In this paper, slim hole refers that the nominal diameter of production casing is less than 5 inch. In many problem wells, production casing is destroyed and new casing is reinstalled to continue oil production. And sidetrack drilling in old well is an effective method to find residual oil. Slim-hole drilling is widely used in low productivity, low permeability or low reservoir pressure oilfield for low drilling cost. So the number of slim-hole wells increases quickly. None of artificial lifts turns out to be a good option in slim well. The sucker rod pump system is mainly used. As a result, pump depth and daily fluid production rate are limited by the slim tubing, and oil test isn't available because of the small annulus.

The new tubingless sucker rod pump system can solve some of these problems. It adopts a packer to suspend tail pipe and seal the annulus between tail pipe and the casing, and fixing mechanism and sealing mechanism work together to fix pump system and seal the joint between tail pipe and pump system. Consequently the flow passage of the fluid is built: the mixture from the reservoir flow in tail pipe, then enter pump system to increase the pressure and eventually come into the annulus between rod string and the casing through special screen section. The pump efficiency is high and the production cost is greatly reduced for the tubing string is omitted and most of the conventional equipments are used.

The new system was successfully used in 4 inch and 51/2 inch casing wells in Zhongyuan oilfield, increasing the daily fluid production rate, as compared to the conventional sucker rod pump system. This paper presents description of the new tubingless sucker rod system, and reports the results obtained in two stages of field tests. The design method is also given.

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