Effect of Time-Dependent Changes in Pore Pressure on Geomechanical and Acoustic Properties of Shale Formations

2012 ◽  
Author(s):  
Mehdi Mokhtari ◽  
Azra N. Tutuncu
Keyword(s):  
Pore Pressure ◽  
Acoustic Properties ◽  
Time Dependent ◽  
Shale Formations

Pore Pressure Prediction in Sandstone Using a Lateral Transfer Approach

2021 ◽  
Author(s):  
Jose Francisco Consuegra
Keyword(s):  
Pore Pressure ◽  
Seismic Data ◽  
Strong Relationship ◽  
Lateral Transfer ◽  
Earth Model ◽  
Driving Mechanism ◽  
Shale Formations ◽  
Sand Body ◽  
Pore Pressure Prediction ◽  
Normal Trend

Abstract Accurate pore pressure prediction is required to determine reliable static mud weights and circulating pressures, necessary to mitigate the risk of influx, blowouts and borehole instability. To accurately estimate the pore pressure, the over-pressure mechanism has to be identified with respect to the geological environment. One of the most widely used methods for pore pressure prediction is based on Normal Compaction Trend Analysis, where the difference between a ‘normal trend' and log value of a porosity indicator log such as sonic or resistivity is used to estimate the pore pressure. This method is biased towards shales, which typically exhibit a strong relationship between porosity and depth. Overpressure in non-shale formations has to be estimated using a different method to avoid errors while predicting the pore pressure. In this study, a different method for pore pressure prediction has been performed by using the lateral transfer approach. Many offset wells were used to predict the pore pressure. Lateral transfer in the sand body was identified as the mechanism for overpressure. This form of overpressure cannot be identified by well logs, which makes the pore pressure prediction more complex. Building a 2D geomechanical model, using seismic data as an input and following an analysis methodology that considered three type of formation fluids - gas, oil and water in the sand body, all pore pressure gradients related to lateral transfer for the respective fluids were evaluated. This methodology was applied to a conventional reservoir in a field in Colombia and was helpful to select the appropriate mud weight and circulating pressure to mitigate drilling risks associated to this mechanism of overpressure. Seismic data was critical to identifying this type of overpressure mechanism and was one of the main inputs for building the geomechanical earth model. This methodology enables drilling engineers and geoscientists to confidently predict, assess and mitigate the risks posed by overpressure in non-shale formations where lateral transfer is the driving mechanism of overpressure. This will ensure a robust well plan and minimize drilling/well control hazards associated with this mode of overpressure.

The Effect of Capillary Condensation on the Geomechanical and Acoustic Properties of Tight Formations: An Experimental Study

2021 ◽  
Author(s):  
Aamer Albannay ◽  
Binh Bui ◽  
Daisuke Katsuki
Keyword(s):  
Pore Pressure ◽  
Capillary Condensation ◽  
Pore Space ◽  
Dew Point ◽  
Acoustic Properties ◽  
Point Pressure ◽  
Tight Formations ◽  
Dew Point Pressure ◽  
Compressional Velocity

