INTERPRETATION OF HYDROFRACTURE GEOMETRY DURING STEAM INJECTION USINGTEMPERATURE TRANSIENTS .2. ASYMMETRIC HYDROFRACTURES

This is the second part of a two-paper series illustrating the results of a steam drive pilot in the South Belridge Diatomite, Kern County, California. In this pilot, steam is injected through two noncommunicat ing, vertical hydrofractures that nearly span the entire 1000-ft-tall diatomite column. The first paper examined steam convection and heatin g resulting from injection into the lower hydrofracture. Here, we appl y a high-resolution numerical model developed in the first paper and i nterpret the results of steam injection through the upper hydrofractur e in the pilot between October 1989 and January 1994. Results of this analysis indicate that the upper injection hydrofracture was highly dy namic and asymmetrical while undergoing steam injection. Steam flowed preferentially into the northern wing of the hydrofracture, which reac hed a final wing length of 250 ft. To the south, hydrofracture wing le ngth reached roughly 75 ft and diatomite heating was weak. A dramatic temperature response above the perforated interval of the upper inject ion well suggests that a horizontal fracture, or network of natural fr actures, opened within the formation and linked to the injection hydro fracture. Our analysis indicates that roughly 43 percent of the total injected steam migrated above the perforations of the injection well, but remained within the Diatomite, and flowed rapidly away from the fr acture face because of a large increase of hydraulic diffusivity of th e formation.