A Comprehensive Wellbore Stability Model Considering Poroelastic and Thermal Effects for Inclined Wellbores in Deepwater Drilling

Abstract

Exploring and developing oil and gas in deepwater field is an important trend of the oil and gas industry. Development of deepwater oil and gas fields from a platform always requires a number of directional wells or extended reach wells targeting to different depth of water in various azimuth. Drilling of these wells is mostly associated with a series of wellbore instability problems that are not encountered in onshore or shallow water drilling. In the past decades, a number of studies on wellbore stability have been conducted. However, few of the models are specific for wellbore stability of the inclined deepwater wellbores. In this work, a comprehensive wellbore stability model considering poroelastic and thermal effects for inclined wellbores in deepwater drilling is developed. The numerical method of the model is also presented. The study shows that for a strike-slip stress regime, the wellbore with a low inclination poses more risk of wellbore instability than the wellbore with a high inclination. It also shows that cooling the wellbore will stabilize the wellbore while excessive cooling could cause wellbore fracturing, and the poroelastic effect could narrow the safe mud weight window. The highest wellbore collapse pressure gradients at all of the analyzed directions are obtained when poroelastic effect is taken into account meanwhile the lowest wellbore fracture pressure gradients at all of the analyzed directions are obtained when both of poroelastic effect and thermal effect are taken into account. For safe drilling in deepwater, both of thermal and poroelastic effects are preferably considered to estimate wellbore stability. The model provides a practical tool to predict the stability of inclined wellbores in deepwater drilling.

Wellbore Stability in a Depleted Reservoir by Finite Element Analysis of Coupled thermo-poro-elastic Units in an Oilfield, SW Iran

“…Shahbazi and Hosseini (2018) presented a case study on the behavior of wellbores in shale formations using the finite difference method. Chen et al (2018) provided a practical wellbore stability model considering poro-elastic and thermal effects for deep-water drilling, especially Inclined wells. Cheng et al (2019) revealed the borehole instability mechanism and optimized a drilling mud scheme for continental shale wellbore stability by a porochemo-thermo-elastic coupling model case analysis.…”

Properties of Bentonite Slurry Drilling Fluid in Shallow Formations of Deepwater Wells and the Optimization of Its Wellbore Strengthening Ability While Drilling

“…The deepwater shallow geological environment is more complex, with low temperatures, shallow faults, hydrates, and abnormal pressures creating many difficulties and uncertainties for shallow drilling fluids. , Taking the Ledong area of the Yingqiong Basin in the South China Sea as an example, the correspondence between drilling fluid and strata during deepwater drilling is shown in Figure . The shallow deepwater strata are generally distributed in the Ledong Formation, mainly between 800 and 1500 m at the beginning of the subsea mudline, and the drilling fluid is seawater or bentonite slurry drilling fluid. , The deepwater shallow geological features of the China Yingqiong Basin are mainly the following: (1) Physical characteristics of the shallow lithology: in general, the upper part is dominated by large sets of mudstone with thin layers of siltstone and muddy siltstone in a muddy background.…”

“…The deepwater shallow geological environment is more complex, with low temperatures, shallow faults, hydrates, and abnormal pressures creating many difficulties and uncertainties for shallow drilling fluids. 7 , 8 Taking the Ledong area of the Yingqiong Basin in the South China Sea as an example, the correspondence between drilling fluid and strata during deepwater drilling is shown in Figure 1 . The shallow deepwater strata are generally distributed in the Ledong Formation, mainly between 800 and 1500 m at the beginning of the subsea mudline, and the drilling fluid is seawater or bentonite slurry drilling fluid.…”

Wellbore Stability of a Deep-Water Shallow Hydrate Reservoir Based on Strain Softening Characteristics

“…There has been a series of studies investigating the borehole stability of the hydrate layer. Thermal and poroelastic effects are preferably considered to estimate wellbore stability [4]. Birchwood et al proposed an elastic-plastic wellbore stability prediction model based on the Mohr-Coulomb criterion, which took into account the effect of temperature on the thermodynamic state of the hydrate layer [5].…”