In situ pyrolysis of oil shale formations

Claim 1

AN IN SITU METHOD OF RECOVERING SHALE OIL FROM A SUBSURFACE OIL SHALE FORMATION, COMPRISING: (A) DRILLING A SUBSTANTIALLY VERTICAL SHAFT INTO SAID OIL SHALE FORMATION; (B) FROM SAID VERTICAL SHAFT, DRILLING A PLURALITY OF SUBSTANTIALLY HORIZONTAL SHAFTS INTO THE FORMATION; (C) FROM AT LEAST ONE OF SAID HORIZONTAL SHAFTS HYDRAULICALLY FRACTURING SAID FORMATION SO THAT THE PLANE OF THE RESULTING FRACTURE IS VERTICALLY DISPOSED TO OPEN FLUID COMMUNICATION BETWEEN SAID AT LEAST ONE HORIZONTAL SHAFT AND AT LEAST ONE ADJACENT SHAFT; (D) INTRODUCING A FLUID INTO THE FORMATION ALONG THE PARTED FRACTURED PLANE, SAID FLUID BEING AT A TEMPERATURE SUFFICIENT TO PYROLYZE THE OIL SHALE, WHEREBY THE SENSIBLE HEAT OF THE FLUID IS TRANSFERRED TO THE SURROUNDING OIL SHALE FORMATION AND PYROLYSIS AND VAPORIZATION OF THE KEROGEN CONTENT OF THE OIL SHALE OCCUR; (E) RECOVERING THE FLUID WITH PRODUCTS OF PYROLYSIS ENTRAINED THEREIN; AND (F) AFTER THE PORTION OF THE OIL SHALE AROUND SAID RESULTING FRACTURE IS DEPLETED OF HYDROCARBONS, SUCCESSIVELY REPEATING STEPS (C), (D), AND (E), EACH FRACTURE INITIATED AS THE RESULT OF REPETITION OF STEP (C) BEING A DIFFERENT DISTANCE FROM SAID VERTICAL SHAFT IN SAID AT LEAST ONE HORIZONTAL SHAFT.