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Abstract The failure probability of wellbore is high in HPHT gas wells because of the effect of the hole angle, the cementing complications and the high pressure high temperature environment. However, most of the researches about the cement problems are studied by two dimensional modeling. The effect of hole angle and cement complications on HPHT well integrity in three dimension is hardly studied. In the analysis, the finite element method was used to build a three dimension simulation model where the hole angle, casing eccentricity, and cement channels are considered. One cement system (118-lbm/ft) commonly applied in oil field is used to study the effect of cement complications on the wellbore integrity. The hole angle, cement channel angle, and casing eccentricity are the variables taken into account and an attempt is made to which parameter is the most important and its effects on wellbore failure. In the cement channeling, the casing has highest von Mises stress at the hole angle of 90°, and the cement tends to fail in tension. The casing eccentricity tends to reduce cement shear stress, and tensile stress but increase cement compressive stress. The cement has the highest compressive failure probability in casing eccentricity condition. At the casing eccentricity lower than 40%, for different hole angle, the casing eccentricity has minor effect on the casing. This paper presents the sensitivities of the variables and gives a better understanding of the effect of hole angle and cement complications on the HPHT well integrity.
Abstract Cementing a string in one stage is a challenging task, especially in the presence of weak formations. Cement slurry losses during placement is highly possible if the equivalent circulating density (ECD) exceeds 82 pcf during placement. A conventional method to overcome this challenge is to use multi-stage cementing by setting the stage tool above the loss circulation zone. However, field data indicate that the tool can fail, thus causing serious delay and economic loss. In addition, stage tools are considered weak point and not good for long term seal. A second method for zonal isolation is to use low density cement. In this study, we present extensive lab evaluation of a low density system based on the use of hollow microspheres for one year at field conditions. The tests included one year mechanical properties measurement such as compressive strength development, Young's modulus and Poisson's ratio. The low-density system (70 pcf) was tested at 300 ºF. An earlier study has shown the suitability of using low density cement in the field, Al-Yami et al. (2007). However, there is no available Investigation in the literature about the durability of low density cement at higher temperature and at different operational scenarios. The finite element method was used to analyze the failure probability of HPHT wells over with time. At the variation of bottom whole pressure, the casing, cement, and formation system failure probability was studied for this type of cement. This paper introduces the operational envelope for this type of cement in order to achieve successful operations. Field cases were discussed to validate the results of this investigation.
- North America > United States > Texas (0.69)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate (0.28)
- North America > United States > New Mexico > San Juan Basin (0.99)
- North America > United States > Colorado > San Juan Basin (0.99)
- North America > United States > Arizona > San Juan Basin (0.99)
- (14 more...)
- Well Drilling > Pressure Management > Well control (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Well Drilling > Casing and Cementing > Cement formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.94)
Abstract Cement durability is very important to maintain proper well isolation and stability under HPHT conditions. In the process of well completion and production, pressure decline and temperature variation with time can contribute to cement failure and wellbore stability issues. However, there is no available investigation in the durability and comparison of different types of cement at higher temperature and at different operational scenarios. Three different types of cement (72 pcf, 101 pcf and 118 pcf) commonly used in the Middle East were cured and tested at 300°F in the study. The tests included one year mechanical properties measurement such as compressive strength development, Young's modulus and Poisson's ratio. Finite element method was used to analyze the failure probability of HPHT wells over with time. At the variation of bottom hole pressure and temperature, the casing, cement, and formation system failure probability was studied for these types of cement. The results show that the pressure variation has more effect on the wellbore stability than the temperature variation for HPHT wells. Low density cement can improve the wellbore stability issues due to the cement elastic behavior. This paper introduces the operational envelope for every type of cement investigated in order to achieve successful operations based on field conditions. Field cases were discussed to validate the results of this investigation.
- North America > United States > Texas (0.70)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate (0.28)
- North America > United States > New Mexico > San Juan Basin (0.99)
- North America > United States > Colorado > San Juan Basin (0.99)
- North America > United States > Arizona > San Juan Basin (0.99)
- (16 more...)
Abstract The failure probability of casing collapse is high in HPHT gas wells because of the cementing complications and the operational environment. In the life of a well, the cement sheath not only provides zonal isolation but also supports casing and increases casing collapse resistance. Due to the high temperature high pressure conditions, the cement sheath plays a more important role in maintaining wellbore integrity. During the production process in HPHT gas wells, the pressure differential inside the casing and the surrounding formation is larger than the conventional wells, this presents a greater challenge to the casing integrity. Casing eccentricity, cement voids and cement channels usually are cementing complications in HPHT gas wells. Pore-pressure was also considered in this study. In the analysis, the finite element method was used and 2D simulation model was built to study the effect of cementing complications on casing collapse resistance. In the study, two cement systems, brittle cement system and elastic cement system, were used to analyze the effect of the cement property on the casing collapse resistance. In the sensitivity analysis, void location, void size and shape, casing eccentricity, pore pressure, casing internal pressure, horizontal stress, cement Young’s Modulus, cement Poisson ratio, hole diameter, and formation temperature were considered to study their effect on casing collapse resistance. The results showed that an improvement of collapse resistance of 12% is observed in various conditions in elastic cement system. Casing collapse resistance is very sensitive to void location, cement Poisson’s Ratio, cement Young’s Modulus, and pore-pressure. Casing eccentricity and voids shape have minor effect on the casing collapse resistance. Simultaneous cement channeling and casing eccentricity is the worst case scenario in casing collapse resistance. This study gives a better understanding of casing collapse failure in HPHT gas wells and helps improve cement and casing design to maintain wellbore integrity that can be expected to last for the life of the well.
- North America > United States > Texas (0.29)
- Europe > Norway > Norwegian Sea (0.24)
Abstract The new quest of unconventional resources is the achievement of well integrity which is highlighted by the inadequacy of conventional cementing procedures to provide zonal isolation. High temperatures and pressures or even post-cementing stresses imposed on the cement sheath as a result of casing pressure testing and formation integrity tests set in motion events which could compromise the long term integrity of the cement sheath due to fatigue. Knowledge of the mechanism of fatigue in cement and factors that affect it such as the magnitude of the load, strength and composition of the cement, mechanical properties of the cement and pattern of load cycles are important to achieve a realistic design of a cement system that will be subjected to fatigue loading. Such a design will go a long way to ensure the long term integrity of a well operating under downhole conditions. Finite element investigations help engineers to assess the stress magnitude and evolution for a given well configuration, but when structural calculations for casing-cement system are required, missing input parameters reduce the quality of the results. In order to have reliable data we performed an extensive experimental work using Class G cement in order to measure the principal parameters for mechanical structural calculations: compressive and tensile strength, Young modulus, Poison Ratio. The data was measured under room conditions and elevated temperature and pressure. The results were also extrapolated for a time period for more than 300 days. The paper will provide an excellent data inventory for class G cement that can be used when mechanical studies on cement, like finite element studies, are required.
- Europe (1.00)
- North America > United States > Texas (0.48)