Using Crosswell Electromagnetics to Map Water Saturation and Formation Structure at Lost Hills

Abstract In 1992, Chevron USA initiated a large waterflood program in the Belridge Diatomite at Lost Hills Field. Injection and production wells are hydraulically propped-fractured, and water is injected across a vertical interval of approximately 600 ft. The injected water is assumed to follow the hydraulic fractures and spread laterally outward. However, the extent of flooding, the saturation variations between individual layers, and the connection between waterflood patterns are poorly understood. During this same time period, crosswell electromagnetic technology was developed and tested in other fields in the San Joaquin Valley. This technology can provide an interwell resistivity distribution from wells separated by up to 1000 ft, and thus, may be suitable for mapping water saturation variation and reservoir structure. In this paper we describe the application of crosswell EM technology to several waterflood patterns at Lost Hills. The first cases involve surveys between closely spaced fiberglass-cased observation wells across and perpendicular to a hydraulic fracture. The interwell resistivity distribution identified the edge of the waterflooded region and mapped saturation variation between the layers that were affected by the flood. In another example, crosswell data that were collected parallel to hydraulic fracture planes show the connection of injection plumes and also significant saturation variation between layers