Determination of flow characteristics of petroliferous formations

#This invention relates to a method for determining the flow characteristics of subterranean formations by analyzing polysaccharide polymers recovered from production wells. More particularly, this invention relates to an improved method for determining flow characteristics of such polymers through petroliferous formations by hydrolyzing the polymer to separate glucose moieties contained therein and analyzing for the concentration of such moieties.

#As available oil supplies in producing formations have been depleted, additional recovery techniques have been developed to further extract oil trapped in petroliferous formations. Among such tertiary recovery techniques is waterflooding, generally carried out by injecting water at an injection well and displacing oil from the formation toward a producing well. Often polymers and other ingredients are added to such waterflood solutions to thicken and stabilize the solution, thus controlling the viscosity of the waterflood and adjusting the viscosity to the particular formation under development. In such cases the polymer often acts as a "piston" as relates to the less viscous hydrocarbons and pushes them toward the production well.

#It is important that the characteristics of the formation undergoing tertiary recovery techniques be determined. Methods commonly used for detecting formation structures such as acoustical techniques are insufficiently precise for determining the porosity and flow characteristics of a formation. This information is needed in order to adequately design the most efficient tertiary recovery techniques. Since tertiary recovery techniques are extremely expensive to implement, it is of great importance to determine the particular treatment which provides maximum recovery.

#Equal amounts by weight of a tracer material, thiocyanate ion, and a polysaccharide polymer (a Kelzan polymer sold by Kelco Company) is injected into a subterranean petroliferous formation. The injection is continued for several days or weeks. Effluent from a production well is periodically analyzed until traces of the faster eluting polymer are detected. Analysis for both the tracer and the polymer begins at this time and continues until approximately 95% of both have been eluted. The sample for determination of polymers is hydrolyzed in an acid media, reacted with orthotoluidine and the concentration is determined using standard colorimetric methods. A comparison of the rate of elution of the tracer material and the polymer will accurately portray the ratio of larger interstices to small interstices within the formation, and allow an accurate determination of the relative rates of the elution through the formation for various types of waterflood materials.

#The produced effluent samples are analyzed for thiocyanate ion tracer by adjusting the pH to about neutral, filtering to remove particulate matter and developing the Iron (III) thiocyanate color using an automated Auto-Analyzer instrument. This device mixes the reagent (iron (III) in about 0.1 N acid) with the sample, passes it through a colorimeter and calculates the concentration by comparing to standards run the same way. Table 1 shows typical calibration data for this system.

#TABLE 1 ______________________________________ Calibration Curve for Thyocycnate ion tracer Determination Tracer Concentration, ppm Absorbance as NH.sub.4 SCN ______________________________________ 1.20 20.0 1.90 15.0 0.58 10.0 0.44 7.5 0.29 5.0 0.14 2.5 0.05 1.0 ______________________________________