Downhole Oil Water Separation (DOWS)

DOWS addresses a worldwide problem within the oil industry - the costs and liabilities associated with produced water. Water produced from oilfields is typically a heavy brine several times as salty as sea water (actual range from 60,000 to 180,000 mg/L of Total Dissolved Solids). Water production results in the #1 oilfield waste - oilfield brine. Oilfield brine, while low in toxicity, is present in very large volumes. In mature oil fields, water-cut may be as much as 99% of the produced fluid. It is a significant expense for the operator to handle this water whether he chooses to truck it off or pipeline it to injection/disposal wells.

Operators must bear the expense of handling this water. These costs can vary from approximately $0.10/barrel for an existing waterflood operation to over $1.00/barrel for trucking water to a commercial disposal facility to over $2.00/barrel for treatment processes such as Reverse Osmosis and evaporation.

In addition to operating costs, produced water represents a potential threat to soil and water resources in the event of accidental releases. Leaks from pipelines or tanks can impact large areas of surface soil and can migrate to surface waters or groundwater. Produced brines have the ability to sterilize surface soil and to make large volumes of fresh water undrinkable. A long-term leak from a saltwater pipeline has the potential of being a major liability for an oil producer. DOWS technology gives operators the option of leaving most of the brine underground.

DOWS equipment is of two basic types - gravity separators and hydrocyclones.

Gravity separators utilize the borehole as a separation chamber where oil will rise to the top and water will be in the bottom of the chamber. Widely separated inlets help direct water through the packer and into the receiving zone while oil is pumped to the surface. Gravity separators must allow the produced fluid to stay in the borehole for sufficient time to segregate and because of that, wells cannot produce at high volumes. Rod pumps, most widely used with gravity separators, can only support modest pressure differentials to the disposal zone.

Hydro-cyclones utilize a moving stream of produced fluid to accentuate density differences; they are frequently powered by Electric Submersible Pumps (ESPs) that have the ability to pump large volumes of water at high pressures. Hydro-cyclone DOWS units have the ability to take several thousands of barrels per day of fluid consisting of 90% water and split it into two streams - one clean salt water stream is pumped through a packer into a disposal zone while another stream of 50-50 oil and water is pumped to the surface. In this manner approximately 85% of the produced water can remain downhole. The economic advantages are such that the equipment can pay for itself in a matter of several months.

ALL Consulting has been involved with this technology for five years. We have played a major role in US Department of Energy research into DOWS trials around the world. We have worked with equipment suppliers including Schlumberger-REDA, Baker-Centrilift, Wood Group-ESPI, Dresser-Axelson, and Promore. We have evaluated and advised operators including Chevron, UNOCAL, and Texaco concerning operations in Texas, New Mexico, Oklahoma, and Canada. We have interpreted real-time monitoring data from DOWS installations to recommend changes to operating conditions or repairs.

ALL staff wrote the nation's first regulations concerning DOWS operations in the state of Oklahoma; these regulations have been the model for several other states. The regulations classify DOWS wells as legitimate Class II (oil and gas wastes) injection wells to be considered with other Class II injection wells that primarily handle produced salt water such as deep disposal wells and waterflood injectors. We also advised the US EPA and their National Underground Injection Control Working Group on the regulation of DOWS wells. The product of the Working Group, EPA UIC Program Guidance #82 is attached.