This study examines the effects of drilling, completion, and production operations and their associated cyclic stresses on a cement sheath. The operations performed after cement placement can damage cement sheath integrity and bond with the casing or formation resulting in loss of zonal isolation and sustained casing pressure often requiring remediation and reducing productivity. This paper describes evaluation of cement sheath failure resulting from cyclic stresses experienced while drilling, fracturing, and producing shale gas wells and showcases optimization of cement systems used for Marcellus shale play intermediate casing strings. This study correlates the durability of each cement system with mechanical properties of the cements to determine each system's ability to resist failure under cyclic stresses. Two different cement compositions were used to cement intermediate casings on a number of wells. Both had similar performance properties and were designed to prevent gas migration following cementing. Wells cemented with one of the blends experienced a higher incidence of seal failure as evidenced by sustained casing pressure. In laboratory stress endurance testing, each cement system failed at a specific quantified magnitude of cumulative energy input. The results show a higher maximum endurance for the more durable cement, which also exhibits the higher field success rate. The fatigue endurance limit gives an approximation of the stress magnitude that a cement composition can withstand. Correlating laboratory endurance measurements and mechanical properties of the cement systems to field performance further quantifies the mechanical properties needed to optimize zonal isolation. U.S. shale gas production is a major component in the future of U. S. energy supply. As such, there is focus on the drilling and production of U.S. shale plays. This study takes measured look at annular seal failure and lays the ground work to calibrate it to actual field results allowing operators and service companies to select more durable cement systems. Results from this study can ultimately decrease time and funds spent repairing compromised cement seals. Furthermore, improved seal performance equates to improved well performance with lessened environmental risk and impact. IntroductionThe study reported here is a derivative of a long--term investigation aimed to improve zonal isolation for horizontal wells drilled in the Marcellus shale with the Research Partnership to Secure Energy for America (RPSEA). The impetus for this long--term study is to optimize drilling and completion practices to reduce cost, improve zonal isolation, and improve well success rate. Due to the complex environment encountered in drilling and completing horizontal shale wells, it can be difficult to determine all of the factors necessary to optimize zonal isolation. One of the initial actions of the long--term study was assessment of well performance in the Marcellus play. Interestingly, the well success rate was much lower in the intermediate strin...
The material IS subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write: 6200 N. Central Expwy., Dallas, Texas 75206.Gas flow fol lowing cementing has hindered the completion of wei Is for a number of years. Research of this problem has indicated many solutions which have been either partially successful or unsuccessful in control I ing gas flow fol lowing actual cementing operations.A theory describing the cause of this problem and a novel solution to the problem were presented in SPE 8257; 1 This paper summarized the results obtained during a fifteen-month field appl ication of the control method. Results of 250 cement jobs performed world-wide are summarized and specific examples are discussed in detal I.
Just afew years ago, there existed a great uncertainty regarding the durability of oi/well cements in geothermal wells. Limited, and at times apparently unreliable, information suggested that conventional well cements may not be sufficiently resistant to geothermal well fluids and temperatures for the expected 20-or 30-year service life of the average geothermal well. Therefore, we began to investigate the performance of numerous oi/well cementing compositions in actual geothermal environments.Duplicate samples were exposed to actual geothermal well temperatures and fluids in the Baca, NM, and Imperial Valley, CA, geothermal fields for periods of up to 1 year.A novel testing procedure for geothermal cements was developed and successfully applied in these experiments. Laboratory evaluation of the exposed samples measured the durability of various compositions.The work indicated that some oi/well cements apparently can be rendered sufficiently resistant to geothermal well conditions for the service life of a geothermal well.
after receiving an M.S. degree in chemical engineering from the University of Oklahoma. His areas of research include cements for geothermal use, low-density cements and control of gas flow through cement. ABSTRACT Until recently, attempts to improve extra-low density cement grout slurries (1000 to 1300 kglm3) suitablefor oil and gas well cementing have accomplished little except to define a disappointingly low strength-density ratio and confirm the low density limit for useful com-pressive strengths. Commonly available porous, light-weight fillers which yield good strength-density ratios at surface conditions seldom provide the desired benefits under high pressure conditions. The use of water-extended admixtures results in little or no useful strength at slurry densities below 1300 kglm-1, and the amount of gas entrainment needed for low-density foam or cellular grout is often impractical at high pressures. This paper describes the use of a new light-weight admixture which maintains low density, even at high pressures, and has a relatively low mixing water re-quirement. Slurries using this new ma-terial have greatly improved strength as compared to other types of low-density slurry systems. Final compressive strengths for slurries with densities of only 1050 kgIm3 easily exceed 3.5 MPa. This new admixture consists of small (10-100 jam) diameter inorganic high-strength microspheres (HSMS). It can be used with any type of cement, survive under hydraulic pressures approaching 50 MPa and withstand geothermal well temperatures.TO date, proven applications range from cementing conductor pipe and cas-ings where fast strength development is TABLE 1. Sieveanalysis slave Size (.UM)Weight %
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