Field Results of Cementing Operations Using Slurries Containing a Fluid-Loss Additive for Cement

Abstract

Abstract A survey of 1,000 squeeze-cementing jobs in different areas of the United States indicates that cement slurries having low-fluid-loss properties can be used successfully in conventional squeeze operations employing the "hesitation" technique. It has been found that high pressures are not essential to obtaining a successful dry test following squeeze. Also, zone isolation to reduce high gas-oil or water-oil ratios has been achieved by notching the casing with high-velocity jets of an abrasive-laden fluid and subsequent displacement of low-fluid-loss cement at high injection rates. Bridging agents in gel-cements containing the fluid-loss additive have been used to squeeze naturally fractured formations which previously required numerous stages with large volumes of cement. Drilling-out was not required in many cases, because the cement was circulated out of the perforated interval. Casing cementing operations have been particularly successful when using lightweight slurries containing pozzolanic extender, bentonite and sufficient fluid-loss additive to reduce the fluid-loss to 120 cc/30 minutes at the cementing temperature. Cement bond logs indicate that these slurries, when used with scratchers and reciprocation of the pipe during the cementing operation, increase the probability of desired fill-up and minimize the necessity for block-squeezing. Introduction A study of treatment reports from over 1,000 cementing jobs, using slurries with controlled fluid-loss properties, indicates that in most applications controlled filtration provides definite advantages in achieving the purpose of the cementing operation. Analysis of the economic aspects of squeeze cementing indicates that the use of a low-fluid-loss additive in the slurry provides at least 10 per cent lower cost over conventional squeeze-cementing operations employing neat cement by eliminating extra stages. Unsuccessful squeeze jobs were studied from the standpoint of formation characteristics, cementing materials aid techniques in an effort to determine causes of failure and possible remedies. Casing cementing operations utilizing low-fluid-loss slurries showed an extremely high success ratio, confirming the fact that this type of cement will help minimize channeling, prevent sticking of casing during cementing, increase the probability of desired fill-up and reduce the necessity for block squeezing. The application of cement slurries during oilwell cementing operations is frequently complicated by excessive water loss into permeable formations. This results in premature thickening of the slurry and possible bridging of cement solids before placement of the slurry is complete. The attainment of high squeeze pressures is frequently misleading in that they may be due to blockage by dehydrated slurry in a region of fluid-loss, rather than in the zone to be sealed off. The inclusion of fluid-loss additives in cement slurries reduces premature fluid-loss and minimizes the possibility of improper placement of the cement and subsequent job failure. In the past, many fluid-loss control additives have resulted in undesirable modification of many slurry properties, complicating application procedures and often requiring the use of additional corrective additives. A recently developed fluid-loss additive, FLAC, is relatively inert and in most cases does not affect the desirable properties of either the cement slurry or the set cement. The summary chart shown in Table 1 is a breakdown of over 1,000 cementing jobs using this fluid-loss-control additive which have been performed in the major oil fields of the U. S. and Canada. These treatments are divided into the following broad categories. 1. ZONE ABANDONMENT--shutting-off perforations to exclude undesirable fluids and to permit reworking of well. JPT P. 477^