Abstract Capillary condensation is the condensation of the gas inside nano-pore space at a pressure lower than the bulk dew point pressure as the result of multilayer adsorption due to the high capillary pressure inside the small pore throat of unconventional rocks. The condensation of liquid in nano-pore space of rock changes its mechanical and acoustic properties. Acoustic properties variation due to capillary condensation provides us a tool to monitor phase change in reservoir as a result of nano-confinement as well as mapping the area where phase change occurs as well as characterize pore size distribution. This is particularly important for tight formations where confinement has a strong effect on phase behavior that is challenging to measure experimentally. Theoretical studies have examined the effects of capillary condensation; however, these findings have not been verified experimentally. The main objective of this study is to experimentally investigate the effect of capillary condensation on the mechanical and acoustic properties of shale samples. The mechanical and acoustic characterization of the samples was carried out experimentally using a state-of-the-art tri-axial facility at the Colorado School of Mines. The experimental set-up is capable of the simultaneous acquisition of coupled stress, strain, resistivity, acoustic and flow data. Carbon dioxide was used as the pore pressure fluid in these experiments. After a comprehensive characterization of shale samples, experiments were conducted by increasing the pore pressure until condensation occurs while monitoring the mechanical and acoustic properties of the sample to quantify the effect of capillary condensation on the mechanical and acoustic properties of the sample. Experimental data show a 5% increase in Young's Modulus as condensation occurs. This increase is attributed to the increase in pore stiffness as condensation occurs reinforcing the grain contact. An initial decrease in compressional velocity was observed as pore pressure increases before condensation occurs which is attributed to the expansion of the pore volume when pore pressure increases. After this initial decrease, compressional velocity slightly increases at a pressure around 750 - 800 psi which is close to the condensation pressure. We also observed a noticeable increase in shear velocity when capillary condensation occurs, this could be due to the immobility of the condensed liquid phase at the pore throats. The changes of geomechanical and acoustic signatures were observed at around 750 - 800 psi at 27°C, which is the dew point pressure of the fluid in the nano-pore space of the sample at this temperature. While the unconfined bulk dew point pressure of carbon dioxide at the same temperature is 977 psi. Hence, this study marks the first measurement of the dew point of fluid in nano-pore space and potentially leads to the construction of the phase envelope of fluid under confinement.

scholarly journals Transient response of near-wellbore supercharging during filter cake growth

2021 ◽  
Vol 76 ◽  
pp. 46
Author(s):  
Tianshou Ma ◽  
Nian Peng ◽  
Ping Chen ◽  
Yang Liu
Keyword(s):  
Pore Pressure ◽  
Filter Cake ◽  
Early Stage ◽  
Drilling Fluid ◽  
Reduction Rate ◽  
Time Dependent ◽  
Low Permeability ◽  
Drilling Fluids ◽  
Dynamic Filter ◽  
Cake Porosity

Supercharging in the vicinity of a borehole is an important factor that affects formation damage and drilling safety, and the filter cake growth process has a significant impact on supercharging in the vicinity of the borehole. However, existing models that predict pore pressure distribution overlook dynamic filter cake growth. Thus, an analytical supercharging model was developed that considers time-dependent filter cake effects, and this model was verified using a two-dimensional numerical model. The influences of filter cake, formation, and filtrate properties on supercharging were investigated systematically. The results indicate that time-dependent filter cake effects have significant influence on supercharging. Supercharging increases in the early stage but decreases over time because of the dynamic growth of filter cake, and the supercharging magnitude decreases along the radial direction. Because of filter cake growth, the magnitude of supercharging falls quickly across the filter cake, and the decreased magnitude of pore pressure caused by the filter cake increases. Supercharging in low-permeability formations is more obvious and the faster rate of filter cake growth, a lower filtrate viscosity and faster reduction rate of filter cake permeability can help to weaken supercharging. The order of importance of influencing factors on supercharging is overbalance pressure > formation permeability > formation porosity ≈ filtrate viscosity > filter cake permeability attenuation coefficient > initial filter cake permeability control ratio > filter cake growth coefficient > filter cake porosity. To alleviate supercharging in the vicinity of the borehole, adopting drilling fluids that allow a filter cake to form quickly, optimizing drilling fluid with a lower filtrate viscosity, keeping a smaller overbalance pressure, and precise operation at the rig site are suggested for low-permeability formations during drilling.

