Wet Underground Combustion, State of the Art
Authors: Dietz D.N. 
Published: December 2007

Research results and field experience are analyzed to arrive at a system for designing and evaluating large-scale projects.

Introduction

Dietz and Weijdema, in a paper titled "Wet and Partially Quenched Combustion", reduced the Partially Quenched Combustion", reduced the process of wet combustion to the barest essentials. process of wet combustion to the barest essentials. The most important simplifying assumptions were: no gravity segregation, no heat exchange with cap and base rock, no heat conduction in the direction of flow. They thus arrived at three possible processes for different ranges of water to air injection ratios: dry combustion, normal wet combustion, partially quenched combustion. Partially quenched combustion is defined as a process whereby part of the available fuel is left behind unburnt. One of the assumptions made in the paper is that this process is identical with super-wet paper is that this process is identical with super-wet combustion, where super wet indicates that more water flows through the temperature wave than can be evaporated. Under the conditions of their laboratory experiments, this assumption is almost correct. Beckers and Harmsen took heat conduction in the direction of flow into account and looked into the influence of injection rate and of residual fuel. They found that, subject to the combination of parameters, there are in principle many more processes than the three derived from the simple Dietz-Weijdema theory. Within the range of field values of these parameters, only some of the processes will occur in practice; another group of their processes may be encountered in laboratory experiments. In an as yet unpublished study, E. Baskir, H. L. Beckers, D. N. Dietz, L. G. J. ter Haar and J. H. Kruizinga confined themselves to the case in which combustion is both partially quenched and super wet. In this mainly mathematical study, they included not only heat conduction in the direction of flow, but also the heat exchange with cap and base rock by conduction. The studies mentioned above dealt mainly with the heat flow. Fluid flow was considered only as far as the conservation of mass is concerned. The mechanism of oil displacement and its stability and the gravity segregation of air and water were disregarded. To solve a set of equations describing the heat flow as well as multidimensional, multiphase fluid flow would seem to be a task beyond man and digital computer. J. Weijdema has therefore tackled the combined problem with the aid of (unpublished) scaled model experiments. As in many other types of model investigation, the scaling rules cannot be made to fit rigidly all requirements, and some compromise has to be accepted. This model technique is imperfect in the sense that the combustion zone is too long and moves too fast. The only occasions when all aspects of the process are fully represented are in a limited number of field pilot tests. The wet combustion tests in Schoonebeek, pilot tests. The wet combustion tests in Schoonebeek, the Netherlands, and in East Tia Juana, Venezuela, confirmed in broad outline the theoretical expectations. The tests also drew attention to problems of a different nature. The Schoonebeek test suffered from severe plugging, a phenomenon not observed in other thermal plugging, a phenomenon not observed in other thermal Schoonebeek operations nor in combustion tests elsewhere.

JPT

P. 605