Interpretation of hydrofracture geometry during steam injection using temperature transients II. 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 noncommunicating, vertical hydrofractures that nearly span the entire 1000-ft-tall diatomite column. The first paper examined steam convection and heating resulting from injection into the lower hydrofracture. Here, we apply a high-resolution numerical model developed in the first paper and interpret the results of steam injection through the upper hydrofracture in the pilot between October 1989 and January 1994. Results of this analysis indicate that the upper injection hydrofracture was highly dynamic and asymmetrical while undergoing steam injection. Steam flowed preferentially into the northern wing of the hydrofracture, which reached a final wing length of 250 ft. To the south, hydrofracture wing length reached roughly 75 ft and diatomite heating was weak. A dramatic temperature response above the perforated interval of the upper injection well suggests that a horizontal fracture, or network of natural fractures, opened within the formation and linked to the injection hydrofracture. 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 fracture face because of a large increase of hydraulic diffusivity of the formation.