A Proven Technique for Liner Cementing in the Greater Green River Basin, Wyoming
Authors: Sauvageau Kent A. 
Published: December 2007

Summary
An Improved cementing technique has been initiated in he Wamsutter area in the Greater Green River basin of Wyoming. The technique addresses eight problems associated with liner cementing: restricted clearances, conditioning of the drilling mud, pipe movement, centralizers and scratchers, spacers and preflushes, cement slurry design, displacement rates, and use of liner top packers with squeeze. Before this cementing technique packers with squeeze. Before this cementing technique was initiated, only 21 % of the liners we cemented in this area during 1980 could be classified as successful. Since initiating this technique, 100% success in cementing liners has been achieved. The technique, started in Oct. 1980, has been implemented on 14 wells, and all 14 were completed without a remedial squeeze.

Introduction
In the part of the Wamsutter area commonly called the ‘sweetspot" (Fig. 1), the Mesaverde formation has a bottomhole pressure (BHP) requiring mud weights greater than 11 Ibm/gal [1318 kg/m3]. Typically, the overlying Lewis formation will not withstand mud weights exceeding 10 lbm/gal [1198 kg/m3]. Consequently, the hydrostatic pressure required to control and stabilize the wellbore will break down the upper Lewis formation. This results in lost circulation, which can lead to stuck pipe, possible water flows, and gas kicks.
Incorporating 7-in. [17.8-cm] intermediate strings to topset the Mesaverde and running a 4V2-in. [11 .4-cm] liner through the pay section has alleviated many previous drilling problems in the sweetspot area. previous drilling problems in the sweetspot area. However, there have been problems associated with runfling and cementing these liners, the major being poor primary cement jobs. During 1976–80, 59 liner jobs primary cement jobs. During 1976–80, 59 liner jobs were performed. In this time period, six modifications were implemented to improve the primary cementing of the liner. However, the changes made in some instances actually decreased the number of successful liner jobs.
Because of the poor performance of liner cementing jobs in 1980, a complete review was made of the liner cementing technique. The variables we studied includedrestricted clearance,conditioning of the drilling mud,pipe movement,centralizers and scratchers,spacers and preflushes,cement slurry design,displacement rates, anduse of packers with squeeze.
The liner cementing procedure currently used in Wamsutter was derived from a thorough review of these eight variables.

Restricted Clearance
In early 1980, the Wamsutter casing program was changed. This change resulted from the burst failure of a liner during a fracture stimulation. The 4 1/2-in. [11 .4-cm] liner and 7-in. [17.8-cm] intermediate casing were upgraded from 11.6 to 13.5 Ibm/ft [17.3 to 20.1 kg/m] and from 26 to 29 Ibm/ft [38.7 to 43.2 kg/m], respectively. The increase in strength of the 7-in. [l7.8-cm] casing reduced its drift diameter from 6.151 to 6.059 in. [15.62 to 15.39 cm]. This required the bit size to be reduced from 6 1/8 in. to 6 in. [15.56 cm to 15.24 cm], which caused a reduction in annular capacity between the liner and borehole of 8.8% (Fig. 2). Comparing pre-1980 jobs (4 1/2-in. [11-cm] liners in a 61/s-in. [15.6-cm] hole) with jobs of the first 8 months of 1980 (4 1/2-in. [1 1-cm] liners in a 6-in. [15.6-cm] hole) showed a big difference in the percentage of successful jobs-100% vs. 21%. The only difference in procedure was a change in annular capacity. It is not conclusive that this is the only contributing factor to poor cement jobs, but the success rate difference presents a strong argument that reduction of annular volume in the Wamsutter area is detrimental to successful liner cementing.

Conditioning the Drilling Fluid
Special conditioning of the drilling mud after the well has been drilled is a common practice in the Wamsutter area. In the past, well circulation was maintained after the liner was on bottom to ensure trouble-free circulation while cementing and to remove any excess gas buildup in the borehole.
Mud properties that can lead to poor cement jobs are high gel strengths, high viscosity, high density, and excessive chemical content. A review of mud properties at the time liners were run was conducted on wells drilled in the first half of 1980. It indicated that those mud properties were generally on the high side and could be properties were generally on the high side and could be detrimental to successful cementing. In the liner cementing technique used now, after total depth (TD) is reached the mud is conditioned and dispersed with an organic dispersant to obtain these mud properties (i.e., viscosity: 38 to 45 sec/qt [36 to 43 s/dm3]; plastic viscosity: 10 to 15 cp [0.01 to 0.015 Pa s]; yield point: 4 to 8 lbf/100sq ft [2 to 4 Pa]; gels: 2 to 8 lbf/100 sq ft [0.9 to 4 Pa]). These properties tend to increase the success of mud removal from behind the liner during cementing, which is beneficial in obtaining a good primary cementing job.
Pipe Movement Pipe Movement Reciprocation and/or rotation while cementing greatly enhances the possibility of a good cement job. The technology is available to move a liner while cementing.
JPT
P. 1353