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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)
The Application of Cement Sheath Failure Criterion in Determining the Wellbore Internal Pressure Window
Li, Wenda (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Chen, Mian (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Jin, Yan (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Yang, Shuai (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Zhang, Yayun (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Chen, Yun (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing) | Tan, Peng (State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum-Beijing)
Abstract: Cement sheath is expected to provide mechanical zonal isolation and borehole integrity during well construction and well life. The damage of the cement sheath may result in abnormal annulus pressure and potential leakage. So internal wellbore pressure window based on cement failure is introduced to preserve zonal isolation during different well stages. A Two-dimensional analytical model using a multi-layer thick-wall cylinder is applied for calculating stress distribution in the casing-cement-formation system. In the model, we assumed perfect bonding (continuous stress and displacement) at the interfaces and plane-strain condition. Then the internal pressure limits can be obtained using the cement failure criteria for both axisymmetric and non-axisymmetric stress fields. Analytical solutions of the 2D model subjected to the axisymmetric stress field showed that the stress state, the mechanical properties of casing, cement sheath and formation, cased wellbore geometry and cement strength parameters both have effects on the internal pressure window, which provides guidance for the cement design. This method provides petroleum engineers a robust tool to maintain cement sheath integrity. Introduction Cement sheath, as a part of well barriers, is expected to provide mechanical zonal isolation and borehole integrity during well construction and well life [1]. The damage of the cement sheath may result in abnormal annulus pressure and potential leakage. Hence, the increasing awareness of avoiding the cement sheath failure has been raised among researchers. Thus internal wellbore pressure window based on the cement failure is introduced to control the wellbore pressure during different well stages for safety. After cement sets, casing-cement-sheath system withstand the stresses induced by the well events and maintain integrity during the life of well [2]. However, Cement sheath, casing and formation with different mechanical properties have different failure conditions. Many cases showed that abnormal annular pressure occurs without casing failure [1], which means that in some conditions the possibility of cement failure is higher than that of casing failure. So it is necessary to develop a model based on cement failure instead of casing failure, since cement failure happens prior to casing failure. On the other side, cement failure may destroy the wellbore integrity, creating flow channel for oil/gas migration between different formations. Excessive pressure and temperature change during well operations lead to significant damage to the cement sheath [3]. Thus we need to develop a model to determine the internal wellbore pressure window maintaining cement sheath integrity (neglecting temperature variation) during different well stages.
ABSTRACT: The integrity of the cement sheath is the key part to maintain zonal isolation and prevent the inter-zonal communication. Loads arising from multiple stages of wellbore life span may induce various modes of cement failure within the cement (disking and radial cracks) and at the cement-casing and the cement-formation interfaces (debonding fractures). Micro-annuli (MA) are the systematic and inter-connected debonding fractures which is the most hazardous mode of cement failure and can cause serious wellbore leakage problems. This paper utilizes the extended finite element method (XFEM) to study the cement failure under various loading conditions (i.e. cement volume change during hardening, mechanical loads due to borehole pressure change) and investigate the influence of the cement failure to the MA generation during the latter operation stages. A staged 3D finite element analysis approach including loads from various operation procedures during the life cycle of a composite wellbore system is used to establish an in-situ downhole condition and study the conditions of MA generation and evolution. Modeling results indicate that radial cracks are likely to occur during the cement volume shrinkage during the cement hardening and MA (debonding fractures) tend to occur under the periodically cooling during the injection stage. The results also show that the initial stress state in the cement for each procedure is a key factor determining the initiation of different cement failure types. In summary, the more compressive the cement state of stress, the lower the likelihood for radial cracks to initiate and the more likely debonding occurs during thermal cycling. The results with respect to varying cement Young’s modulus show that a high Young’s modulus promotes the initiation of radial cracks. The initiation of interface debonding is independent of cement Young’s modulus. The results presented indicate that a cement system with a low Young’s modulus and high tensile strength provides favorable conditions to promote the cement sheath integrity.
