An Economic Evaluation of Solvent/Steam Stimulation
Authors: Doscher T.M. , Ershaghi Iraj , Herzberg D.E. , Gourene Z.S. 
Published: December 2007

This paper describes the economics of steam/solvent stimulation. The performance of steam-soaking operations, with or without solvent performance of steam-soaking operations, with or without solvent stimulation, is simulated using the Boberg and Lantz analytical model. Indications are that solvents provide no economic advantage in steam-soaking operations where steam/oil ratios are economical.

Introduction
Steam stimulation currently is a proven process for stimulating production from low-gravity and viscous crude-oil reservoirs. A great deal of attention has focused on finding a way to increase the economic efficiency of the steam-soaking process.In the steam-stimulation process, the objectives are to use the heat from the injected steam to reduce the oil viscosity around the wellbore for a limited distance out into the formation. The viscosity of the reservoir crude oil is a function of temperature, which in turn depends on the total heat captured in the zone around the wellbore.If one could reduce the viscosity of crude oil before its contact with steam by using a solvent, the overall steam requirement to achieve similar productivity might be lower. The success of such a proposal depends more on securing a marginally greater reduction in viscosity by solution of solvent in crude oil than by using an economically equivalent amount of steam.To compare the steam requirements for the two cases (that is, with or without solvent stimulation), a prediction model was necessary. The literature contains prediction model was necessary. The literature contains many reports of analytical and numerical reservoir models that may be used to calculate the response of a steam-stimulation project. The method proposed by Boberg and Lantz was used here. This method is analytical and simple enough so that it can be used with hand calculations. Because the calculations are laborious, however, the method was programmed for a PDP-10 digital computer. A brief review of the Boberg and Lantz model is described.We recognize that this model does not constitute a complete description of the steam-stimulation process. The model does not include the effects of steam-zone collapse or formation compressibility. However, these effects, if active in a particular application, are common to both steam and steam-plus-solvent stimulation. The effects will be experienced primarily in the early part of the production cycle. The primary object of this study is to distinguish between the cost of realizing a terminal producing rate due to viscosity reduction caused by producing rate due to viscosity reduction caused by steam alone and that caused by steam plus solvent.This study focuses on the performance of a Kern River crude oil. We determined the viscosity/temperature relationships for this crude oil at different solvent cuts and show them here.

Method of Study
The following procedure was used to arrive at economic feasibility of solvent/steam stimulation under several conditions.Step. 1. Using die Boberg and Lantz model, the cumulative stimulated production (Delta Np) of crude oil from a viscous oil reservoir by the injection of a quantity of steam (Vs1) is determined.
JPT
P. 951