Using Improved Technology to Obtain Better Cement Jobs on Deep, Hot Liners

Abstract

Critical to the success of a cement job are an accurate knowledge of downhole temperatures, adequate laboratory simulation of field conditions, proper regard for the effects of mud contamination of cement, and efficient proper regard for the effects of mud contamination of cement, and efficient mud displacement. All of these factors are discussed here, particularly in the context of a two-well testing project in Southwest Texas. Introduction The design of cementing slurries is always critical on deep wells; however, it is even more so on liner casings because of the performance requirements that exist almost simultaneously at both the top and the bottom of the liner. In cementing full strings of casing, the cement's initial performance is usually judged only in relation to the producing zones near the bottom of the casing. On liner casings, the cement must also set up and provide an adequate seal at the top of the liner, which may be several thousand feet back up the hole. Static formation temperatures at the top of the liner may be much lower than at the bottom. and may in fact be less than the circulating temperature for which the cement slurry was designed. This cement must be efficient in displacing the drilling mud from behind the entire liner, and must have reached the top of the liner sufficiently uncontaminated to set up, it must have adequate compressive strength to hold a pressure test. Mud-contaminated cement at the top of the liner is almost always a problem because of the relatively small volumes of cement required to fill the annulus, and there is a hesitancy to use much excess cement. The use of large volumes of cement behind the drillpipe can have disastrous results if the cement sets up before the drillpipe is removed from the well. In addition to the primary performance criteria discussed above, a deep-liner cementing slurry must also have adequate density to prevent the flow of formation fluids, particularly gas, into the wellbore. The slurry must also have satisfactory rheological properties to prevent formation breakdown while it is properties to prevent formation breakdown while it is being pumped into the annulus. Because many of these factors are ignored, the success ratio of liner cementing has been less than satisfactory. However, analyses indicate that many more successful jobs may be obtained if careful engineering is used to achieve the following: 1. Better analysis of well temperature conditions. 2. Closer laboratory simulation of actual well conditions to yield accurate results. 3. Greater compatibility between oil mud and cement. 4. More thorough mud displacement. With the objective of improving primary cementing success, these concepts were tested on two wells drilled in areas of Southwest Texas where previous experience showed that conventional approaches were inadequate.