Cementing Displacement Practices Field Applications
Authors: Smith Terry R. 
Published: December 2007

Most remedial cementing operations and related problem costs result fromannular gas leakage or zonal communication in the annulus after primarycementing. After the physical properties of the cement, the most importantfactor in successful primary cementing is good mud removal by the cementslurry. Good mud removal is achieved through high displacement rates. Laboratory investigations conducted with fullscale models have determined thatthe factors contributing to high displacement efficiencies include annularvelocity, hole conditioning time, casing movement, preflush fluids, drilling-fluid condition, mechanical aids, and wellbore condition. In thefield, however, it is often very difficult to implement all these goodpractices. To optimize cementing operations, we studied these practices andtheir implications in field operations. An extensive cementing-operations database was developed to relate historical problems to current operationalpractices. These historical data practices. These historical data were combinedwith field testing programs to determine the significance programs to determinethe significance of various displacement parameters. The field tests indicatedthat annular velocity is one of the most important factors affectingdisplacement efficiency. As a result, a practical cement placement program wasdeveloped. Since implementation of this program, the numbers of primarycementing failures and remedial cementations have decreased.

Introduction

The key to a successful primary cement job is a hydraulic seal in theannulus that inhibits the flow of formation fluids. To accomplish this, all (orat least a large percentage of) the drilling fluid must be displaced with agood-quality cement. Placement of cement in the annulus is probably the mostcritical phase of the cementing process. 1–4 Most phase of the cementingprocess. 1–4 Most authors agree that a number of factors influencedisplacement. Several test programs have been conducted with scale models toinvestigate many of these displacement parameters, and a number of practicesparameters, and a number of practices have been recommended.

These recommended practices are valid and have sound bases, but cannotpossibly be applied in many field situations. A 100% displacement efficiency(Fig. 1) is the ideal objective, but even in controlled laboratory conditionsthis was found to be very difficult to attain. To evaluate some of thesedisplacement practices and their significance in specific field conditions, afield test program was conducted. These results were used to develop casingcementing procedures that optimize displacement efficiency.

CORS Computer Program

The first step of the program was to conduct an extensive field study todetermine the common practices in the field. One persistent problem encounteredduring field persistent problem encountered during field studies is the lack ofcomplete operational data. I Therefore, a computer database system, CementingOperations Retrieval System (CORS), was developed to provide an efficientmethod of storing and extracting cementing-operations information. Field data, laboratory tests, and any remedial cementing operations are combined into onecomplete well history. CORS has proved to be very valuable in determining fieldpractices and relating these practices to practices and relating thesepractices to cementing successes and failures.

Fluid-Caliper Tests

We investigated displacement procedures in the field with fluid calipers(Fig. 2), a procedure used by other researchers in similar investigations. Thefunction of a fluid caliper is to determine the amount of mobile drilling fluidin the wellbore. A marker is placed in the drilling mud that can be placed inthe drilling mud that can be detected at the mud return line. Various types ofmarkers have been used, but we found that the carbide pill is the mosteffective when a mud logger is on location. The acetylene is detected by thegas chromatograph at the flowline. If a mud logger is not available, then avisible dye pi is used that consists of an oil-based paint mixed with polymer. A coarse material, such as polymer. A coarse material, such as sawdust, issometimes used to make the marker more visible at the shale shaker. The fluidcaliper procedure consists of the following steps. 1. Run a multiarm caliperlog over the entire openhole interval to determine the total hole volume withthe casing in the hole. 2. Determine the mud pump efficiency by isolating thesuction tank and correlating the pump strokes with the volume pumped from pumpstrokes with the volume pumped from the tank.3. Place the marker in the casingand monitor the volume of fluid pumped until the marker is detected at the mudreturn line. 4. Determine the displacement efficiency by dividing the volume offluid pumped (as determined in Step 3) by the hole volume (as determined inStep 1) and expressing this value as a percentage.

The displacement efficiency determined from this test indicates thepercentage of fluid in the wellbore that is active or circulatable. It has beenstated that the cement will displace only the circulatable drilling fluid. 8These fluid caliper tests will give a good indication of the displacementefficiency that will be achieved during the cementing operation.

This paper presents the results of 22 fluid-caliper tests performed on 17wells (Table 1). In all cases, a similar water-based drilling fluid was used. The drilling-fluid properties are also included in Table 1. These propertiesare also included in Table 1. These field tests were run on casing stringsranging in depth from I 100 to 4880 m [3,609 to 16,010 ft]. The casing sizeswere 177.8, 139.7, and 114.3 mm [7, 5 1/2 and 4 1/2 in. ]. Multiple tests wererun on three wells. The results of these tests were used to analyze the variousdisplacement parameters addressed in this paper.

JPT

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