Improved Cementing Practices Reduce Cementing Failures
Authors: Hart W.A. , Smith T.R. 
Published: March 2010

Abstract
The key to successful primary cementation is a hydraulic seal in the annulus area to inhibit flow of formation fluids. To accomplish this, all or a large percentage of drilling fluid must be displaced with good quality cement. Placement of cement in the annulus is probably the most critical phase of the cementing process, Many papers have been published on this topic(1–4). Most authors agree that a number of factors influence the displacement process. Several test programs have been conducted using scale models to investigate several displacement parameter (3–5). As a result of laboratory investigations and field observations a number of practices have been recommended.
While these practices are valid and have a sound basis, it is not possible to apply all or the parameters in many field situations. Ideally, 100% displacement efficiency is the objective, but even in controlled laboratory conditions this is very difficult, if not almost impossible to attain. Displacement efficiency is defined as the cemented area divided by the total annular area (Fig. 1). To evaluate displacement practices and their significance in special field conditions, a field test program was conducted, the results of which were used to develop casing cementing procedures to optimize displacement efficiency.

CORS Computer Program
The first step involved conducting an extensive field study to determine what the common practices were and what was done in the field. A persistent problem encountered while conducting the field study was lack of complete operation data(1). To overcome this, a computer data base system was developed to efficiently store and extract cementing operations information. Field data, laboratory tests and remedial cementing operations were combined into one complete well history. Figure 2 represents an outline of the Cementing Operations Retrieval System (CORS) computer program. CORS has proven to be most valuable when determining field practices, and relating them to cementing successes and failures.

Field Testing - Fluid Calipers
A program was conducted to investigate displacement procedures in the field utilizing fluid calipers (Fig. 3). This procedure has been used by other researchers in similar investigation(6,7). A fluid caliper determines the amount of mobile drilling fluid in the wellbore. A marker is placed in the drilling mud which can be detected at the mud return line. Various types of markers have been utilized, and it was found that the most effective is the carbide pill, if a mud logger is on location. Acetylene is detected by the gas chromatograph at the flow line. If a mud logger is not available, a visible dye pill is used, consisting of an oil base paint mixed with polymer and sometimes, coarse material such as sawdust to make the marker more visible at the shale shaker.
The following describes the fluid caliper procedure.Run a multi-arm caliper log over the open hole interval to determine total hole volume with casing in the hole.Determine mud pump efficiency by isolating the suction tank and correlating pump strokes with the volume pumped from the tank.