Double Casing Exit for Side-Track to Commingle Two Borehole Sizes Based Sections in One Slim Shot to Well TD

Abstract

This project began when a 9-5/8" in 43.5 ppf production casing became inaccessible due to the existing cemented pipe inside, preventing further reservoir section exposure and necessitating a mechanical side-track meanwhile introducing the challenge of loosing one section and imposimg slim hole challenges. The size and weight of the double-casing made for challenging drilling, as did the eight very different formations, which were drilled. The side-track was accomplished in two steps, an 8½ in hole followed by a single long 6⅛ in section, rather than the three steps (16 in, 12¼ in, 8½ in) that are typically required. The optimal kick off point carfully located across the dual casing by running electromagnetic diagnostics, the casing collar locator, and the cement bond log. The double casing mill was carefully tailored to successfully accomplish the exit in one run. Moreover, an extra 26 ft. MD rathole was drilled, which helped to eliminate the mud motor elongation run. A rotary steerable system was utilized directly in a directional BHA to drill an 8½ in open hole building section from vertical to a 30⁰ inclination. A 7.0 in liner was then set to isolate weak zones at the equivalent depth of the outer casing (13-3/8"). Subsequently, a single 6⅛ in section was drilled to the well TD through the lower eight formations. Drilling a 6⅛ in section through eight formations came with a variety of challenges. These formations have different challenging behaviors relative to the wellbore pressure that typically leads to the drilling being done in two sections. Modeling the geo-mechanical characteristics of each formation allowed the determination of a mud weight range and rheology that would stabilize the wellbore through all eight formations. The slim, 6⅛ in, hole was stabilized with higher equivalent circulating density (ECD) values than is typically used in larger boreholes. Optimizing mud weight and drilling parameters, while managing differential sticking with close monitoring of real-time ECD, helped to stabilize the high-pressurized zones to deliver the well to the desired TD with a single borehole. This project represents the first time in Kuwait that double casings in such large sizes have been cut and sidetracked. It is also the first time these eight formations have been cut across such a smaller hole size, slim hole (6⅛ in) in a single shot. Geo-mechanical modeling allowed us to stabilize the pressurized formations and to control the ECD. The well also deployed the longest production liner in the field commingling multiple reservoirs with differnt pore pressure ramps, with excellent cement quality providing optimal zonal isolation.