Full-Life-Cycle Analysis of Cement Sheath Integrity in HPHT Shale Formations
Li, Xiaorong (China University of Petroleum) | Ding, Zechen (China University of Petroleum) | Gu, Chenwang (China University of Petroleum) | An, Chen (China University of Petroleum) | Feng, Yongcun (China University of Petroleum)
ABSTRACT: Cement sheath should provide zonal isolation and structural support during the full life cycle of a well. However, achieving long-term cement sheath integrity under complex geological and operational conditions, especially in the high pressure and high temperature shale formation, is still a great challenge. To better understand the long-term failure mechanism of cement sheath, this paper developed a 3D coupled thermal-hydro-mechanical model of the cement sheath system by considering the accumulation of stress-strain state in all stages of the well life cycle using a finite-element method. The model is validated against analytical solutions of the wellbore stress-strain distribution and shows high accuracy. Sensitivity analyses were performed on the variations in pressure, temperature, and anisotropy of deep shale formation. The results show that pressure and the temperature difference between wellbore and formation results in transient flow and thermal diffusion processes with time and the resulting stress change around the well affect the integrity of the cement sheath system. Debonding occurs at the cement-formation interface with a relatively large temperature difference, while the crack tends to heal with a relatively small temperature difference. Besides, a novelty of this modeling approach is that it incorporates the initial stress state in the cement sheath immediately after hardening of the cement slurry, providing more realistic simulation results for considering the accumulation of stress-strain during the full life cycle of wells. The results also indicate that increasing the initial stress of cement sheath is beneficial for reducing the risk of debonding failure of the cement-formation interface. 1 Introduction As the core component of a typical oil/gas well structure, cement sheath provides zonal isolation and structural support to the full life cycle of wells. Failure of cement sheath can lead to a series of wellbore integrity problems, such as sustained casing pressure, blowout, etc. Unfortunately, achieving long-term cement sheath integrity under complex geological and operational conditions is still a great challenge, especially in the deep shale formation which is mainly characterized by high pressure, high temperature, and high horizontal stress difference (GUO Jianchun et al., 2021; HE et al., 2021; ZENG Bo et al., 2020).
- North America > United States > Texas (0.28)
- Europe > Norway > Norwegian Sea (0.26)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Asia > China > Sichuan > Sichuan Basin (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Roebuck Basin > Bedout Basin > Milne Sandstone Formation (0.98)
- Oceania > Australia > Western Australia > North West Shelf > Roebuck Basin > Bedout Basin > Baxter Sandstone Formation (0.98)
ABSTRACT Cement sheath is an important barrier to provide a hydraulic seal and establish zonal isolation, preventing fluid communication in the wellbore. The goal of this study is to investigate cement integrity in casing-cement-formation system by using both experiments and finite element models. A3D numerical model was established based on the diametric compression test setup. The Digital image correlation (DIC) technology was employed to examine strain distribution within the cement sheath. The compressive test system was utilized to record the relationship between applied load and axial strain. Cylindrical stresses (i.e. radial and hoop stress) in the cement were used to evaluate the structural and mechanical integrity of the cement sheath. The comparison between simulation and experimental results indicated a reasonable match. The results showed that the casing-cement interface has the highest risk of failure. The failure initiated at the orientation parallel (θ=0°) to the applied load followed by in perpendicular (θ=90°) direction. In general, flexible cement with low Young's modulus and high Poisson's ratio and thick cement has low risk of failure. The evaluation of different lithology indicated that elastic lithology prevents high stresses in the cement to avoid failure. 1. INTRODUCTION The increasing development of unconventional wellbores (i.e. shale gas and oil exploration) using well stimulation techniques has boosted the recovery of fossil energy in the United States. The complicated operations raise the possibility of well integrity issues regarding the possible environmental risks, such as groundwater contamination, gas leakage, and fluid spills and seepage at the surface (Jackson et al. 2013; Vidic et al. 2013). Cement sheath, as an essential part of the oil well, is a major barrier to prevent the formation fluid flow to an unintended area ensuring the safety of the wellbore. A recent survey collected the reasons of secondary barrier failure during drilling and production from 156 loss of well control cases between 2000 and 2015. The statistic study showed that 13% of failure during drilling is induced by the poor cement and 30% during the production stage (Patel et al. 2019). Cement integrity in the harsh operational environments (i.e. high temperature and high pressure wells, deep water wells, geothermal wells, etc.) is not understand comprehensively. The Oil and Gas iQ (2015) showed that cement design has more technological knowledge gaps than others (Figure 1).
- Europe (1.00)
- North America > United States > Texas (0.29)
- North America > United States > Oklahoma (0.29)
- (2 more...)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.50)