Contribution: $649,000
Performer Contribution: $183,000 (22% of total)
NETL - Purna Halder (firstname.lastname@example.org or 918-699-2083)
UT Austin- Roger Bonnecaze (email@example.com or 512-471-1497)
The topography (left) over which 325 turbidity depositional events are simulated, giving the total deposit (right). Note the mounding of sediment. From the deposition, a detailed porosity and permeability map of the simulated deposit can be generated.
Permeability for a single deposition event composed of particles of three sizes.
" Lakshminarasimhan, S., "Study of the Flow and Deposition from Turbidity Currents," Ph.D dissertation, The University of Texas at Austin, May 2004.
" Srivatsan, L., Lake, L.W., and Bonnecaze, R.T., 2004 "Scaling analysis of deposition from turbidity currents," Geo-Marine Letters 24, 63-74.
" Bonnecaze, R.T., and Lakshminarasimhan, S., "Characterization of turbiditic oil reservoirs based on geophysical models of their formation," US DOE Technical Report , June 1, 2003.
" Bonnecaze, R.T., and Lakshminarasimhan, S., "Characterization of turbiditic oil reservoirs based on geophysical models of their formation," US DOE Technical Report, April 1, 2004.
" Bonnecaze, R.T., Lake, L.W., and Lakshminarasimhan, S., Final Report on Characterization of Turbiditic Oil Reservoirs Based on Geophysical Models of Their Formation (in preparation)