Abstract

Interpretive methods for the evaluation of miscible flood performance have been under considerable scrutiny over the last five years, It has been recently, shown that some of the more conventional procedures for miscibility determination might be inadequate for certain oil/solvent systems. Along with these developments, the importance of mechanism identification has been shown.

This paper provides an initial review of some of the ambiguities associated with miscible flood interpretation followed by a discussion of the tests commonly used to ascertain miscibility limns. An analysis of experimental procedures is included with a detailed description of the method for maximizing miscibility information. This is done by reference to seven miscible flood designs which the authors have completed over the last two years covering a very diverse set of solvent/oil systems. The specific contributions of flashed liquid compositions, effluent density profiles and dynamic displacement residue analysis are shown pertaining to miscibility classification.

As a conclusion, a generic checklist is proposed for evaluation of the type of laboratory program which should be entertained in order to determine miscibility limns. Using this checklist one can determine what types of laboratory tests should be considered, which tests are required, and which are optional. Use of this checklist will tend to optimize the miscible data acquired for the research dollar invested.

Introduction

Miscible flooding was formally invented in the 1950's according to the literature. The first contact miscible (FCM) process was described by Koch(l) and Hall et al(2). The high pressure vaporizing miscible process was discussed by Whorton et al(3,4,5) and, the condensing mechanism was described by Stone et al(6) and by Kehn(7). Since that time considerable work has been implemented in the laboratory and the field to take advantage of the miscible processes.

In the last decade there have been new theories proposed including combined condensing/ vaporizing(B) and Iiquid-liquid extraction(9) mechanisms. Some groups are now beginning to leave the conventional terminology of vaporizing/condensing and dwell more on the pattern of contacting: forward zone and swept-zone contacting for example. Moreover, with the description of new theories regarding miscibility development there has been a revision in some interpretations. Novosad et al(9) show the comparison between original interpretation and a more recent conclusion based on the liquid-liquid extraction theory (Table 1). If the assumed mechanism was erroneous then, in the worst case, what was almost FCM would have been immiscible by the new interpretation. Although a conservative approach dictates a certain degree of overdesign one must be certain that the miscible mechanism assumed is correct in order to make the correct conclusion. Indeed if one misinterprets the miscible lab data and includes a conservative cushion on the solvent design one may still be deficient in the field implementation.

This paper discusses laboratory responses from a number of oil-solvent systems covering condensing and vaporizing systems from immiscible (IMM) to FCM. Emphasized herein is the information available from a broad variety of experimental apparatus and how they contribute to conclusive evidence of miscibility.

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