Multistage hydraulic fracturingturing treatments in unconventional wells have greatly increased the number and magnitude of stress cycles that must be withstood by primary cement jobs. The stress cycling of hydraulic fracturingturing on Portland Cement, with its intrinsic mechanical properties, may present a risk to long-term well integrity. By modifying the mechanical properties of the set-cement to make it more flexible, the risk of compromising well integrity during hydraulic fracturingturing treatments can be reduced. The mechanical properties of set-cement designs can be tested in a laboratory setting. This allows quantification of the compressive strength, tensile strength, Young's modulus, and Poisson's ratio of the set cement. Hydraulic fracturingturing design software can be used to quantify the pressure and temperature cycles to which the inner diameter of the primary casing string will be subjected. A mathematical model is used to predict the potential risk of mechanical failure of the set cement based on the mechanical properties and the pressure and temperature cycles of the expected treatment. The mathematical model identifies risk of failure in tension, compression, and de-bonding. By adding flexible materials to Portland Cement in a reduced water, tri-modal particle-size-distribution blend, the Young's modulus can be reduced while relatively high compressive and tensile strength is maintained. According to the mathematical model, a cement sheath with these properties is at a low risk of mechanical failure in any of the three failure modes up to a certain hydraulic fracturingturing pressure. Wireline logging tools use ultrasonic waves to measure acoustic impedance and flexural attenuation for cement evaluation. These readings are used to assess the integrity of the cement sheath in a 360° solid/liquid/gas map around the casing. These logging data can be used to determine the presence and extent of damage to the cement sheath during the hydraulic fracturingturing operation. A hydraulic fracturingturing treatment was applied to a well cemented with optimized flexible and trimodal properties. Cement evaluation logs were run before and after treatment for comparison. The post-fracturingturing log showed no damage to the annular cement sheath.
The intermediate casing hole size can be calculated from empirical data in the Williston basin. Using this calculation reduces the cement excess required, helps achieve the top of cement objectives, and reduces the cementing costs. Many operators in the Williston basin are using an outdated assumption of average hole size for calculation of cement volumes on their intermediate casing section. This results in excessive cement volumes to sometimes detrimental effect; breakdown is occurring frequently at the Mission Canyon. This occasionally causes operators to fail to meet cementing job objectives. Very few open hole calipers are run in the intermediate section in this basin, making direct measurements very rare.In an extensive review, cement evaluation logs from approximately 300 wells in a 15-month period from January 2014 through March 2015 were used to approximate top of cement and then derive an average effective hole size. The logs evaluated were from cement bond log (CBL) and ultrasonic imaging tools. The data are controlled in a statistical manner for cement job anomalies such as losses or severe channeling.The findings prove that intermediate casing hole size in the Williston basin is much smaller today than in the recent past. The switch from water-base mud to oil-base mud and a marked improvement in drilling speed have limited the size of the intermediate section hole. One operator was able to substantially reduce cement volumes, keeping the top of tail slurry a minimal height above the weakest formation and thus avoiding losses. As a result, this operator is achieving top of cement objectives more frequently and has substantially reduced cementing cost.This analysis contributes to the community valuable empirical data about intermediate section hole size in the Williston basin using a large dataset and statistical controls to ensure quality of the conclusions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.