Organic Solid Blocking Mechanism and Unblocking Technology for Ultra-Deep and High Pressure Oil Wells from Tarim Basin

Abstract In the Tarim Basin, the wellbore blockage problem of HTHP oil wells was very severe, especially in Fuman, Donghe 1 and Yudong 7 oil fields. The total number of blocked Wells is 95, Over 24% oil wells have organic solid phase plugging problem. More than 64% of the Wells in Donghe 1 oilfield were blocked, resulting in difficulties in testing, wellbore blockage and surface pipeline burst, affecting annual production of 8,500 tons. In this paper, a fast analysis method of blockage was established, and an organic solid phase deposition test device was innovated. The law of solid phase blocking under different reservoir conditions, development modes and crude oil properties was systematically analyzed. The dynamic prediction model of organic solid phase blocking was established to realize the visualization prediction of blocking position, and the unblocking measures technology of organic solid phase blocking was formed to comprehensively solve the organic solid phase blocking problem in oil Wells. It was shown that the blockages in the Fuman carbonate reservoirs were dominated by wax-asphalt organic compound and sand burial, and t he gas injection development in Donghe 1 Oilfield is dominated by asphalt deposition, while that in Yudong 7 Oilfield is dominated by asphalt and wax plugging. Gas injection extraction, crude oil composition change, pressure drop and sand production are the main factors of solid phase blockage, and organic solid phase blockage exists in "wellbore + reservoir near the wellbore "; The dynamic prediction model of composite plug deposition is established to realize the "visualization"of plug location and degree, and the prediction accuracy is ≥ 80 %. The efficient unblocking agent have been developed based on the understanding of the blockage composition, to achieve high-efficiency dissolution of the blockage (the dissolving rate 90%) and the effective inhibition (85.84%). Based on the understanding of the blockage law, 4 sets of unblocking processes had been developed with "plugging degree" and "whether there was a squeeze channel" as the main considerations, For the first time, the "system blockage unblocking "design method based on the composite plugging mode of "wellbore + reservoir near the wellbore " is proposed, which realizes the efficient plugging removal. The field application of 477 wells improves the success rate of reproduction from 53 % to 100 %, and effectively reduces the risk of plugging. This successful experience could provide guidance for blockage treatment in other oil fields with asphalt deposition and organic solid plugging such as wax.