A reduction in near wellbore permeability can dramatically decrease hydrocarbon production. This study examines the extent of formation damage caused by 1) incompatibility between the formation and injected fluids, 2) exposure times and 3) leakoff volumes. Dynamic fluid loss studies are presented to illustrate the effects of some drilling muds, spacer fluids and cement slurries on typical Berea sandstone. The studies were conducted using 2×5" inch long, pre-saturated, 500 millidarcy core specimens to evaluate the damage potential from fines and filtrates. These tests simulated applications at typical bottom hole circulating temperatures and differential pressures. Permeability was measured at depths of 0.5, 3.0, 5.5 and 8.0 inches from the exposed formation faces. Prior industry studies have concentrated on using filtrates and small core specimens to measure changes in permeability. Although beneficial, these tests do not simulate filter cake deposition or exposure time for different fluid phases during a cementing application. Drilling muds may be exposed to a formation for many days, while most spacer fluids only contact the formation for 5 to 15 minutes, and cement slurries for a few hours. Test results indicated that lignin or PHPA muds cause minimal formation damage to Berea sandstone. They also built very dense, low permeability filter cakes which restricted invasion of fines and filtrate from spacers and cement slurries. Most formation damage was confined to within 1–2 inches of the exposed core face. The studies also showed that fresh water spacers were much more damaging than those containing small concentrations of potassium chloride (KCl). Tests incorporating API cement slurries demonstrated their excellent bridging and cake building characteristics. The addition of fluid loss additives such as hydroxyethylcellulose (HEC) polymer or polyvinyl alcohol (PVA) latex decreased filtrate loss and formation damage. These tests also revealed that the selection of the polymer for fluid loss control is important. Duplicate tests using styrene butadiene resin (SBR) latex resulted in excessive formation damage at penetration depths up to eight (8) inches. Scanning electron microscopic (SEM) analysis was conducted to further illustrate the results obtained from the dynamic fluid loss studies. While these results are not considered quantitative, the apparatus and procedure permitted dynamic fluid loss testing under simulated downhole conditions using whole treating fluids. The extent of formation damage caused by some drilling muds, spacer fluids and various cement slurry formulations were evaluated. These test methods can be used to improve critical job designs for problematic reservoirs and to screen for damaging additives.

A unique cementing system is presented which provides improved cement bonding and zonal isolation in wells haVing bottom hole static temperatures (BRST) below 175 0 F. Selectively formulated with components common to the industry. this system is reliable and versatile.Latex cement additives are excellent bonding aids. gas migration preventers. matrix intensifiers and fluid loss additives.They improve cement's elasticity and resistance to corrosive flUids.Thixotropic. expanding cements excel in prOViding annular fill. zonal isolation and lost circulation control. Combining these two technologies into a single. efficient. low cost system has prOVided technical and economic properties which have had significant impact on cementing operations. This new cementing system is hereafter referred to as LXT for latex. e~anding. thixotropic cement.The properties engineered into the LXT system provide better primary and remedial cementing applications through: (1) reduced invasion of permeable. unconsolidated or "weak" zones by whole cement or cement filtrate. (2) prevention of gas or fluid migration in hydrating cement columns. (3) greater zonal isolation between differentially pressured intervals separated by thin. shale barriers. and (4) rapid compressive strength development and minimal waiting-oncement (WOC) time. Laboratory studies and case histories are presented to show the merits of this cement system over conventional low water loss (LWL) systems. Numerous applications in East Texas. West Texas (Permian Basin) and on References and illustrations at end of paper. 125 the West Coast have resulted in marked improvements in job quality and success rates over prior cementing practices.

Cement bond logs (CBL's) are typically used to approve or condemn cement jobs. This "report card" has caused disputes between the cementing and logging companies for years because typically the CBL is interpreted independently from the cementing operation. Thus, a bad "report card" is usually translated into a bad cement job, which is often not the case. This paper illustrates the value of integrating cementing with bond logging to give a clearer picture of the actual quality of the cement downhole. Logs should be used as a tool to understand the cement quality and determine what improvements need to be made to enhance cementing job success. Four examples are presented which show that factors such as 1) borehole conditions, 2) cement job design, 3) displacement practices and 4) tool selection and calibration all have an effect on the bond log interpretation. However, in all cases, integrating the log response with a thorough cement evaluation results in a more accurate analysis of the cement quality, and a better educated decision on the necessity for remedial work. Introduction Complete isolation of production intervals from non-bearing intervals, water sands and thief zones is vitally important for successful exploration and development wells. Much care needs to be taken when engineering the cementing design and placement program necessary to obtain proper isolation. A few days after the cement is placed, a wireline company may run one or more cement bond logs to measure cement quality. Essentially, these logs represent the "report card" for the cement job. The tool calibration and logging parameters are determined by the cement properties measured in a laboratory. However, the true properties of the cement in the wellbore may be much different than those measured in the lab. This discrepancy is due to a number of environmental, operational and downhole parameters which are seldom incorporated into the cement design and lab test programs. Ignoring these factors can result in a log interpretation that is not representative of the true wellbore cement quality. This can lead to an ill-advised, unnecessary and costly decisions about remedial (squeeze) cementing. Integrating a thorough cement job evaluation with the log interpretation produces a much better picture of the true cement quality. It also allows for a more comprehensive decision about the squeeze cementing, this can save time and money! Discussion Cement Design and Testing From the cement designers point of view, the factors usually considered when designing a cement slurry and lab test program are: P. 819^