Annular Isolation of Horizontal Slotted Liners With Chemical External Casing Packers

Abstract

Abstract Slotted liners are a simple and cost-effective method for completing horizontal wells that can provide sand control and wellbore stability. The uncemented annulus between the slotted liner and the openhole makes selective stimulation, isolation, and remediation challenging unless mechanical isolation devices such as external casing packers or swellable packers are added to the outside of the slotted liner at the time of the initial completion. For existing wells without these mechanical isolation devices, Chemical External Casing Packers (CECP) can be used to isolate the annulus while leaving an unobstructed flow path through the internal bore of the slotted liner. In this study, the authors tested two CECP systems. The first was a highly-thixotropic cement slurry and the second was a Fiber-Reinforced Neutral-Density (FReND) cement. Testing consisted of an evaluation of the pumpability of the thixotropic slurry through coiled tubing and the ability of the two CECP systems to efficiently displace existing annular fluids and effectively isolate the annulus between a 4-1/2-in. slotted liner and an 8-in. openhole without significant fall back into the slotted liner. The pumpability test showed that the thixotropic slurry could be pumped at a rate of 2.5 bbl/min with a treating pressure of less than 4000 psi through a 10,500 ft string of 2-in. OD coiled tubing. The testing showed that both CECPs were able to effectively displace existing annular fluids, and isolate the slotted liner annulus. An error in the testing procedure for the thixotropic blend resulted in no quantifiable measurement in percentage of cement fall-back into the liner. However, samples of the pumped thixotropic slurry were shown to have significant resistance to falling back into the liner once pumped into the liner annulus. The FReND system showed only minor fall back of cement into the slotted liner that still left an open flowpath through the liner. With the ability to selectively isolate portions of the slotted liner annulus, the CECP's can target areas of water influx and shut them off while still allowing flow from below. Additionally, by straddling two separate CECP isolated areas, treatment fluids such as stimulation fluids, cements, or permeability modifiers can be accurately placed into the desired location of the well. Many existing horizontal wells completed with slotted liners do not have swellable packers or external casing packers installed. The development of an effective and easily placeable CECP provides options for remedial operations in these wells that were not available before.