Enhanced Oil Recovery Through the Use of Chemicals-Part 2
Authors: Gogarty W.B. 
Published: December 2007

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering.

Where Do the Expensive Fluids Go?

Perhaps the most important question to be answered when designing a Perhaps the most important question to be answered when designing a chemical EOR process is, "Where do the expensive fluids go?" To answer this question, reservoir heterogeneities need to be considered since they affect vertical and areal conformance of fluids being injected. Injection profiles can be used to show where fluids enter the reservoir through the profiles can be used to show where fluids enter the reservoir through the wellbore. Where zones are separated, mechanical methods can be used to isolate them for flooding. If high-permeability zones with oil saturations are not isolated in the wellbore by shale or other lithological features, gelled polymer treatments may beeffective in providing a more uniform vertical distribution of fluids. Interference testing, use of tracers, and development of flood fronts with computer models are good diagnostic methods for predicting areal conformance. If injectivity tests show significant directional permeability, these resultsneed to be considered in locating wells. Injection and producing wells should be placed parallel to the maximum permeability direction. Injection and production rates can be estimated by using results from computer models. Fig. 1shows tracer results from the southwest part of the M-1 project. Tritiated water was injected into Well E-5 before the start of project. Tritiated water was injected into Well E-5 before the start of micellar solution injection. Time lines are shown under some of the producing wells. The length of a timeline indicates how long samples were producing wells. The length of a time line indicates how long samples were taken from a given producing well. The magnitude of the radioactive tracer response at a given time is shown above the line. No tracer was detected in Wells F-4 and F-6, even though these are two of the four wells surrounding Injection Well E-5. Significant and lengthy responses were observed in Wells D-4 and D-6. Responses in B-4 and D-2 are significant since both of these wells are outside the inverted five-spotserviced by Injection Well E-5. These tracer results indicate the degree of heterogeneity that can exist in a reservoir. Application of an EOR process without understanding reservoir heterogeneity can lead to disastrous results. In the North Burbank tertiary recovery pilot, gelled polymer treatments were used to correct vertical conformance problems. The location of this pilot is shown in Fig. 2. A profile of one of the injection wells of the North Burbank project is shown in Fig. 3. On the left, the Burbank sand is defined by porosity as determined from a gamma-ray log. On the right, results from an injection profile indicate a severe vertical conformance problem. Fig. 4 shows tracer concentrations measured in one of the production wells of the North Burbank pilot. The results shown are before and after applying a gelled polymer treatment to one of the offsetting injection wells. Results indicate that the high transmissibility between the injection well and this producing well has decreased.

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