Under certain conditions, unconsolidated sand is remobilized and forced upward through overlying layers. Called injectites, these sands can have high porosity and permeability and play a huge role in planning and optimizing hydrocarbon recovery.Injectites are found in many parts of the world, including several important petroleum basins. Geologists and other E&P professionals are using surface exposures, along with core, borehole images, and surface seismic data, to understand injectite shape and distribution in the subsurface. An article in the Summer 2008 issue of the Schlumberger Oilfield Review, "Sand Injectites," describes how injectites form, what they look like, and how they can affect reservoir development. Examples include case studies on outcrops and injectites associated with oil and gas fields.Outcrops in California reveal vast networks of sandstone dikes and sills that were injected into overlying mudstones about 65 million years ago. These surface exposures are used as analogs, or models, for injectites encountered in the subsurface.Subsurface examples come mostly from the North Sea. In the Gryphon field, operator Maersk Oil used seismic imaging and deep-reading LWD resistivity tools to help geosteer horizontal wells into sand-injection wings. Oil produced from sand-injection features now accounts for about 80% of Gryphon field's daily production.Another case study describes Marathon's oil discovery in the giant sand-injection complex of the Volund field in the Norwegian North Sea. Seismic inversion and calibration of seismically derived rock properties with well log data helped to differentiate sand-rich units from surrounding mudstones. The discovery contains 40 to 50 million bbl of oil equivalent. Read about these and other examples in the full article at the Oilfield Review Web site. Clients are invited to register as premium content users to access this and other recent articles in Oilfield Review.
Braccini E, de Boer W, Hurst A, Huuse M, Vigorito M and Templeton G: "Sand Injectites," Oilfield Review 20, no. 2 (Summer 2008): 34-49.