Integrated Primary Cementing Study Defines Key Factors for Field Success

Abstract

Summary This paper describes new research into cement placement. The research used a novel placement. The research used a novel large-scale flow loop with 49 ft [15 m] of 8 1/2-in. [21.6-cm] open hole that can be deviated from 0 to 90 deg. A distinction is made between mud displacement and cement placement and some of the problems associated with each process are described. Examples are given from the largescale flow loop. Other work that used a flow-visualization loop and mathematical modeling is also discussed. Preliminary conclusions confirm the long-held intuitive view that correct casing centralization, circulation rate, and mud properties are critical for mud displacement. The paper also presents a technique to quantify the role of each variable. Efficient cement placement is influenced by spacer properties and centralization. Introduction The goal of successful primary cementing on every casing string continues to evade the oil industry and, despite advances in equipment and technique, remedial cementing is often required. This is particularly true in highly deviated wells. Remedial work is very expensive, and one of its common causes is poor cement placement. To solve this problem, we need to understand placement mechanisms better and to take more placement mechanisms better and to take more care in designing the slurry. In view of the complexity of annular flow, it is important to work on a realistic scale to eliminate scale-up effects. We therefore decided to build a large-scale flow loop to study cement placement in a full-scale annulus. Because of the problems associated with deviated wells, an inclined loop was designed to simulate all possible deviations. Mathematical modeling and flow-visualization studies with model fluids are being done to back up this work. The flow-visualization loop is a small perspex loop that allows us to study displacement directly using different-colored fluids. When these studies are combined, we will understand cement-placement mechanisms better. This paper is the first of these studies, and it concentrates on the research with the large-scale flow loop. The paper describes the facility and some of the early experimental results and interpretations. The target audience is operational staff responsible for planning and implementing cement jobs. planning and implementing cement jobs. Defining the Problem Frequently, there are primary and secondary objectives for cementing operations. For example, on long, intermediate casing strings, a complete cement sheath from top to bottom is ideal, but realistically, a good seal around the shoe is all that is required. In other cases, isolation away from the shoe may be important (e.g., a liner overlap). Therefore, the objectives of the cement job must determine how the cement job is designed. Gelled mud must be removed before cement is placed in an annulus. In an eccentric annulus, the mud on the narrow side will be very difficult to remove. Once the gel strength is broken down, however, and the mud is moving throughout the annulus, we must consider how the cement will flow. If the cement flows largely on the wide side of the annulus and leaves a slowly moving channel of mud on the narrow side, then we are unlikely to get good cement placement and zonal isolation away from the placement and zonal isolation away from the shoe. The problem of cementing, therefore, should be considered in two parts, mud displacement and cement placement. Mud displacement is important for all cement jobs. Cement placement also needs to be considered in some circumstances.