Abstract

Management of produced water presents challenges and costs to operators. If the entire process of lifting, treating, and reinjecting can be avoided, costs are likely to be reduced. Oil and gas industry engineers have developed various technologies that separate oil from water or gas from water inside wells. These devices are known as downhole oil/water separators (DOWS, or according to some, DHOWS) and downhole gas/water separators (DGWS).This paper summarizes a recent report by Argonne National Laboratory that provides data on 59 DOWS trials and 62 DGWS trials from around the world. The report focused on the performance success of each trial and the geological conditions of the producing and injection formations.The goal of the study was to identify the types of geological formations that would present the best chance of success for future DOWS or DGWS trials.Upon reviewing these DOWS and DGWS installations, we concluded that it was not possible to predict the success of an installation solely on the basis of the geology of the production formation or injection formation.

Introduction

Produced water is underground formation water that is brought to the surface along with oil or gas. It is by far the largest (in volume) by-product or waste stream associated with oil and gas production. Management of produced water presents challenges and costs to operators. The cost of managing produced water after it is already lifted to the surface and separated from the oil or gas product can range from less than $0.01 to more than several dollars per barrel. If the entire process of lifting, treating, and reinjecting can be avoided, costs would be reduced. With this idea in mind, during the 1990s, oil and gas industry engineers developed various technologies to separate oil or gas from water inside wells. The oil- or gas-rich stream is produced to the surface, while the water-rich stream is injected to an underground formation without ever being lifted to the surface. These devices are known as downhole oil/water separators (DOWS, or according to some, DHOWS) and downhole gas/water separators (DGWS).

DOWS and DGWS Technologies

DOWS technology has two primary components - an oil/water separation component and one or more pumps.Two basic methods of separation have been developed. One type uses hydrocyclones to mechanically separate oil and water, and the other relies on gravity separation that takes place in the well bore. Various types of pumps have been used (i.e., rod pumps, electric submersible pumps [ESPs], progressive cavity pumps, hydraulic pumps).A more detailed description of the technologies, with figures and references, can be found in previous publications [1–3].

DGWS technologies can be classified into four main categories: bypass tools, modified plunger rod pumps, ESPs, and progressive cavity pumps. There are tradeoffs among the various types, depending on the depth involved and the specific application. Produced water rates and well depth control which type of DGWS tool is appropriate. A good reference on DGWS technology is a 1999 report prepared by Radian International for the Gas Research Institute [4].

These studies pointed out the potential for cost savings resulting from DOWS and DGWS installations. DOWS and DGWS technologies received a great deal of attention in the late 1990s. Over the past few years, however, few installations of either technology have been made.

Data on Performance and Geological Settings

In early 2003, Argonne National Laboratory was contacted by the U.S. Department of Energy's (DOE's) National Energy Technology Laboratory and asked to compile databases of as many DOWS and DGWS trials as possible and determine what set of production formation geology and injection formation geology offered the greatest chance for a successful installation.Although the field of geology encompasses many aspects and properties of underground formations, Argonne focused on the basic types of rocks (i.e., carbonate, sandstone, or other).

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