Research on the Application of Sidetracking Technology to Recover Residual Oil from Old Wells in Shallow and High-Water-Cut Oil Reservoirs in Nanpu Onshore Oilfield

The shallow land oil reservoir in Nanpu has entered a high water-cut stage, facing difficulties such as dispersed remaining oil, low CO2 flooding recovery efficiency, high proportion of low and ineffective wells, and low benefits of infilled well pattern investment. To further improve the oil recovery rate of the shallow land oil reservoir in Nanpu, this paper takes the NG12 reservoir of the heavy oil reservoir in block G104-5 in the high shallow north area as an example. Using the numerical simulation method, a multi-stage fracturing horizontal well development mechanism model for the bottom-water heavy oil reservoir is established, and the advancing law of bottom and edge water in shallow heavy oil reservoirs under different completion methods is clarified. Based on the research results of the three-dimensional distribution of remaining oil, a technical method of digging latent remaining oil with old well sidetracking is proposed, and differentiated development technology policies are optimized. The research results show that: (1) the remaining oil in shallow heavy oil reservoirs can be classified into low-water retention type, low potential zone shielding type, high position in structure, water flooding around the flow area, and interlayer shielding type; (2) the optimal length of sidetracked horizontal wells for mining special high-water-cut oil reservoirs is 50 m, and the reasonable water avoidance height is that the sidetracked horizontal well is more than 5 m away from the bottom water and more than 150 m away from the edge water; (3) the optimal development method for CO2 flooding mining of special high-water-cut oil reservoirs in shallow formations is the first round of CO2 injection of 200–350 tons, 20 days of soaking the well, and the initial liquid production rate after soaking the well is 8–10 tons/day; (4) numerical simulation studies show that the initial production capacity of the Ng12 layer of the G104-5 block with a 150 m sidetracked horizontal well is about 6.0 tons/day. The research results are of great significance for guiding the efficient development of shallow special high-water-cut oil reservoirs.