Abstract

Numbers of oil fields in China had entered high water cut stage. The inefficiency circulation happened frequently during water flooding of these oil fields because of seriously intraformational heterogeneity in thick reservoir. Based on oilfield development dynamic data, it indicated that the problems of inefficiency fluid injection and futility circulation could not be solved in vertical well exploitation, no matter using water flood or chemical flood. There was a certain thickness of unexploited or low flushing efficiency oil remained on the top of thick reservoir. The traditional lateral drilling techniques could not be applied in short radius within 5 1/2 inches to 7 inches casing which were regular casing sizes of injection well in these oil fields. To exploit remained oil, the recent method to increase flow conductivity was hydraulic jet technology. But it had several disadvantages, like small aperture diameter, short drilling distance, inaccuracy orientation and limited flow conductivity.

This paper introduces an ultrashort radius lateral drilling technique (URLD) which provides an efficient method to increase production by drilling into the target reservoir to build a flow channel between unexploited reservoir and wellbore. The ultrashort radius lateral drilling technique includes flexible lateral drilling tool, deflecting tool, directional tool, etc. The flexible lateral drilling tool, which is the key in URLD technique, is consisted of several flexible nipples in the length of 15 cm. It is connected by double offset universal joint between adjacent flexible nipples. The movable angle between adjacent flexible nipples is 4-6 degree. And a PDC drill bit is connected in front end of tool. The URLD technique can realize lateral drilling within 5 1/2 inches to 7 inches casing. It can be applied to target reservoir thicker than 2 m. The drilling track is controllable. Target error is within ±1 %. Minimum deflecting radius is 1.8 m. The drilling hole diameter is 114 mm. The length of lateral drilling is more than 100m in 5 1/2 inches casing and 200 m in 7 inches casing.

The URLD technique has applied in more than 20 wells in China, and barels oil per day increases by 3 to 5 times in average. The URLD technique provides a solution to exploit remained oil after long term water flooding, and increases the production of mature oil field in economical way.

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