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

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.

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.

scholarly journals Increased likelihood of induced seismicity in highly overpressured shale formations

2018 ◽  
Vol 214 (1) ◽  
pp. 751-757 ◽  
Author(s):  
David W Eaton ◽  
Ryan Schultz
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Induced Earthquakes ◽  
Shale Formations ◽  
Western Canada Sedimentary Basin ◽  
Natural Processes ◽  
Negligible Probability ◽  
Pore Pressure Gradient ◽  
Geological Timescale

SUMMARY Fluid-injection processes such as disposal of saltwater or hydraulic fracturing can induce earthquakes by increasing pore pressure and/or shear stress on faults. Natural processes, including transformation of organic material (kerogen) into hydrocarbon and cracking to produce gas, can similarly cause fluid overpressure. Here, we document two examples from the Western Canada Sedimentary Basin where earthquakes induced by hydraulic fracturing are strongly clustered within areas characterized by pore-pressure gradient in excess of 15 kPa m−1. Despite extensive hydraulic-fracturing activity associated with resource development, induced earthquakes are virtually absent in the Montney and Duvernay Formations elsewhere. Statistical analysis suggests a negligible probability that this spatial correlation developed by chance. This implies that, in addition to known factors such as anthropogenic pore-pressure increase and proximity to critically stressed faults, high in situ overpressure of shale formations may also represent a controlling factor for inducing earthquakes by hydraulic fracturing. On a geological timescale, natural pore-pressure generation may lead to fault-slip episodes that regulate the magnitude of formation overpressure.

scholarly journals Wellbore stability analysis in chemically active shale formations

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 911-917 ◽  
Author(s):  
Xiang-Chao Shi ◽  
Xu Yang ◽  
Ying-Feng Meng ◽  
Gao Li
Keyword(s):  
Pore Pressure ◽  
Early Stage ◽  
Solute Concentration ◽  
Strength Degradation ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Drilling Mud ◽  
Shale Formations ◽  
Tangential Stresses ◽  
Poroelastic Model

Maintaining wellbore stability involves significant challenges when drilling in low-permeability reactive shale formations. In the present study, a non-linear thermo-chemo-poroelastic model is provided to investigate the effect of chemical, thermal, and hydraulic gradients on pore pressure and stress distributions near the wellbores. The analysis indicates that when the solute concentration of the drilling mud is higher than that of the formation fluid, the pore pressure and the effective radial and tangential stresses decrease, and v. v. Cooling of the lower salinity formation decreases the pore pressure, radial and tangential stresses. Hole enlargement is the combined effect of shear and tensile failure when drilling in high-temperature shale formations. The shear and tensile damage indexes reveal that hole enlargement occurs in the vicinity of the wellbore at an early stage of drilling. This study also demonstrates that shale wellbore stability exhibits a time-delay effect due to changes in the pore pressure and stress. The delay time computed with consideration of the strength degradation is far less than that without strength degradation.

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