Geologic Problems Related to Characterization of Clastic Reservoirs for EOR

Abstract

Geologic problems encountered in four U.S. DOE-sponsored EOR projects in clastic reservoirs were analyzed. The reservoir heterogeneities were grouped into four categories: depositional, diagenetic, structural, and formation-fluid composition/distribution. Each category had a variable effect on the performance of the EOR projects.Requirements for developing one static geologic model for each category of heterogeneity are proposed. The interrelationship of geologic factors and the effect of heterogeneities resulting from the origin and timing of geologic events are described.Besides heterogeneities associated with the depositional environment, which has a significant effect on EOR performance, diagenetic effects resulting from geochemical alterations and different types and polymorphs of clays are also important but are often neglected. The structural component of the model needs to be improved through the application of new methodology or improvements in existing technology (e.g., remote sensing, high-resolution seismic). A realistic prediction of fluid movement in clastic reservoirs subjected to EOR requires the integration of the four models that define all the heterogeneities.

Determining the Productivity of a Barrier Island Sandstone Deposit From Integrated Facies Analysis

“…3), did not provide the anticipated recovery. Subsequent data analyses [14][15][16] indicated that reservoir geology and the poor quality of sulfonate used in the polymer flood were probably responsible for the less-than-optimum recovery. As discussed previously, the relatively poorer permeability and porosity of the sediments deposited under lower-energy conditions in this region resulted in more clay content in the sandstone, although faulting or the presence of a permeability barrier is also suspected in the eastern part of the pilot and may have contributed to the poor sweep and displacement efficiencies of the chemical flood.…”

“…The second micellar-polymer pilot was located in the central part (the TIP area) 14,16 of Unit A (location in Fig. 3) where the highly productive facies is thick and the sandstones have good porosity and permeability, except in a small area in the southwest of the TIP area.…”

Research needs for strandplain/barrier island reservoirs in the United States

“…Problems related to reservoir heterogeneity encountered in four EOR pilot projects in clastic reservoirs sponsored by the Department of Energy (DOE) were analyzed in detail by Szpakiewicz et al (1987). Two of these reservoirs, the Big Muddy field producing from the Upper Cretaceous Frontier formation in Wyoming and the Bell Creek field producing from the Lower Cretaceous Muddy formation have been classified as barrier island deposits (i.e., Class 4).…”

“…The Bell Creek field consists of six separate barrier island reservoir compartments in which the trapping mechanism is the updip pinch-out of barrier core facies into lagoonal shales. The predominant heterogeneities affecting production in this micellar-polymer project were (1) facies architecture and the presence of incised valleys with lithologically variable fill (Szpakiewicz et al, 1987;Honarpour et al, 1988;Sharma et al, 1990;Burt et al, 1975); (2) distribution, type, and amount of authigenic clay minerals; and (3) presence of previously unrecognized fractures and faults between wells and groups of wells. Production data and pressure-pulse tests confirmed many of these naturally occurring heterogeneities, but interpretation of tracer survey results was not clear because of chemical interaction between the preflush and micellar-polymer solution (Szpakiewicz et al, 1987).…”

Integrated seismic study of naturally fractured tight gas reservoirs. Final report, September 1991--January 1995

“…In tight formations, which can include sandstones, shales, limestones, and coal, often the only practical means to extract hydrocarbons is by exploiting the increased drainage surface provided by natural fracture zones (Szpakiewicz et al, 1986;Lorenz et al, 1986). The practical difficulties that must be overcome before effectively using these fractures include: locating the position and orientation of fracture zones, determining the intensity of fracturing, and characterizing the spatial relationships of these fractures relative to reservoir heterogeneities which might enhance or inhibit the eventual gas flow.…”