Features of West Hackberry SPR Caverns and Internal Structure Of the Salt Dome
The intent of this report is to examine the internal structure of the West Hackberry salt dome utilizing the information from the geometric configuration of the internal cavern surfaces obtained from graphical representations of sonar survey data. In a general sense, the caverns of West Hackberry are remarkable in the symmetry of their shapes. There are only rather moderate deviations from what would be considered an ideal cylindrical solution mining geometry in these caverns. This finding is in marked contrast to the directional solutioning found in the elliptical cross sectioned, sometimes winged, caverns of Big Hill. None of the persistent lineaments prevalent in Big Hill caverns are evident in West Hackberry caverns. Irregularities of the West Hackberry caverns are restricted to preferential solution formed pits and protuberances with moderate dimensions. In fact, the principal characteristic of West Hackberry caverns is the often large sections of smooth and cylindrical cavern wall. Differences in the cavern characteristics between West Hackberry and Big Hill suggest that the former dome is quite homogeneous, while the latter still retains strong remnants of the interbeds of the original bedded Louann salt. One possible explanation is that the source of the two domes, while both from the Louann mother salt, differs. While the source of the Big Hill dome is directly from the mother salt bed, it appears that the West Hackberry arises from a laterally extruded sill of the mother salt. Consequently, the amount of deformation, and hence, mixing of the salt and interbed material in the extruded sill is significantly greater than would be the case for the directly formed diapir. In West Hackberry, remnants of interbeds apparently no longer exist. An important aspect of the construction of the West Hackberry caverns is the evidence of an attempt to use a uniform solutioning construction practice. This uniformity involved the utilization of single well solutioning and the consistent physical location of the inlet/outlet tubing in each solutioning stage, although the process did evolve with time as would be expected in a large construction project. In this study of the construction of the West Hackberry caverns, it was possible to examine the apparent effects of flow rate (solutioning rate) and salt removal quantities during each of the solutioning stages of construction. Interestingly, there appeared to be no real influence of these factors on the details of the cavern characteristics. Any of the flow rates or removal quantities could produce significant irregularities at discrete cavern wall locations, whether or not these irregularities influence the cavern behavior remains unclear. It seems that subsequent solutioning stages could either remove irregularities from earlier stages or generate irregularities of their own. In the study, no apparent influence of the material factors of creep resistance or impurity content of the salt could be found. As has been previously speculated from the earlier study of Big Hill caverns, some irregularities of the cavern wall are thought to be the formation sites of potential salt falls, this thought pertains to the West Hackberry caverns, as well. Considering the extent of the West Hackberry cavern facility, the relative uniformity of the solution mined caverns throughout the facility is impressive. This uniformity is certainly the result of homogeneity of the salt dome, and the uniformity of the solutioning practice in these single well caverns.