Foam Cement Engineering and Implementation for Cement Sheath Integrity at High Temperature and High Pressure

Abstract

Cementing high-pressure, high-temperature (HPHT) wells poses various challenges not seen at normal well conditions. For instance, the following objectives are critical for HPHT wells:Prevent losses during drilling fluid circulation and cement slurry placement.Displace the drilling fluid and place the cement slurry effectively.Prevent free-water or gas-channel development.Reduce slurry fluid loss.Provide support for the production packers.Decrease compression loads on casing connectors.Prevent damage to cement sheath.Prevent annular gas pressure over the life of the well. The industry is recognizing the interaction between these factors to determine the optimal cement job design for accomplishing these objectives. This paper presents and discusses the engineering analysis to determine the optimum foamed cement sheath properties for integrity during the life of the well at HPHT conditions. Also, this paper compares foamed cement to nonfoamed slurries in achieving these objectives. Other important issues discussed are the performance of nitrogen at HPHT conditions and the rheological properties of the foams. Key issues addressed are the state and solubility of nitrogen under downhole conditions and the integrity of the cement sheath during the life of the well. Thermodynamic solution theory and experimental studies are applied to the former, and finite element analysis is applied to the later. Case examples are presented discussing foamed and conventional operations at near HPHT conditions for some Norwegian, North Sea wells. Cement properties are contrasted for the different foamed and conventional cement slurry properties with respect to:Achieving the HPHT objectives, such as placement efficiency and sheath propertiesPrejob design to obtain the objectivesJob planning and proceduresJob executionLogging of foamed cementPost-job evaluation of the cement systems Introduction Traditionally, the industry has concentrated on the short-term properties that are applicable when the cement is still in slurry form. This effort is necessary and important for effective cement-slurry mixing and placement. However, the long-term integrity of cement depends on the material/mechanical properties of the cement sheath, such as Young's modulus, tensile strength, and resistance to downhole chemical attack. Considering properties of the cement sheath for long-term integrity is critical if the well is subjected to large changes in stress levels such as with HPHT wells. Recent experience has shown that after well operations such as completing, pressure testing, injecting, stimulating, and producing, the cement sheath could lose its ability to provide zonal isolation.1 Failure of the cement sheath is most often caused by pressure- or temperature-induced stresses inherent in well operations. This failure can create a path for formation fluids to enter the annulus, which can pressurize the well and render it unsafe to operate. Failure can also cause premature water production that can limit the economic life of the well. Consequently, if the cement sheath fails during its active life, the objective of producing hydrocarbons safely and economically may not be met. The cement sheath should have optimum properties so it can withstand the stresses from well operations. In general, cement slurry should be compensated for volume reduction during hydration and the mechanical properties should be optimized for the well operations.

Foamed Cement Applications in Oil Industry Based on Field Experience: A Comprehensive Review

“…Excessive N 2 injection negatively affects the downhole quality of the cement more than the use of low amounts of N 2 . 77 One of the critical issues associated with squeeze cementing using conventional material is the accurate estimation of fluid loss, which complicates the operations and may lead to the failure of the squeeze job.…”

“…Recently, the field experience showed that CBL was effectively used to evaluate many foamed cement jobs. 77 Consideration of the cementing operations simulation results is important to predict any anticipated cement loss, especially across weak formations. For squeeze treatment, although the foam cement operation is costly compared to class G cement usage, the necessity to perform the operation in more than a single squeeze for class G cement system increases the overall job cost.…”

Innovation of Annular Sealants During the Past Decades and Their Direct Relationship with On/Offshore Wellbore Economics

“…To address potential issues and help operators make well-informed decisions regarding the long-term integrity of oil and gas wells, many companies, both in the service and operation sectors, have applied to some extent a more comprehensive approach when designing OWCs, taking advantage of the evolution of OWCs, both from the chemical (new systems) and engineering (new characterization tools) perspectives, to create an optimal sealant to help ensure integrity for the life of the well (Fig. In support of this statement, many studies report successful use of such techniques in yielding optimum long-term wellbore integrity in actual or simulated downhole environments (Krusche et al 2006;Shadravan et al 2014Shadravan et al , 2015aShadravan et al , 2015bGarnier et al 2007;De Andrade et al 2015;Godoy et al 2015;McDaniel et al 2014b;Griffith et al 2004;Jain et al 2014;Wang and Dahi Taleghani 2014b;Ramos et al 2009). Multiple datasets indicate significant variations in wellbore integrity (2.6 to 75%) over different time periods (Davies et al 2014).…”

Techniques for the Study of Foamed Cement Rheology

“…The increased elasticity of foamed cement imparts flexibility to the cement sheath allowing it to expand/contract with the casing as various pressures and temperatures are experienced during wellbore operations (Griffith et al 2004;Kopp et al 2000). This flexibility helps improve the durability of the cement sheath in the well, allowing the cement sheath to last for a longer period of time.…”