Waste Water Disposal Above Fracture Gradients in California

Doscher, T.M. (Tosco Enhanced Oil Recovery Corp.) | El-Arabi, M.A. (Tosco Enhanced Oil Recovery Corp.)

OnePetro 

Abstract In order to permit economic operation of Placerita Oil Field leases, a request was Placerita Oil Field leases, a request was made of the Division of Oil and Gas of the State of California for a waiver on the regulation limiting the sand face pressure of water disposal operations to a value less than the apparent frac gradient. This is an account of the justification presented to the DOG for seeking a variance from the regulations, the DOG's positive response, and subsequent field operations. Introduction Water disposal operations are a necessary part of oil production in today's oil field practices. It follows that it is the goal of the operator to dispose of the maximum quantity of water in a single well as is compatible with the needs of protecting the environment and securing the maximum efficient recovery of crude oil. Presently, the Division of Oil and Gas of the State of California (DOG) limits the sand face pressure in disposal wells to 80% of the lithological gradient, 1 psi./ft, or that lower pressure at which a break in the rate vs. pressure curve occurs in a step-rate test. The reason for limiting the disposal pressure is the fear that pressures in excess pressure is the fear that pressures in excess of those cited above may induce vertical fractures in the reservoir. A possible consequence of such a fracture is that the injected after may invade reservoirs of potable water or of penetrating through an oil potable water or of penetrating through an oil bearing stratum either above or below the point of injection. point of injection. Because of the limitations on disposal well head pressures, the operator in many fields is faced with drilling a large number of disposal wells and experiencing high operating costs to dispose of produced water. The profitability of oil production is thereby jeopardized. The Tosco Enhanced Oil Recovery Corporation encountered such a problem in operating the Placerita Field, Los Angeles County, and an expansion project aimed at the recovery of some ten million barrels of oil by steam injection was threatened because of the burdens put on the project by the limitation in disposal well head pressure. This was brought to the attention of the Division of Oil and Gas of the State of California, and Tosco submitted a brief in request for a variance from the regulations which would permit them to demonstrate that water disposal above fracturing pressures, or following the propagation of a fracture in the disposal sand would not jeopardize either potable water sands nor adjacent oil potable water sands nor adjacent oil producing reservoirs. producing reservoirs. The Division of Oil and Gas granted such a variance. This is an account of the brief that was submitted to the DOG and the actions that have transpired since the variance was approved. "Orientation of Induced Fractures" The literature refers to two types of induced fractures: horizontal and vertical. The implication of the former term is that the entire overburden of rock is lifted and floated on a horizontal sheet of water that courses through the rock from the point of injection, and the implication of the latter term is that the rock is torn apart in a vertical plane and the separation is maintained by a vertical sheet of water coursing through the plane of separation. P. 143

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