Fred Sabins

Problems in Cementing Horizontal Wells

This paper addresses hole-cleaning problems, displacement mechanics in the hole, pipe centralization, cement slurry design, and the use of acoustic tools to evaluate cement jobs. Settling of solids on the low side of a hole during drilling should be avoided through proper selection of the drilling fluid, especially its dynamic setting characteristics. Uneven clearances between pipe and hole wall resulting from eccentric location of pipe within the hole will lead to uneven cement tops (by as much as hundreds of feet). Spacing between centralizers should be calculated to minimize the effect of pipe sag while maintaining drag at reasonable levels and obtaining the desired displacement performance by the cement slurry. Pipe rotation or reciprocation, especially when properly installed wall cleaners are used in centralized pipe, is beneficial in dislodging and removing solids and gelled cement slurries from the low side of holes. Methods for testing the free-water content of cement slurries (which should be zero) at simulated downhole conditions are suggested.

The Relationship of Thickening Time, Gel Strength, and Compressive Strength of Oilwell Cements

A previous investigation of the effect of thickening times on early compressive-strength and gel-strength development has been expanded to include a wider range of well conditions, a greater variety of slurry types, and a more thorough evaluation of static gel strength. No positive relationship between thickening time and the onset or the rate of static-gel-strength development could be found. With few exceptions, all slurries tested developed values greater than 48 Pa (100lbf/100 sq ft) gel strength is less than 20 minutes. Data presented show that times needed to develop a specific static gel strength are more closely related to the type of slurry than to thickening time. A calculation method is given for estimating shutdown factor from static-gel-strength data. New data confirm that 12- and 24-hour compressive strengths are not significantly reduced by reasonable increases in thickening time. The maximum single-stage cement interval without an unreasonable waiting-on-cement (WOC) time for specified compressive strength has been redefined in terms of interval temperature differences.

Microannulus Leaks Repaired with Pressure-Activated Sealant

Sustained casing pressure is a serious problem that is prevalent in most of the oil producing regions of the world. Annular pressure can be a significant safety hazard and, on a number of occasions, has resulted in blowouts. Sustained casing pressure results from the migration of fluids in the annulus. The most common path for migration of fluids is through channels in the annular cement. To safely and economically eliminate sustained casing pressure on a well in the Gulf of Mexico, W& T Offshore, Inc. utilized an injectable pressure-activated sealant technology to seal channels in the annular cement of their well and eliminate the casing pressure. The mechanical integrity of the well was restored, saving over

A study of bulk cement handling and testing procedures

1,000,000 compared to a conventional rig workover.

Attenuation of Casing Cemented With Conventional and Expanding Cements Across Heavy-Oil and Sandstone Formations

The variation between thickening-time test results from test on pilot blends cement-blend sample tests has been a subject of frequent investigation. Disagreement between these test results is often blamed on improper additive proportioning, inadequate blending, or incorrect sampling techniques. A study of blending, sampling, and testing variables was conducted. This paper describes the results of this research testing with a full-scale laboratory bulk plant. It also includes the results of a south Texas field study in which thickening time test results from more than 300 cement-blend samples were examined. Results of these studies suggest that significant statistical variations may be involved in blending, sampling, and testing procedures under deep-well conditions. The variabilities are used as guidelines for determining thickening-time acceptance windows. Variabilities or uncertainties can be minimized by optimization and standardization of these procedures.

Effect of Excessive Retardation on the Physical Properties of Cement Slurries

Studies were conducted with a large-scale displacement model containing manmade tar and competent (hard) manmade sandstone formations. This paper investigates the cement placement process and the acoustic response with standard logging tools. This investigation revealed that the formations behind the cement make a significant contribution to the pipe-attenuation rate. The large-scale acoustic experiments indicate that lower pipe-attenuation-rate levels are measured when tar formations are cemented. This occurs even with the same type of cement and the same annular clearances

Method of using thixotropic cements for combating gas migration problems

As well depths become greater over-retardation becomes more and more commonplace. Precise retarder response is difficult to attain at high temperatures and many cementing slurries end up with thickening times far in excess of what is considered good practice. To avoid sensitive retarder concentration, field blends often show thickening times of more than 6 hours for jobs where 3 to 4 hours is sufficient. Excessive thickening time has been commonly considered detrimental to good cement jobs, but the effect of over-retardation on cement properties was mostly derived from theoretical speculation. Through an extensive laboratory study, thickening time retardation is correlated to static gel strength development, initial set, and early compressive strength. The results indicate that moderate retardation has minimal effect on static cement properties. For deep wells, thickening times up to 10 hours do not appear to be detrimental to early compressive strength at bottomhole static temperature (BHST).