A Study and Application of Multi-section Acidizing Technology with Original Production String in Horizontal Well

Abstract The formation damageability of drilling and completion fluids on horizontal wells is more critical than on vertical wells, due to longer horizontal section of horizontal wells and the larger reservoir exposure area during operations, resulting in rapid productivity decrease. As such, acidizing techniques for horizontal well is an important solution to increase the reservoir productivity. However, the long horizontal section passes through various lithology layers due to geological heterogeneity. This cause the mud invasion time and formation damage degrees are different in various layers. All factors will bring in potential negative impacts derived from common acidizing and coiled tubing acidizing and lead to non-uniform acid distribution and poor acidizing effect. Therefore, it is necessary to make use the mechanical multi-section acidizing technology. For that, the wellbore should be divided into several sections according to the reservoir lithology, physical characteristics, and damage degree to realize the purposes of acid uniform distribution and productivity increase. Conventional process is hard to acidize the multi-sections in horizontal wells, because the deflected section exist in horizontal well and the target layer is located at horizontal section, which make downhole string operations more complicated, and stresses in horizontal well is quite different from that of vertical well. The ball-shooting sliding sleeve mechanical multi-section acidizing string is available to resolve these problems successfully. This string is made up with safety joint, connected vessel, hydraulic anchor, centralizer, spring sand blasting devise, K344-110 packer, low density ball, etc, with 40 MPa tolerance pressure and 90°C tolerance temperature. It can perform enforced sectionalizing. Four times shooting, five sections treatments, and residual liquid's reverse circulation cleanup and backflow after acidizing process can be carried out through the original production string in this technique. In addition, only 110 mm diameter of the packer outer, additional installation of centralizer at two ends and the application of connected vessel can reduce not only upward loads of the string, but also potential hazards of pipe stuck, and provide the feasibility for releasing pipes and fishing operations. Up to now, 12 wells and 36 layers have been conducted the multi-section acidizing technique in Daqing Oilfield, the greatest treatment is up to 4 sections with one trip string, the success rate is 100%. Considerable yield increase effect is available. It is statistic 5.9 m3/d average fluid increase, 4.8 t/d average oil increase, and 182% the average productivity increase rate of single well in the early stage after the operation. The horizontal well acidizing technique provides an efficient way to develop oil field in the peripheral areas of Daqing Oilfield and has a wide application in prospect with lower costs, higher efficiency and simpler operation.