ABSTRACT

Recognition of the pathways that channel kilometer-scale vertical fluid movements around salt domes is important to the understanding of petroleum migration and injection-well disposal. It is hypothesized that the vertical component of flow is accommodated by fractures, faults, porosity developed in the margin of the salt, and through complexly interconnected sands. By means of geochemical and petrographic techniques, specific fluid migration pathways have been identified on the southwest flank of the Iberia salt dome, Iberia Parish, Louisiana.

Brine samples from the Iberia oil field have been analyzed by ICP-AES for dissolved Na, K, Mg, Ca, Sr, Ba, Mn, Fe, Cu, Pb, Zn, Al, Si, and B. The concentration data were contoured on a cross section developed from well logs to identify spatial correspondence between structures or sand bodies, and compositional gradients of solutes within the pore fluids. Contour lines for Ba, B, Ca, Fe, and Sr deflect from sub-parallel with formation dip, to sub-parallel with high-angle faults. This suggests that the faults either directly accommodate vertical fluid movement, or serve to juxtapose permeable sands in sand/mudstone successions, thus forming vertical pathways of complexly interconnected sands.

SEM-EDS inspection of well cuttings reveals the presence of diagenetic calcite, pyrite, vermiform kaolinite, barite, and sphalerite in pore spaces. In some samples, mineralization in dilated micro-fractures reveals that fracture porosity also contributes to pore-fluid movement in the Iberia flank sediments.

Thus, faults and fractures contribute to vertical fluid flow and solute transport over a wide range of dimensional scales at the Iberia salt dome.