Modeling Chemically Induced Pore Pressure Alterations in Near Wellbore Region of Shale Formations

2011 ◽  
Author(s):  
Lu Huang ◽  
Mengjiao Yu ◽  
Stefan Z. Miska ◽  
Nicholas Takach ◽  
James Benjamin Bloys
Keyword(s):  
Pore Pressure ◽  
Shale Formations ◽  
Chemically Induced

The Effects of Filter-Cake Buildup and Time-Dependent Properties on the Stability of Inclined Wellbores

SPE Journal ◽  
2011 ◽  
Vol 16 (04) ◽  
pp. 1010-1028 ◽  
Author(s):  
Minh H. Tran ◽  
Younane N. Abousleiman ◽  
Vinh X. Nguyen
Keyword(s):  
Pore Pressure ◽  
Filter Cake ◽  
Wellbore Stability ◽  
Time Dependent ◽  
Transient Effects ◽  
Drilling Mud ◽  
Property Variation ◽  
Lost Circulation ◽  
Wellbore Strengthening ◽  
Formation Pore Pressure

Summary The effects of filter-cake buildup and/or filter-cake-property variation with time on wellbore stability have been plaguing the industry. The increasing use of lost-circulation materials (LCMs) in recent years for wellbore strengthening in weak and/or depleted formations necessitates models that can predict these effects. However, the complexities of effective-stress and pore-pressure evolution around the borehole while drilling, coupled with the transient variation of mud-filtration properties, have delayed such modeling efforts. In this paper, the analytical solutions for the time-dependent effects of mudcake buildup and mudcake properties on the wellbore stresses and formation pore pressure, and thus the safe-drilling-mud-weight window, are derived. The transient effects of mudcake buildup and mudcake buildup coupled with its permeability reduction during filtration on the safe-drilling-mudweight window are illustrated through numerical examples. The results showed that the safe-mudweight windows were greatly affected by the buildup of filter cake and its permeability variation. For example, the analysis for filter-cake buildup with cake permeability of 10–2 md showed that the safe-mudweight window was widened by 0.5 g/cc after 2.5 hours post-excavation when compared to the case of a wellbore without mudcake. On the other hand, a lower mudcake permeability of 10–3 md widened the mudweight window by as much as 1 g/cc. Last but not least, the analyses revealed that even for mudcake permeability as low as 10–3 md, neglecting the permeable nature of the mudcake can result in overestimation of the safe-drilling-mudweight window.

Investigating the Relation Between Sorption Tendency and Hydraulic Properties of Shale Formations

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Vahid Dokhani ◽  
Mengjiao Yu ◽  
Chao Gao ◽  
James Bloys
Keyword(s):  
Pore Pressure ◽  
Adsorption Isotherms ◽  
Hydraulic Properties ◽  
Transport Coefficients ◽  
Exchange Capacity ◽  
Wellbore Stability ◽  
Experimental Results ◽  
Shale Formations ◽  
Hydraulic Diffusivity ◽  
Rock Types

Routine measurement of hydraulic diffusivity of ultralow permeability rocks, such as shale, is a prolonged process. This study explores the effects of a sorptive characteristic of the porous medium on hydraulic diffusivities of shale rocks. The examined rock types include Mancos Shale, Catoosa Shale, Eagle Ford Shale, and core samples from the Gulf of Mexico. First, the adsorption isotherms of the selected shale rocks were obtained. Then, the hydraulic properties of the selected shale rocks were determined using Shale/Fluid Interaction Testing Cell, which employs pore pressure transmission technique. The experimental results show that the moisture content of shale is correlated with water activity using a multilayer adsorption theory. It is found that the adsorption isotherms of various shale formations can be scaled using their respective cation exchange capacity (CEC) into a single adsorption curve. Analyzing the transient pore pressure response in the downstream side of shale sample allows calculating the transport coefficients of shale samples. Hydraulic properties of shales are obtained by matching the pore pressure history with one-dimensional coupled fluid flow model. The experimental results indicate that sorptive properties can be inversely related to the hydraulic diffusivity of shale rocks. It is found that with an increase in the magnitude of sorption potential of shale, the hydraulic diffusivity decreases. This study is useful for shale characterization and provides a correlation, which can have various applications including, but not limited to, wellbore stability prediction during well planning.

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