American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Neat Portland cement systems lose strength and become permeable at temperatures above 250 degrees F. This deterioration usually is more extreme over the first few days or month of heating but is usually not severe enough to cause disintegration of the neat cement. After this initial regression many neat Portland systems will regain a portion of Portland systems will regain a portion of their strength and reduce in permeability. This temperature regression of cement can largely be prevented by using about 35 per cent very fine silica sand. The strength can be maintained or increased but permeability will increase. Most additives for oil well cements can be included in such a silica stabilized system without extensive effect due to temperatures up to 600 degrees F. An exception to this is fly ashes and, to some degree, natural pozzolans. These are stable at 450 degrees but are losing strength and recrystalizing 600 degrees F. Introduction The deterioration of Neat Portland cement at temperatures above 250 degrees F (120 degrees C) has been known for many years. Menzel proved that fine silica added to a Portland cement paste would improve the strength of cements cured at elevated temperatures. An increasing number of wells are being subjected to these elevated temperatures each year. Deeper and hotter oil and gas wells are being drilled and other wells are being subjected to hot water, steam, or fire flood methods. High temperature geothermal wells are also increasing in number each year. The cement in these wells will be subjected to elevated temperatures from bottom to top. It is probable, therefore, that the surface and intermediate strings on many of these wells are not adequately protected from deterioration.
The process of foaming cement to make lightweight slurries is well known and documented in the literature.However, the technology for applying this process to oil and gas-well cementing has been lacking. New techniques and treatment designs have now been developed which show that the use of lightweight foamed cements in oil field operations can solve many problems.Treatments can be performed with the current equipment and personnel operating in the field.When compared to other processes for making ultra-lightweight slurries, foamed cements are very economical.
American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and with the paper, may be considered for publication in one of the two SPE magazines. Abstract There is very little information available as to the long-term effects of high temperatures on the strength and permeability of cements, especially with additives. permeability of cements, especially with additives. Most strength tests are run for short periods of time, possibly 30 to 90 days and these extrapolated to long-term effects. There are few short-term permeability results and very few attempts extrapolate these results. This report presents the results of study of cement systems at 450 deg. F for two years and 600 deg. F for one year under steam pressure. At these conditions we found that most changes did occur within the first week to one month and that extrapolation to longer periods was usually valid. Certain pozzolan (fly ash) systems, however, showed signs of deterioration only after several months at 600 deg. F and one year at 450 deg. F. There was also some variation in results between various sizes of silica, especially as to the effect on permeability. Introduction The deterioration of neat Portland cement (cement + water) at temperatures above 250 deg. F has been known for many years. The use of fine silica to reduce such deterioration has been practiced in oil and gas well cementing for about the last 20 years. Today there are numerous wells in which the cements bonding the steel casing to the formation are subjected to temperatures above 400 deg. F. These are deep petroleum wells drilled in the Gulf Coast area, geothermal wells, or wells being subjected to various thermal recovery methods. There is very little information available as to what effects these high temperatures have on Portland cements over extended periods of Portland cements over extended periods of time. There are results on systems for up to 30 days and a few for up to 3 and 6 months. These have been used to extrapolate to longer time. Recently there have been indications that deterioration was occurring over extended periods of time with certain cements being periods of time with certain cements being used in geothermal steam wells. Tests were therefore conducted at 450 deg. F in sealed tubes under steam pressure for two years and at 600 deg. F for up to one year to determine whether the previous extrapolations were valid. Strengths, permeabilities, specimen weights and specimen dimensions were determined.
One of the most serious problems encountered when cementing casing in a well is the failure of the cement casing and cement formationbond. The failure of the cement bonding is a major problem from the standpoint of allowing migration of fluids from one zone to another. Also, poor bonding can result in large losses of reservoir fluids, premature reservoir depletion, and unsatisfactorystimulationoperations. 'With, these factors in mind, it has long been recognized that superior cementing operations could be achieved if expansion could be induced in oil well cements. Expanaion currently is induced in oil well cements by two methods, addition of salts (salt cements), or addition of an expanding component (chemicallycompensatedcement).The purpose of this paper is to compare the expansion characteristicsof these types of cements. Additional characteristicssuch as pumping time, compressivestrength, and bonding are also compared.
Summary Successful cementing of shallow casing strings (150 to 400 ft) for steamflood operations in Kern County, CA, has been difficult to achieve. Lost-circulation problems accompanied by cement fallback are common. Ultrasonic cement evaluation logs commonly show the cement sheath to be severely cut with gas (air) and show numerous cases of large gaps in the cement column. Extensive remedial work typically is required for effective completions. Numerous cement formulations, including foamed cement, have been pumped to solve these problems, without apparent or consistent success. A system now has been developed that provides operationally precise low-rate nitrogen metering from commercially available nitrogen cylinders to overcome previous metering problems. Several yard tests were conducted, and 26 wells were cemented with foamed cement with a low-rate nitrogen metering system. Surface-stable foamed-cement systems have been created with nitrogen rates as low as 6.4 scf/bbl and densities as low as 6.5 lbm/gal. Results illustrate that, with proper metering equipment, typical field crews can perform foamed-cementing treatments with minimum equipment. Posttreatment evaluations demonstrate that properly designed and executed foamed-cement treatments virtually have eliminated the lostcirculation problems and gaps in the cement sheath. Introduction Shallow casing strings (150 to 400 ft) in California historically have been very easy to cement, if the definition of successful cementing is limited to pumping the cement down the hole without mechanical or operational problems. However, proof of the cement-sheath quality and placement efficiency is required in critical operations, such as steamflooding, which introduces significantly different criteria on the definition of successful cementations. In areas to be steamflooded, the cement sheath must provide isolation for annular steam control to prevent steam from escaping to the surface and to ensure isolation of the steam bank to the injection zone. The wells located in the Lost Hills field typically have been drilled with freshwater drilling muds that vary in density from 8.5 to 9.0 lbm/gal. Depending on location, lost-circulation problems during drilling, circulating before cementing, or cement placement are common. Fracture gradients range from about 0.416 to 0.468 psi/ft. Not surprisingly, cement fallback is common. Fallback merely indicates lost circulation during placement in cases where the rate of mud/cement returns during circulation is not measured and, in fact, is less than the pumping rate. Cement sheath evaluations of conventional cement systems (Fig. 1) typically illustrated cemented sections with gaps where there appeared to be nothing (or gas) in the annulus, generally one or two sections of what appeared to be good cement, some gas-cut cement, and free casing. Fig. 1 shows typical acoustic impedance character signatures. The question of hole stability or formation sensitivity to drilling fluids was not considered a problem during the planning and early drilling phases in the Lost Hills field. Cement evaluation logs indicated severe problems with what was thought to be cement solids separation after placement. In the Lost Hills program, almost every log illustrated segments of "gas-cut" cement in the lower portion of the hole, topped by free casing with water and gas in the annulus, which in turn was topped by segments of what appeared to be 15 to 20 ft of good cement (Segment B). These upper segments of "cement" were thought to be caused by formation collapse into the annulus after cement placement. In two of the wells in Lost Hills, samples of the material were retrieved by use of coiled tubing.
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