The continuous pack-off technology: A novel water-control method and application to offshore horizontal wells of limestone reservoir

Abstract

Water-control for horizontal wells is a worldwide problem, while it is even harder for limestone reservoir because of the developed fractures and caves.The formation water can be connected to the wellbore by fractures or caves directly or indirectly. Make the wells easily water flooded.Segmented water-control is the consensus of the current mainstream mechanical water-control technologies for horizontal wells, the segments confine the water break-through influence scope to the segment where the water break-through formed. In order to achieve that, all the potential water break-through fractures and caves connected to wellbore should be concentratedly divided into less segments, but that depends on the distribution of fractures and caves. Otherwise, the number and the sealing location of the packers are also relying on the engineering technology and the well status.Fracture/cave axial channeling inside the formation is another problem. The fractures and caves interwoven inside the formation. The formation water can easily flow around the packers by fractures/caves and cause the sealing failure of packers and invalid segment.Meanwhile the conventional mechanical water-control methods have no ability to limit the flow conductivity of fractures and caves. In the segments with fractures/caves developed, the producing degree of the matrix will be low.As a result, the application effect of conventional water-control methods in limestone reservoir horizontal wells is limited.To conquer the fracture/cave channeling and achieve the water-control effect at the meantime, the article proposed a novel mechanical water-control method which combined particle-filling with inflow control device screens. The particle-filling is not an absolute sealing, but a limitation of flow rate in the pack area. Calculations show that the flow conductivity of a 5 mm fracture will decreased to 0.1% of the original after particle-filling. The particles filled into the annulus between the screens and the borehole wall can limit the axial annulus flow enormously, replaces the traditional packer sealing. The particles filled into the fractures will reduce the flow conductivity sharply, and no need to concern about the channeling inside the fractures and caves interwoven. Inflow-control devices are utilized to control radius flow rate and balance the production profile near well. The novel water-control method obtained the outstanding application results especially in the limestone reservoir, with the function of deep production profile control combined with wellbore water control, has the advantage of both chemical water shut-off and mechanical water-control methods.Successful application in reef limestone reservoir demonstrates the excellent feasibility of this novel water-control method. The oil rate increased 3.9 times after application to well A4A in Liuhua oil field South China Sea. For well A3, the initial water-cut is only one third of the average value compared with wells drilled in recent years at the same layer.It is found that the production effect of oil wells is positively correlated with overfilling amount. For higher overfilling amount, filling process optimization is carried out, and micro-fracturing is formed by increasing filling rate to the target reservoir. The max filling rate of oil well reached 292% by the improvement of filling technology.