Wells – Processes – Separating material entering well
Reexamination Certificate
1999-09-24
2001-02-20
Tsay, Frank (Department: 3672)
Wells
Processes
Separating material entering well
C166S369000, C166S105500
Reexamination Certificate
active
06189613
ABSTRACT:
This invention relates to a downhole oil/water separation process which separates solids to remove them from the disposal water stream.
BACKGROUND OF THE INVENTION
Many oil wells experience high water production. High water production is undesirable because it necessitates artificial lift systems which must accommodate the volume of water produced as well as water handling facilities at surface. These requirements add significantly to the operational and capital expenditures associated with production. In some circumstances, the production of wells and fields have been suspended or abandoned with significant volumes of oil left in the ground as a result of the poor economics resulting from excessive water production.
Downhole oil/water separation (“DHOWS”) systems have been developed to contend with increased water production. Such systems incorporate the use of downhole liquid/liquid cyclones to separate the oil from the water. The separated oil is lifted to surface and the water is reinjected downhole. Unfortunately, the application of DHOWS systems in these wells is complicated by the inherent production of solids, such as sand, with the oil. The solids that are produced tend to remain in the disposal water stream which is reinjected downhole. Depending on the solids volume and well conditions, the solids may invade and plug the disposal zone or they may accumulate in the well bore. In either case, the situation ultimately leads to a reduction in injectivity which reduces the effectiveness or precludes the further use of a DHOWS system.
Attempts have been made to remove sand from the disposal water stream. One such method is disclosed in International PCT Application No. GB96/02282 published as WO 97/12254 on Mar. 17, 1997. According to that method, a liquid/liquid cyclone may be used to separate the production fluid into an oil enriched stream and a water enriched stream. The oil enriched stream is transported to the surface and the water enriched stream proceeds to a solid/liquid cyclone where the water is separated from the sand and then transported to a downhole disposal site. While this method does provide a means for removing solids from production water before reinjecting it downhole, the presence of solids in the liquid/liquid cyclone causes significant erosion of that apparatus and the geometry and plumbing of the system have been found unfavourable. In addition, a system which removes solids downstream of the liquid/liquid cyclone cannot be easily incorporated into existing commercially available DHOWS systems.
SUMMARY OF THE INVENTION
The present invention provides a method for removing solids from total production fluid prior to separating the oil from the water by means of a downhole oil/water separation system. Production fluid is passed to a downhole solid/liquid cyclone which separates the fluid into a solids enriched stream and an oil/water stream. The oil/water stream then enters a liquid/liquid cyclone which separates the oil from the water. The oil is then commingled with the solids enriched stream and brought to surface. The water is reinjected downhole. The method effectively removes solids from the disposal fluid and thus avoids injectivity impairment caused by solids plugging.
Thus in accordance with the present invention there is provided a method for separating oil well production fluid containing oil, water and solids comprising: transporting the production fluid to a downhole liquid/solid cyclone; separating the production fluid in the liquid/solid cyclone into a solids enriched stream at the cyclone underflow and a oil and water enriched stream at the cyclone overflow; transporting the oil and water enriched stream to a liquid/liquid cyclone; separating the oil and water enriched stream in the liquid/liquid cyclone into an oil enriched stream at the cyclone overflow and a water enriched stream at the cyclone underflow; transporting the water enriched stream to a downhole disposal site; and transporting the oil enriched stream and the solids enriched stream to surface.
In accordance with another aspect of the present invention, there is provided an apparatus for separating oil well production fluid containing oil, water and solids downhole comprising: at least one liquid/solid cyclone adapted to receive the production fluid and separate it into a solid enriched stream at an underflow outlet of said cyclone and an oil and water enriched stream at the overflow outlet of said cyclone; at least one liquid/liquid cyclone adapted to receive the oil and water enriched stream from the overflow of the liquid/solid cyclone and separate said stream into an oil enriched stream at an overflow outlet of said cyclone and a water enriched stream at an underflow outlet of said outlet; a mixing means to mix the oil enriched stream with the solids enriched stream and produce an oil/solids stream; a first duct means to transport the oil enriched stream from the overflow outlet of the liquid/liquid cyclone to the mixing means; a second duct means to transport the solid enriched stream to the mixing means; and a third duct means to transport the oil/solids stream to surface.
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Chachula Ryan C.
Solanki Sandeep C.
Morgan & Lewis & Bockius, LLP
Pan Canadian Petroleum Limited
Tsay Frank
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