Reverse-Circulation Cementing To Seal a Tight Liner Lap

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling in the Arctic can present a number of challenges even before the drilling begins. Among the challenges are logistic difficulties, weather extremes, and environmental sensitivities. To offset the production decline for natural gas in North America operators must confront these challenges by resuming exploration in the Arctic.The target in this case study is a well in the Paktoa field. The design challenge presented by this well was to drill the well to total depth (TD) with the lowest number of casing strings while avoiding remedial cementing operations. Given that the mud-weight window predicted for this wellbore was quite narrow, well planners determined that no fewer than five casing strings were needed to reach TD. Multiple casing strings can lead to tighter annuli and more challenging cementing operations.Using modeling software as an aid to cement design, planners determined that the cement on the first liner, from 1,300 to 2,600 ft, could not be circulated conventionally without breaking down the formation because of the high equivalent circulating density (ECD). The greatest contributor to the high ECD is the tight annulus of the liner lap. The model parameters were reversed and the model predicted that a reverse-circulation cementing (RCC) operation would be successful.RCC is a method of pumping cement down the annulus and receiving returns inside the casing. One advantage of reverse circulating is that the ECD is reduced and less pressure is exerted on the formation. This will help reduce or eliminate cement losses into weak formations.Placing the cement down the annulus appeared to be feasible with the computer model but to conduct the operation in the field, other challenges were addressed. In a reverse operation, the float valve is removed or sheared out before pumping cement. This is not of concern with a normal casing * Formerly employed by Devon-Canada